namespace HeuristicLab.Problems.ProgramSynthesis.Push.Expressions {
  using HeuristicLab.Problems.ProgramSynthesis.Push.Attributes;
  using HeuristicLab.Problems.ProgramSynthesis.Push.Interpreter;
  using HeuristicLab.Problems.ProgramSynthesis.Push.Stack;

  /// <summary>
  ///     Pushes a copy of an indexed item "deep" in the stack onto the top of the stack, without removing the deep item.
  ///     The index is taken from the INTEGER stack, and the indexing is done after the index is removed.
  /// </summary>
  /// <typeparam name="T">Stacktype</typeparam>
  public abstract class YankDuplicateExpression<T> : StatelessExpression {
    public void Eval(IStack<T> stack, IStack<long> integerStack) {
      T item;
      if (this.TryGetItem(stack, integerStack, out item)) stack.Push(item);
    }

    public void Eval(IStack<Expression> stack, IStack<long> integerStack) {
      Expression item;
      if (this.TryGetItem(stack, integerStack, out item)) stack.Push(item);
    }

    public void Eval(IStack<long> integerStack) {
      if ((integerStack.Count < 2) || (integerStack.Top > integerStack.Count - 2) ||
          (integerStack.Top < 0)) return;

      var index = (int)integerStack.Pop();
      var item = integerStack.ReverseElementAt(index);

      integerStack.Push(item);
    }

    private bool TryGetItem<E>(IStack<E> stack, IStack<long> integerStack, out E item) {
      if ((integerStack.Count == 0) ||
          (integerStack.Top >= stack.Count) ||
          (integerStack.Top < 0) ||
          (stack.Count < 2)) {
        item = default(E);
        return false;
      }

      var index = (int)integerStack.Pop();
      item = stack.ReverseElementAt(index);

      return true;
    }
  }

  [PushExpression(StackType.Integer, "INTEGER.YANKDUP")]
  public class IntegerYankDuplicateExpression : YankDuplicateExpression<long> {
    public override void Eval(IPushGpInterpreter interpreter) {
      this.Eval(interpreter.IntegerStack);
    }
  }

  [PushExpression(StackType.Float, "FLOAT.YANKDUP")]
  public class FloatYankDuplicateExpression : YankDuplicateExpression<double> {
    public override void Eval(IPushGpInterpreter interpreter) {
      this.Eval(interpreter.FloatStack, interpreter.IntegerStack);
    }
  }

  [PushExpression(StackType.Boolean, "BOOLEAN.YANKDUP")]
  public class BooleanYankDuplicateExpression : YankDuplicateExpression<bool> {
    public override void Eval(IPushGpInterpreter interpreter) {
      this.Eval(interpreter.BooleanStack, interpreter.IntegerStack);
    }
  }

  [PushExpression(StackType.Name, "NAME.YANKDUP")]
  public class NameYankDuplicateExpression : YankDuplicateExpression<string> {
    public override void Eval(IPushGpInterpreter interpreter) {
      this.Eval(interpreter.NameStack, interpreter.IntegerStack);
    }
  }

  [PushExpression(StackType.Exec, "EXEC.YANKDUP")]
  public class ExecYankDuplicateExpression : YankDuplicateExpression<Expression> {
    public override void Eval(IPushGpInterpreter interpreter) {
      this.Eval(interpreter.ExecStack, interpreter.IntegerStack);
    }
  }

  [PushExpression(StackType.Code, "CODE.YANKDUP")]
  public class CodeYankDuplicateExpression : YankDuplicateExpression<Expression> {
    public override void Eval(IPushGpInterpreter interpreter) {
      this.Eval(interpreter.CodeStack, interpreter.IntegerStack);
    }
  }
}