# frozen_string_literal: true

require_relative "prompt/argument"
require_relative "prompt/message"
require_relative "prompt/result"

module MCP
  class Prompt
    class << self
      NOT_SET = Object.new

      attr_reader :title_value
      attr_reader :description_value
      attr_reader :icons_value
      attr_reader :arguments_value
      attr_reader :meta_value

      def template(args, server_context: nil)
        raise NotImplementedError, "Subclasses must implement template"
      end

      def to_h
        {
          name: name_value,
          title: title_value,
          description: description_value,
          icons: icons_value&.then { |icons| icons.empty? ? nil : icons.map(&:to_h) },
          arguments: arguments_value.empty? ? nil : arguments_value.map(&:to_h),
          _meta: meta_value,
        }.compact
      end

      def inherited(subclass)
        super
        subclass.instance_variable_set(:@name_value, nil)
        subclass.instance_variable_set(:@title_value, nil)
        subclass.instance_variable_set(:@description_value, nil)
        subclass.instance_variable_set(:@icons_value, nil)
        subclass.instance_variable_set(:@arguments_value, [])
        subclass.instance_variable_set(:@meta_value, nil)
      end

      def prompt_name(value = NOT_SET)
        if value == NOT_SET
          @name_value
        else
          @name_value = value
        end
      end

      def name_value
        @name_value || StringUtils.handle_from_class_name(name)
      end

      def title(value = NOT_SET)
        if value == NOT_SET
          @title_value
        else
          @title_value = value
        end
      end

      def description(value = NOT_SET)
        if value == NOT_SET
          @description_value
        else
          @description_value = value
        end
      end

      def icons(value = NOT_SET)
        if value == NOT_SET
          @icons_value
        else
          @icons_value = value
        end
      end

      def arguments(value = NOT_SET)
        if value == NOT_SET
          @arguments_value
        else
          @arguments_value = Array(value)
        end
      end

      def meta(value = NOT_SET)
        if value == NOT_SET
          @meta_value
        else
          @meta_value = value
        end
      end

      def define(name: nil, title: nil, description: nil, icons: [], arguments: [], meta: nil, &block)
        Class.new(self) do
          prompt_name name
          title title
          description description
          icons icons
          arguments arguments
          define_singleton_method(:template) do |args, server_context: nil|
            instance_exec(args, server_context: server_context, &block)
          end
          meta meta
        end
      end

      def validate_arguments!(args)
        args ||= {}
        missing = required_args - args.keys
        return if missing.empty?

        # The explicit `error_code` maps a missing prompt argument to Invalid Params (-32602) rather
        # than the default Internal Error (-32603); a missing required argument is client input, not a
        # server fault. `error_type: :missing_required_arguments` keeps the descriptive message and
        # instrumentation label. Mirrors `MCP::Server::ResourceNotFoundError`.
        raise MCP::Server::RequestHandlerError.new(
          "Missing required arguments: #{missing.join(", ")}",
          nil,
          error_type: :missing_required_arguments,
          error_code: JsonRpcHandler::ErrorCode::INVALID_PARAMS,
        )
      end

      private

      def required_args
        arguments_value.filter_map { |arg| arg.name.to_sym if arg.required }
      end
    end
  end
end