defmodule Firebird.Target.Config do
  @moduledoc """
  Configuration for the Firebird WASM compilation target.

  Holds all settings needed to discover, compile, and output WASM modules
  from Elixir source files.

  ## Creating a Config

      # From keyword options
      config = Firebird.Target.Config.new(
        output_dir: "_build/wasm",
        sources: ["lib/wasm_modules"],
        optimize: true
      )

      # From Mix project config
      config = Firebird.Target.Config.from_mix_project()

      # Merge CLI options on top of project config
      config = Firebird.Target.Config.from_mix_project()
               |> Firebird.Target.Config.merge(cli_opts)

  ## Options

  - `:output_dir` - Directory for compiled WASM output (default: `"_build/wasm"`)
  - `:sources` - List of source directories to scan (default: `["lib"]`)
  - `:files` - Explicit list of files to compile (overrides source scanning)
  - `:optimize` - Enable IR optimizations like constant folding (default: `false`)
  - `:tco` - Enable tail call optimization (default: `false`)
  - `:inline` - Enable function inlining (default: `false`)
  - `:cse` - Enable common subexpression elimination (default: `false`)
  - `:licm` - Enable loop-invariant code motion (default: `false`)
  - `:wat_only` - Only generate WAT text, skip binary compilation (default: `false`)
  - `:verify` - Load and verify compiled WASM modules (default: `false`)
  - `:source_map` - Generate source maps (default: `false`)
  - `:verbose` - Enable verbose output (default: `false`)
  - `:force` - Force recompilation of all files (default: `false`)
  """

  @type t :: %__MODULE__{
          output_dir: String.t(),
          sources: [String.t()],
          files: [String.t()] | nil,
          optimize: boolean(),
          tco: boolean(),
          inline: boolean(),
          cse: boolean(),
          licm: boolean(),
          wat_only: boolean(),
          verify: boolean(),
          source_map: boolean(),
          verbose: boolean(),
          force: boolean()
        }

  defstruct output_dir: "_build/wasm",
            sources: ["lib"],
            files: nil,
            optimize: false,
            tco: false,
            inline: false,
            cse: false,
            licm: false,
            wat_only: false,
            verify: false,
            source_map: false,
            verbose: false,
            force: false

  @doc """
  Create a new Config from keyword options.

  ## Examples

      config = Config.new(output_dir: "priv/wasm", optimize: true)
      config = Config.new([])  # all defaults
  """
  @spec new(keyword()) :: t()
  def new(opts \\ []) when is_list(opts) do
    struct(__MODULE__, opts)
  end

  @doc """
  Create a Config from the current Mix project's `:firebird` configuration.

  Reads from `mix.exs`:

      def project do
        [
          firebird: [
            wasm_output: "_build/wasm",
            wasm_sources: ["lib/wasm_modules"],
            optimize: true
          ]
        ]
      end
  """
  @spec from_mix_project() :: t()
  def from_mix_project do
    config = get_project_firebird_config()

    new(
      output_dir: Keyword.get(config, :wasm_output, "_build/wasm"),
      sources: Keyword.get(config, :wasm_sources, ["lib"]),
      optimize: Keyword.get(config, :optimize, false),
      tco: Keyword.get(config, :tco, false),
      inline: Keyword.get(config, :inline, false),
      cse: Keyword.get(config, :cse, false),
      licm: Keyword.get(config, :licm, false),
      wat_only: Keyword.get(config, :wat_only, false),
      verify: Keyword.get(config, :verify, false),
      source_map: Keyword.get(config, :source_map, false)
    )
  end

  @doc """
  Merge additional options into an existing config.

  CLI options override existing config values. Only non-nil values
  from `opts` are merged.

  ## Examples

      config = Config.from_mix_project()
      config = Config.merge(config, output_dir: "custom/output", verbose: true)
  """
  @spec merge(t(), keyword()) :: t()
  def merge(%__MODULE__{} = config, opts) when is_list(opts) do
    # Only merge non-nil values
    filtered =
      opts
      |> Enum.filter(fn {_k, v} -> v != nil end)

    struct(config, filtered)
  end

  @doc """
  Validate the config and return a list of warnings.

  Checks for common misconfigurations like nonexistent directories
  or missing prerequisites.
  """
  @spec validate(t()) :: {:ok, [String.t()]}
  def validate(%__MODULE__{} = config) do
    warnings = []

    # Check output dir parent exists
    warnings =
      if String.starts_with?(config.output_dir, "/") and
           not File.dir?(Path.dirname(config.output_dir)) do
        ["Output directory parent doesn't exist: #{Path.dirname(config.output_dir)}" | warnings]
      else
        warnings
      end

    # Check source dirs exist
    warnings =
      Enum.reduce(config.sources || [], warnings, fn dir, acc ->
        if not File.dir?(dir) do
          ["Source directory not found: #{dir}" | acc]
        else
          acc
        end
      end)

    # Check explicit files exist
    warnings =
      Enum.reduce(config.files || [], warnings, fn file, acc ->
        if not File.regular?(file) do
          ["Source file not found: #{file}" | acc]
        else
          acc
        end
      end)

    # Check wat2wasm availability
    warnings =
      if not config.wat_only and not Firebird.Compiler.wat2wasm_available?() do
        ["wat2wasm not found - binary compilation will fail" | warnings]
      else
        warnings
      end

    {:ok, Enum.reverse(warnings)}
  end

  defp get_project_firebird_config do
    case Mix.Project.config() do
      config when is_list(config) -> Keyword.get(config, :firebird, [])
      _ -> []
    end
  rescue
    _ -> []
  end
end