refactor: change the architecture to allow different search backends

Right now this solves no issue, but I want to experiment with adding
more search backends in the future. For this to be easier, it's probably
good to have an idea of what a "backend" actually is 🙂

I think they can help solve performance issues in massive
repositories. For example, I found out that "git grep" is much faster
than ripgrep in some cases (5s vs 40s).

Related to #110

lua/blink-ripgrep/backends/ripgrep/ripgrep.lua

@@ -0,0 +1,146 @@
+---@class blink-ripgrep.Backend
+---@field config blink-ripgrep.Options
+local RipgrepBackend = {}
+
+---@param config table
+function RipgrepBackend.new(config)
+  local self = setmetatable({}, { __index = RipgrepBackend })
+  self.config = config
+  return self --[[@as blink-ripgrep.Backend]]
+end
+
+function RipgrepBackend:get_matches(prefix, context, resolve)
+  if self.config.mode ~= "on" then
+    if self.config.debug then
+      local debug = require("blink-ripgrep.debug")
+      debug.add_debug_message("mode is off, skipping the search")
+      debug.add_debug_invocation({ "ignored-because-mode-is-off" })
+    end
+    resolve()
+    return
+  end
+
+  if string.len(prefix) < self.config.prefix_min_len then
+    resolve()
+    return
+  end
+
+  -- builtin default command
+  local command_module =
+    require("blink-ripgrep.backends.ripgrep.ripgrep_command")
+  local cmd = command_module.get_command(prefix, self.config)
+
+  if cmd == nil then
+    if self.config.debug then
+      local debug = require("blink-ripgrep.debug")
+      debug.add_debug_message("no command returned, skipping the search")
+      debug.add_debug_invocation({ "ignored-because-no-command" })
+    end
+
+    resolve()
+    return
+  end
+
+  if vim.tbl_contains(self.config.ignore_paths, cmd.root) then
+    if self.config.debug then
+      local debug = require("blink-ripgrep.debug")
+      debug.add_debug_message("skipping search in ignored path" .. cmd.root)
+      debug.add_debug_invocation({ "ignored", cmd.root })
+    end
+    resolve()
+
+    return
+  end
+
+  if self.config.debug then
+    if cmd.debugify_for_shell then
+      cmd:debugify_for_shell()
+    end
+
+    require("blink-ripgrep.visualization").flash_search_prefix(prefix)
+    require("blink-ripgrep.debug").add_debug_invocation(cmd)
+  end
+
+  local rg = vim.system(cmd.command, nil, function(result)
+    vim.schedule(function()
+      if result.code ~= 0 then
+        resolve()
+        return
+      end
+
+      local lines = vim.split(result.stdout, "\n")
+      local cwd = vim.uv.cwd() or ""
+
+      local parsed =
+        require("blink-ripgrep.backends.ripgrep.ripgrep_parser").parse(
+          lines,
+          cwd,
+          self.config.context_size
+        )
+      local kinds = require("blink.cmp.types").CompletionItemKind
+
+      ---@type table<string, blink.cmp.CompletionItem>
+      local items = {}
+      for _, file in pairs(parsed.files) do
+        for _, match in pairs(file.matches) do
+          local matchkey = match.match.text
+
+          -- PERF: only register the match once - right now there is no useful
+          -- way to display the same match multiple times
+          if not items[matchkey] then
+            local label = match.match.text
+            local docstring = ""
+            for _, line in ipairs(match.context_preview) do
+              docstring = docstring .. line.text .. "\n"
+            end
+
+            local draw_docs = function(draw_opts)
+              require("blink-ripgrep.documentation").render_item_documentation(
+                self.config,
+                draw_opts,
+                file,
+                match
+              )
+            end
+
+            ---@diagnostic disable-next-line: missing-fields
+            items[matchkey] = {
+              documentation = {
+                kind = "markdown",
+                value = docstring,
+                draw = draw_docs,
+                -- legacy, will be removed in a future release of blink
+                -- https://github.com/Saghen/blink.cmp/issues/1113
+                render = draw_docs,
+              },
+              source_id = "blink-ripgrep",
+              kind = kinds.Text,
+              label = label,
+              insertText = matchkey,
+            }
+          end
+        end
+      end
+
+      vim.schedule(function()
+        resolve({
+          is_incomplete_forward = false,
+          is_incomplete_backward = false,
+          items = vim.tbl_values(items),
+          context = context,
+        })
+      end)
+    end)
+  end)
+
+  return function()
+    rg:kill(9)
+    if self.config.debug then
+      require("blink-ripgrep.debug").add_debug_message(
+        "killed previous invocation"
+      )
+    end
+  end
+end
+
+return RipgrepBackend

lua/blink-ripgrep/documentation.lua

@@ -0,0 +1,70 @@
+local documentation = {}
+
+local highlight_ns_id = 0
+pcall(function()
+  highlight_ns_id = require("blink.cmp.config").appearance.highlight_ns
+end)
+vim.api.nvim_set_hl(0, "BlinkRipgrepMatch", { link = "Search", default = true })
+
+---@param config blink-ripgrep.Options
+---@param draw_opts blink.cmp.CompletionDocumentationDrawOpts
+---@param file blink-ripgrep.RipgrepFile
+---@param match blink-ripgrep.RipgrepMatch
+function documentation.render_item_documentation(config, draw_opts, file, match)
+  local bufnr = draw_opts.window:get_buf()
+  ---@type string[]
+  local text = {
+    file.relative_to_cwd,
+    string.rep(
+      "─",
+      -- TODO account for the width of the scrollbar if it's visible
+      draw_opts.window:get_width()
+        - draw_opts.window:get_border_size().horizontal
+        - 1
+    ),
+  }
+  for _, data in ipairs(match.context_preview) do
+    table.insert(text, data.text)
+  end
+
+  -- TODO add extmark highlighting for the divider line like in blink
+  vim.api.nvim_buf_set_lines(bufnr, 0, -1, true, text)
+
+  local filetype = vim.filetype.match({ filename = file.relative_to_cwd })
+  local parser_name = vim.treesitter.language.get_lang(filetype or "")
+  local parser_installed = parser_name
+    and pcall(function()
+      return vim.treesitter.get_parser(nil, file.language, {})
+    end)
+
+  if not parser_installed and config.fallback_to_regex_highlighting then
+    -- Can't show highlighted text because no treesitter parser
+    -- has been installed for this language.
+    --
+    -- Fall back to regex based highlighting that is bundled in
+    -- neovim. It might not be perfect but it's much better
+    -- than no colors at all
+    vim.schedule(function()
+      vim.api.nvim_set_option_value("filetype", file.language, { buf = bufnr })
+      vim.api.nvim_buf_call(bufnr, function()
+        vim.cmd("syntax on")
+      end)
+    end)
+  else
+    assert(parser_name, "missing parser") -- lua-language-server should narrow this but can't
+    require("blink.cmp.lib.window.docs").highlight_with_treesitter(
+      bufnr,
+      parser_name,
+      2,
+      #text
+    )
+  end
+
+  require("blink-ripgrep.highlighting").highlight_match_in_doc_window(
+    bufnr,
+    match,
+    highlight_ns_id
+  )
+end
+
+return documentation