defmodule Mix.Tasks.Compile.Hologram do
  @moduledoc """
  Builds Hologram project JavaScript bundles, the call graph of the code,
  PLTs needed by the runtime and PLTs needed to speed up future compilation.
  """

  use Mix.Task.Compiler

  require Logger

  alias Hologram.Commons.PLT
  alias Hologram.Commons.SystemUtils
  alias Hologram.Compiler
  alias Hologram.Compiler.CallGraph
  alias Hologram.Reflection

  @ls_build_dirs [".elixir_ls", ".elixir-tools", ".expert", ".lexical"]

  @impl Mix.Task.Compiler
  # If the options are strings, it means that the task was executed directly by the Elixir compiler.
  def run([hd | _tail]) when is_binary(hd) do
    run(build_default_opts())
  end

  @doc """
  Benchmarks: https://github.com/bartblast/hologram/blob/master/benchmarks/mix/tasks/compile.hologram/README.md
  """
  @impl Mix.Task.Compiler
  def run(opts) do
    opts = Keyword.merge(build_default_opts(), opts)

    cond do
      opts[:force?] -> compile_with_lock(opts)
      language_server_build?(opts) -> :noop
      !compiler_enabled?() -> :noop
      true -> compile_with_lock(opts)
    end
  end

  defp build_default_opts do
    root_dir = Reflection.root_dir()
    assets_dir = Path.join([root_dir, "deps", "hologram", "assets"])
    build_dir = Reflection.build_dir()
    node_modules_path = Path.join(assets_dir, "node_modules")

    [
      assets_dir: assets_dir,
      build_dir: build_dir,
      esbuild_bin_path: Path.join([node_modules_path, ".bin", "esbuild"]),
      js_dir: Path.join(assets_dir, "js"),
      node_modules_path: node_modules_path,
      static_dir: Path.join([root_dir, "priv", "static", "hologram"]),
      tmp_dir: Path.join(build_dir, "tmp")
    ]
  end

  defp compile(opts) do
    {:ok, sup} = DynamicSupervisor.start_link(strategy: :one_for_one)

    try do
      Logger.info("Hologram: compiler started")

      assets_dir = opts[:assets_dir]
      build_dir = opts[:build_dir]

      File.mkdir_p!(build_dir)
      File.mkdir_p!(opts[:static_dir])
      File.mkdir_p!(opts[:tmp_dir])

      Compiler.maybe_install_js_deps(assets_dir, build_dir)

      {old_module_digest_plt, module_digest_plt_dump_path} =
        Compiler.maybe_load_module_digest_plt(build_dir, supervisor: sup)

      new_module_digest_plt = Compiler.build_module_digest_plt!(supervisor: sup)

      module_digests_diff =
        Compiler.diff_module_digest_plts(old_module_digest_plt, new_module_digest_plt)

      # Building IR PLT from scratch is faster that dumping it to a file,
      # and then loading and patching it (benchmarked on an app with 1628 modules):
      # build: ~310 ms
      # dump: ~350 ms
      # load: ~465 ms
      # patch: not benchmarked
      ir_plt = Compiler.build_ir_plt(supervisor: sup)

      {call_graph, call_graph_dump_path} =
        Compiler.maybe_load_call_graph(build_dir, supervisor: sup)

      call_graph
      |> CallGraph.patch(ir_plt, module_digests_diff)
      |> CallGraph.add_non_discoverable_edges()

      # Must be computed before remove_manually_ported_mfas/1 strips the Task.await/1 vertex.
      async_mfas = CallGraph.list_async_mfas(call_graph)

      call_graph_for_runtime =
        call_graph
        |> CallGraph.clone(supervisor: sup)
        # DEFER: In case the list of manually ported MFAs grows to ~32 vertices,
        # consider using similar strategy to CallGraph.remove_runtime_mfas!/2
        # or implement opts param for Digraph.remove_vertices/2 to allow rebuilding the graph.
        |> CallGraph.remove_manually_ported_mfas()

      runtime_mfas = CallGraph.list_runtime_mfas(call_graph_for_runtime)

      runtime_entry_file_path =
        Compiler.create_runtime_entry_file(runtime_mfas, ir_plt, async_mfas, opts)

      page_modules = Reflection.list_pages()

      Compiler.validate_page_modules(page_modules)

      call_graph_for_pages = CallGraph.remove_runtime_mfas!(call_graph_for_runtime, runtime_mfas)

      page_entry_files_info =
        page_modules
        |> Compiler.create_page_entry_files(call_graph_for_pages, ir_plt, async_mfas, opts)
        |> Enum.map(fn {entry_name, entry_file_path} ->
          {entry_name, entry_file_path, "page"}
        end)

      entry_files_info = [{"runtime", runtime_entry_file_path, "runtime"} | page_entry_files_info]

      old_build_static_artifacts =
        opts[:static_dir]
        |> File.ls!()
        |> Enum.map(fn file_name -> Path.join(opts[:static_dir], file_name) end)

      bundles_info = Compiler.bundle(entry_files_info, opts)

      new_build_static_artifacts =
        Enum.reduce(bundles_info, [], fn bundle_info, acc ->
          [bundle_info.static_bundle_path, bundle_info.static_source_map_path | acc]
        end)

      {page_digest_plt, page_digest_plt_dump_path} =
        Compiler.build_page_digest_plt(bundles_info, Keyword.put(opts, :supervisor, sup))

      PLT.dump(page_digest_plt, page_digest_plt_dump_path)
      CallGraph.dump(call_graph, call_graph_dump_path)
      PLT.dump(new_module_digest_plt, module_digest_plt_dump_path)

      Enum.each(old_build_static_artifacts -- new_build_static_artifacts, &File.rm!/1)

      Logger.info("Hologram: compiler finished")

      :ok
    after
      DynamicSupervisor.stop(sup)
    end
  end

  defp compile_with_lock(opts) do
    lock_path = Path.join(opts[:build_dir], Reflection.compiler_lock_file_name())

    with_lock(lock_path, fn ->
      compile(opts)
    end)
  end

  defp compiler_enabled? do
    # credo:disable-for-next-line Credo.Check.Warning.MixEnv
    Mix.env() not in [:dev, :test] or System.get_env("HOLOGRAM_START") == "1"
  end

  defp language_server_build?(opts) do
    path_components = Path.split(opts[:build_dir])
    Enum.any?(@ls_build_dirs, fn dir -> dir in path_components end)
  end

  defp maybe_remove_file(lock_path) do
    if File.exists?(lock_path) do
      File.rm(lock_path)
    end
  end

  defp maybe_remove_stale_lock(lock_path) do
    if File.exists?(lock_path) do
      case File.read(lock_path) do
        {:ok, os_pid_str} ->
          validate_lock_file_and_proceed_accordingly(lock_path, os_pid_str)

        {:error, _reason} ->
          remove_unreadable_lock_file(lock_path)
      end
    end
  end

  defp remove_lock_file_with_invalid_os_pid(lock_path) do
    Logger.info("Hologram: removing lock file with invalid OS-level PID format")
    File.rm(lock_path)
  end

  defp remove_lock_for_dead_process(lock_path, os_pid) do
    Logger.info(
      "Hologram: removing stale lock file (OS-level process #{os_pid} no longer exists)"
    )

    File.rm(lock_path)
  end

  defp remove_unreadable_lock_file(lock_path) do
    Logger.info("Hologram: removing unreadable lock file")
    File.rm(lock_path)
  end

  defp validate_lock_file_and_proceed_accordingly(lock_path, os_pid_str) do
    case Integer.parse(os_pid_str) do
      {os_pid, _remainder} ->
        if not SystemUtils.os_process_alive?(os_pid) do
          remove_lock_for_dead_process(lock_path, os_pid)
        end

      :error ->
        remove_lock_file_with_invalid_os_pid(lock_path)
    end
  end

  defp with_lock(lock_path, fun) do
    lock_path
    |> Path.dirname()
    |> File.mkdir_p!()

    maybe_remove_stale_lock(lock_path)

    case File.open(lock_path, [:write, :exclusive]) do
      {:ok, file} ->
        # Write OS-level PID to lock file for stale lock detection
        IO.write(file, "#{System.pid()}")
        File.close(file)

        try do
          fun.()
        catch
          kind, reason ->
            maybe_remove_file(lock_path)
            :erlang.raise(kind, reason, __STACKTRACE__)
        after
          maybe_remove_file(lock_path)
        end

      {:error, :eexist} ->
        Logger.info("Hologram: compiler already running, waiting...")
        :timer.sleep(1_000)
        with_lock(lock_path, fun)

      {:error, reason} ->
        raise "Hologram: failed to acquire compiler lock: #{inspect(reason)}"
    end
  end
end