module Chervil
  RSpec.describe Parser do
    def parse(source)
      lexer = Lexer.new(source)
      parser = Parser.new(lexer)
      parser.parse
    end

    it 'parses a number' do
      expect(parse('1').first).to eq(AST::Number.new(1.0))
    end

    it 'parses a string' do
      expect(parse('"hello world"').first).to eq(AST::String.new('hello world'))
    end

    it 'parses an identifier' do
      expect(parse('+').first).to eq(AST::Identifier.new('+'))
    end

    it 'parses booleans' do
      expect(parse('#t #f')).to eq(
        [
          AST::Boolean.new(true),
          AST::Boolean.new(false),
        ]
      )
    end

    it 'parses an application' do
      expect(parse('(+ 1 2)').first).to eq(
        AST::Application.new(
          AST::Identifier.new('+'),
          [AST::Number.new(1.0), AST::Number.new(2.0)]
        )
      )
    end

    it 'parses a definition' do
      expect(parse('(define x 5)').first).to eq(
        AST::Definition.new(AST::Identifier.new('x'), AST::Number.new(5.0))
      )
    end

    it 'parses a nested expression' do
      expect(parse('(+ (+ 1 2) (- 3 4))').first).to eq(
        AST::Application.new(
          AST::Identifier.new("+"),
          [
            AST::Application.new(
              AST::Identifier.new("+"),
              [
                AST::Number.new(1.0),
                AST::Number.new(2.0),
              ]
            ),
            AST::Application.new(
              AST::Identifier.new("-"),
              [
                AST::Number.new(3.0),
                AST::Number.new(4.0),
              ]
            ),
          ]
        )
      )
    end

    it 'parses a function definition' do
      expect(parse('(define (square x) (* x x))').first).to eq(
        AST::Definition.new(
          AST::Identifier.new("square"),
          AST::Function.new(
            AST::Identifier.new("square"),
            [
              AST::Identifier.new("x")
            ],
            [
              AST::Application.new(
                AST::Identifier.new("*"),
                [
                  AST::Identifier.new("x"),
                  AST::Identifier.new("x"),
                ]
              )
            ]
          )
        )
      )
    end

    it 'returns a syntax error object instead of raising' do
      expect(parse('(+ 1')).to eq(Error.new("Expected rparen but got eof"))
      expect(parse('1)')).to eq(Error.new("Unexpected token rparen: )"))
    end

    it 'parses a conditional' do
      expect(parse('(if #t 1 0)').first).to eq(
        AST::Conditional.new(
          AST::Boolean.new(true),
          AST::Number.new(1.0),
          AST::Number.new(0.0),
        )
      )
    end
  end
end