# encoding: utf-8
# frozen_string_literal: true
require "strscan"
require "carbon/compiler/scanner/main"
require "carbon/compiler/scanner/token"

module Carbon
  module Compiler
    # Scans over the file, taking a squence of characters and turning them into
    # tokens.
    class Scanner
      include Main
      include Enumerable

      # The file that the scanner will run over.
      #
      # @return [Project::File]
      attr_reader :file

      # Initialize the scanner.  Takes a file, which contains information about
      # the file, and can read from the file.
      #
      # @param file [Project::File]
      def initialize(file)
        @file = file
        @scanner = StringScanner.new(@file.read)
        @line = 1
        @last = 0
      end

      # Pretty inspect.
      #
      # @return [void]
      def inspect
        "#<#{self.class} #{@file.name}>"
      end

      # Yields each token to the block, if one is given.  Returns an
      # enumerator that enumerates over all generated tokens.
      #
      # @yield [token]
      # @yieldparam token [Token]
      # @return [Enumerator<Token>]
      def each
        return to_enum unless block_given?
        until @scanner.eos?
          token = scan
          yield token if token.is_a?(Token)
        end

        yield Token.new(:EOF, "", location)
        @scanner.reset
      end

    private

      def match(string, name = :"#{string}")
        if string.is_a?(::String)
          string = /#{::Regexp.escape(string.to_s)}/
        elsif string.is_a?(::Symbol)
          string = /#{::Regexp.escape(string.to_s)}(?![\w])/
        end

        if @scanner.scan(string)
          Token.new(name, @scanner[0], location(@scanner[0].length))
        end
      end

      def location(length = 0)
        lines = @line..@line
        start = @scanner.charpos - @last
        columns = (start - length)..start
        Location.new(lines, columns, @file.short)
      end

      def error!
        @file.emit("Syntax/Token/Unknown", location,
          [@scanner.string[@scanner.charpos]])
      end
    end
  end
end