source: branches/HeuristicLab.Problems.GrammaticalOptimization/HeuristicLab.Problems.GrammaticalOptimization/Sequence.cs @ 11733

using System;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace HeuristicLab.Problems.GrammaticalOptimization {
  // represents a sequence of symbols (non-terminal and terminal symbols)
  // a sequence consisting only of terminal symbols can be a sentence of a language
  // the class supports in-place manipulation of the sequence symbols (replace NT with another sequence)
  // sequences provide efficient support left-canonical derivation by storing the index of the first non-terminal symbol
  // maximal length of sequences is limited to 1000 symbols

  // for symbols the same assumptions for the implementation of grammars apply
  // - non-terminal symbols must be characters in the range [A..Z]
  // - terminal symbols can be almost all other characters
  public class Sequence : IEnumerable<char> {
    private const int maxIdx = 200;

    private int len;
    private int idxOfFirstNt;
    private readonly char[] symbols;

    public char this[int idx] {
      get { return symbols[idx]; }
      set { throw new NotSupportedException(); }
    }

    public int Length {
      get { return len; }
      private set { len = value; }
    }

    public bool IsTerminal {
      get { return idxOfFirstNt == -1; }
    }

    public int FirstNonTerminalIndex {
      get { return idxOfFirstNt; }
    }

    public char FirstNonTerminal {
      get { return symbols[idxOfFirstNt]; }
    }

    private Sequence() {
      this.symbols = new char[maxIdx + 1];
    }

    // create a sequence from a character
    public Sequence(char ch)
      : this() {
      this.len = 1;
      symbols[0] = ch;

      if (ch >= 'A' && ch <= 'Z') idxOfFirstNt = 0;
      else idxOfFirstNt = -1;
    }

    // create a sequence from a string
    public Sequence(string s)
      : this() {
      if (string.IsNullOrEmpty(s)) throw new ArgumentException();
      if (s.Length > (maxIdx + 1)) throw new ArgumentException();
      this.len = s.Length;
      this.idxOfFirstNt = -1;

      for (int i = 0; i < len; i++) {
        symbols[i] = s[i];
        if (idxOfFirstNt == -1 && symbols[i] >= 'A' && symbols[i] <= 'Z') {
          idxOfFirstNt = i;
        }
      }
    }

    // cloning ctor
    public Sequence(Sequence original)
      : this() {
      this.len = original.len;
      Array.Copy(original.symbols, this.symbols, len);
      this.idxOfFirstNt = original.idxOfFirstNt;
    }

    public virtual void ReplaceAt(int position, int len, Sequence replacement) {
      if (replacement == null) throw new ArgumentNullException();
      if (len <= 0) throw new ArgumentException();
      if (position + len >= maxIdx) throw new ArgumentException();
      if (Length - len + replacement.Length > (maxIdx + 1)) throw new ArgumentException();
      var lenDelta = replacement.Length - len;
      var remainingPartLen = Length - position - len;
      var startIdxOfRemainingPart = position + len + lenDelta;
      Array.Copy(symbols, position + len, symbols, startIdxOfRemainingPart, remainingPartLen);
      Array.Copy(replacement.symbols, 0, symbols, position, replacement.Length);

      this.len = Length + lenDelta;
      // when the first part contains an NT then it's not necessary to update the index
      if (idxOfFirstNt >= 0 && idxOfFirstNt < position) return;
      // if the replacement contains an NT then we can directly calculate the idx of that NT in the new sequence
      if (replacement.idxOfFirstNt >= 0) {
        this.idxOfFirstNt = position + replacement.idxOfFirstNt;
      } else {
        // otherwise we must find the first NT in the remaining part
        idxOfFirstNt = -1;
        for (int i = startIdxOfRemainingPart; idxOfFirstNt == -1 && i < Length; i++) {
          if (symbols[i] >= 'A' && symbols[i] <= 'Z') idxOfFirstNt = i;
        }
      }
    }

    public IEnumerator<char> GetEnumerator() {
      return symbols.AsEnumerable().Take(len).GetEnumerator();
    }

    public override string ToString() {
      var sb = new StringBuilder(len);
      sb.Append(symbols, 0, len);
      return sb.ToString();
    }

    IEnumerator IEnumerable.GetEnumerator() {
      return GetEnumerator();
    }

    public Sequence Subsequence(int startIdx, int len) {
      if (startIdx < 0 || len < 0) throw new ArgumentException();
      if (startIdx >= this.len) throw new ArgumentException();
      if (startIdx + len > this.len) throw new ArgumentException();
      var subsequence = new Sequence { len = len };

      Array.Copy(this.symbols, startIdx, subsequence.symbols, 0, len);
      if (idxOfFirstNt < 0) {
        subsequence.idxOfFirstNt = -1;
      } else if (idxOfFirstNt < startIdx) {
        // need to find first nt in subsequence
        subsequence.idxOfFirstNt = -1;
        for (int i = 0; subsequence.idxOfFirstNt == -1 && i < len; i++) {
          if (subsequence.symbols[i] >= 'A' && subsequence.symbols[i] <= 'Z') subsequence.idxOfFirstNt = i;
        }
      } else if (idxOfFirstNt >= startIdx && idxOfFirstNt < startIdx + len) {
        subsequence.idxOfFirstNt = idxOfFirstNt;
      } else {
        Debug.Assert(idxOfFirstNt >= startIdx + len);
        subsequence.idxOfFirstNt = -1;
      }
      return subsequence;
    }
  }
}