using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;

namespace HeuristicLab.Problems.GrammaticalOptimization {
  // 4-bit even parity
  public class EvenParityProblem : IProblem {
    // + == OR
    // * == AND
    private const string grammarString = @"
G(S):
S -> N | N*S | N+S | !S | (S)
N -> a | b | c | d
";

    private readonly IGrammar grammar;
    private readonly ExpressionInterpreter interpreter = new ExpressionInterpreter();
    public EvenParityProblem() {
      this.grammar = new Grammar (grammarString);
    }

    public double BestKnownQuality(int maxLen) {
      // for now only an upper bound is returned, ideally all fitness cases are predicted correctly
      return Math.Pow(2, 4);
    }

    public IGrammar Grammar {
      get { return grammar; }
    }

    public double Evaluate(string sentence) {
      var vars = new bool[4];
      var nCorrect = 0;
      for (int b0 = 0; b0 <= 1; b0++)
        for (int b1 = 0; b1 <= 1; b1++)
          for (int b2 = 0; b2 <= 1; b2++)
            for (int b3 = 0; b3 <= 1; b3++) {
              vars[0] = b0 > 0;
              vars[1] = b1 > 0;
              vars[2] = b2 > 0;
              vars[3] = b3 > 0;

              var pred = interpreter.Interpret(sentence, vars);
              var target = (b0 > 0) ^ (b1 > 0) ^ (b2 > 0) ^ (b3 > 0);
              if (pred == target) nCorrect++;
            }
      return nCorrect;
    }

    public string CanonicalRepresentation(string terminalPhrase) {
      return terminalPhrase;
    }
  }
}