defmodule Mix.Tasks.Jetons.Build do
  @moduledoc """
  Generates output from design tokens.

  ## Config-based

      config :jetons,
        css: [
          transformer: Jetons.CSS.Transformer,
          resolver: "tokens.resolver.json",
          set: [theme: "dark"],
          output: "priv/static/tokens.css"
        ]

      # Or with Token Studio directory
      config :jetons,
        css: [
          transformer: Jetons.CSS.Transformer,
          token_studio: "tokens/",
          set: [theme: "light"],
          output: "priv/static/tokens.css"
        ]

      mix jetons.build           # All transformers
      mix jetons.build css      # Specific

  ## CLI-based

      mix jetons.build -f tokens.json -o output.css
      mix jetons.build -f design.resolver.json -o output.css --set theme=dark
      mix jetons.build -f tokens/ -o output.css --set theme=ACME-Light  # Token Studio directory
      mix jetons.build -m MyApp.Tokens -o output.css

  Token Studio directories are auto-detected when they contain a `$themes.json` file.
  """

  use Mix.Task

  alias Jetons.{CSS, Resolver, TokenStudio}
  alias Jetons.Map, as: JMap

  @shortdoc "Generate output from design tokens"

  @switches [
    file: [:string, :keep],
    module: :string,
    output: :string,
    set: [:string, :keep],
    inline: [:string, :keep],
    selector: :string,
    transformer: :string
  ]

  @aliases [f: :file, m: :module, o: :output, t: :transformer]

  @impl true
  def run(args) do
    {opts, targets} = OptionParser.parse!(args, strict: @switches, aliases: @aliases)

    cond do
      opts[:file] || opts[:module] ->
        run_cli_mode(opts)

      targets != [] ->
        Enum.each(targets, &run_config_transformer(&1, opts))

      true ->
        run_all_transformers(opts)
    end
  end

  defp run_all_transformers(cli_opts) do
    keys = Application.get_all_env(:jetons)

    if keys == [] do
      raise Mix.Error, """
      No transformers configured. Options:

        # Config-based (recommended):
        config :jetons,
          css: [transformer: MyApp.CSSTransformer, ...]

        mix jetons.build css

        # CLI-based (legacy):
        mix jetons.build -f tokens.json -o output.css
      """
    end

    Enum.each(keys, fn {key, _config} ->
      run_config_transformer(key, cli_opts)
    end)
  end

  # ── Config-based mode ────────────────────────────────────────────────

  defp run_config_transformer(key, cli_opts) when is_binary(key) do
    case Enum.find(Application.get_all_env(:jetons), fn {k, _} -> Atom.to_string(k) == key end) do
      nil -> raise Mix.Error, "Unknown transformer key: #{key}"
      {atom_key, config} -> run_transformer(atom_key, config, cli_opts)
    end
  end

  defp run_config_transformer(key, cli_opts) do
    config =
      Application.get_env(:jetons, key) ||
        raise Mix.Error,
              "No transformer config for :#{key}. Add config :jetons, :#{key}, [transformer: ...] in config.exs"

    run_transformer(key, config, cli_opts)
  end

  defp run_transformer(key, config, cli_opts) do
    transformer = Keyword.fetch!(config, :transformer)
    merged_config = Keyword.merge(config, cli_opts)
    {:ok, state} = transformer.init(merged_config)

    with {:ok, raw_config} <- resolve_raw_config(merged_config),
         {:ok, files} <- transformer.transform(raw_config, merged_config, state) do
      write_files(files)
      Mix.shell().info("Generated #{length(files)} file(s) for #{key}")
    else
      {:error, reason} -> raise Mix.Error, "Transformer #{key} failed: #{reason}"
    end
  end

  defp resolve_raw_config(config) do
    cond do
      config[:token_studio] -> resolve_token_studio(config)
      config[:resolver] -> resolve_resolver_file(config)
      true -> {:ok, config[:input] || %{}}
    end
  end

  defp resolve_token_studio(config) do
    path = Path.expand(config[:token_studio])
    inputs = inputs_from_set(config)

    with {:ok, resolver} <- load_token_studio_resolver(path) do
      if inputs == %{} do
        # No --set provided: pass resolver doc for multi-theme output
        {:ok, %{"$resolver" => resolver, "$base_dir" => path}}
      else
        resolve_token_studio_inputs(resolver, inputs, path)
      end
    end
  end

  defp load_token_studio_resolver(path) do
    resolver =
      path
      |> TokenStudio.load()
      |> TokenStudio.to_resolver(token_dir: path, output_dir: path)

    {:ok, resolver}
  rescue
    e in [ArgumentError, File.Error] -> {:error, Exception.message(e)}
  end

  defp resolve_token_studio_inputs(resolver, inputs, path) do
    {:ok, Resolver.resolve!(resolver, inputs, base_dir: path)}
  rescue
    e in [ArgumentError, File.Error] -> {:error, Exception.message(e)}
  end

  defp resolve_resolver_file(config) do
    path = config[:resolver]
    base_dir = Path.dirname(Path.expand(path))

    with {:ok, raw} <- File.read(path),
         {:ok, doc} <- Jason.decode(raw) do
      inputs = inputs_from_set(config)

      if inputs == %{} do
        # No --set provided: pass resolver doc for multi-theme output
        {:ok, %{"$resolver" => doc, "$base_dir" => base_dir}}
      else
        {:ok, Resolver.resolve!(doc, inputs, base_dir: base_dir)}
      end
    else
      {:error, %Jason.DecodeError{} = e} -> {:error, Exception.message(e)}
      {:error, posix} -> {:error, "could not read #{path}: #{posix}"}
    end
  end

  # ── CLI mode (backward compatibility) ───────────────────────────────

  defp run_cli_mode(opts) do
    transformer = resolve_transformer(opts[:transformer])
    config = build_cli_config(opts)

    {:ok, state} = transformer.init(config)

    raw_config = load_cli_files(opts)

    case transformer.transform(raw_config, config, state) do
      {:ok, files} ->
        write_files(files)
        Mix.shell().info("Generated #{length(files)} file(s)")

      {:error, reason} ->
        raise Mix.Error, "Transform failed: #{reason}"
    end
  end

  defp resolve_transformer(nil), do: CSS.Transformer

  defp resolve_transformer(name) do
    Module.safe_concat([name])
  end

  defp build_cli_config(opts) do
    []
    |> put_if(opts[:output], :output)
    |> put_if(opts[:selector], :selector)
    |> merge_list_opts(opts, :inline)
    |> merge_list_opts(opts, :set)
  end

  defp put_if(list, nil, _key), do: list
  defp put_if(list, value, key), do: [{key, value} | list]

  defp merge_list_opts(list, opts, key) do
    values = Keyword.get_values(opts, key)

    if values == [] do
      list
    else
      [{key, values} | list]
    end
  end

  defp load_cli_files(opts) do
    files = Keyword.get_values(opts, :file)
    set_values = Keyword.get_values(opts, :set)
    inputs = parse_set_values(set_values)

    files
    |> Enum.map(&load_single_file/1)
    |> Enum.reduce(%{}, fn
      {:config, config}, acc ->
        JMap.deep_merge(acc, config)

      {:resolver, doc, base_dir}, acc ->
        if inputs == %{} do
          # No --set provided: pass resolver doc for multi-theme output
          # Only works if this is the only file (no merging)
          %{"$resolver" => doc, "$base_dir" => base_dir}
        else
          resolved = Resolver.resolve!(doc, inputs, base_dir: base_dir)
          JMap.deep_merge(acc, resolved)
        end
    end)
  end

  defp parse_set_values(set_list) do
    set_list
    |> Enum.flat_map(fn set_str ->
      case String.split(set_str, "=", parts: 2) do
        [key, value] -> [{key, value}]
        _ -> []
      end
    end)
    |> Map.new()
  end

  defp load_single_file(path) do
    expanded = Path.expand(path)

    cond do
      File.dir?(expanded) and File.exists?(Path.join(expanded, "$themes.json")) ->
        resolver =
          expanded
          |> TokenStudio.load()
          |> TokenStudio.to_resolver(token_dir: expanded, output_dir: expanded)

        {:resolver, resolver, expanded}

      String.ends_with?(path, ".resolver.json") ->
        {:resolver, Jason.decode!(File.read!(path)), Path.dirname(expanded)}

      true ->
        {:config, Jason.decode!(File.read!(path))}
    end
  end

  # ── Helpers ─────────────────────────────────────────────────────────

  defp write_files(files) do
    Enum.each(files, fn {path, content} ->
      expanded = Path.expand(path)
      File.mkdir_p!(Path.dirname(expanded))
      File.write!(expanded, content)
    end)
  end

  defp inputs_from_set(config) do
    config
    |> Keyword.get(:set, [])
    |> Map.new(fn {k, v} -> {to_string(k), v} end)
  end
end