defmodule Hotline.Generator do
  @moduledoc false

  @api_url "https://raw.githubusercontent.com/PaulSonOfLars/telegram-bot-api-spec/main/api.json"
  @types_dir "lib/hotline/types"
  @generated_api_file "lib/hotline/generated_api.ex"

  def run do
    IO.puts("Fetching Telegram Bot API spec...")
    {:ok, %{status: 200, body: body}} = Req.get(@api_url, decode_body: false)
    spec = JSON.decode!(body)

    IO.puts("Found #{map_size(spec["types"])} types and #{map_size(spec["methods"])} methods.")

    IO.puts("Generating types...")
    generate_types(spec["types"])

    IO.puts("Generating API methods...")
    generate_methods(spec["methods"], spec["types"])

    IO.puts("Done! Run `mix format` to format generated files.")
  end

  # --- Type Generation ---

  defp generate_types(types) do
    File.mkdir_p!(@types_dir)

    for {name, type_def} <- types do
      filename = Macro.underscore(name) <> ".ex"
      path = Path.join(@types_dir, filename)
      content = generate_type_module(name, type_def, types)
      File.write!(path, content)
    end
  end

  defp generate_type_module(name, type_def, all_types) do
    module_name = "Hotline.Types.#{name}"
    fields = type_def["fields"] || []
    description = type_def["description"] || ""

    field_atoms = Enum.map(fields, fn f -> ":#{f["name"]}" end)
    nested = find_nested_fields(fields, all_types)
    typespecs = Enum.map(fields, &generate_typespec(&1, all_types))

    nested_block =
      if nested != [] do
        entries =
          Enum.map_join(nested, ",\n      ", fn {field, parser} -> "#{field}: #{parser}" end)

        """
          def parse_nested(_map) do
            %{
              #{entries}
            }
          end
        """
      else
        ""
      end

    typespec_block =
      if typespecs != [] do
        entries = Enum.map_join(typespecs, ",\n        ", fn {n, s} -> "#{n}: #{s}" end)

        """
          @type t :: %__MODULE__{
                #{entries}
              }
        """
      else
        "  @type t :: %__MODULE__{}\n"
      end

    """
    defmodule #{module_name} do
      @moduledoc \"\"\"
      #{String.replace(description, "\"\"\"", ~S(\\\"\\\"\\\""))}
      \"\"\"

      use Hotline.Type

      defstruct [#{Enum.join(field_atoms, ", ")}]

    #{typespec_block}
    #{nested_block}end
    """
  end

  defp find_nested_fields(fields, all_types) do
    for %{"name" => name, "types" => types} <- fields,
        parser = find_parser(types, all_types),
        parser != nil do
      {String.to_atom(name), parser}
    end
  end

  defp find_parser(types, all_types) do
    cond do
      Enum.any?(types, &match?("Array of " <> _, &1)) ->
        inner =
          types
          |> Enum.find(&match?("Array of " <> _, &1))
          |> String.replace_prefix("Array of ", "")

        # Handle "Array of Array of X"
        inner =
          if String.starts_with?(inner, "Array of ") do
            String.replace_prefix(inner, "Array of ", "")
          else
            inner
          end

        if Map.has_key?(all_types, inner) do
          "&Hotline.Types.#{inner}.parse_list/1"
        else
          nil
        end

      Enum.any?(types, &Map.has_key?(all_types, &1)) ->
        type_name = Enum.find(types, &Map.has_key?(all_types, &1))
        "&Hotline.Types.#{type_name}.parse/1"

      true ->
        nil
    end
  end

  defp generate_typespec(%{"name" => name, "types" => types} = field, all_types) do
    required = Map.get(field, "required", false)

    spec =
      types
      |> Enum.map(&map_type(&1, all_types))
      |> Enum.uniq()
      |> Enum.join(" | ")

    spec = if required, do: spec, else: "#{spec} | nil"
    {String.to_atom(name), spec}
  end

  defp map_type("Integer", _), do: "integer()"
  defp map_type("String", _), do: "String.t()"
  defp map_type("Boolean", _), do: "boolean()"
  defp map_type("Float", _), do: "float()"
  defp map_type("Float number", _), do: "float()"
  defp map_type("True", _), do: "true"
  defp map_type("InputFile", _), do: "term()"

  defp map_type("Array of " <> inner, all_types) do
    "[#{map_type(inner, all_types)}]"
  end

  defp map_type(type_name, all_types) do
    if Map.has_key?(all_types, type_name) do
      "Hotline.Types.#{type_name}.t()"
    else
      "term()"
    end
  end

  # --- Method Generation ---

  defp generate_methods(methods, types) do
    functions =
      methods
      |> Enum.sort_by(fn {name, _} -> name end)
      |> Enum.map(fn {name, method_def} -> generate_method(name, method_def, types) end)

    content = """
    defmodule Hotline.GeneratedAPI do
      @moduledoc \"\"\"
      Auto-generated Telegram Bot API methods.

      Generated by `mix hotline.gen` from the official Bot API spec.
      \"\"\"

      alias Hotline.Client

    #{Enum.join(functions, "\n")}end
    """

    File.write!(@generated_api_file, content)
  end

  defp generate_method(name, method_def, types) do
    description =
      (method_def["description"] || "")
      |> String.slice(0..500)
      |> String.replace("\"\"\"", ~S(\\\"\\\"\\\""))

    returns = method_def["returns"] || []
    func_name = Macro.underscore(name)
    return_parser = find_return_parser(returns, types)

    body =
      if return_parser do
        """
            with {:ok, result} <- Client.request("#{name}", Map.new(params), opts) do
              {:ok, #{return_parser}}
            end\
        """
      else
        """
            Client.request("#{name}", Map.new(params), opts)\
        """
      end

    """
      @doc \"\"\"
      #{description}
      \"\"\"
      def #{func_name}(params \\\\ %{}, opts \\\\ []) do
    #{body}
      end
    """
  end

  defp find_return_parser(returns, types) do
    cond do
      Enum.any?(returns, &match?("Array of " <> _, &1)) ->
        inner =
          returns
          |> Enum.find(&match?("Array of " <> _, &1))
          |> String.replace_prefix("Array of ", "")

        if Map.has_key?(types, inner) do
          "Hotline.Types.#{inner}.parse_list(result)"
        else
          nil
        end

      Enum.any?(returns, &Map.has_key?(types, &1)) ->
        type_name = Enum.find(returns, &Map.has_key?(types, &1))
        "Hotline.Types.#{type_name}.parse(result)"

      true ->
        nil
    end
  end
end

Hotline.Generator.run()