defmodule Mix.Tasks.Test.Seq do
  @moduledoc """
  Runs all test files sequentially, each in its own OS process.

  This avoids SQLite's global VFS contention that causes spurious
  "out of memory" errors when test files run in parallel.

  ## Usage

      mix test.seq
      mix test.seq --trace
  """

  use Mix.Task

  @shortdoc "Run tests sequentially, one file at a time"

  def run(args) do
    test_files = find_test_files()

    IO.puts("Found #{length(test_files)} test files")
    IO.puts("Running tests sequentially...")

    failed_files = run_test_files(test_files, args, [])

    if failed_files != [] do
      IO.puts("\nFailed files: #{Enum.join(failed_files, ", ")}")
      Mix.raise("#{length(failed_files)} test file(s) failed")
    else
      IO.puts("\n✓ All tests passed!")
    end
  end

  defp run_test_files([], _args, failed_files), do: failed_files

  defp run_test_files([file | rest], args, failed_files) do
    IO.puts("\n=== Running #{file} ===")

    case System.cmd("mix", ["test", file] ++ args, into: IO.stream()) do
      {_, 0} ->
        IO.puts("✓ #{file} passed")
        run_test_files(rest, args, failed_files)

      {_, exit_code} ->
        IO.puts("✗ #{file} failed (exit code: #{exit_code})")
        run_test_files(rest, args, [file | failed_files])
    end
  end

  defp find_test_files do
    Path.wildcard("test/**/*_test.exs")
    |> Enum.sort()
  end
end