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

namespace HeuristicLab.Algorithms.Bandits {
  public class EpsGreedyPolicy : BanditPolicy {
    private readonly Random random;
    private readonly double eps;
    private readonly int[] tries;
    private readonly double[] sumReward;
    private readonly RandomPolicy randomPolicy;

    public EpsGreedyPolicy(Random random, int numActions, double eps)
      : base(numActions) {
      this.random = random;
      this.eps = eps;
      this.randomPolicy = new RandomPolicy(random, numActions);
      this.tries = new int[numActions];
      this.sumReward = new double[numActions];
    }

    public override int SelectAction() {
      Debug.Assert(Actions.Any());
      if (random.NextDouble() > eps) {
        // select best
        var bestQ = double.NegativeInfinity;
        int bestAction = -1;
        foreach (var a in Actions) {
          if (tries[a] == 0) return a;
          var q = sumReward[a] / tries[a];
          if (bestQ < q) {
            bestQ = q;
            bestAction = a;
          }
        }
        Debug.Assert(bestAction >= 0);
        return bestAction;
      } else {
        // select random
        return randomPolicy.SelectAction();
      }
    }
    public override void UpdateReward(int action, double reward) {
      Debug.Assert(Actions.Contains(action));

      randomPolicy.UpdateReward(action, reward); // does nothing
      tries[action]++;
      sumReward[action] += reward;
    }

    public override void DisableAction(int action) {
      base.DisableAction(action);
      randomPolicy.DisableAction(action);
      sumReward[action] = 0;
      tries[action] = -1;
    }

    public override void Reset() {
      base.Reset();
      randomPolicy.Reset();
      Array.Clear(tries, 0, tries.Length);
      Array.Clear(sumReward, 0, sumReward.Length);
    }
    public override void PrintStats() {
      for (int i = 0; i < sumReward.Length; i++) {
        if (tries[i] >= 0) {
          Console.Write(" {0,5:F2} {1}", sumReward[i] / tries[i], tries[i]);
        } else {
          Console.Write("-", "");
        }
      }
      Console.WriteLine();
    }
    public override string ToString() {
      return string.Format("EpsGreedyPolicy({0:F2})", eps);
    }
  }
}