defmodule Mix.Tasks.Jetons.Convert do
  @moduledoc """
  Converts Token Studio folder structure to DTCG resolver format.

  Token Studio exports tokens as a folder with:
  - `$metadata.json` - contains `tokenSetOrder` for merge precedence
  - `$themes.json` - array of theme definitions with `selectedTokenSets`
  - Individual token set files in subdirectories (e.g., `acme/base.json`)

  This task generates a `.resolver.json` file that can be used with
  `mix jetons.build` or `Jetons.Resolver.resolve_file!/2`.

  ## Usage

      mix jetons.convert path/to/tokens -o tokens.resolver.json

  ## Options

    * `-o, --output` - Output file path (default: `tokens.resolver.json`)
    * `--modifier` - Name for the theme modifier (default: `theme`)

  ## Example

      # Convert Token Studio export
      mix jetons.convert ./tokens -o design.resolver.json

      # Then use with build
      mix jetons.build -f design.resolver.json --set theme=light -o tokens.css

  """

  use Mix.Task

  alias Jetons.TokenStudio

  @shortdoc "Convert Token Studio format to DTCG resolver"

  @switches [output: :string, modifier: :string]
  @aliases [o: :output]

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

    token_dir = Path.expand(dir)
    output_path = Path.expand(opts[:output] || "tokens.resolver.json")
    modifier_name = opts[:modifier] || "theme"

    validate_directory!(token_dir)

    resolver =
      token_dir
      |> TokenStudio.load()
      |> TokenStudio.to_resolver(
        modifier_name: modifier_name,
        token_dir: token_dir,
        output_dir: Path.dirname(output_path)
      )

    write_json!(output_path, resolver)

    Mix.shell().info("Generated #{output_path}")
  end

  defp validate_directory!(dir) do
    unless File.dir?(dir) do
      raise Mix.Error, "Not a directory: #{dir}"
    end
  end

  defp write_json!(path, data) do
    File.write!(path, Jason.encode!(data, pretty: true))
  end
end