require "./parser.cr"
require "./sequence.cr"

module Parcom
  # `TokenSeq` is a `Parser` that attempts to parse a specific
  # string of tokens. If the expected tokens are not at the start
  # of the input stream, the parser fails.
  #
  # Example:
  # ```
  # parse_test = TokenSeq(Char).new("test".chars)
  # tokens = Tokens.from_string("testing")
  #
  # result = parse_test.parse(tokens)
  #
  # puts result.value  # => ['t', 'e', 's', 't'] 
  # puts result.tokens # => ['i', 'n', 'g']
  # ```
  class TokenSeq(T) < Parser(T, Array(T))
    @p : Sequence(T, T)

    # Accepts the tokens to try and parse, in order.
    def initialize(expected : Iterable(T))
      ps = [] of Parser(T, T)
      expected.each { |t| ps << Token.new(t) }

      @p = Sequence.new(ps)
    end

    # Tries to parse the list of tokens.
    def parse(tokens : Tokens(T)) : Result(T, Array(T))
      @p.parse(tokens)
    rescue ex : ParserFail
      raise ParserFail.new("TokenSeq: #{ex.message}")
    end
  end
end