#ifndef EXPRESSION_FILTER
#define EXPRESSION_FILTER

#include "LikelihoodTable.h"
#include "InputVector.h"
#include <float.h>
#include <string>

// Number of expression state: 3 for now (absent, present, no-face)
#define NUM_STATES 3
// Approximate number of frames processed per second */
#define FRAME_RATE 4 /* fps */

// Probability of the face detector correctly rejecting a non-face
#define CORRECT_REJECTION_RATE (0.96)
// Probability of the face detector INcorrectly rejecting a non-face
#define FALSE_POSITIVE_RATE (1 - CORRECT_REJECTION_RATE)
// Probability of the face detector missing a face when the expression is absent
#define MISS_ABSENT_RATE (0.38)
// Probability of the face detector finding a face when the expression is absent
#define HIT_ABSENT_RATE (1 - MISS_ABSENT_RATE)
// Probability of the face detector missing a face when the expression is present
#define MISS_PRESENT_RATE (0.31)
// Probability of the face detector finding a face when the expression is present
#define HIT_PRESENT_RATE (1 - MISS_PRESENT_RATE)

// Transition probabilities from each state to each other state.
// P stands for present, A for absent, and NF for no-face
// These should sum to 1
#define P_TO_P   (1 - 1.0/(2 * FRAME_RATE))
#define P_TO_A  (1.0/(4 * FRAME_RATE))
#define P_TO_NF  (1.0/(4 * FRAME_RATE))
// These should sum to 1
#define A_TO_P (1.0/(4 * FRAME_RATE))
#define A_TO_A  (1 - 1.0/(2 * FRAME_RATE))
#define A_TO_NF (1.0/(4 * FRAME_RATE))
// These should sum to 1
#define NF_TO_P  (1.0/(20 * FRAME_RATE))
#define NF_TO_A (1.0/(20 * FRAME_RATE))
#define NF_TO_NF (1 - 1.0/(10 * FRAME_RATE))

// Order of states: PRESENT, ABSENT, NO_FACE
const double PRIOR_PROBABILITIES[NUM_STATES] = { 0.5, 0.125, 0.375 };
const double TRANSITION_PROBABILITIES[NUM_STATES][NUM_STATES] = {
  { P_TO_P,  P_TO_A,  P_TO_NF  },
  { A_TO_P, A_TO_A, A_TO_NF },
  { NF_TO_P, NF_TO_A, NF_TO_NF }
};

class ExpressionFilter {
public:
typedef enum { PRESENT=0, ABSENT=1, NO_FACE=2 } expr_state;
protected:
  double probabilities[NUM_STATES];
  LikelihoodTable nonfaceLikelihoods, presentLikelihoods, absentLikelihoods;
  
  double TransitionProb (expr_state from, expr_state to);
  double CalcLikelihood (expr_state state, InputVector input);
  void NextTimeStepGivenLikelihoods (double likelihoods[NUM_STATES]);
  std::string BuildFileName( const std::string &dir, const std::string &prefix, int expression_num, bool face );

public:
	  ExpressionFilter (int _expression_num, std::string dir = "" );

  void NextTimeStep (InputVector input);
  double GetProbability (expr_state state);
  
private:
	  int expression_num;
};
#endif