require "./spec_helper"

require "../src/parcom.cr"

include Parcom

describe TokenStream do
  describe ".from_string" do
    it "constructs a TokenStream(Char) from a String" do
      tokens = TokenStream.from_string("abcd")
      tokens.tokens.should eq("abcd".chars)
    end
  end

  describe "#initialize" do
    it "wraps an array with the contents of the given iterable" do
      set = Set{'a', 'b', 'c', 'd'}
      tokens = TokenStream.new(set)
      tokens.tokens.should eq(set.to_a)

      arr = "abcd".chars
      tokens = TokenStream.new(arr)
      tokens.tokens.should eq(arr)
    end
  end

  context do
    tokens_empty = TokenStream.new([] of Char)
    tokens = TokenStream.from_string("abcd")

    describe "#[]" do
      it "returns the token at the given index" do
        tokens[2].should eq('c')
        expect_raises(IndexError) { tokens_empty[2] }
      end

      it "returns a new TokenStream similar to Array#[](Int, Int)" do
        tokens[1, 5].should eq(TokenStream.new(['b', 'c', 'd']))
        expect_raises(IndexError) { tokens_empty[1, 5] }
      end

      it "returns a new TokenStream similar to Array#[](Range)" do
        tokens[1..3].should eq(TokenStream.new(['b', 'c', 'd']))
        expect_raises(IndexError) { tokens_empty[1..3] }
      end
    end

    describe "#[]?" do
      it "analogous to `Array#[]?`" do
        # we should only need to check the nil-returning cases
        tokens_empty[2]?.should be_nil
        tokens_empty[1, 5]?.should be_nil
        tokens_empty[1..3]?.should be_nil
      end
    end

    describe "#empty?" do
      it "exposes the `#empty?` method of the wrapped array" do
        tokens.empty?.should be_false
        tokens_empty.empty?.should be_true
      end
    end
  end
end

describe Result do
  describe "#initialize" do
    it "sets values for #tokens and #value" do
      tokens = TokenStream.from_string("esting")
      value  = 't'
      result = Result(Char, Char).new(tokens, value)

      result.tokens.should eq(tokens)
      result.value.should eq(value)
    end
  end
end

describe Parser do
  p = AnyToken(Char).new

  describe "#parse?" do
    it "returns `nil` if the parser fails" do
      result = p.parse?(TokenStream.new([] of Char))

      result.should be_nil
    end

    it "returns a `Result(T, V)` if the parser succeeds" do
      tokens = TokenStream.from_string("testing")
      result = p.parse(tokens)

      result.should be_a(Result(Char, Char))
    end
  end
end

describe Flunk do
  describe "#parse" do
    it "always fails" do
      tokens = TokenStream.from_string("testing")

      expect_raises(ParserException) { Flunk(Char, Char).new.parse(tokens) }
    end
  end
end

describe AnyToken do
  context do
    p = AnyToken(Char).new

    describe "#parse" do
      it "succeeds when input is non-empty" do
        tokens = TokenStream.from_string("testing")
        result = p.parse(tokens)

        result.tokens.should eq(tokens[1..])
        result.value.should eq('t')
      end

      it "fails when input is empty" do
        expect_raises(ParserException) { p.parse(TokenStream.new([] of Char)) }
      end
    end
  end
end

describe Eof do
  p = Eof(Char).new

  describe "#parse" do
    it "succeeds when input is empty" do
      result = p.parse(TokenStream.new([] of Char))

      result.tokens.empty?.should be_true
      result.value.should be_nil
    end

    it "fails when input is non-empty" do
      tokens = TokenStream.from_string("testing")

      expect_raises(ParserException) { p.parse(tokens) }
    end
  end
end

describe Peek do
  tokens = TokenStream.from_string("testing")
  p = AnyToken(Char).new
  result_normal = p.parse(tokens)
  result_peek = Peek.new(p).parse(tokens)

  describe "#parse" do
    it "does not modify the result of the wrapped parser" do
      result_peek.value.should eq(result_normal.value)
    end

    it "does not consume any input" do
      result_peek.tokens.should eq(tokens)
    end
  end
end

describe Assert do
  test_f = ->(x : Char) { x == 't' }
  p = AnyToken(Char).new.assert { |x| x == 't' }

  describe "#parse" do
    it "fails if the wrapped parser fails" do
      expect_raises(ParserException) do
        p.parse(TokenStream.new([] of Char))
      end
    end

    it "fails if the result value fails the test" do
      tokens = TokenStream.from_string("_testing")

      expect_raises(ParserException) { p.parse(tokens) }
    end

    it "succeeds if the wrapped parser succeeds and the test passes" do
      tokens = TokenStream.from_string("testing")
      expected_char = tokens[0]
      result = p.parse(tokens)

      result.value.should eq(expected_char)
      test_f.call(expected_char).should be_true 
    end
  end
end

describe Satisfy do
  p = Satisfy(Char).new { |x| x == 't' }

  describe "#parse" do
    it "fails if the input is empty" do
      expect_raises(ParserException) { p.parse(TokenStream.new([] of Char)) }
    end

    it "fails if the token fails the test" do
      tokens = TokenStream.from_string("_testing")

      expect_raises(ParserException) { p.parse(tokens) }
    end

    it "succeeds if the token passes the test" do
      tokens = TokenStream.from_string("testing")
      expected_char = tokens[0]
      result = p.parse(tokens)

      result.value.should eq(expected_char)
    end
  end
end

describe Token do
  tokens = TokenStream.from_string("testing")

  describe "#parse" do
    it "fails if the input is empty" do
      p = Token(Char).new('t')

      expect_raises(ParserException) { p.parse(TokenStream.new([] of Char)) }
    end

    it "fails if the token is not the expected token" do
      p = Token(Char).new('#')

      expect_raises(ParserException) { p.parse(tokens) }
    end

    it "succeeds if the token is the expected token" do
      expected_char = tokens[0]
      p = Token(Char).new(expected_char)
      result = p.parse(tokens)

      result.value.should eq(expected_char)
    end
  end
end

describe Map do
  describe "#parse" do
    it "fails if the wrapped parser fails" do
      p = AnyToken(Char).new.map { |x| x }

      expect_raises(ParserException) { p.parse(TokenStream.new([] of Char)) }
    end

    it "changes the result value via the provided proc" do
      p = AnyToken(Char).new.map { |x| x.letter? }

      result = p.parse(TokenStream.from_string("testing"))
      result.value.should be_true

      result = p.parse(TokenStream.from_string("_testing"))
      result.value.should be_false
    end
  end
end

describe Plus do
  describe "#parse" do
    tokens = TokenStream.from_string("testing")
    p_t = Token(Char).new('t')
    p_e = Token(Char).new('e')
    p_at = Token(Char).new('@')

    it "fails if the first parser fails" do
      p = p_at + p_e
      expect_raises(ParserException) { p.parse(tokens) }
    end

    it "fails if the second parser fails" do
      p = p_t + p_at
      expect_raises(ParserException) { p.parse(tokens) }
    end

    it "fails if both parsers fail" do
      p = p_at + p_at
      expect_raises(ParserException) { p.parse(tokens) }
    end

    it "succeeds if both parsers succeed" do
      p = p_t + p_e
      result = p.parse(tokens)

      result.tokens.should eq(tokens[2..])
      result.value[0].should eq('t')
      result.value[1].should eq('e')
    end

    it "evaluates parsers from left to right (left associative)" do
      p_succeeds = p_t + p_e
      p_fails = p_e + p_t

      p_succeeds.parse(tokens) # should not raise an exception
      expect_raises(ParserException) { p_fails.parse(tokens) }

      p_s = Token(Char).new('s')

      r = (p_t + p_e + p_s).parse(tokens) # should not raise an exception
      r.value.should be_a({ {Char, Char}, Char})

      r = (p_t + (p_e + p_s)).parse(tokens) # should not raise an exception
      r.value.should be_a({Char, {Char, Char} })
    end
  end
end

describe Phrase do
  p = Phrase.new(Token.new('t'))

  describe "#parse" do
    it "fails if the wrapped parser fails" do
      tokens = TokenStream.from_string("_")

      expect_raises(ParserException) { p.parse(tokens) }
    end

    it "fails if not all of the input tokens are parsed" do
      tokens = TokenStream.from_string("tt")

      expect_raises(ParserException) { p.parse(tokens) }
    end

    it "succeeds if the wrapped parser successfully parses all of the input" do
      tokens = TokenStream.from_string("t")
      result = p.parse(tokens)

      result.tokens.empty?.should be_true
      result.value.should eq('t')
    end
  end
end

describe Recover do
  p = Token.new('t').recover('@')

  describe "#parse" do
    it "succeeds and returns the wrapped parser's value if it succeeds" do
      tokens = TokenStream.from_string("testing")
      result = p.parse(tokens)

      result.tokens.should eq(tokens[1..])
      result.value.should eq('t')
    end

    it "succeeds and returns the default value without modifying the input if the wrapped parser fails" do
      tokens = TokenStream.from_string("_____")
      result = p.parse(tokens)

      result.tokens.should eq(tokens)
      result.value.should eq('@')
    end
  end
end

describe Optional do
  p = Optional.new(Token.new('t'))

  describe "#parse" do
    it "succeeds and returns the wrapped parser's value if it succeeds" do
      tokens = TokenStream.from_string("testing")
      result = p.parse(tokens)

      result.tokens.should eq(tokens[1..])
      result.value.should eq('t')
    end

    it "succeeds and returns a value of `nil` without modifying the input if the wrapped parser fails" do
      tokens = TokenStream.from_string("_____")
      result = p.parse(tokens)

      result.tokens.should eq(tokens)
      result.value.should be_nil
    end
  end
end

describe Sequence do
  # HACK: ps has to be declared this way due to contravariance
  # https://crystal-lang.org/reference/1.7/syntax_and_semantics/inheritance.html#covariance-and-contravariance
  ps = [] of Parser(Char, Char)
  ps = ps + "abcd".chars.map { |c| Token.new(c) }
  p = Sequence.new(ps)

  describe "#parse" do
    it "runs each wrapped parser in order, returns each result" do
      tokens = TokenStream.from_string("abcd")
      result = p.parse(tokens)

      result.value.should eq("abcd".chars)
      result.tokens.empty?.should be_true
    end

    it "fails if any of the wrapped parsers fail" do
      fail_strings = ["", "abed", "bbcd", "abce"]
      fail_strings.each do |s|
        tokens = TokenStream.from_string(s)
        expect_raises(ParserException) { p.parse(tokens) }
      end
    end

    it "succeeds and returns empty array if parser iterable is empty" do
      tokens = TokenStream.from_string("abcd")
      empty_p = Sequence.new([] of Parser(Char, Char))
      result = empty_p.parse(tokens)

      result.value.empty?.should be_true
      result.tokens.should eq(tokens)
    end
  end
end

describe Tokens do
  p = Tokens.new("test".chars)

  describe "#parse" do
    it "fails if the input stream is too short" do
      input = TokenStream.from_string("")
      expect_raises(ParserException) { p.parse(input) }
    end

    it "fails if it encounters an unexpected token" do
      input = TokenStream.from_string("text")
      expect_raises(ParserException) { p.parse(input) }
    end

    it "succeeds if the input starts with the expected tokens" do
      input = TokenStream.from_string("testing")
      result = p.parse(input)

      result.tokens.should eq(input[4..])
      result.value.should eq("test".chars)
    end
  end
end

describe Many do
  p = Many.new(Token.new('a'))

  describe "#parse" do
    it "returns an empty array if the wrapped parser never succeeds" do
      tokens = TokenStream.from_string("bb")
      result = p.parse(tokens)

      result.value.empty?.should be_true
      result.tokens.should eq(tokens)
    end

    it "stops parsing when the wrapped parser fails, returns all successes" do
      tokens = TokenStream.from_string("aaabcd")
      result = p.parse(tokens)

      result.value.should eq("aaa".chars)
      result.tokens.should eq(tokens[3..])

      tokens = TokenStream.from_string("aaa")
      result = p.parse(tokens)

      result.value.should eq("aaa".chars)
      result.tokens.should eq(tokens[3..])
    end
  end
end

describe Some do
  p = Some.new(Token.new('a'))
  describe "#parse" do
    it "fails if the wrapped parser never succeeds" do
      tokens = TokenStream.from_string("")
      expect_raises(ParserException) { p.parse(tokens) }
    end

    it "stops parsing when the wrapped parser fails, returns all successes" do
      tokens = TokenStream.from_string("aaabcd")
      result = p.parse(tokens)

      result.value.should eq("aaa".chars)
      result.tokens.should eq(tokens[3..])

      tokens = TokenStream.from_string("aaa")
      result = p.parse(tokens)

      result.value.should eq("aaa".chars)
      result.tokens.should eq(tokens[3..])
    end
  end
end

describe Exactly do
  letter_a = Token.new('a')
  tokens = TokenStream.from_string("aaabcd")

  describe "#parse" do
    it "tries to parse exactly n of the wrapper parser" do
      p = Exactly.new(3, letter_a)
      result = p.parse(tokens)

      result.value.should eq("aaa".chars)
      result.tokens.should eq(tokens[3..])
    end

    it "always succeeds with an empty array if n < 1" do
      p = Exactly.new(0, letter_a)
      result = p.parse(tokens)

      result.value.empty?.should be_true
      result.tokens.should eq(tokens)

      p = Exactly.new(-42, letter_a)
      result = p.parse(tokens)

      result.value.empty?.should be_true
      result.tokens.should eq(tokens)
    end

    it "does not take extra matching tokens" do
      p = Exactly.new(2, letter_a)
      result = p.parse(tokens)

      result.value.should eq("aa".chars)
      result.tokens.should eq(tokens[2..])
    end

    it "fails if there are not enough matching tokens" do
      p = Exactly.new(60, letter_a)
      expect_raises(ParserException) { p.parse(tokens) }
    end
  end
end

pending AtLeast do
end

pending AtMost do
end

pending Between do
end

pending StopAt do
end

pending StopAfter do
end

pending StopIf do
end

pending FirstOf do
end

pending SepBy do
end