defmodule ExDoc.Formatter.EPUB do
  @moduledoc false

  @mimetype "application/epub+zip"
  alias __MODULE__.{Assets, Templates}
  alias ExDoc.Formatter.HTML

  @doc """
  Generate EPUB documentation for the given modules.
  """
  @spec run([ExDoc.ModuleNode.t()], [ExDoc.ModuleNode.t()], ExDoc.Config.t()) :: String.t()
  def run(project_nodes, filtered_modules, config) when is_map(config) do
    config = normalize_config(config)
    File.rm_rf!(config.output)
    File.mkdir_p!(Path.join(config.output, "OEBPS"))

    project_nodes =
      HTML.render_all(project_nodes, filtered_modules, ".xhtml", config, highlight_tag: "samp")

    nodes_map = %{
      modules: HTML.filter_list(:module, project_nodes),
      tasks: HTML.filter_list(:task, project_nodes)
    }

    extras = config |> HTML.build_extras(".xhtml") |> group_extras()
    config = %{config | extras: extras}

    assets_dir = "OEBPS/assets"
    static_files = HTML.generate_assets(config, assets_dir, default_assets(config))
    HTML.generate_logo(assets_dir, config)
    HTML.generate_cover(assets_dir, config)

    uuid = "urn:uuid:#{uuid4()}"
    datetime = format_datetime()

    generate_content(config, nodes_map, uuid, datetime, static_files)
    generate_nav(config, nodes_map)
    generate_title(config)
    generate_extras(config)
    generate_list(config, nodes_map.modules)
    generate_list(config, nodes_map.tasks)

    {:ok, epub} = generate_epub(config.output)
    File.rm_rf!(config.output)
    Path.relative_to_cwd(epub)
  end

  defp normalize_config(config) do
    output =
      config.output
      |> Path.expand()
      |> Path.join("#{config.project}")

    %{config | output: output}
  end

  defp generate_extras(config) do
    for {_title, extras} <- config.extras do
      Enum.each(extras, fn %{id: id, title: title, title_content: title_content, content: content} ->
        output = "#{config.output}/OEBPS/#{id}.xhtml"
        html = Templates.extra_template(config, title, title_content, content)

        if File.regular?(output) do
          IO.puts(:stderr, "warning: file #{Path.relative_to_cwd(output)} already exists")
        end

        File.write!(output, html)
      end)
    end
  end

  defp generate_content(config, nodes, uuid, datetime, static_files) do
    static_files =
      static_files
      |> Enum.filter(fn name ->
        String.contains?(name, "OEBPS") and config.output |> Path.join(name) |> File.regular?()
      end)
      |> Enum.map(&Path.relative_to(&1, "OEBPS"))

    content = Templates.content_template(config, nodes, uuid, datetime, static_files)
    File.write("#{config.output}/OEBPS/content.opf", content)
  end

  defp generate_nav(config, nodes) do
    content = Templates.nav_template(config, nodes)
    File.write("#{config.output}/OEBPS/nav.xhtml", content)
  end

  defp group_extras(extras) do
    {extras_by_group, groups} =
      extras
      |> Enum.with_index()
      |> Enum.reduce({%{}, %{}}, fn {x, index}, {extras_by_group, groups} ->
        group = if x.group != "", do: x.group, else: "Extras"
        extras_by_group = Map.update(extras_by_group, group, [x], &[x | &1])
        groups = Map.put_new(groups, group, index)
        {extras_by_group, groups}
      end)

    groups
    |> Map.to_list()
    |> List.keysort(1)
    |> Enum.map(fn {k, _} -> {k, Enum.reverse(Map.get(extras_by_group, k))} end)
  end

  defp generate_title(config) do
    content = Templates.title_template(config)
    File.write("#{config.output}/OEBPS/title.xhtml", content)
  end

  defp generate_list(config, nodes) do
    nodes
    |> Task.async_stream(&generate_module_page(&1, config), timeout: :infinity)
    |> Enum.map(&elem(&1, 1))
  end

  defp generate_epub(output) do
    :zip.create(
      String.to_charlist("#{output}.epub"),
      [{~c"mimetype", @mimetype} | files_to_add(output)],
      compress: [
        ~c".css",
        ~c".xhtml",
        ~c".html",
        ~c".ncx",
        ~c".js",
        ~c".opf",
        ~c".jpg",
        ~c".png",
        ~c".xml"
      ]
    )
  end

  ## Helpers

  defp default_assets(config) do
    [
      {Assets.dist(config.proglang), "OEBPS/dist"},
      {Assets.metainfo(), "META-INF"}
    ]
  end

  defp files_to_add(path) do
    Enum.reduce(Path.wildcard(Path.join(path, "**/*")), [], fn file, acc ->
      case File.read(file) do
        {:ok, bin} ->
          [{file |> Path.relative_to(path) |> String.to_charlist(), bin} | acc]

        {:error, _} ->
          acc
      end
    end)
  end

  # Helper to format Erlang datetime tuple
  defp format_datetime do
    {{year, month, day}, {hour, min, sec}} = :calendar.universal_time()
    list = [year, month, day, hour, min, sec]

    "~4..0B-~2..0B-~2..0BT~2..0B:~2..0B:~2..0BZ"
    |> :io_lib.format(list)
    |> IO.iodata_to_binary()
  end

  defp generate_module_page(module_node, config) do
    content = Templates.module_page(config, module_node)
    File.write("#{config.output}/OEBPS/#{module_node.id}.xhtml", content)
  end

  # Helper to generate an UUID v4. This version uses pseudo-random bytes generated by
  # the `crypto` module.
  defp uuid4 do
    <<u0::48, _::4, u1::12, _::2, u2::62>> = :crypto.strong_rand_bytes(16)
    bin = <<u0::48, 4::4, u1::12, 2::2, u2::62>>
    <<u0::32, u1::16, u2::16, u3::16, u4::48>> = bin

    Enum.map_join(
      [<<u0::32>>, <<u1::16>>, <<u2::16>>, <<u3::16>>, <<u4::48>>],
      <<45>>,
      &Base.encode16(&1, case: :lower)
    )
  end
end