defmodule Mix.Tasks.Six do
  @shortdoc "Runs tests with coverage analysis"
  @moduledoc """
  Runs `mix test --cover` with Six as the coverage tool.

      mix six [options] [-- test_args]

  ## Options

    * `--threshold N` - Report threshold for formatter output (default: 90)
    * `--minimum-coverage N` - Fail if total coverage drops below N
    * `--output-dir DIR` - Output directory (default: .six/)
    * `--skip FILE` - Additional file pattern to skip (repeatable)
    * `--track-ignores` - Write a `.sixignore` file at the project root
      tracking all explicit coverage exclusions. Commit this file to
      review ignore changes in PRs.
    * `--import-cover DIR` - Import .coverdata files from DIR and generate
      a report without running tests. Used to merge coverage from
      partitioned CI runs.

  Any arguments after `--` are passed through to `mix test`.
  """

  use Mix.Task

  Module.register_attribute(__MODULE__, :six, accumulate: true)

  @six :ignore
  @impl true
  def run(args) do
    {opts, test_args} = split_args(args)

    Mix.env(:test)

    with_track_ignores(opts, fn ->
      if import_dir = opts[:import_cover] do
        import_and_report(import_dir, opts)
      else
        run_tests(opts, test_args)
      end
    end)
  end

  @six :ignore
  defp with_track_ignores(opts, fun) do
    if Keyword.get(opts, :track_ignores) do
      original = Application.get_env(:six, :track_ignores)
      Application.put_env(:six, :track_ignores, true)

      try do
        fun.()
      after
        case original do
          nil -> Application.delete_env(:six, :track_ignores)
          val -> Application.put_env(:six, :track_ignores, val)
        end
      end
    else
      fun.()
    end
  end

  @six :ignore
  defp run_tests(opts, test_args) do
    project = Mix.Project.config()
    test_coverage = Keyword.get(project, :test_coverage, [])
    test_coverage = Keyword.put(test_coverage, :tool, Six)
    test_coverage = merge_cli_opts(test_coverage, opts)

    Application.put_env(:mix, :test_coverage, test_coverage)

    Mix.Task.run("test", ["--cover" | test_args])
  end

  @six :ignore
  defp import_and_report(dir, opts) do
    unless File.dir?(dir) do
      Mix.raise("--import-cover directory does not exist: #{dir}")
    end

    :cover.start()

    compile_path = Mix.Project.compile_path()
    Six.Cover.compile_modules(compile_path)

    {imported, errors} = Six.Cover.import_all_coverdata(dir)

    Enum.each(errors, fn {file, reason} ->
      IO.warn("Failed to import #{file}: #{inspect(reason)}")
    end)

    if imported == 0 do
      Mix.raise("No .coverdata files found in #{dir}")
    end

    IO.puts("Imported #{imported} coverdata file(s) from #{dir}")

    Six.Report.run(opts)
  end

  @doc false
  def split_args(args) do
    {args_before, args_after} =
      case Enum.split_while(args, &(&1 != "--")) do
        {before, ["--" | after_]} -> {before, after_}
        {before, []} -> {before, []}
      end

    {parsed, _, _} =
      OptionParser.parse(args_before,
        strict: [
          threshold: :integer,
          minimum_coverage: :float,
          output_dir: :string,
          skip: :keep,
          track_ignores: :boolean,
          import_cover: :string
        ],
        aliases: [t: :threshold, o: :output_dir]
      )

    {parsed, args_after}
  end

  @doc false
  def merge_cli_opts(test_coverage, opts) do
    Enum.reduce(opts, test_coverage, fn
      {:threshold, val}, acc ->
        summary = Keyword.get(acc, :summary, [])
        Keyword.put(acc, :summary, Keyword.put(summary, :threshold, val))

      {:minimum_coverage, val}, acc ->
        Keyword.put(acc, :minimum_coverage, val)

      {:output_dir, val}, acc ->
        Keyword.put(acc, :output_dir, val)

      {:skip, val}, acc ->
        acc ++ [skip: val]

      _, acc ->
        acc
    end)
  end
end