#region License Information
/* HeuristicLab
 * Copyright (C) 2002-2016 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
 *
 * This file is part of HeuristicLab.
 *
 * HeuristicLab is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * HeuristicLab is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
 */
#endregion

using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Text;
using HeuristicLab.Core;
using HeuristicLab.Random;

namespace HeuristicLab.ExpressionGenerator {
  public class Expression : IExpression {
    // unique name for each expression 
    public string Name { get; set; }
    // optional label (non-unique) - useful for string (infix) representations
    public string Label { get; set; }

    public ExpressionType Type { get; private set; }

    private readonly List<Expression> arguments; // only for functions
    public IEnumerable<Expression> Arguments {
      get { return arguments ?? Enumerable.Empty<Expression>(); }
    }

    public IRandom Distribution { get; private set; }  // only for random variables

    public Func<IEnumerable<double>, double> Transform { get; private set; } // only for functions

    public double Value { get; private set; } // only for constants

    public Expression(string name, double value) {
      Type = ExpressionType.Constant;
      Value = value;
      Name = name;
    }

    public Expression(string name, IRandom distribution) {
      Type = ExpressionType.RandomVariable;
      Distribution = distribution;
      Name = name;
    }

    public Expression(string name, Func<IEnumerable<double>, double> transform, IEnumerable<Expression> arguments) {
      Type = ExpressionType.Function;
      Transform = transform;
      this.arguments = this.arguments ?? new List<Expression>();
      this.arguments.AddRange(arguments);
      Name = name;
    }

    public static Expression Constant(string name, double value) {
      return new Expression(name, value);
    }

    public static Expression RandomVariable(string name, IRandom distribution) {
      return new Expression(name, distribution);
    }

    public static Expression Function(string name, Func<IEnumerable<double>, double> transform, IEnumerable<Expression> arguments) {
      return new Expression(name, transform, arguments);
    }

    public override string ToString() {
      var sb = new StringBuilder();

      switch (Type) {
        case ExpressionType.Constant:
          sb.Append(Value.ToString("E4", CultureInfo.InvariantCulture));
          break;
        case ExpressionType.RandomVariable:
          sb.Append(string.Format("{0} ~ {1}", Name, GetStringDescription(Distribution)));
          break;
        case ExpressionType.Function:
          sb.Append(string.Format("{0} = f(", Name));
          if (Arguments.Any()) {
            for (int i = 0; i < arguments.Count - 1; ++i)
              sb.Append(string.Format("{0}, ", arguments[i].Name));
            sb.Append(string.Format("{0})", arguments.Last().Name));
          }
          break;
      }

      return sb.ToString();
    }

    public string PrintInfix() {
      var sb = new StringBuilder();
      switch (Type) {
        case ExpressionType.Constant:
          sb.Append(Value < 0
              ? string.Format("(- {0})", Math.Abs(Value).ToString("E4", CultureInfo.InvariantCulture))
              : Value.ToString("E4", CultureInfo.InvariantCulture));
          break;
        case ExpressionType.RandomVariable:
          sb.Append(Name);
          break;
        case ExpressionType.Function:
          if (!Arguments.Any())
            break;
          var args = Arguments.ToList();
          // the Label should be known to the infix parser
          if (Label == "+" || Label == "-" || Label == "*" || Label == "/") {
            if (args.Count == 1) {
              sb.Append(string.Format(Label == "/" ? "1 / {0}" : "{0}", args[0].PrintInfix()));
            } else {
              if (Label == "/") {
                sb.Append(string.Format("{0} / ", args[0].PrintInfix()));
                var remaining = args.Count - 1;
                if (remaining == 1)
                  sb.Append(args[1].PrintInfix());
                else {
                  sb.Append("(");
                  var last = args.Last();
                  for (int i = 1; i < args.Count - 1; ++i) {
                    var arg = args[i];
                    sb.Append(string.Format("{0} {1} ", arg.PrintInfix(), "*"));
                  }
                  sb.Append(string.Format("{0})", last.PrintInfix()));
                }
              } else {
                sb.Append("(");
                var last = args.Last();
                for (int i = 0; i < args.Count - 1; ++i) {
                  var arg = args[i];
                  sb.Append(string.Format("{0} {1} ", arg.PrintInfix(), Label));
                }
                sb.Append(string.Format("{0})", last.PrintInfix()));
              }
            }
          } else {
            sb.Append(string.Format("{0}(", Label));
            var last = args.Last();
            for (int i = 0; i < args.Count - 1; ++i) {
              var arg = args[i];
              sb.Append(string.Format("{0}, ", arg.PrintInfix()));
            }
            sb.Append(string.Format("{0})", last.PrintInfix()));
          }
          break;
      }
      return sb.ToString();
    }

    public string PrintDot() {
      var stack = new Stack<Expression>();
      stack.Push(this);

      var sb = new StringBuilder();
      sb.AppendLine("digraph g {");

      while (stack.Count > 0) {
        var top = stack.Pop();

        if (!top.Arguments.Any())
          continue;

        foreach (var arg in top.Arguments) {
          var from = top.Arguments.Any() ? top.Name : top.ToString();
          var to = arg.Arguments.Any() ? arg.Name : arg.ToString();
          sb.AppendLine(string.Format("\"{0}\" -> \"{1}\";", from, to));
          stack.Push(arg);
        }
      }

      sb.AppendLine("}");
      return sb.ToString();
    }

    private static string GetStringDescription(IRandom random) {
      var normal = random as NormalDistributedRandom;
      if (normal != null)
        return string.Format("N({0}, {1})", normal.Mu, normal.Sigma);

      var uniform = random as UniformDistributedRandom;
      if (uniform != null)
        return string.Format("U({0}, {1})", uniform.Min, uniform.Max);

      var gamma = random as GammaDistributedRandom;
      if (gamma != null)
        return string.Format("G({0}, {1})", gamma.Shape, gamma.Rate);

      return random.ToString();
    }
  }
}