defmodule Firebird.Compiler.SourceMap do
  @moduledoc """
  Source mapping for compiled WASM modules.

  Tracks which Elixir functions map to which WASM exports,
  enabling better error reporting and debugging.

  ## Usage

      {:ok, source_map} = SourceMap.generate(module_ir, source_path)

      # Look up Elixir source info for a WASM export
      SourceMap.lookup(source_map, "fibonacci")
      # => %{module: :Math, function: :fibonacci, arity: 1, source: "lib/math.ex"}
  """

  alias Firebird.Compiler.IR

  @type t :: %__MODULE__{
          module: atom(),
          source: String.t() | nil,
          entries: [entry()],
          compiled_at: DateTime.t()
        }

  @type entry :: %{
          function: atom(),
          arity: non_neg_integer(),
          export_name: String.t(),
          params: [atom()],
          tail_recursive: boolean()
        }

  defstruct [:module, :source, :entries, :compiled_at]

  @doc """
  Generate a source map from a module IR.

  ## Parameters

  - `module_ir` - The IR module
  - `source` - Optional source file path

  ## Returns

  - `{:ok, %SourceMap{}}` with mapping information
  """
  @spec generate(IR.Module.t(), String.t() | nil) :: {:ok, t()}
  def generate(%IR.Module{} = module_ir, source \\ nil) do
    entries =
      Enum.map(module_ir.functions, fn func ->
        %{
          function: func.name,
          arity: func.arity,
          export_name: Atom.to_string(func.name),
          params: func.params,
          tail_recursive: is_tail_loop?(func.body)
        }
      end)

    source_map = %__MODULE__{
      module: module_ir.name,
      source: source,
      entries: entries,
      compiled_at: DateTime.utc_now()
    }

    {:ok, source_map}
  end

  @doc """
  Look up source information for a WASM export name.
  """
  @spec lookup(t(), String.t()) :: entry() | nil
  def lookup(%__MODULE__{} = source_map, export_name) do
    Enum.find(source_map.entries, fn entry ->
      entry.export_name == export_name
    end)
  end

  @doc """
  List all exported function names.
  """
  @spec exports(t()) :: [String.t()]
  def exports(%__MODULE__{} = source_map) do
    Enum.map(source_map.entries, & &1.export_name)
  end

  @doc """
  Serialize source map to JSON-compatible format.
  """
  @spec to_json(t()) :: map()
  def to_json(%__MODULE__{} = sm) do
    %{
      "module" => Atom.to_string(sm.module),
      "source" => sm.source,
      "compiled_at" => DateTime.to_iso8601(sm.compiled_at),
      "exports" =>
        Enum.map(sm.entries, fn e ->
          %{
            "function" => Atom.to_string(e.function),
            "arity" => e.arity,
            "export_name" => e.export_name,
            "params" => Enum.map(e.params, &Atom.to_string/1),
            "tail_recursive" => e.tail_recursive
          }
        end)
    }
  end

  defp is_tail_loop?({:tail_loop, _, _}), do: true
  defp is_tail_loop?(_), do: false
end