using System;

using Dungeoneer.Error;

namespace Dungeoneer.Interpreter {

	public static class Parser {

		public static int ParseRoll(string text) { return ParseRoll(Lexer.Tokenize(text)); }
		public static int ParseRoll(TokenSet tokens) {
			int result = 0;
			bool wasValue = false;
			char operation = '+';
			int? rollDc = null;
			foreach(Token token in tokens) {
				switch(token) {
					case ValueToken value:
						if(wasValue)
							throw new SyntaxException("Value followed by value");
						result = Operate(result, value.Value, operation);
						wasValue = true;
						break;
					case OperatorToken op:
						if(!wasValue)
							throw new SyntaxException("Operator followed by operator");
						operation = op.Value;
						wasValue = false;
						break;
					case DcToken dc:
						if(rollDc.HasValue)
							throw new SyntaxException("Duplicate element: DC");
						rollDc = dc.Value;
						break;
					default:
						throw new SyntaxException($"invalid token: {token.GetType()}");
				}
			}
			return result;
		}

		public static int Operate(int a, int b, char op) {
			switch(op) {
				case '+':	return (a + b);
				case '-':	return (a - b);
				case '*':	return (a * b);
				case '/':	return (a / b);
				case '%':	return (a % b);
				case '^':	return (int)Math.Pow(a, b);
				default:	throw new SyntaxException("unmatched operator");
			}
		}

	}

}