# frozen_string_literal: true

module Vernacular
  module AST
    # Represents a modification that will be performed against the AST between
    # the time that the source code is read and the time that it is compiled
    # down to YARV instruction sequences.
    class Modifier
      BuilderExtension =
        Struct.new(:method, :block) do
          def components
            [method, block.source_location]
          end
        end
      attr_reader :builder_extensions

      ParserExtension =
        Struct.new(:symbol, :pattern, :code) do
          def components
            [symbol, pattern, code]
          end
        end
      attr_reader :parser_extensions

      attr_reader :rewriter_block

      def initialize
        @builder_extensions = []
        @parser_extensions = []
        yield self if block_given?
      end

      def build_rewriter(&block)
        @rewriter_block = block
      end

      def extend_builder(method, &block)
        builder_extensions << BuilderExtension.new(method, block)
      end

      def extend_parser(symbol, pattern, code)
        parser_extensions << ParserExtension.new(symbol, pattern, code)
      end

      def modify(source)
        raise 'You must first configure a rewriter!' unless rewriter_block

        rewriter = Class.new(Parser::Rewriter, &rewriter_block).new
        rewriter.instance_variable_set(:@parser, ASTParser.parser)

        buffer = Parser::Source::Buffer.new('<dynamic>')
        buffer.source = source

        ast = ASTParser.parse(source)
        rewriter.rewrite(buffer, ast)
      end

      def components
        (builder_extensions + parser_extensions).flat_map(&:components) +
          rewriter_block.source_location
      end
    end
  end
end

Vernacular::ASTModifier = Vernacular::AST::Modifier