source: branches/2895_PushGP_GenealogyAnalysis/HeuristicLab.Problems.ProgramSynthesis/Push/Parser/PushParser.cs @ 16099

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

namespace HeuristicLab.Problems.ProgramSynthesis {
  public static class PushParser {
    private const char delimiter = ' ';

    private static readonly CultureInfo cultureInfo = CultureInfo.CreateSpecificCulture("en-US");

    private static readonly char[] symbolTrim = { '\r', '\n' };

    public static Expression Parse(string source, int startIndex = 0) {
      bool error;
      var symbols = GetSymbols(source, out error); // source.Split(delimiter);

      int endIndex;
      return Parse(symbols, startIndex, out endIndex);
    }

    public static PushProgram ParseProgram(string source, int startIndex = 0) {
      var expression = Parse(source, startIndex);

      return expression as PushProgram ?? new PushProgram(new[] { expression });
    }

    private static IReadOnlyList<string> GetSymbols(string source, out bool error) {
      var chars = source.ToCharArray();
      var symbols = new List<string>();

      for (var i = 0; i < chars.Length; i++) {
        var cur = chars[i];
        int endIndex;
        int length;
        string str;

        switch (cur) {
          case delimiter: break;
          case PushEnvironment.StringSymbol:
            endIndex = source.IndexOf(PushEnvironment.StringSymbol, i + 1);
            if (endIndex < i) {
              error = true;
              return symbols;
            }

            length = endIndex - i + 1;
            str = source.Substring(i, length);
            symbols.Add(str);
            i += length; // skip following space

            break;

          case PushEnvironment.CharSymbol:
            endIndex = source.IndexOf(PushEnvironment.CharSymbol, i + 1);
            if (endIndex < i) {
              error = true;
              return symbols;
            }

            length = endIndex - i + 1;
            str = source.Substring(i, length);
            str = EscapeLikeALiteral(str);
            symbols.Add(str);
            i += length; // skip following space

            break;

          case PushEnvironment.VectorStartSymbol:
            endIndex = source.IndexOf(PushEnvironment.VectorEndSymbol, i + 1);
            if (endIndex < i) {
              error = true;
              return symbols;
            }

            length = endIndex - i + 1;
            str = source.Substring(i, length);
            symbols.Add(str);
            i += length; // skip following space
            break;

          default:
            endIndex = source.IndexOf(' ', i + 1);

            length = endIndex < i
              ? chars.Length - i
              : endIndex - i;

            str = source.Substring(i, length);
            symbols.Add(str);
            i += length; // skip following space

            break;
        }
      }

      error = true;
      return symbols;
    }

    private static Expression Parse(IReadOnlyList<string> symbols, int startIndex, out int endIndex) {
      var expressions = new List<Expression>();

      for (var i = startIndex; i < symbols.Count; i++) {
        var symbol = symbols[i].TrimEnd(symbolTrim);

        if (string.IsNullOrWhiteSpace(symbol)) continue;

        switch (symbol) {
          case PushEnvironment.ProgramStartSymbolStr:
            var subExpression = Parse(symbols, i + 1, out endIndex);
            expressions.Insert(0, subExpression);
            i = endIndex;
            continue;
          case PushEnvironment.ProgramEndSymbolStr:
            endIndex = i;
            return new PushProgram(expressions);
        }

        // literal
        Expression expression;
        if (TryParseLiteral(symbol, out expression)) {
          expressions.Insert(0, expression);
          continue;
        }

        // expression
        if (ExpressionTable.TryGetStatelessExpression(symbol, out expression)
         || ExpressionTable.TryGetStatefulExpression(symbol, out expression)) {
          expressions.Insert(0, expression);
          continue;
        }

        // identifier - custom expression or named literals
        expressions.Insert(0, new NameDefineXExecExpression(symbol));
      }

      endIndex = symbols.Count - 1;

      switch (expressions.Count) {
        case 0:
          return PushProgram.Empty;
        case 1:
          return expressions[0];
        default:
          return new PushProgram(expressions);
      }
    }

    private static bool TryParseLiteral(string word, out Expression expression) {
      if (word.StartsWith(PushEnvironment.CharSymbolStr) &&
          word.EndsWith(PushEnvironment.CharSymbolStr) &&
          word.Length == 3) {
        expression = new CharPushExpression(word[1]);
        return true;
      }

      if (word.StartsWith(PushEnvironment.StringSymbolStr) &&
          word.EndsWith(PushEnvironment.StringSymbolStr)) {
        var stringValue = word.Length == 0 ? string.Empty : word.Substring(1, word.Length - 2);
        expression = new StringPushExpression(stringValue);
        return true;
      }

      // "[]" has no values and can therefor not parsed correctly as vector of a specific type
      if (word.StartsWith(PushEnvironment.VectorStartSymbolStr) &&
          word.EndsWith(PushEnvironment.VectorEndSymbolStr) &&
          word.Length > 2) {

        var vectorEntries = word
          .Substring(1, word.Length - 2)
          .Split(PushEnvironment.VectorSeparatorSymbol)
          .ToList();

        if (vectorEntries.Count == 0) {
          expression = null;
          return false;
        }

        Expression e;
        var first = vectorEntries.First();
        if (!TryParseLiteral(first, out e)) {
          expression = null;
          return false;
        }

        if (e.GetType() == typeof(IntegerPushExpression)) {
          var integerValues = vectorEntries.Select(long.Parse).ToList();
          expression = new IntegerVectorPushExpression(integerValues);
        } else if (e.GetType() == typeof(FloatPushExpression)) {
          var doubleValues = vectorEntries.Select(x => double.Parse(x, NumberStyles.Float, cultureInfo)).ToList();
          expression = new FloatVectorPushExpression(doubleValues);
        } else if (e.GetType() == typeof(StringPushExpression)) {
          var stringValues = vectorEntries.Select(str => str.Substring(1, str.Length - 2)).ToList();
          expression = new StringVectorPushExpression(stringValues);
        } else if (e.GetType() == typeof(BooleanPushExpression)) {
          var booleanValues = vectorEntries.Select(bool.Parse).ToList();
          expression = new BooleanVectorPushExpression(booleanValues);
        } else {
          expression = null;
          return false;
        }

        return true;
      }

      long longValue;
      if (long.TryParse(word, out longValue)) {
        expression = new IntegerPushExpression(longValue);
        return true;
      }

      double floatValue;
      if (double.TryParse(word, NumberStyles.Float, cultureInfo, out floatValue)) {
        expression = new FloatPushExpression(floatValue);
        return true;
      }

      bool booleanValue;
      if (bool.TryParse(word, out booleanValue)) {
        expression = new BooleanPushExpression(booleanValue);
        return true;
      }

      expression = null;
      return false;
    }

    private static string EscapeLikeALiteral(string src) {
      return Regex.Replace(src, @"\\(?<simple>['""\\0abfnrtv])", m => {
        var s = m.Groups["simple"].Value;
        switch (s) {
          case "'": return "'";
          case "\"": return "\"";
          case "0": return "\0";
          case "a": return "\a";
          case "b": return "\b";
          case "f": return "\f";
          case "n": return "\n";
          case "r": return "\r";
          case "t": return "\t";
          case "v": return "\v";
          default:
            throw new InvalidOperationException();
        }
      });
    }
  }
}