defmodule Mix.Tasks.Compile.CljElixir do
  @moduledoc """
  Mix compiler plugin for CljElixir `.clje` files.

  Integrates `.clje` source files into the standard Mix build pipeline.
  Supports incremental compilation via a manifest that tracks source file
  modification times and the modules they produce.

  ## Configuration

  In your `mix.exs`, add `:compile.clj_elixir` to your compilers and
  configure source paths:

      def project do
        [
          compilers: [:clj_elixir] ++ Mix.compilers(),
          clj_elixir_paths: ["src"]
        ]
      end

  ## How It Works

  1. Scans configured source paths for `.clje` files
  2. Checks the manifest for previously compiled files and their mtimes
  3. Compiles only stale files (new or modified since last build)
  4. Writes `.beam` files to the build output directory
  5. Updates the manifest with new module info
  6. Returns `{:ok, diagnostics}` or `{:error, diagnostics}`

  ## Manifest

  The manifest is stored at `_build/ENV/.clj_elixir_manifest` and tracks
  `{source_path, mtime, [module_names]}` tuples for incremental compilation.
  """

  use Mix.Task.Compiler

  @manifest_filename ".clj_elixir_manifest"
  @recursive true

  @impl true
  def run(argv) do
    {opts, _, _} =
      OptionParser.parse(argv,
        switches: [force: :boolean, verbose: :boolean],
        aliases: [f: :force, v: :verbose]
      )

    force? = opts[:force] || false
    verbose? = opts[:verbose] || false

    project = Mix.Project.config()
    source_paths = project[:clj_elixir_paths] || ["src"]
    build_path = Mix.Project.compile_path(project)

    # Ensure build directory exists
    File.mkdir_p!(build_path)

    # Find all .clje source files
    sources = find_sources(source_paths)

    if sources == [] do
      {:noop, []}
    else
      manifest_path = manifest_path()
      manifest = load_manifest(manifest_path)

      # Determine which files need recompilation
      {stale, removed} = partition_sources(sources, manifest, force?)

      if stale == [] and removed == [] do
        if verbose?, do: Mix.shell().info("All .clje files are up to date")
        {:noop, []}
      else
        # Clean up modules from removed source files
        removed_diagnostics = clean_removed(removed, manifest, build_path, verbose?)

        # Compile stale files
        {compiled, diagnostics} = compile_stale(stale, build_path, verbose?)

        # Build new manifest from existing (unchanged) + newly compiled
        unchanged_entries =
          manifest
          |> Enum.reject(fn {path, _mtime, _modules} ->
            path in stale or path in removed
          end)

        new_manifest = unchanged_entries ++ compiled
        save_manifest(manifest_path, new_manifest)

        all_diagnostics = removed_diagnostics ++ diagnostics

        has_errors? = Enum.any?(all_diagnostics, &(&1.severity == :error))

        if has_errors? do
          {:error, to_mix_diagnostics(all_diagnostics)}
        else
          {:ok, to_mix_diagnostics(all_diagnostics)}
        end
      end
    end
  end

  @impl true
  def manifests do
    [manifest_path()]
  end

  @impl true
  def clean do
    manifest_path = manifest_path()
    manifest = load_manifest(manifest_path)
    build_path = Mix.Project.compile_path()

    Enum.each(manifest, fn {_path, _mtime, modules} ->
      Enum.each(modules, fn module ->
        beam_file = Path.join(build_path, "#{module}.beam")
        File.rm(beam_file)
      end)
    end)

    File.rm(manifest_path)
    :ok
  end

  # ---------------------------------------------------------------------------
  # Source discovery
  # ---------------------------------------------------------------------------

  defp find_sources(paths) do
    paths
    |> Enum.flat_map(fn path ->
      path
      |> Path.join("**/*.clje")
      |> Path.wildcard()
    end)
    |> Enum.sort_by(fn path ->
      parts = Path.split(path)
      basename = Path.basename(path, ".clje")
      # Protocols must compile first (priority 0), then everything else (priority 1)
      priority = if basename == "protocols", do: 0, else: 1
      {-length(parts), priority, path}
    end)
  end

  # ---------------------------------------------------------------------------
  # Staleness detection
  # ---------------------------------------------------------------------------

  defp partition_sources(sources, manifest, force?) do
    manifest_map = Map.new(manifest, fn {path, mtime, modules} -> {path, {mtime, modules}} end)

    stale =
      if force? do
        sources
      else
        Enum.filter(sources, fn source ->
          case Map.get(manifest_map, source) do
            nil ->
              true

            {old_mtime, _modules} ->
              current_mtime = file_mtime(source)
              current_mtime > old_mtime
          end
        end)
      end

    source_set = MapSet.new(sources)

    removed =
      manifest
      |> Enum.map(fn {path, _mtime, _modules} -> path end)
      |> Enum.reject(&MapSet.member?(source_set, &1))

    {stale, removed}
  end

  # ---------------------------------------------------------------------------
  # Compilation
  # ---------------------------------------------------------------------------

  defp compile_stale(sources, build_path, verbose?) do
    results =
      Enum.map(sources, fn source ->
        if verbose?, do: Mix.shell().info("Compiling #{source}")
        compile_source(source, build_path)
      end)

    {compiled, diagnostics} =
      Enum.reduce(results, {[], []}, fn
        {:ok, entry, diags}, {compiled, all_diags} ->
          {[entry | compiled], all_diags ++ diags}

        {:error, diags}, {compiled, all_diags} ->
          {compiled, all_diags ++ diags}
      end)

    {Enum.reverse(compiled), diagnostics}
  end

  defp compile_source(source, build_path) do
    case CljElixir.Compiler.compile_file_to_beam(source,
           output_dir: build_path,
           vector_as_list: true
         ) do
      {:ok, modules} ->
        mtime = file_mtime(source)
        module_names = Enum.map(modules, fn {mod, _binary} -> mod end)
        entry = {source, mtime, module_names}

        diagnostics =
          if module_names == [] do
            [
              %{
                severity: :warning,
                message: "#{source} produced no modules",
                file: source,
                line: 0,
                col: 0
              }
            ]
          else
            []
          end

        {:ok, entry, diagnostics}

      {:error, diagnostics} ->
        enriched =
          Enum.map(diagnostics, fn diag ->
            Map.put_new(diag, :file, source)
          end)

        {:error, enriched}
    end
  end

  # ---------------------------------------------------------------------------
  # Cleanup
  # ---------------------------------------------------------------------------

  defp clean_removed(removed, manifest, build_path, verbose?) do
    manifest_map = Map.new(manifest, fn {path, mtime, modules} -> {path, {mtime, modules}} end)

    Enum.flat_map(removed, fn path ->
      case Map.get(manifest_map, path) do
        nil ->
          []

        {_mtime, modules} ->
          if verbose?, do: Mix.shell().info("Cleaning removed source #{path}")

          Enum.each(modules, fn module ->
            beam_file = Path.join(build_path, "#{module}.beam")
            File.rm(beam_file)

            # Purge the module from the code server
            :code.purge(module)
            :code.delete(module)
          end)

          []
      end
    end)
  end

  # ---------------------------------------------------------------------------
  # Manifest I/O
  # ---------------------------------------------------------------------------

  defp manifest_path do
    Path.join(Mix.Project.manifest_path(), @manifest_filename)
  end

  defp load_manifest(path) do
    case File.read(path) do
      {:ok, contents} ->
        try do
          contents
          |> :erlang.binary_to_term()
          |> validate_manifest()
        rescue
          _ -> []
        end

      {:error, _} ->
        []
    end
  end

  defp validate_manifest(data) when is_list(data) do
    Enum.filter(data, fn
      {path, mtime, modules}
      when is_binary(path) and is_integer(mtime) and is_list(modules) ->
        true

      _ ->
        false
    end)
  end

  defp validate_manifest(_), do: []

  defp save_manifest(path, entries) do
    File.mkdir_p!(Path.dirname(path))
    File.write!(path, :erlang.term_to_binary(entries))
  end

  # ---------------------------------------------------------------------------
  # Diagnostics
  # ---------------------------------------------------------------------------

  defp to_mix_diagnostics(diagnostics) do
    Enum.map(diagnostics, fn diag ->
      %Mix.Task.Compiler.Diagnostic{
        file: Map.get(diag, :file, "unknown"),
        severity: diag.severity,
        message: diag.message,
        position: diag.line,
        compiler_name: "clj_elixir"
      }
    end)
  end

  # ---------------------------------------------------------------------------
  # File utilities
  # ---------------------------------------------------------------------------

  defp file_mtime(path) do
    case File.stat(path, time: :posix) do
      {:ok, %{mtime: mtime}} -> mtime
      {:error, _} -> 0
    end
  end
end