From f54c3fae89c618b9135ad23b5f974e10bd7e3243 Mon Sep 17 00:00:00 2001
From: Kim Pepper <kim@previousnext.com.au>
Date: Sat, 13 Jan 2024 10:53:32 +1100
Subject: [PATCH] Modernise codebase (#8)

* Replace hard-coded Guzzle  with PSR implementation
*  Strict types
* Replace GitHub action workflow
*  Add PHPStan baseline
---
 .github/workflows/build.yml                   |  43 ++++
 .github/workflows/continuous-integration.yml  |  34 ---
 .gitignore                                    |   3 +-
 README.md                                     |   6 +-
 composer.json                                 |  30 ++-
 phpcs.xml                                     |  26 +--
 phpstan-baseline.neon                         |  31 +++
 phpstan.neon                                  |  11 +
 phpunit.xml                                   |  64 ++----
 src/BomClient.php                             |  91 +++-----
 src/Forecast/Area.php                         |  24 +-
 src/Forecast/Forecast.php                     |  34 +--
 src/Forecast/ForecastPeriod.php               | 210 +++---------------
 src/Forecast/Serializer/AreaNormalizer.php    |   9 +-
 .../Serializer/ForecastNormalizer.php         |   9 +-
 .../Serializer/ForecastPeriodNormalizer.php   |  18 +-
 .../Serializer/ForecastSerializerFactory.php  |   9 +-
 src/Observation/Observation.php               | 102 ++-------
 src/Observation/ObservationList.php           |  30 +--
 src/Observation/Pressure.php                  |  34 +--
 .../Serializer/ObservationListNormalizer.php  |   7 +-
 .../Serializer/ObservationNormalizer.php      |  11 +-
 .../ObservationSerializerFactory.php          |   7 +-
 src/Observation/Station.php                   |  74 ++----
 src/Observation/Temperature.php               |  98 ++------
 src/Observation/Wind.php                      |  79 ++-----
 src/Util/BaseNormalizer.php                   |  20 +-
 src/Util/ClassNameSupportNormalizerTrait.php  |  42 ++--
 tests/Functional/BomClientTest.php            |  64 ------
 tests/bootstrap.php                           |   2 -
 tests/src/Functional/BomClientTest.php        |  88 ++++++++
 .../Serializer/ForecastSerializerTest.php     |  36 +--
 .../Serializer/ObservationSerializerTest.php  |   9 +-
 33 files changed, 483 insertions(+), 872 deletions(-)
 create mode 100644 .github/workflows/build.yml
 delete mode 100644 .github/workflows/continuous-integration.yml
 create mode 100644 phpstan-baseline.neon
 create mode 100644 phpstan.neon
 delete mode 100644 tests/Functional/BomClientTest.php
 create mode 100644 tests/src/Functional/BomClientTest.php
 rename tests/{ => src}/Unit/Forecast/Serializer/ForecastSerializerTest.php (87%)
 rename tests/{ => src}/Unit/Observation/Serializer/ObservationSerializerTest.php (90%)

diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
new file mode 100644
index 0000000..27f9284
--- /dev/null
+++ b/.github/workflows/build.yml
@@ -0,0 +1,43 @@
+name: 🏗 Build
+
+on:
+  pull_request:
+    types: [ synchronize, opened, reopened, ready_for_review ]
+  push:
+    branches: [ main ]
+
+permissions:
+  checks: write
+  pull-requests: write
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        prefer_lowest: ["", "--prefer-lowest"]
+        php: ["8.1", "8.2", "8.3"]
+    container:
+      image: skpr/php-cli:${{ matrix.php }}-dev-v2-edge
+      options:
+        --pull always
+        --user 1001:1001
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          show-progress: false
+      - name: 📦 Composer Update
+        run: composer update --with-all-dependencies --prefer-dist --no-progress --no-interaction ${{ matrix.prefer_lowest }}
+      - name: 🧹 PHPCS
+        run: ./bin/phpcs --report=checkstyle -q | ./bin/cs2pr
+      - name: 🧹 PHPStan
+        run: ./bin/phpstan --error-format=github analyse
+      - name: ⚡ Run Tests
+        run: ./bin/phpunit --log-junit phpunit-results.xml
+      - name: 📝 Publish Test Results
+        uses: EnricoMi/publish-unit-test-result-action@v2
+        if: always()
+        with:
+          files: phpunit-results.xml
+          check_name: Test Results ${{ matrix.php }} ${{ matrix.prefer_lowest }}
diff --git a/.github/workflows/continuous-integration.yml b/.github/workflows/continuous-integration.yml
deleted file mode 100644
index fa809a0..0000000
--- a/.github/workflows/continuous-integration.yml
+++ /dev/null
@@ -1,34 +0,0 @@
-name: "Continuous Integration"
-
-on:
-  pull_request:
-  push:
-    branches:
-      - '[0-9]+.[0-9]+.x'
-      - 'refs/pull/*'
-    tags:
-      - '[0-9]+.[0-9]+.x'
-
-jobs:
-  matrix:
-    name: Generate job matrix
-    runs-on: ubuntu-latest
-    outputs:
-      matrix: ${{ steps.matrix.outputs.matrix }}
-    steps:
-      - name: Gather CI configuration
-        id: matrix
-        uses: laminas/laminas-ci-matrix-action@v1
-
-  qa:
-    name: QA Checks
-    needs: [matrix]
-    runs-on: ${{ matrix.operatingSystem }}
-    strategy:
-      fail-fast: false
-      matrix: ${{ fromJSON(needs.matrix.outputs.matrix) }}
-    steps:
-      - name: ${{ matrix.name }}
-        uses: laminas/laminas-continuous-integration-action@v1
-        with:
-          job: ${{ matrix.job }}
\ No newline at end of file
diff --git a/.gitignore b/.gitignore
index 9902d7b..55b5178 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,4 @@
+/composer.lock
+/.phpunit.cache
 /bin
 /vendor
-/composer.lock
diff --git a/README.md b/README.md
index da4db89..a4a603a 100644
--- a/README.md
+++ b/README.md
@@ -16,8 +16,7 @@ composer require previousnext/bom-weather
 ### Forecasts
 
 ```php
-$logger = new NullLogger();
-$client = new BomClient($logger);
+$client = new BomClient(new Client(), new RequestFactory(), new NullLogger());
 $forecast = $client->getForecast('IDN10031');
 
 $issueTime = $forecast->getIssueTime();
@@ -46,8 +45,7 @@ foreach ($locations as $location) {
 ### Observations
 
 ```php
-$logger = new NullLogger();
-$client = new BomClient($logger);
+$client = new BomClient(new Client(), new RequestFactory(), new NullLogger());
 $observationList = $client->getObservationList('IDN60901', '95757');
 
 $refreshMessage = $observationList->getRefreshMessage();
diff --git a/composer.json b/composer.json
index 11d566c..ef93c23 100644
--- a/composer.json
+++ b/composer.json
@@ -9,29 +9,39 @@
     }
   ],
   "require": {
-    "php": "^7.1",
-    "ext-curl": "*",
+    "php": "^8.1",
     "ext-xml": "*",
-    "guzzlehttp/guzzle": "~6.3",
-    "psr/log": "~1.0",
-    "symfony/serializer": "~3.4"
+    "psr/http-client-implementation": "^1.0",
+    "psr/http-factory-implementation": "^1.0",
+    "psr/http-message-implementation": "^1.0",
+    "psr/log": "^3.0",
+    "symfony/serializer": "^6.4"
   },
   "require-dev": {
-    "drupal/coder": ">=8.2.12",
-    "phpunit/phpunit": "~6.5",
-    "symfony/phpunit-bridge": "~3.4"
+    "dealerdirect/phpcodesniffer-composer-installer": "^1.0",
+    "guzzlehttp/psr7": "^2.6",
+    "http-interop/http-factory-guzzle": "^1.2",
+    "php-http/mock-client": "^1.0",
+    "phpstan/phpstan": "^1.10",
+    "phpunit/phpunit": "^9.6",
+    "previousnext/coding-standard": "^0.1.3",
+    "staabm/annotate-pull-request-from-checkstyle": "^1.8"
   },
   "autoload": {
     "psr-4": {"BomWeather\\": "src/"}
   },
   "autoload-dev": {
-    "psr-4": {"BomWeather\\Tests\\": "tests/"}
+    "psr-4": {"BomWeather\\Tests\\": "tests/src"}
   },
   "config": {
     "bin-dir": "bin/",
     "preferred-install": {
       "*": "dist"
     },
-    "sort-packages": true
+    "sort-packages": true,
+    "allow-plugins": {
+      "dealerdirect/phpcodesniffer-composer-installer": true,
+      "php-http/discovery": true
+    }
   }
 }
diff --git a/phpcs.xml b/phpcs.xml
index 2eb97a7..0253d5a 100644
--- a/phpcs.xml
+++ b/phpcs.xml
@@ -1,26 +1,8 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<ruleset name="bom-weather">
-  <description>PHP CodeSniffer configuration for BOM Weather</description>
-  <!-- folders to scan -->
+<ruleset name="PNX Standard">
   <file>./src</file>
-  <file>./tests</file>
-  <!-- extensions to scan -->
-  <arg name="extensions" value="php"/>
-  <!-- additional arguments -->
+  <file>./tests/src</file>
+  <rule ref="PreviousNextDrupal" />
+  <rule ref="SlevomatCodingStandard.Namespaces.FullyQualifiedGlobalFunctions" />
   <arg name="report" value="full"/>
-  <!-- inherit from coder -->
-  <rule ref="./vendor/drupal/coder/coder_sniffer/Drupal"/>
-  <!-- Additional detailed sniff configuration -->
-  <!-- You can determine sniff names by running with -s flag -->
-  <!-- Example 1 - ignore Drupal.NamingConventions.ValidFunctionName.ScopeNotCamelCaps
-    <rule ref="Drupal.NamingConventions.ValidFunctionName.ScopeNotCamelCaps">
-      <severity>0</severity>
-    </rule>
-  // End example 1 -->
-  <!-- Example 2 - ignore rule for specific files
-    <rule ref="Drupal.NamingConventions.ValidVariableName.LowerCamelName">
-      <exclude-pattern>OfferNormalizerTrait.php</exclude-pattern>
-      <exclude-pattern>TimeOfUseValidationTrait.php</exclude-pattern>
-    </rule>
-  // End example 2 -->
 </ruleset>
diff --git a/phpstan-baseline.neon b/phpstan-baseline.neon
new file mode 100644
index 0000000..3313301
--- /dev/null
+++ b/phpstan-baseline.neon
@@ -0,0 +1,31 @@
+parameters:
+	ignoreErrors:
+		-
+			message: "#^Method BomWeather\\\\Util\\\\BaseNormalizer\\:\\:normalize\\(\\) return type with generic class ArrayObject does not specify its types\\: TKey, TValue$#"
+			count: 1
+			path: src/Util/BaseNormalizer.php
+
+		-
+			message: "#^Call to method getEndTime\\(\\) on an unknown class BomWeather\\\\Forecast\\\\RegionForecastPeriod\\.$#"
+			count: 1
+			path: tests/src/Unit/Forecast/Serializer/ForecastSerializerTest.php
+
+		-
+			message: "#^Call to method getForecast\\(\\) on an unknown class BomWeather\\\\Forecast\\\\RegionForecastPeriod\\.$#"
+			count: 1
+			path: tests/src/Unit/Forecast/Serializer/ForecastSerializerTest.php
+
+		-
+			message: "#^Call to method getStartTime\\(\\) on an unknown class BomWeather\\\\Forecast\\\\RegionForecastPeriod\\.$#"
+			count: 1
+			path: tests/src/Unit/Forecast/Serializer/ForecastSerializerTest.php
+
+		-
+			message: "#^Parameter \\#1 \\$periods of method BomWeather\\\\Tests\\\\Unit\\\\Forecast\\\\Serializer\\\\ForecastSerializerTest\\:\\:assertRegionPeriods\\(\\) expects array\\<BomWeather\\\\Forecast\\\\RegionForecastPeriod\\>, array\\<BomWeather\\\\Forecast\\\\ForecastPeriod\\> given\\.$#"
+			count: 1
+			path: tests/src/Unit/Forecast/Serializer/ForecastSerializerTest.php
+
+		-
+			message: "#^Parameter \\$periods of method BomWeather\\\\Tests\\\\Unit\\\\Forecast\\\\Serializer\\\\ForecastSerializerTest\\:\\:assertRegionPeriods\\(\\) has invalid type BomWeather\\\\Forecast\\\\RegionForecastPeriod\\.$#"
+			count: 1
+			path: tests/src/Unit/Forecast/Serializer/ForecastSerializerTest.php
diff --git a/phpstan.neon b/phpstan.neon
new file mode 100644
index 0000000..c488226
--- /dev/null
+++ b/phpstan.neon
@@ -0,0 +1,11 @@
+includes:
+	- phpstan-baseline.neon
+
+parameters:
+	level: 6
+	paths:
+		- src
+		- tests/src
+	checkMissingIterableValueType: false
+	ignoreErrors:
+		- "#^Call to an undefined method Symfony\\\\Component\\\\Serializer\\\\SerializerInterface\\:\\:denormalize\\(\\)\\.$#"
diff --git a/phpunit.xml b/phpunit.xml
index 2cf0a05..e63b442 100644
--- a/phpunit.xml
+++ b/phpunit.xml
@@ -1,43 +1,27 @@
 <?xml version="1.0" encoding="UTF-8"?>
-
-<!-- TODO set checkForUnintentionallyCoveredCode="true" once https://www.drupal.org/node/2626832 is resolved. -->
-<!-- PHPUnit expects functional tests to be run with either a privileged user
- or your current system user. See core/tests/README.md and
- https://www.drupal.org/node/2116263 for details.
--->
-<phpunit bootstrap="tests/bootstrap.php" colors="true"
-         beStrictAboutTestsThatDoNotTestAnything="true"
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.6/phpunit.xsd"
+         bootstrap="tests/bootstrap.php"
+         cacheResultFile=".phpunit.cache/test-results"
+         executionOrder="depends,defects"
+         forceCoversAnnotation="true"
+         beStrictAboutCoversAnnotation="true"
          beStrictAboutOutputDuringTests="true"
-         beStrictAboutChangesToGlobalState="true"
-         checkForUnintentionallyCoveredCode="false">
-  <php>
-    <!-- Set error reporting to E_ALL. -->
-    <ini name="error_reporting" value="32767"/>
-    <!-- Do not limit the amount of memory tests take to run. -->
-    <ini name="memory_limit" value="-1"/>
-    <const name="BOOTSTRAP_IS_PHPUNIT" value="true"/>
-  </php>
-  <testsuites>
-    <testsuite name="unit">
-      <directory>./tests/Unit</directory>
-    </testsuite>
-    <testsuite name="functional">
-      <directory>./tests/Functional</directory>
-    </testsuite>
-  </testsuites>
-  <listeners>
-    <listener class="Symfony\Bridge\PhpUnit\SymfonyTestsListener">
-    </listener>
-  </listeners>
-  <!-- Filter for coverage reports. -->
-  <filter>
-    <whitelist>
-      <directory>./src</directory>
-      <!-- By definition test classes have no tests. -->
-      <exclude>
-        <directory suffix="Test.php">./</directory>
-        <directory suffix="TestBase.php">./</directory>
-      </exclude>
-    </whitelist>
-  </filter>
+         beStrictAboutTodoAnnotatedTests="true"
+         convertDeprecationsToExceptions="true"
+         failOnRisky="true"
+         failOnWarning="true"
+         verbose="true">
+    <testsuites>
+        <testsuite name="default">
+            <directory>tests/src</directory>
+        </testsuite>
+    </testsuites>
+
+    <coverage cacheDirectory=".phpunit.cache/code-coverage"
+              processUncoveredFiles="true">
+        <include>
+            <directory suffix=".php">src</directory>
+        </include>
+    </coverage>
 </phpunit>
diff --git a/src/BomClient.php b/src/BomClient.php
index 3d2d6fe..a704b2a 100644
--- a/src/BomClient.php
+++ b/src/BomClient.php
@@ -1,14 +1,16 @@
 <?php
 
+declare(strict_types = 1);
+
 namespace BomWeather;
 
 use BomWeather\Forecast\Forecast;
 use BomWeather\Forecast\Serializer\ForecastSerializerFactory;
 use BomWeather\Observation\ObservationList;
 use BomWeather\Observation\Serializer\ObservationSerializerFactory;
-use GuzzleHttp\Client;
-use GuzzleHttp\ClientInterface;
-use GuzzleHttp\Exception\ClientException;
+use Psr\Http\Client\ClientExceptionInterface;
+use Psr\Http\Client\ClientInterface;
+use Psr\Http\Message\RequestFactoryInterface;
 use Psr\Log\LoggerInterface;
 use Symfony\Component\Serializer\SerializerInterface;
 
@@ -18,59 +20,15 @@
 class BomClient {
 
   /**
-   * The Guzzle client.
-   *
-   * @var \GuzzleHttp\Client
-   */
-  protected $httpClient;
-
-  /**
-   * The serializer.
-   *
-   * @var \Symfony\Component\Serializer\SerializerInterface
-   */
-  protected $forecastSerializer;
-
-  /**
-   * The logger.
-   *
-   * @var \Psr\Log\LoggerInterface
-   */
-  protected $logger;
-
-  /**
-   * The observation serializer.
-   *
-   * @var \Symfony\Component\Serializer\SerializerInterface
-   */
-  private $observationSerializer;
-
-  /**
-   * ForecastClient constructor.
-   *
-   * @param \Psr\Log\LoggerInterface $logger
-   *   The logger.
-   * @param \GuzzleHttp\ClientInterface $httpClient
-   *   The HTTP client.
-   * @param \Symfony\Component\Serializer\SerializerInterface $forecastSerializer
-   *   The serializer.
-   * @param \Symfony\Component\Serializer\SerializerInterface $observationSerializer
-   *   The observation serializer.
+   * Constructs a new instance.
    */
   public function __construct(
-    LoggerInterface $logger,
-    ClientInterface $httpClient = NULL,
-    SerializerInterface $forecastSerializer = NULL,
-    SerializerInterface $observationSerializer = NULL
+    protected ClientInterface $httpClient,
+    protected RequestFactoryInterface $requestFactory,
+    protected LoggerInterface $logger,
+    protected ?SerializerInterface $forecastSerializer = NULL,
+    protected ?SerializerInterface $observationSerializer = NULL
   ) {
-    $this->logger = $logger;
-    if ($httpClient == NULL) {
-      $httpClient = new Client([
-        'headers' => ['Accept-Encoding' => 'gzip'],
-      ]);
-    }
-    $this->httpClient = $httpClient;
-
     if ($forecastSerializer == NULL) {
       $forecastSerializer = ForecastSerializerFactory::create();
     }
@@ -90,22 +48,23 @@ public function __construct(
    *
    * @return \BomWeather\Forecast\Forecast|null
    *   The forecast, or NULL if not found.
-   *
-   * @throws \GuzzleHttp\Exception\GuzzleException
    */
   public function getForecast(string $productId): ?Forecast {
     try {
-      $response = $this->httpClient->request('GET', "http://www.bom.gov.au/fwo/$productId.xml");
+      $request = $this->requestFactory->createRequest('GET', "http://www.bom.gov.au/fwo/$productId.xml")
+        ->withHeader('Accept-Encoding', 'gzip');
+      $response = $this->httpClient->sendRequest($request);
 
       /** @var \BomWeather\Forecast\Forecast $forecast */
       $forecast = $this->forecastSerializer->deserialize($response->getBody(), Forecast::class, 'xml');
       return $forecast;
     }
-    catch (ClientException $e) {
-      $this->logger->error("Failed to fetch forecast for ID $productId");
+    catch (ClientExceptionInterface $e) {
+      $this->logger->error("Failed to fetch forecast for ID $productId", [
+        'exception' => $e,
+      ]);
       return NULL;
     }
-
   }
 
   /**
@@ -118,17 +77,21 @@ public function getForecast(string $productId): ?Forecast {
    *
    * @return \BomWeather\Observation\ObservationList|null
    *   The observation, or null if not found.
-   *
-   * @throws \GuzzleHttp\Exception\GuzzleException
    */
   public function getObservationList(string $productId, string $wmo): ?ObservationList {
     try {
-      $response = $this->httpClient->request('GET', "http://reg.bom.gov.au/fwo/$productId/$productId.$wmo.json");
+      $request = $this->requestFactory->createRequest('GET', "http://reg.bom.gov.au/fwo/$productId/$productId.$wmo.json")
+        ->withHeader('Accept-Encoding', 'gzip');
+      $response = $this->httpClient->sendRequest($request);
+
+      /** @var \BomWeather\Observation\ObservationList $observationList */
       $observationList = $this->observationSerializer->deserialize($response->getBody(), ObservationList::class, 'json');
       return $observationList;
     }
-    catch (ClientException $e) {
-      $this->logger->error("Failed to fetch observation list for product $productId and WMO $wmo");
+    catch (ClientExceptionInterface $e) {
+      $this->logger->error("Failed to fetch observation list for product $productId and WMO $wmo", [
+        'exception' => $e,
+      ]);
       return NULL;
     }
   }
diff --git a/src/Forecast/Area.php b/src/Forecast/Area.php
index b9f85a7..cea835c 100644
--- a/src/Forecast/Area.php
+++ b/src/Forecast/Area.php
@@ -1,11 +1,13 @@
 <?php
 
+declare(strict_types = 1);
+
 namespace BomWeather\Forecast;
 
 /**
  * A value object for forecast areas.
  */
-class Area {
+final class Area {
 
   /**
    * Location type.
@@ -35,45 +37,37 @@ class Area {
 
   /**
    * The unique AAC identifier.
-   *
-   * @var string
    */
-  protected $aac;
+  protected string $aac;
 
   /**
    * The forecast periods.
    *
    * @var \BomWeather\Forecast\ForecastPeriod[]
    */
-  protected $forecastPeriods;
+  protected array $forecastPeriods;
 
   /**
    * The area type.
-   *
-   * @var string
    */
-  protected $type;
+  protected string $type;
 
   /**
    * The description.
-   *
-   * @var string
    */
-  protected $description;
+  protected string $description;
 
   /**
    * The parent AAC.
-   *
-   * @var string
    */
-  protected $parentAac;
+  protected string $parentAac;
 
   /**
    * Factory method.
    *
    * @return $this
    */
-  public static function create() {
+  public static function create(): static {
     return new static();
   }
 
diff --git a/src/Forecast/Forecast.php b/src/Forecast/Forecast.php
index 09c8e3d..afbe9d9 100644
--- a/src/Forecast/Forecast.php
+++ b/src/Forecast/Forecast.php
@@ -1,60 +1,58 @@
 <?php
 
+declare(strict_types = 1);
+
 namespace BomWeather\Forecast;
 
 /**
  * A value object for weather forcasts.
  */
-class Forecast {
+final class Forecast {
 
   /**
    * The regions.
    *
    * @var \BomWeather\Forecast\Area[]
    */
-  protected $regions = [];
+  protected array $regions = [];
 
   /**
    * The districts.
    *
    * @var \BomWeather\Forecast\Area[]
    */
-  protected $districts = [];
+  protected array $districts = [];
 
   /**
    * The metropolitan areas.
    *
    * @var \BomWeather\Forecast\Area[]
    */
-  protected $metropolitanAreas = [];
+  protected array $metropolitanAreas = [];
 
   /**
    * The locations.
    *
    * @var \BomWeather\Forecast\Area[]
    */
-  protected $locations = [];
+  protected array $locations = [];
 
   /**
    * The coastal waters.
    *
    * @var \BomWeather\Forecast\Area[]
    */
-  protected $coasts = [];
+  protected array $coasts = [];
 
   /**
    * The issue time.
-   *
-   * @var \DateTime
    */
-  protected $issueTime;
+  protected \DateTimeImmutable $issueTime;
 
   /**
    * Factory method.
-   *
-   * @return $this
    */
-  public static function create() {
+  public static function create(): static {
     return new static();
   }
 
@@ -204,23 +202,15 @@ public function addLocation(Area $location): Forecast {
 
   /**
    * Gets the issue time.
-   *
-   * @return \DateTime
-   *   The issue time.
    */
-  public function getIssueTime(): \DateTime {
+  public function getIssueTime(): ?\DateTimeImmutable {
     return $this->issueTime;
   }
 
   /**
    * Sets the issue time.
-   *
-   * @param \DateTime $issueTime
-   *   The issue time.
-   *
-   * @return $this
    */
-  public function setIssueTime(\DateTime $issueTime): Forecast {
+  public function setIssueTime(\DateTimeImmutable $issueTime): Forecast {
     $this->issueTime = $issueTime;
     return $this;
   }
diff --git a/src/Forecast/ForecastPeriod.php b/src/Forecast/ForecastPeriod.php
index 824f621..22f9918 100644
--- a/src/Forecast/ForecastPeriod.php
+++ b/src/Forecast/ForecastPeriod.php
@@ -1,177 +1,130 @@
 <?php
 
+declare(strict_types = 1);
+
 namespace BomWeather\Forecast;
 
 /**
  * A value object for forecast periods.
  */
-class ForecastPeriod {
+final class ForecastPeriod {
 
   /**
    * The start time.
-   *
-   * @var \DateTime
    */
-  protected $startTime;
+  protected ?\DateTimeImmutable $startTime = NULL;
 
   /**
    * The end time.
-   *
-   * @var \DateTime
    */
-  protected $endTime;
+  protected ?\DateTimeImmutable $endTime = NULL;
 
   /**
    * The air temp maximum in Celsius.
-   *
-   * @var int
    */
-  protected $airTempMaximum;
+  protected ?int $airTempMaximum = NULL;
 
   /**
    * The probability of precipitation.
-   *
-   * @var string
    */
-  protected $probabilityOfPrecipitation;
+  protected ?string $probabilityOfPrecipitation = NULL;
 
   /**
    * The precipitation range.
-   *
-   * @var string
    */
-  protected $precipitationRange;
+  protected ?string $precipitationRange = NULL;
 
   /**
    * The forecast icon code.
-   *
-   * @var string
    */
-  protected $iconCode;
+  protected ?string $iconCode = NULL;
 
   /**
    * The air temp minimum in Celsius.
-   *
-   * @var int
    */
-  protected $airTempMinimum;
+  protected ?int $airTempMinimum = NULL;
 
   /**
    * The precis.
-   *
-   * @var string
    */
-  protected $precis;
+  protected ?string $precis = NULL;
 
   /**
    * The UV alert.
-   *
-   * @var string
    */
-  protected $uvAlert;
+  protected ?string $uvAlert = NULL;
 
   /**
    * The forecast.
-   *
-   * @var string
    */
-  protected $forecast;
+  protected ?string $forecast = NULL;
 
   /**
    * The synoptic situation.
-   *
-   * @var string
    */
-  protected $synoptic;
+  protected ?string $synoptic = NULL;
 
   /**
    * The seas.
-   *
-   * @var string
    */
-  protected $seas;
+  protected ?string $seas = NULL;
 
   /**
    * The swell.
-   *
-   * @var string
    */
-  protected $swell;
+  protected ?string $swell = NULL;
 
   /**
    * The weather.
-   *
-   * @var string
    */
-  protected $weather;
+  protected ?string $weather = NULL;
 
   /**
    * The winds.
-   *
-   * @var string
    */
-  protected $winds;
+  protected ?string $winds = NULL;
 
   /**
    * Factory method.
    *
    * @return $this
    */
-  public static function create() {
+  public static function create(): static {
     return new static();
   }
 
   /**
    * Gets the start time.
-   *
-   * @return \DateTime
-   *   The start time.
    */
-  public function getStartTime(): \DateTime {
+  public function getStartTime(): ?\DateTimeImmutable {
     return $this->startTime;
   }
 
   /**
    * Sets the start time.
-   *
-   * @param \DateTime $startTime
-   *   The start time.
-   *
-   * @return $this
    */
-  public function setStartTime(\DateTime $startTime): ForecastPeriod {
+  public function setStartTime(\DateTimeImmutable $startTime): ForecastPeriod {
     $this->startTime = $startTime;
     return $this;
   }
 
   /**
    * Gets the end time.
-   *
-   * @return \DateTime
-   *   The end time.
    */
-  public function getEndTime(): \DateTime {
+  public function getEndTime(): ?\DateTimeImmutable {
     return $this->endTime;
   }
 
   /**
    * Sets the end time.
-   *
-   * @param \DateTime $endTime
-   *   The end time.
-   *
-   * @return $this
    */
-  public function setEndTime(\DateTime $endTime): ForecastPeriod {
+  public function setEndTime(\DateTimeImmutable $endTime): ForecastPeriod {
     $this->endTime = $endTime;
     return $this;
   }
 
   /**
    * Gets the icon code.
-   *
-   * @return string
-   *   The icon code.
    */
   public function getIconCode(): ?string {
     return $this->iconCode;
@@ -179,11 +132,6 @@ public function getIconCode(): ?string {
 
   /**
    * Sets the icon code.
-   *
-   * @param string $iconCode
-   *   The icon code.
-   *
-   * @return $this
    */
   public function setIconCode(string $iconCode): ForecastPeriod {
     $this->iconCode = $iconCode;
@@ -192,9 +140,6 @@ public function setIconCode(string $iconCode): ForecastPeriod {
 
   /**
    * Gets the precipitation range.
-   *
-   * @return string
-   *   The precipitation range.
    */
   public function getPrecipitationRange(): ?string {
     return $this->precipitationRange;
@@ -202,23 +147,14 @@ public function getPrecipitationRange(): ?string {
 
   /**
    * Sets the precipitation range.
-   *
-   * @param string $precipitationRange
-   *   The precipitation range.
-   *
-   * @return $this
    */
-  public function setPrecipitationRange(string $precipitationRange
-  ): ForecastPeriod {
+  public function setPrecipitationRange(string $precipitationRange): ForecastPeriod {
     $this->precipitationRange = $precipitationRange;
     return $this;
   }
 
   /**
    * Gets the air temp minimum.
-   *
-   * @return int
-   *   The air temp minimum.
    */
   public function getAirTempMinimum(): ?int {
     return $this->airTempMinimum;
@@ -226,11 +162,6 @@ public function getAirTempMinimum(): ?int {
 
   /**
    * Sets the air temp minimum.
-   *
-   * @param int $airTempMinimum
-   *   The air temp minimum.
-   *
-   * @return $this
    */
   public function setAirTempMinimum(int $airTempMinimum): ForecastPeriod {
     $this->airTempMinimum = $airTempMinimum;
@@ -239,9 +170,6 @@ public function setAirTempMinimum(int $airTempMinimum): ForecastPeriod {
 
   /**
    * Gets the air temp maximum.
-   *
-   * @return int
-   *   The air temp maximum.
    */
   public function getAirTempMaximum(): ?int {
     return $this->airTempMaximum;
@@ -249,23 +177,14 @@ public function getAirTempMaximum(): ?int {
 
   /**
    * Sets the air temp maximum.
-   *
-   * @param int $airTempMaximum
-   *   The air temp maximum.
-   *
-   * @return $this
    */
-  public function setAirTempMaximum(int $airTempMaximum
-  ): ForecastPeriod {
+  public function setAirTempMaximum(int $airTempMaximum): ForecastPeriod {
     $this->airTempMaximum = $airTempMaximum;
     return $this;
   }
 
   /**
    * Gets the precis.
-   *
-   * @return string
-   *   The precis.
    */
   public function getPrecis(): ?string {
     return $this->precis;
@@ -273,11 +192,6 @@ public function getPrecis(): ?string {
 
   /**
    * Sets the precis.
-   *
-   * @param string $precis
-   *   The precis.
-   *
-   * @return $this
    */
   public function setPrecis(string $precis): ForecastPeriod {
     $this->precis = $precis;
@@ -286,9 +200,6 @@ public function setPrecis(string $precis): ForecastPeriod {
 
   /**
    * Gets the probability of precipitation.
-   *
-   * @return string
-   *   The probability of precipitation.
    */
   public function getProbabilityOfPrecipitation(): ?string {
     return $this->probabilityOfPrecipitation;
@@ -296,11 +207,6 @@ public function getProbabilityOfPrecipitation(): ?string {
 
   /**
    * Sets the probability of precipitation.
-   *
-   * @param string $probabilityOfPrecipitation
-   *   The probability of precipitation.
-   *
-   * @return $this
    */
   public function setProbabilityOfPrecipitation(
     string $probabilityOfPrecipitation
@@ -311,9 +217,6 @@ public function setProbabilityOfPrecipitation(
 
   /**
    * Gets the forecast.
-   *
-   * @return string
-   *   The forecast.
    */
   public function getForecast(): ?string {
     return $this->forecast;
@@ -321,11 +224,6 @@ public function getForecast(): ?string {
 
   /**
    * Sets the forecast.
-   *
-   * @param string $forecast
-   *   The forecast.
-   *
-   * @return $this
    */
   public function setForecast(string $forecast): ForecastPeriod {
     $this->forecast = $forecast;
@@ -334,9 +232,6 @@ public function setForecast(string $forecast): ForecastPeriod {
 
   /**
    * Gets the UV alert.
-   *
-   * @return string
-   *   The UV alert.
    */
   public function getUvAlert(): ?string {
     return $this->uvAlert;
@@ -344,11 +239,6 @@ public function getUvAlert(): ?string {
 
   /**
    * Sets the UV alert.
-   *
-   * @param string $uvAlert
-   *   The UV alert.
-   *
-   * @return $this
    */
   public function setUvAlert(string $uvAlert): ForecastPeriod {
     $this->uvAlert = $uvAlert;
@@ -357,21 +247,13 @@ public function setUvAlert(string $uvAlert): ForecastPeriod {
 
   /**
    * Gets the synoptic.
-   *
-   * @return string
-   *   The synoptic.
    */
-  public function getSynoptic(): string {
+  public function getSynoptic(): ?string {
     return $this->synoptic;
   }
 
   /**
    * Sets the synoptic.
-   *
-   * @param string $synoptic
-   *   The synoptic.
-   *
-   * @return $this
    */
   public function setSynoptic(string $synoptic): ForecastPeriod {
     $this->synoptic = $synoptic;
@@ -380,21 +262,13 @@ public function setSynoptic(string $synoptic): ForecastPeriod {
 
   /**
    * Gets the seas.
-   *
-   * @return string
-   *   The seas.
    */
-  public function getSeas(): string {
+  public function getSeas(): ?string {
     return $this->seas;
   }
 
   /**
    * Sets the seas.
-   *
-   * @param string $seas
-   *   The seas.
-   *
-   * @return $this
    */
   public function setSeas(string $seas): ForecastPeriod {
     $this->seas = $seas;
@@ -403,21 +277,13 @@ public function setSeas(string $seas): ForecastPeriod {
 
   /**
    * Gets the swell.
-   *
-   * @return string
-   *   The swell.
    */
-  public function getSwell(): string {
+  public function getSwell(): ?string {
     return $this->swell;
   }
 
   /**
    * Sets the swell.
-   *
-   * @param string $swell
-   *   The swell.
-   *
-   * @return $this
    */
   public function setSwell(string $swell): ForecastPeriod {
     $this->swell = $swell;
@@ -426,21 +292,13 @@ public function setSwell(string $swell): ForecastPeriod {
 
   /**
    * Gets the weather.
-   *
-   * @return string
-   *   The weather.
    */
-  public function getWeather(): string {
+  public function getWeather(): ?string {
     return $this->weather;
   }
 
   /**
    * Sets the weather.
-   *
-   * @param string $weather
-   *   The weather.
-   *
-   * @return $this
    */
   public function setWeather(string $weather): ForecastPeriod {
     $this->weather = $weather;
@@ -449,21 +307,13 @@ public function setWeather(string $weather): ForecastPeriod {
 
   /**
    * Gets the winds.
-   *
-   * @return string
-   *   The winds.
    */
-  public function getWinds(): string {
+  public function getWinds(): ?string {
     return $this->winds;
   }
 
   /**
    * Sets the winds.
-   *
-   * @param string $winds
-   *   The winds.
-   *
-   * @return $this
    */
   public function setWinds(string $winds): ForecastPeriod {
     $this->winds = $winds;
diff --git a/src/Forecast/Serializer/AreaNormalizer.php b/src/Forecast/Serializer/AreaNormalizer.php
index 14d9b2b..ee15051 100644
--- a/src/Forecast/Serializer/AreaNormalizer.php
+++ b/src/Forecast/Serializer/AreaNormalizer.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types = 1);
+
 namespace BomWeather\Forecast\Serializer;
 
 use BomWeather\Forecast\Area;
@@ -12,13 +14,12 @@
  */
 class AreaNormalizer extends BaseNormalizer {
 
-  protected $supportedInterfaceOrClass = Area::class;
+  protected string|array $supportedInterfaceOrClass = Area::class;
 
   /**
    * {@inheritdoc}
    */
-  public function denormalize($data, $class, $format = NULL, array $context = []) {
-
+  public function denormalize($data, $type, $format = NULL, array $context = []) {
     if (!$this->serializer instanceof DenormalizerInterface) {
       throw new \RuntimeException('The serializer must implement the DenormalizerInterface.');
     }
@@ -38,7 +39,7 @@ public function denormalize($data, $class, $format = NULL, array $context = [])
         $area->addForecastPeriod($this->serializer->denormalize($period, ForecastPeriod::class));
       }
       else {
-        array_map(function ($period) use ($area) {
+        \array_map(function ($period) use ($area): void {
           $area->addForecastPeriod($this->serializer->denormalize($period, ForecastPeriod::class));
         }, $data['forecast-period'], [$area]);
 
diff --git a/src/Forecast/Serializer/ForecastNormalizer.php b/src/Forecast/Serializer/ForecastNormalizer.php
index 189e414..5b9c7df 100644
--- a/src/Forecast/Serializer/ForecastNormalizer.php
+++ b/src/Forecast/Serializer/ForecastNormalizer.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types = 1);
+
 namespace BomWeather\Forecast\Serializer;
 
 use BomWeather\Forecast\Area;
@@ -15,7 +17,7 @@ class ForecastNormalizer extends BaseNormalizer {
   /**
    * {@inheritdoc}
    */
-  protected $supportedInterfaceOrClass = Forecast::class;
+  protected string|array $supportedInterfaceOrClass = Forecast::class;
 
   /**
    * {@inheritdoc}
@@ -26,15 +28,14 @@ public function denormalize($data, $class, $format = NULL, array $context = [])
     }
 
     $forecast = Forecast::create()
-      ->setIssueTime($this->serializer->denormalize($data['amoc']['issue-time-utc'], \DateTime::class));
+      ->setIssueTime($this->serializer->denormalize($data['amoc']['issue-time-utc'], \DateTimeImmutable::class));
 
     if ($this->isAssoc($data['forecast']['area'])) {
       $area = $data['forecast']['area'];
       $this->setValue($area, $forecast);
     }
     else {
-      array_map(function ($area) use ($forecast) {
-
+      \array_map(function ($area) use ($forecast): void {
         $this->setValue($area, $forecast);
       }, $data['forecast']['area'], [$forecast]);
     }
diff --git a/src/Forecast/Serializer/ForecastPeriodNormalizer.php b/src/Forecast/Serializer/ForecastPeriodNormalizer.php
index 1cd695c..eb52a5e 100644
--- a/src/Forecast/Serializer/ForecastPeriodNormalizer.php
+++ b/src/Forecast/Serializer/ForecastPeriodNormalizer.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types = 1);
+
 namespace BomWeather\Forecast\Serializer;
 
 use BomWeather\Forecast\ForecastPeriod;
@@ -10,15 +12,15 @@
  */
 class ForecastPeriodNormalizer extends BaseNormalizer {
 
-  protected $supportedInterfaceOrClass = ForecastPeriod::class;
+  protected string|array $supportedInterfaceOrClass = ForecastPeriod::class;
 
   /**
    * {@inheritdoc}
    */
   public function denormalize($data, $class, $format = NULL, array $context = []) {
     $period = ForecastPeriod::create()
-      ->setStartTime($this->serializer->denormalize($data['@start-time-utc'], \DateTime::class))
-      ->setEndTime($this->serializer->denormalize($data['@end-time-utc'], \DateTime::class));
+      ->setStartTime($this->serializer->denormalize($data['@start-time-utc'], \DateTimeImmutable::class))
+      ->setEndTime($this->serializer->denormalize($data['@end-time-utc'], \DateTimeImmutable::class));
 
     if (isset($data['text'])) {
       if ($this->isAssoc($data['text'])) {
@@ -26,7 +28,7 @@ public function denormalize($data, $class, $format = NULL, array $context = [])
         $this->setTextValue($text, $period);
       }
       else {
-        array_map(function ($text) use ($period) {
+        \array_map(function ($text) use ($period): void {
           $this->setTextValue($text, $period);
         }, $data['text'], [$period]);
       }
@@ -38,7 +40,7 @@ public function denormalize($data, $class, $format = NULL, array $context = [])
         $this->setElementValue($element, $period);
       }
       else {
-        array_map(function ($element) use ($period) {
+        \array_map(function ($element) use ($period): void {
           $this->setElementValue($element, $period);
         }, $data['element'], [$period]);
       }
@@ -54,18 +56,18 @@ public function denormalize($data, $class, $format = NULL, array $context = [])
    * @param \BomWeather\Forecast\ForecastPeriod $period
    *   The period.
    */
-  protected function setElementValue(array $element, ForecastPeriod $period) {
+  protected function setElementValue(array $element, ForecastPeriod $period): void {
     switch ($element['@type']) {
       case 'forecast_icon_code':
         $period->setIconCode($element['#']);
         break;
 
       case 'air_temperature_minimum':
-        $period->setAirTempMinimum($element['#']);
+        $period->setAirTempMinimum((int) $element['#']);
         break;
 
       case 'air_temperature_maximum':
-        $period->setAirTempMaximum($element['#']);
+        $period->setAirTempMaximum((int) $element['#']);
         break;
 
       case 'precipitation_range':
diff --git a/src/Forecast/Serializer/ForecastSerializerFactory.php b/src/Forecast/Serializer/ForecastSerializerFactory.php
index 48a1c30..8d79ef2 100644
--- a/src/Forecast/Serializer/ForecastSerializerFactory.php
+++ b/src/Forecast/Serializer/ForecastSerializerFactory.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types = 1);
+
 namespace BomWeather\Forecast\Serializer;
 
 use Symfony\Component\Serializer\Encoder\XmlEncoder;
@@ -20,11 +22,10 @@ class ForecastSerializerFactory {
    * @return \Symfony\Component\Serializer\Serializer
    *   The serializer.
    */
-  public static function create($rootNode = 'product') {
-
-    $encoders = [new XmlEncoder($rootNode)];
+  public static function create(string $rootNode = 'product'): Serializer {
+    $encoders = [new XmlEncoder([XmlEncoder::ROOT_NODE_NAME => $rootNode])];
     $normalizers = [
-      new DateTimeNormalizer(\DateTime::RFC3339, new \DateTimeZone('UTC')),
+      new DateTimeNormalizer([DateTimeNormalizer::TIMEZONE_KEY => 'UTC']),
       new ForecastNormalizer(),
       new AreaNormalizer(),
       new ForecastPeriodNormalizer(),
diff --git a/src/Observation/Observation.php b/src/Observation/Observation.php
index 8692dfc..acc17c9 100644
--- a/src/Observation/Observation.php
+++ b/src/Observation/Observation.php
@@ -1,91 +1,68 @@
 <?php
 
+declare(strict_types = 1);
+
 namespace BomWeather\Observation;
 
 /**
  * Value object for an observation.
  */
-class Observation {
+final class Observation {
 
   /**
    * The date time.
-   *
-   * @var \DateTime
    */
-  protected $dateTime;
+  protected ?\DateTimeImmutable $dateTime = NULL;
 
   /**
    * The weather station.
-   *
-   * @var \BomWeather\Observation\Station
    */
-  protected $station;
+  protected ?Station $station = NULL;
 
   /**
    * The temperature observation.
-   *
-   * @var \BomWeather\Observation\Temperature
    */
-  protected $temperature;
+  protected ?Temperature $temperature = NULL;
 
   /**
    * The wind observation.
-   *
-   * @var \BomWeather\Observation\Wind
    */
-  protected $wind;
+  protected ?Wind $wind = NULL;
 
   /**
    * The pressure observation.
-   *
-   * @var \BomWeather\Observation\Pressure
    */
-  protected $pressure;
+  protected ?Pressure $pressure = NULL;
 
   /**
    * The rain since 9am, in millimetres.
-   *
-   * @var int
    */
-  protected $rainSince9am;
+  protected ?string $rainSince9am = NULL;
 
   /**
    * Factory method.
-   *
-   * @return $this
    */
-  public static function create() {
+  public static function create(): static {
     return new static();
   }
 
   /**
    * Gets the DateTime.
-   *
-   * @return \DateTime
-   *   The DateTime.
    */
-  public function getDateTime(): \DateTime {
+  public function getDateTime(): ?\DateTimeImmutable {
     return $this->dateTime;
   }
 
   /**
    * Sets the DateTime.
-   *
-   * @param \DateTime $dateTime
-   *   The DateTime.
-   *
-   * @return $this
    */
-  public function setDateTime(\DateTime $dateTime): Observation {
+  public function setDateTime(\DateTimeImmutable $dateTime): self {
     $this->dateTime = $dateTime;
     return $this;
   }
 
   /**
    * Gets the Station.
-   *
-   * @return \BomWeather\Observation\Station
-   *   The Station.
    */
   public function getStation(): Station {
     return $this->station;
@@ -93,105 +70,68 @@ public function getStation(): Station {
 
   /**
    * Sets the Station.
-   *
-   * @param \BomWeather\Observation\Station $station
-   *   The Station.
-   *
-   * @return $this
    */
-  public function setStation(Station $station): Observation {
+  public function setStation(Station $station): self {
     $this->station = $station;
     return $this;
   }
 
   /**
    * Gets the Temperature.
-   *
-   * @return \BomWeather\Observation\Temperature
-   *   The Temperature.
    */
-  public function getTemperature(): Temperature {
+  public function getTemperature(): ?Temperature {
     return $this->temperature;
   }
 
   /**
    * Sets the Temperature.
-   *
-   * @param \BomWeather\Observation\Temperature $temperature
-   *   The Temperature.
-   *
-   * @return $this
    */
-  public function setTemperature(Temperature $temperature): Observation {
+  public function setTemperature(Temperature $temperature): ?Observation {
     $this->temperature = $temperature;
     return $this;
   }
 
   /**
    * Gets the Wind.
-   *
-   * @return \BomWeather\Observation\Wind
-   *   The Wind.
    */
-  public function getWind(): Wind {
+  public function getWind(): ?Wind {
     return $this->wind;
   }
 
   /**
    * Sets the Wind.
-   *
-   * @param \BomWeather\Observation\Wind $wind
-   *   The Wind.
-   *
-   * @return $this
    */
-  public function setWind(Wind $wind): Observation {
+  public function setWind(Wind $wind): self {
     $this->wind = $wind;
     return $this;
   }
 
   /**
    * Gets the Pressure.
-   *
-   * @return \BomWeather\Observation\Pressure
-   *   The Pressure.
    */
-  public function getPressure(): Pressure {
+  public function getPressure(): ?Pressure {
     return $this->pressure;
   }
 
   /**
    * Sets the Pressure.
-   *
-   * @param \BomWeather\Observation\Pressure $pressure
-   *   The Pressure.
-   *
-   * @return $this
    */
-  public function setPressure(Pressure $pressure): Observation {
+  public function setPressure(Pressure $pressure): self {
     $this->pressure = $pressure;
     return $this;
   }
 
   /**
    * Gets the RainSince9am.
-   *
-   * @return int
-   *   The RainSince9am.
    */
-  public function getRainSince9am(): int {
+  public function getRainSince9am(): ?string {
     return $this->rainSince9am;
   }
 
   /**
    * Sets the RainSince9am.
-   *
-   * @param int $rainSince9am
-   *   The RainSince9am.
-   *
-   * @return $this
    */
-  public function setRainSince9am(int $rainSince9am): Observation {
+  public function setRainSince9am(string $rainSince9am): self {
     $this->rainSince9am = $rainSince9am;
     return $this;
   }
diff --git a/src/Observation/ObservationList.php b/src/Observation/ObservationList.php
index 4db2244..5dfd9c0 100644
--- a/src/Observation/ObservationList.php
+++ b/src/Observation/ObservationList.php
@@ -1,25 +1,25 @@
 <?php
 
+declare(strict_types = 1);
+
 namespace BomWeather\Observation;
 
 /**
  * A value object for a list of observations.
  */
-class ObservationList {
+final class ObservationList {
 
   /**
    * The list of observations.
    *
    * @var \BomWeather\Observation\Observation[]
    */
-  protected $observations;
+  protected array $observations = [];
 
   /**
    * The refresh message.
-   *
-   * @var string
    */
-  protected $refreshMessage;
+  protected ?string $refreshMessage = NULL;
 
   /**
    * Gets the Observations.
@@ -36,10 +36,8 @@ public function getObservations(): array {
    *
    * @param \BomWeather\Observation\Observation[] $observations
    *   The Observations.
-   *
-   * @return $this
    */
-  public function setObservations(array $observations): ObservationList {
+  public function setObservations(array $observations): self {
     $this->observations = $observations;
     return $this;
   }
@@ -49,10 +47,8 @@ public function setObservations(array $observations): ObservationList {
    *
    * @param \BomWeather\Observation\Observation $observation
    *   The observation.
-   *
-   * @return $this
    */
-  public function addObservation(Observation $observation): ObservationList {
+  public function addObservation(Observation $observation): self {
     $this->observations[] = $observation;
     return $this;
   }
@@ -72,23 +68,15 @@ public function getLatest(): ?Observation {
 
   /**
    * Gets the Refresh Message.
-   *
-   * @return string
-   *   The RefreshMessage.
    */
-  public function getRefreshMessage(): string {
+  public function getRefreshMessage(): ?string {
     return $this->refreshMessage;
   }
 
   /**
    * Sets the Refresh Message.
-   *
-   * @param string $refreshMessage
-   *   The RefreshMessage.
-   *
-   * @return $this
    */
-  public function setRefreshMessage(string $refreshMessage): ObservationList {
+  public function setRefreshMessage(string $refreshMessage): self {
     $this->refreshMessage = $refreshMessage;
     return $this;
   }
diff --git a/src/Observation/Pressure.php b/src/Observation/Pressure.php
index fe70acd..5d85cd9 100644
--- a/src/Observation/Pressure.php
+++ b/src/Observation/Pressure.php
@@ -1,40 +1,33 @@
 <?php
 
+declare(strict_types = 1);
+
 namespace BomWeather\Observation;
 
 /**
  * A value object for pressure observations.
  */
-class Pressure {
+final class Pressure {
 
   /**
    * The QNH pressure, in hectopascals.
-   *
-   * @var int
    */
-  protected $qnh;
+  protected ?int $qnh = NULL;
 
   /**
    * The mean sea level pressure, in hectopascals.
-   *
-   * @var int
    */
-  protected $meanSeaLevel;
+  protected ?int $meanSeaLevel = NULL;
 
   /**
    * Factory method.
-   *
-   * @return $this
    */
-  public static function create() {
-    return new static();
+  public static function create(): Pressure {
+    return new Pressure();
   }
 
   /**
    * Gets the PressureQnh.
-   *
-   * @return int
-   *   The PressureQnh.
    */
   public function getQnh(): ?int {
     return $this->qnh;
@@ -42,11 +35,6 @@ public function getQnh(): ?int {
 
   /**
    * Sets the PressureQnh.
-   *
-   * @param int $qnh
-   *   The PressureQnh.
-   *
-   * @return $this
    */
   public function setQnh(int $qnh): Pressure {
     $this->qnh = $qnh;
@@ -55,9 +43,6 @@ public function setQnh(int $qnh): Pressure {
 
   /**
    * Gets the PressureMsl.
-   *
-   * @return int|null
-   *   The PressureMsl.
    */
   public function getMeanSeaLevel(): ?int {
     return $this->meanSeaLevel;
@@ -65,11 +50,6 @@ public function getMeanSeaLevel(): ?int {
 
   /**
    * Sets the PressureMsl.
-   *
-   * @param int $meanSeaLevel
-   *   The PressureMsl.
-   *
-   * @return $this
    */
   public function setMeanSeaLevel(int $meanSeaLevel): Pressure {
     $this->meanSeaLevel = $meanSeaLevel;
diff --git a/src/Observation/Serializer/ObservationListNormalizer.php b/src/Observation/Serializer/ObservationListNormalizer.php
index 0750964..89257aa 100644
--- a/src/Observation/Serializer/ObservationListNormalizer.php
+++ b/src/Observation/Serializer/ObservationListNormalizer.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types = 1);
+
 namespace BomWeather\Observation\Serializer;
 
 use BomWeather\Observation\Observation;
@@ -12,13 +14,12 @@
  */
 class ObservationListNormalizer extends BaseNormalizer {
 
-  protected $supportedInterfaceOrClass = ObservationList::class;
+  protected string|array $supportedInterfaceOrClass = ObservationList::class;
 
   /**
    * {@inheritdoc}
    */
   public function denormalize($data, $class, $format = NULL, array $context = []) {
-
     if (!$this->serializer instanceof DenormalizerInterface) {
       throw new \RuntimeException('The serializer must implement the DenormalizerInterface.');
     }
@@ -26,7 +27,7 @@ public function denormalize($data, $class, $format = NULL, array $context = [])
     $observationList = new ObservationList();
     $observationList->setRefreshMessage($data['observations']['header'][0]['refresh_message']);
 
-    array_map(function ($observationData) use ($observationList) {
+    \array_map(function ($observationData) use ($observationList): void {
       $observationList->addObservation($this->serializer->denormalize($observationData, Observation::class));
     }, $data['observations']['data'], [$observationList]);
 
diff --git a/src/Observation/Serializer/ObservationNormalizer.php b/src/Observation/Serializer/ObservationNormalizer.php
index 3ca33d8..4803354 100644
--- a/src/Observation/Serializer/ObservationNormalizer.php
+++ b/src/Observation/Serializer/ObservationNormalizer.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types = 1);
+
 namespace BomWeather\Observation\Serializer;
 
 use BomWeather\Observation\Observation;
@@ -14,13 +16,12 @@
  */
 class ObservationNormalizer extends BaseNormalizer {
 
-  protected $supportedInterfaceOrClass = Observation::class;
+  protected string|array $supportedInterfaceOrClass = Observation::class;
 
   /**
    * {@inheritdoc}
    */
-  public function denormalize($data, $class, $format = NULL, array $context = []) {
-
+  public function denormalize($data, $type, $format = NULL, array $context = []) {
     $station = Station::create()
       ->setId($data['wmo'])
       ->setLatitude($data['lat'])
@@ -32,7 +33,7 @@ public function denormalize($data, $class, $format = NULL, array $context = [])
       ->setApparentTemp($data['apparent_t'])
       ->setDeltaT($data['delta_t'])
       ->setDewPoint($data['dewpt'])
-      ->setRealtiveHumidity($data['rel_hum']);
+      ->setRelativeHumidity($data['rel_hum']);
 
     $wind = Wind::create()
       ->setDirection($data['wind_dir'])
@@ -50,7 +51,7 @@ public function denormalize($data, $class, $format = NULL, array $context = [])
     }
 
     $observation = Observation::create()
-      ->setDateTime($this->serializer->denormalize($data['aifstime_utc'], \DateTime::class))
+      ->setDateTime($this->serializer->denormalize($data['aifstime_utc'], \DateTimeImmutable::class))
       ->setRainSince9am($data['rain_trace'])
       ->setPressure($pressure)
       ->setTemperature($temperature)
diff --git a/src/Observation/Serializer/ObservationSerializerFactory.php b/src/Observation/Serializer/ObservationSerializerFactory.php
index b3e4cb7..e310f47 100644
--- a/src/Observation/Serializer/ObservationSerializerFactory.php
+++ b/src/Observation/Serializer/ObservationSerializerFactory.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types = 1);
+
 namespace BomWeather\Observation\Serializer;
 
 use Symfony\Component\Serializer\Encoder\JsonEncoder;
@@ -18,13 +20,12 @@ class ObservationSerializerFactory {
    * @return \Symfony\Component\Serializer\Serializer
    *   The serializer.
    */
-  public static function create() {
-
+  public static function create(): Serializer {
     $encoders = [new JsonEncoder()];
     $normalizers = [
       new ObservationListNormalizer(),
       new ObservationNormalizer(),
-      new DateTimeNormalizer(\DateTime::RFC3339, new \DateTimeZone('UTC')),
+      new DateTimeNormalizer([DateTimeNormalizer::TIMEZONE_KEY => 'UTC']),
       new GetSetMethodNormalizer(),
     ];
     return new Serializer($normalizers, $encoders);
diff --git a/src/Observation/Station.php b/src/Observation/Station.php
index 8257e33..d964fcc 100644
--- a/src/Observation/Station.php
+++ b/src/Observation/Station.php
@@ -1,137 +1,97 @@
 <?php
 
+declare(strict_types = 1);
+
 namespace BomWeather\Observation;
 
 /**
  * A value object for a weather observation station.
  */
-class Station {
+final class Station {
 
   /**
    * The station ID.
-   *
-   * @var string
    */
-  protected $id;
+  protected ?int $id = NULL;
 
   /**
    * The station name.
-   *
-   * @var string
    */
-  protected $name;
+  protected ?string $name = NULL;
 
   /**
    * The latitude.
-   *
-   * @var float
    */
-  protected $latitude;
+  protected ?float $latitude = NULL;
 
   /**
    * The longitude.
-   *
-   * @var float
    */
-  protected $longitude;
+  protected ?float $longitude = NULL;
 
   /**
    * Factory method.
-   *
-   * @return $this
    */
-  public static function create() {
-    return new static();
+  public static function create(): Station {
+    return new Station();
   }
 
   /**
    * Gets the Name.
-   *
-   * @return string
-   *   The Name.
    */
-  public function getName(): string {
+  public function getName(): ?string {
     return $this->name;
   }
 
   /**
    * Sets the Name.
-   *
-   * @param string $name
-   *   The Name.
-   *
-   * @return $this
    */
-  public function setName(string $name): Station {
+  public function setName(string $name): self {
     $this->name = $name;
     return $this;
   }
 
   /**
    * Gets the Latitude.
-   *
-   * @return float
-   *   The Latitude.
    */
-  public function getLatitude(): float {
+  public function getLatitude(): ?float {
     return $this->latitude;
   }
 
   /**
    * Sets the Latitude.
-   *
-   * @param float $latitude
-   *   The Latitude.
-   *
-   * @return $this
    */
-  public function setLatitude(float $latitude): Station {
+  public function setLatitude(float $latitude): self {
     $this->latitude = $latitude;
     return $this;
   }
 
   /**
    * Gets the Longitude.
-   *
-   * @return float
-   *   The Longitude.
    */
-  public function getLongitude(): float {
+  public function getLongitude(): ?float {
     return $this->longitude;
   }
 
   /**
    * Sets the Longitude.
-   *
-   * @param float $longitude
-   *   The Longitude.
-   *
-   * @return $this
    */
-  public function setLongitude(float $longitude): Station {
+  public function setLongitude(float $longitude): self {
     $this->longitude = $longitude;
     return $this;
   }
 
   /**
    * Gets the Id.
-   *
-   * @return string
-   *   The Id.
    */
-  public function getId(): string {
+  public function getId(): ?int {
     return $this->id;
   }
 
   /**
    * Sets the Id.
-   *
-   * @param string $id
-   *   The Id.
-   *
-   * @return $this
    */
-  public function setId(string $id): Station {
+  public function setId(int $id): self {
     $this->id = $id;
     return $this;
   }
diff --git a/src/Observation/Temperature.php b/src/Observation/Temperature.php
index 077521d..2d622ae 100644
--- a/src/Observation/Temperature.php
+++ b/src/Observation/Temperature.php
@@ -1,73 +1,55 @@
 <?php
 
+declare(strict_types = 1);
+
 namespace BomWeather\Observation;
 
 /**
  * A value object for temperature observations.
  */
-class Temperature {
+final class Temperature {
 
   /**
-   * The air temperature, in celsius.
-   *
-   * @var float
+   * The air temperature, in Celsius.
    */
-  protected $airTemp;
+  protected ?float $airTemp = NULL;
 
   /**
-   * The apparent temperature, in celsius.
-   *
-   * @var float
+   * The apparent temperature, in Celsius.
    */
-  protected $apparentTemp;
+  protected ?float $apparentTemp = NULL;
 
   /**
-   * The dew point, in celsius.
-   *
-   * @var float
+   * The dew point, in Celsius.
    */
-  protected $dewPoint;
+  protected ?float $dewPoint = NULL;
 
   /**
    * The relative humidity, as a percentage.
-   *
-   * @var int
    */
-  protected $realtiveHumidity;
+  protected ?int $relativeHumidity = NULL;
 
   /**
-   * The wet bulb depression, in celsius.
-   *
-   * @var float
+   * The wet bulb depression, in Celsius.
    */
-  protected $deltaT;
+  protected ?float $deltaT = NULL;
 
   /**
    * Factory method.
-   *
-   * @return $this
    */
-  public static function create() {
-    return new static();
+  public static function create(): Temperature {
+    return new Temperature();
   }
 
   /**
    * Gets the AirTemp.
-   *
-   * @return float
-   *   The AirTemp.
    */
-  public function getAirTemp(): float {
+  public function getAirTemp(): ?float {
     return $this->airTemp;
   }
 
   /**
    * Sets the AirTemp.
-   *
-   * @param float $airTemp
-   *   The AirTemp.
-   *
-   * @return $this
    */
   public function setAirTemp(float $airTemp): Temperature {
     $this->airTemp = $airTemp;
@@ -76,21 +58,13 @@ public function setAirTemp(float $airTemp): Temperature {
 
   /**
    * Gets the ApparentTemp.
-   *
-   * @return float
-   *   The ApparentTemp.
    */
-  public function getApparentTemp(): float {
+  public function getApparentTemp(): ?float {
     return $this->apparentTemp;
   }
 
   /**
    * Sets the ApparentTemp.
-   *
-   * @param float $apparentTemp
-   *   The ApparentTemp.
-   *
-   * @return $this
    */
   public function setApparentTemp(float $apparentTemp): Temperature {
     $this->apparentTemp = $apparentTemp;
@@ -99,21 +73,13 @@ public function setApparentTemp(float $apparentTemp): Temperature {
 
   /**
    * Gets the DewPoint.
-   *
-   * @return float
-   *   The DewPoint.
    */
-  public function getDewPoint(): float {
+  public function getDewPoint(): ?float {
     return $this->dewPoint;
   }
 
   /**
    * Sets the DewPoint.
-   *
-   * @param float $dewPoint
-   *   The DewPoint.
-   *
-   * @return $this
    */
   public function setDewPoint(float $dewPoint): Temperature {
     $this->dewPoint = $dewPoint;
@@ -121,45 +87,29 @@ public function setDewPoint(float $dewPoint): Temperature {
   }
 
   /**
-   * Gets the RealtiveHumidity.
-   *
-   * @return int
-   *   The RealtiveHumidity.
+   * Gets the RelativeHumidity.
    */
-  public function getRealtiveHumidity(): int {
-    return $this->realtiveHumidity;
+  public function getRelativeHumidity(): ?int {
+    return $this->relativeHumidity;
   }
 
   /**
-   * Sets the RealtiveHumidity.
-   *
-   * @param int $realtiveHumidity
-   *   The RealtiveHumidity.
-   *
-   * @return $this
+   * Sets the RelativeHumidity.
    */
-  public function setRealtiveHumidity(int $realtiveHumidity): Temperature {
-    $this->realtiveHumidity = $realtiveHumidity;
+  public function setRelativeHumidity(int $relativeHumidity): Temperature {
+    $this->relativeHumidity = $relativeHumidity;
     return $this;
   }
 
   /**
    * Gets the DeltaT.
-   *
-   * @return float
-   *   The DeltaT.
    */
-  public function getDeltaT(): float {
+  public function getDeltaT(): ?float {
     return $this->deltaT;
   }
 
   /**
    * Sets the DeltaT.
-   *
-   * @param float $deltaT
-   *   The DeltaT.
-   *
-   * @return $this
    */
   public function setDeltaT(float $deltaT): Temperature {
     $this->deltaT = $deltaT;
diff --git a/src/Observation/Wind.php b/src/Observation/Wind.php
index ece15ac..d10f8d4 100644
--- a/src/Observation/Wind.php
+++ b/src/Observation/Wind.php
@@ -1,74 +1,57 @@
 <?php
 
+declare(strict_types = 1);
+
 namespace BomWeather\Observation;
 
 /**
  * Value object for a wind observation.
  */
-class Wind {
+final class Wind {
 
   /**
    * The wind direction.
-   *
-   * @var string
    */
-  protected $direction;
+  protected ?string $direction = NULL;
 
   /**
    * The wind speed, in kilometres per Hour.
-   *
-   * @var int
    */
-  protected $speedKmh;
+  protected ?int $speedKmh = NULL;
 
   /**
    * The wind gusts, in kilometres per Hour.
-   *
-   * @var int
    */
-  protected $gustKmh;
-
+  protected ?int $gustKmh = NULL;
 
   /**
    * The wind speed, in knots.
-   *
-   * @var int
    */
-  protected $speedKnots;
+  protected ?int $speedKnots = NULL;
 
   /**
    * The wind gusts, in knots.
-   *
-   * @var int
    */
-  protected $gustKnots;
+  protected ?int $gustKnots = NULL;
 
   /**
    * Factory method.
    *
    * @return $this
    */
-  public static function create() {
-    return new static();
+  public static function create(): Wind {
+    return new Wind();
   }
 
   /**
    * Gets the Direction.
-   *
-   * @return string
-   *   The Direction.
    */
-  public function getDirection(): string {
+  public function getDirection(): ?string {
     return $this->direction;
   }
 
   /**
    * Sets the Direction.
-   *
-   * @param string $direction
-   *   The Direction.
-   *
-   * @return $this
    */
   public function setDirection(string $direction): Wind {
     $this->direction = $direction;
@@ -77,21 +60,13 @@ public function setDirection(string $direction): Wind {
 
   /**
    * Gets the Speed, in kilometres per hour.
-   *
-   * @return int
-   *   The SpeedKmh.
    */
-  public function getSpeedKmh(): int {
+  public function getSpeedKmh(): ?int {
     return $this->speedKmh;
   }
 
   /**
    * Sets the Speed, in kilometres per hour.
-   *
-   * @param int $speedKmh
-   *   The SpeedKmh.
-   *
-   * @return $this
    */
   public function setSpeedKmh(int $speedKmh): Wind {
     $this->speedKmh = $speedKmh;
@@ -100,21 +75,13 @@ public function setSpeedKmh(int $speedKmh): Wind {
 
   /**
    * Gets the Gust, in kilometres per hour.
-   *
-   * @return int
-   *   The GustKmh.
    */
-  public function getGustKmh(): int {
+  public function getGustKmh(): ?int {
     return $this->gustKmh;
   }
 
   /**
    * Sets the Gust, in kilometres per hour.
-   *
-   * @param int $gustKmh
-   *   The GustKmh.
-   *
-   * @return $this
    */
   public function setGustKmh(int $gustKmh): Wind {
     $this->gustKmh = $gustKmh;
@@ -123,21 +90,13 @@ public function setGustKmh(int $gustKmh): Wind {
 
   /**
    * Gets the Speed, in knots.
-   *
-   * @return int
-   *   The SpeedKnots.
    */
-  public function getSpeedKnots(): int {
+  public function getSpeedKnots(): ?int {
     return $this->speedKnots;
   }
 
   /**
    * Sets the Speed, in knots.
-   *
-   * @param int $speedKnots
-   *   The SpeedKnots.
-   *
-   * @return $this
    */
   public function setSpeedKnots(int $speedKnots): Wind {
     $this->speedKnots = $speedKnots;
@@ -146,21 +105,13 @@ public function setSpeedKnots(int $speedKnots): Wind {
 
   /**
    * Gets the Gust, in knots.
-   *
-   * @return int
-   *   The GustsKnots.
    */
-  public function getGustKnots(): int {
+  public function getGustKnots(): ?int {
     return $this->gustKnots;
   }
 
   /**
    * Sets the Gust, in knots.
-   *
-   * @param int $gustKnots
-   *   The GustsKnots.
-   *
-   * @return $this
    */
   public function setGustKnots(int $gustKnots): Wind {
     $this->gustKnots = $gustKnots;
diff --git a/src/Util/BaseNormalizer.php b/src/Util/BaseNormalizer.php
index 2ed9ba1..f1cc270 100644
--- a/src/Util/BaseNormalizer.php
+++ b/src/Util/BaseNormalizer.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types = 1);
+
 namespace BomWeather\Util;
 
 use Symfony\Component\Serializer\Normalizer\AbstractNormalizer;
@@ -11,6 +13,13 @@ abstract class BaseNormalizer extends AbstractNormalizer {
 
   use ClassNameSupportNormalizerTrait;
 
+  /**
+   * {@inheritdoc}
+   */
+  public function normalize(mixed $object, string $format = NULL, array $context = []) {
+    throw new \RuntimeException("Method not implemented.");
+  }
+
   /**
    * Checks whether the array is associative.
    *
@@ -20,15 +29,8 @@ abstract class BaseNormalizer extends AbstractNormalizer {
    * @return bool
    *   TRUE if the array is associative.
    */
-  protected function isAssoc(array $array) {
-    return (bool) count(array_filter(array_keys($array), 'is_string'));
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function normalize($object, $format = NULL, array $context = []) {
-    throw new \RuntimeException("Method not implemented.");
+  protected function isAssoc(array $array): bool {
+    return (bool) \count(\array_filter(\array_keys($array), 'is_string'));
   }
 
 }
diff --git a/src/Util/ClassNameSupportNormalizerTrait.php b/src/Util/ClassNameSupportNormalizerTrait.php
index 8717a84..45d7e1c 100644
--- a/src/Util/ClassNameSupportNormalizerTrait.php
+++ b/src/Util/ClassNameSupportNormalizerTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types = 1);
+
 namespace BomWeather\Util;
 
 /**
@@ -9,38 +11,25 @@ trait ClassNameSupportNormalizerTrait {
 
   /**
    * The interface or class that this Normalizer supports.
-   *
-   * @var string|array
    */
-  protected $supportedInterfaceOrClass;
+  protected string|array $supportedInterfaceOrClass;
 
   /**
    * The format this Normalizer supports.
-   *
-   * @var string|array
    */
-  protected $format;
+  protected string|array $format;
 
   /**
    * Gets the string or array of supported classes.
-   *
-   * @return array|string
-   *   The string or array of supported classes.
    */
-  public function getSupportedInterfaceOrClass() {
+  public function getSupportedInterfaceOrClass(): string|array {
     return $this->supportedInterfaceOrClass;
   }
 
   /**
    * Sets the string or array of supported classes.
-   *
-   * @param array|string $supported_interface_or_class
-   *   The string or array of supported classes.
-   *
-   * @return $this
-   *   The current object.
    */
-  public function setSupportedInterfaceOrClass($supported_interface_or_class) {
+  public function setSupportedInterfaceOrClass(string|array $supported_interface_or_class): self {
     $this->supportedInterfaceOrClass = $supported_interface_or_class;
     return $this;
   }
@@ -48,16 +37,16 @@ public function setSupportedInterfaceOrClass($supported_interface_or_class) {
   /**
    * {@inheritdoc}
    */
-  public function supportsNormalization($data, $format = NULL) {
+  public function supportsNormalization(mixed $data, string $format = NULL /* , array $context = [] */): bool {
     // If we aren't dealing with an object or the format is not supported return
     // now.
-    if (!is_object($data) || !$this->checkFormat($format)) {
+    if (!\is_object($data) || !$this->checkFormat($format)) {
       return FALSE;
     }
 
     $supported = (array) $this->supportedInterfaceOrClass;
 
-    return (bool) array_filter($supported, function ($name) use ($data) {
+    return (bool) \array_filter($supported, function ($name) use ($data) {
       return $data instanceof $name;
     });
   }
@@ -65,7 +54,7 @@ public function supportsNormalization($data, $format = NULL) {
   /**
    * {@inheritdoc}
    */
-  public function supportsDenormalization($data, $type, $format = NULL) {
+  public function supportsDenormalization(mixed $data, string $type, string $format = NULL /* , array $context = [] */): bool {
     // If the format is not supported return now.
     if (!$this->checkFormat($format)) {
       return FALSE;
@@ -74,30 +63,27 @@ public function supportsDenormalization($data, $type, $format = NULL) {
     $supported = (array) $this->supportedInterfaceOrClass;
 
     $subclass_check = function ($name) use ($type) {
-      return (class_exists($name) || interface_exists($name)) && is_subclass_of($type,
+      return (\class_exists($name) || \interface_exists($name)) && \is_subclass_of($type,
           $name, TRUE);
     };
 
-    return in_array($type, $supported) || array_filter($supported,
+    return \in_array($type, $supported) || \array_filter($supported,
         $subclass_check);
   }
 
   /**
    * Checks if the provided format is supported by this serializer.
    *
-   * @param string $format
-   *   The format to check.
-   *
    * @return bool
    *   TRUE if the format is supported, FALSE otherwise. If no format is
    *   specified this will return TRUE.
    */
-  protected function checkFormat($format = NULL) {
+  protected function checkFormat(string $format = NULL): bool {
     if (!isset($format) || !isset($this->format)) {
       return TRUE;
     }
 
-    return in_array($format, (array) $this->format);
+    return \in_array($format, (array) $this->format);
   }
 
 }
diff --git a/tests/Functional/BomClientTest.php b/tests/Functional/BomClientTest.php
deleted file mode 100644
index 803d6b8..0000000
--- a/tests/Functional/BomClientTest.php
+++ /dev/null
@@ -1,64 +0,0 @@
-<?php
-
-namespace BomWeather\Tests\Functional\Forecast;
-
-use BomWeather\BomClient;
-use PHPUnit\Framework\TestCase;
-use Psr\Log\NullLogger;
-
-/**
- * @coversDefaultClass \BomWeather\BomClient
- */
-class BomClientTest extends TestCase {
-
-  /**
-   * @covers ::__construct()
-   * @covers ::getForecast()
-   */
-  public function testGetForecast() {
-
-    $logger = new NullLogger();
-    $client = new BomClient($logger);
-    $forecast = $client->getForecast('IDN10064');
-
-    $this->assertNotNull($forecast);
-  }
-
-  /**
-   * @covers ::__construct()
-   * @covers ::getObservationList()
-   */
-  public function testGetObservation() {
-
-    $logger = new NullLogger();
-    $client = new BomClient($logger);
-    $observationList = $client->getObservationList('IDN60901', '95757');
-
-    $this->assertNotNull($observationList);
-
-    $refreshMessage = $observationList->getRefreshMessage();
-
-    // Get the latest observation.
-    $observation = $observationList->getLatest();
-    $rain = $observation->getRainSince9am();
-
-    $station = $observation->getStation();
-    $name = $station->getName();
-
-    $temperature = $observation->getTemperature();
-    $airTemp = $temperature->getAirTemp();
-    $apparentTemp = $temperature->getApparentTemp();
-    $relativeHumidity = $temperature->getRealtiveHumidity();
-
-    $wind = $observation->getWind();
-    $direction = $wind->getDirection();
-    $speedKmh = $wind->getSpeedKmh();
-    $gustKmh = $wind->getGustKmh();
-
-    $pressure = $observation->getPressure();
-    $qnh = $pressure->getQnh();
-    $meanSeaLevel = $pressure->getMeanSeaLevel();
-
-  }
-
-}
diff --git a/tests/bootstrap.php b/tests/bootstrap.php
index 7ddf755..2117040 100644
--- a/tests/bootstrap.php
+++ b/tests/bootstrap.php
@@ -5,8 +5,6 @@
  * Boostrap for PHPUnit.
  */
 
-assert_options(ASSERT_ACTIVE, FALSE);
-
 $autoloader = __DIR__ . '/../vendor/autoload.php';
 $loader = require $autoloader;
 
diff --git a/tests/src/Functional/BomClientTest.php b/tests/src/Functional/BomClientTest.php
new file mode 100644
index 0000000..427cefb
--- /dev/null
+++ b/tests/src/Functional/BomClientTest.php
@@ -0,0 +1,88 @@
+<?php
+
+declare(strict_types = 1);
+
+namespace BomWeather\Tests\Functional;
+
+use BomWeather\BomClient;
+use GuzzleHttp\Psr7\Stream;
+use Http\Mock\Client;
+use PHPUnit\Framework\TestCase;
+use Psr\Http\Message\RequestFactoryInterface;
+use Psr\Http\Message\RequestInterface;
+use Psr\Http\Message\ResponseInterface;
+use Psr\Log\NullLogger;
+
+/**
+ * @coversDefaultClass \BomWeather\BomClient
+ */
+class BomClientTest extends TestCase {
+
+  /**
+   * @covers ::__construct()
+   * @covers ::getForecast()
+   */
+  public function testGetForecast(): void {
+    $logger = new NullLogger();
+    $httpClient = new Client();
+    $response = $this->createMock(ResponseInterface::class);
+    $response->method('getBody')
+      ->willReturn(new Stream(\fopen(__DIR__ . '/../../fixtures/IDN10064.xml', 'r')));
+    $httpClient->addResponse($response);
+    $requestFactory = $this->createMock(RequestFactoryInterface::class);
+    $request = $this->createMock(RequestInterface::class);
+    $requestFactory->method('createRequest')
+      ->willReturn($request);
+    $request->method('withHeader')->willReturn($request);
+    $client = new BomClient($httpClient, $requestFactory, $logger);
+    $forecast = $client->getForecast('IDN10064');
+
+    $this->assertNotNull($forecast);
+  }
+
+  /**
+   * @covers ::__construct()
+   * @covers ::getObservationList()
+   */
+  public function testGetObservation(): void {
+    $logger = new NullLogger();
+    $httpClient = new Client();
+    $response = $this->createMock(ResponseInterface::class);
+    $response->method('getBody')
+      ->willReturn(new Stream(\fopen(__DIR__ . '/../../fixtures/IDN60901.94759.json', 'r')));
+    $httpClient->addResponse($response);
+    $requestFactory = $this->createMock(RequestFactoryInterface::class);
+    $request = $this->createMock(RequestInterface::class);
+    $requestFactory->method('createRequest')
+      ->willReturn($request);
+    $request->method('withHeader')->willReturn($request);
+    $client = new BomClient($httpClient, $requestFactory, $logger);
+    $observationList = $client->getObservationList('IDN60901', '95757');
+
+    $this->assertNotNull($observationList);
+
+    $refreshMessage = $observationList->getRefreshMessage();
+
+    // Get the latest observation.
+    $observation = $observationList->getLatest();
+    $rain = $observation->getRainSince9am();
+
+    $station = $observation->getStation();
+    $name = $station->getName();
+
+    $temperature = $observation->getTemperature();
+    $airTemp = $temperature->getAirTemp();
+    $apparentTemp = $temperature->getApparentTemp();
+    $relativeHumidity = $temperature->getRelativeHumidity();
+
+    $wind = $observation->getWind();
+    $direction = $wind->getDirection();
+    $speedKmh = $wind->getSpeedKmh();
+    $gustKmh = $wind->getGustKmh();
+
+    $pressure = $observation->getPressure();
+    $qnh = $pressure->getQnh();
+    $meanSeaLevel = $pressure->getMeanSeaLevel();
+  }
+
+}
diff --git a/tests/Unit/Forecast/Serializer/ForecastSerializerTest.php b/tests/src/Unit/Forecast/Serializer/ForecastSerializerTest.php
similarity index 87%
rename from tests/Unit/Forecast/Serializer/ForecastSerializerTest.php
rename to tests/src/Unit/Forecast/Serializer/ForecastSerializerTest.php
index 05d9827..9adc823 100644
--- a/tests/Unit/Forecast/Serializer/ForecastSerializerTest.php
+++ b/tests/src/Unit/Forecast/Serializer/ForecastSerializerTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types = 1);
+
 namespace BomWeather\Tests\Unit\Forecast\Serializer;
 
 use BomWeather\Forecast\Forecast;
@@ -14,11 +16,11 @@ class ForecastSerializerTest extends TestCase {
   /**
    * @covers ::create
    */
-  public function testDeserializeSydney() {
+  public function testDeserializeSydney(): void {
     $factory = new ForecastSerializerFactory();
     $serializer = $factory->create();
 
-    $xml = file_get_contents(__DIR__ . '/../../../fixtures/IDN10064.xml');
+    $xml = \file_get_contents(__DIR__ . '/../../../../fixtures/IDN10064.xml');
 
     /** @var \BomWeather\Forecast\Forecast $forecast */
     $forecast = $serializer->deserialize($xml, Forecast::class, 'xml');
@@ -30,7 +32,7 @@ public function testDeserializeSydney() {
     $regions = $forecast->getRegions();
     $this->assertCount(1, $regions);
 
-    $region = array_shift($regions);
+    $region = \array_shift($regions);
     $this->assertEquals('NSW_FA001', $region->getAac());
     $this->assertEquals('New South Wales', $region->getDescription());
 
@@ -40,7 +42,7 @@ public function testDeserializeSydney() {
     $metros = $forecast->getMetropolitanAreas();
     $this->assertCount(1, $metros);
 
-    $metro = array_shift($metros);
+    $metro = \array_shift($metros);
     $this->assertEquals('NSW_ME001', $metro->getAac());
     $this->assertEquals('Sydney', $metro->getDescription());
     $this->assertEquals('metropolitan', $metro->getType());
@@ -52,7 +54,7 @@ public function testDeserializeSydney() {
     $locations = $forecast->getLocations();
     $this->assertCount(8, $locations);
 
-    $location = array_shift($locations);
+    $location = \array_shift($locations);
 
     $this->assertEquals('NSW_PT131', $location->getAac());
     $this->assertEquals('Sydney', $location->getDescription());
@@ -61,12 +63,11 @@ public function testDeserializeSydney() {
 
     $this->assertSydneyPeriods($location->getForecastPeriods());
 
-    $location = end($locations);
+    $location = \end($locations);
     $this->assertEquals('NSW_PT237', $location->getAac());
     $this->assertEquals('Bondi', $location->getDescription());
 
     $this->assertBondiPeriods($location->getForecastPeriods());
-
   }
 
   /**
@@ -75,9 +76,9 @@ public function testDeserializeSydney() {
    * @param \BomWeather\Forecast\RegionForecastPeriod[] $periods
    *   The regions.
    */
-  protected function assertRegionPeriods(array $periods) {
+  protected function assertRegionPeriods(array $periods): void {
     $this->assertCount(1, $periods);
-    $period = array_shift($periods);
+    $period = \array_shift($periods);
 
     $this->assertEquals('2018-06-20T21:41:56+00:00', $period->getStartTime()->format(DATE_RFC3339));
     $this->assertEquals('2018-06-20T21:41:56+00:00', $period->getEndTime()->format(DATE_RFC3339));
@@ -90,22 +91,21 @@ protected function assertRegionPeriods(array $periods) {
    * @param \BomWeather\Forecast\ForecastPeriod[] $metroPeriods
    *   The periods.
    */
-  protected function assertMetroPeriods(array $metroPeriods) {
+  protected function assertMetroPeriods(array $metroPeriods): void {
     $this->assertCount(7, $metroPeriods);
-    $period = array_shift($metroPeriods);
+    $period = \array_shift($metroPeriods);
 
     $this->assertEquals('2018-06-20T14:00:00+00:00', $period->getStartTime()->format(DATE_RFC3339));
     $this->assertEquals('2018-06-21T14:00:00+00:00', $period->getEndTime()->format(DATE_RFC3339));
     $this->assertEquals('Cloudy. High (70%) chance of showers along the coastal fringe, slight (30%) chance elsewhere, becoming less likely in the late afternoon and evening. Light winds.', $period->getForecast());
     $this->assertEquals('Sun protection not recommended, UV Index predicted to reach 2 [Low]', $period->getUvAlert());
 
-    $period = array_shift($metroPeriods);
+    $period = \array_shift($metroPeriods);
 
     $this->assertEquals('2018-06-21T14:00:00+00:00', $period->getStartTime()->format(DATE_RFC3339));
     $this->assertEquals('2018-06-22T14:00:00+00:00', $period->getEndTime()->format(DATE_RFC3339));
     $this->assertEquals('Mostly sunny. Fog and patches of light frost in the west in the early morning. Light winds.', $period->getForecast());
     $this->assertNull($period->getUvAlert());
-
   }
 
   /**
@@ -114,9 +114,9 @@ protected function assertMetroPeriods(array $metroPeriods) {
    * @param \BomWeather\Forecast\ForecastPeriod[] $locationPeriods
    *   The location periods.
    */
-  protected function assertSydneyPeriods(array $locationPeriods) {
+  protected function assertSydneyPeriods(array $locationPeriods): void {
     $this->assertCount(7, $locationPeriods);
-    $period = array_shift($locationPeriods);
+    $period = \array_shift($locationPeriods);
 
     $this->assertEquals('2018-06-20T21:37:12+00:00', $period->getStartTime()->format(DATE_RFC3339));
     $this->assertEquals('2018-06-21T14:00:00+00:00', $period->getEndTime()->format(DATE_RFC3339));
@@ -128,7 +128,7 @@ protected function assertSydneyPeriods(array $locationPeriods) {
     $this->assertEquals(16, $period->getAirTempMaximum());
     $this->assertNull($period->getPrecipitationRange());
 
-    $period = array_shift($locationPeriods);
+    $period = \array_shift($locationPeriods);
 
     $this->assertEquals('2018-06-21T14:00:00+00:00', $period->getStartTime()->format(DATE_RFC3339));
     $this->assertEquals('2018-06-22T14:00:00+00:00', $period->getEndTime()->format(DATE_RFC3339));
@@ -147,10 +147,10 @@ protected function assertSydneyPeriods(array $locationPeriods) {
    * @param \BomWeather\Forecast\ForecastPeriod[] $locationPeriods
    *   The location periods.
    */
-  protected function assertBondiPeriods(array $locationPeriods) {
+  protected function assertBondiPeriods(array $locationPeriods): void {
     $this->assertCount(1, $locationPeriods);
 
-    $period = array_shift($locationPeriods);
+    $period = \array_shift($locationPeriods);
     $this->assertEquals('2018-06-20T21:37:12+00:00', $period->getStartTime()->format(DATE_RFC3339));
     $this->assertEquals('2018-06-21T14:00:00+00:00', $period->getEndTime()->format(DATE_RFC3339));
     $this->assertEquals(16, $period->getAirTempMaximum());
diff --git a/tests/Unit/Observation/Serializer/ObservationSerializerTest.php b/tests/src/Unit/Observation/Serializer/ObservationSerializerTest.php
similarity index 90%
rename from tests/Unit/Observation/Serializer/ObservationSerializerTest.php
rename to tests/src/Unit/Observation/Serializer/ObservationSerializerTest.php
index 94e6659..401f51f 100644
--- a/tests/Unit/Observation/Serializer/ObservationSerializerTest.php
+++ b/tests/src/Unit/Observation/Serializer/ObservationSerializerTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types = 1);
+
 namespace BomWeather\Tests\Unit\Observation\Serializer;
 
 use BomWeather\Observation\ObservationList;
@@ -14,9 +16,9 @@ class ObservationSerializerTest extends TestCase {
   /**
    * @covers ::create()
    */
-  public function testDeserialize() {
+  public function testDeserialize(): void {
     $serializer = ObservationSerializerFactory::create();
-    $json = file_get_contents(__DIR__ . '/../../../fixtures/IDN60901.94759.json');
+    $json = \file_get_contents(__DIR__ . '/../../../../fixtures/IDN60901.94759.json');
 
     /** @var \BomWeather\Observation\ObservationList $observationList */
     $observationList = $serializer->deserialize($json, ObservationList::class, 'json');
@@ -41,7 +43,7 @@ public function testDeserialize() {
     $this->assertEquals(7.8, $temperature->getApparentTemp());
     $this->assertEquals(1.1, $temperature->getDeltaT());
     $this->assertEquals(7.5, $temperature->getDewPoint());
-    $this->assertEquals(86, $temperature->getRealtiveHumidity());
+    $this->assertEquals(86, $temperature->getRelativeHumidity());
 
     $wind = $observation->getWind();
     $this->assertEquals('W', $wind->getDirection());
@@ -55,7 +57,6 @@ public function testDeserialize() {
     $this->assertEquals('Terrey Hills', $station->getName());
     $this->assertEquals(-33.7, $station->getLatitude());
     $this->assertEquals(151.2, $station->getLongitude());
-
   }
 
 }