/*
  Glaurung, a UCI chess playing engine.
  Copyright (C) 2004-2008 Tord Romstad

  Glaurung 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.
  
  Glaurung 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 this program.  If not, see <http://www.gnu.org/licenses/>.
*/


////
//// Includes
////

#include <cassert>

#include "history.h"
#include "movegen.h"
#include "movepick.h"
#include "search.h"
#include "value.h"


////
//// Local definitions
////

namespace {

  /// Types

  enum MovegenPhase {
    PH_TT_MOVE,        // Transposition table move
    PH_MATE_KILLER,    // Mate killer from the current ply
    PH_GOOD_CAPTURES,  // Queen promotions and captures with SEE values >= 0
    PH_BAD_CAPTURES,   // Queen promotions and captures with SEE valuse <= 0
    PH_KILLER_1,       // Killer move 1 from the current ply (not used yet).
    PH_KILLER_2,       // Killer move 2 from the current ply (not used yet).
    PH_NONCAPTURES,    // Non-captures and underpromotions
    PH_EVASIONS,       // Check evasions
    PH_QCAPTURES,      // Captures in quiescence search
    PH_QCHECKS,        // Checks in quiescence search
    PH_STOP
  };


  /// Variables

  MovegenPhase PhaseTable[32];
  int MainSearchPhaseIndex;
  int EvasionsPhaseIndex;
  int QsearchWithChecksPhaseIndex;
  int QsearchWithoutChecksPhaseIndex;

}


////
//// Functions
////


/// Constructor for the MovePicker class.  Apart from the position for which
/// it is asked to pick legal moves, MovePicker also wants some information
/// to help it to return the presumably good moves first, to decide which
/// moves to return (in the quiescence search, for instance, we only want to
/// search captures, promotions and some checks) and about how important good
/// move ordering is at the current node.

MovePicker::MovePicker(Position &p, bool pvnode, Move ttm, Move mk,
                       Move k1, Move k2, Depth dpth) {
  pos = &p;
  pvNode = pvnode;
  ttMove = ttm;
  mateKiller = (mk == ttm)? MOVE_NONE : mk;
  killer1 = k1;
  killer2 = k2;
  depth = dpth;
  movesPicked = 0;
  numOfMoves = 0;
  numOfBadCaptures = 0;
  dc = p.discovered_check_candidates(p.side_to_move());

  if(p.is_check())
    phaseIndex = EvasionsPhaseIndex;
  else if(depth > Depth(0))
    phaseIndex = MainSearchPhaseIndex;
  else if(depth == Depth(0))
    phaseIndex = QsearchWithChecksPhaseIndex;
  else
    phaseIndex = QsearchWithoutChecksPhaseIndex;

  pinned = p.pinned_pieces(p.side_to_move());

  finished = false;
}


/// MovePicker::get_next_move() is the most important method of the MovePicker
/// class.  It returns a new legal move every time it is called, until there
/// are no more moves left of the types we are interested in.

Move MovePicker::get_next_move() {
  Move move;

  while(true) {
    // If we already have a list of generated moves, pick the best move from
    // the list, and return it:
    move = this->pick_move_from_list();
    if(move != MOVE_NONE) {
      assert(move_is_ok(move));
      return move;
    }

    // Next phase:
    phaseIndex++;
    switch(PhaseTable[phaseIndex]) {

    case PH_TT_MOVE:
      if(ttMove != MOVE_NONE) {
        assert(move_is_ok(ttMove));
        Move m = generate_move_if_legal(*pos, ttMove, pinned);
        if(m != MOVE_NONE) {
          assert(m == ttMove);
          return m;
        }
      }
      break;

    case PH_MATE_KILLER:
      if(mateKiller != MOVE_NONE) {
        assert(move_is_ok(mateKiller));
        Move m = generate_move_if_legal(*pos, mateKiller, pinned);
        if(m != MOVE_NONE) {
          assert(m == mateKiller);
          return m;
        }
      }
      break;

    case PH_GOOD_CAPTURES:
      // pinned = pos->pinned_pieces(pos->side_to_move());
      numOfMoves = generate_captures(*pos, moves);
      this->score_captures();
      movesPicked = 0;
      break;

    case PH_BAD_CAPTURES:
      badCapturesPicked = 0;
      break;

    case PH_NONCAPTURES:
      numOfMoves = generate_noncaptures(*pos, moves);
      this->score_noncaptures();
      movesPicked = 0;
      break;

    case PH_EVASIONS:
      assert(pos->is_check());
      // pinned = pos->pinned_pieces(pos->side_to_move());
      numOfMoves = generate_evasions(*pos, moves);
      this->score_evasions();
      movesPicked = 0;
      break;

    case PH_QCAPTURES:
      // pinned = pos->pinned_pieces(pos->side_to_move());
      numOfMoves = generate_captures(*pos, moves);
      this->score_qcaptures();
      movesPicked = 0;
      break;

    case PH_QCHECKS:
      numOfMoves = generate_checks(*pos, moves, dc);
      movesPicked = 0;
      break;

    case PH_STOP:
      return MOVE_NONE;

    default:
      assert(false);
      return MOVE_NONE;
    }
  }

  assert(false);

  return MOVE_NONE;
}


/// A variant of get_next_move() which takes a lock as a parameter, used to
/// prevent multiple threads from picking the same move at a split point.

Move MovePicker::get_next_move(Lock &lock) {
   Move m;

   lock_grab(&lock);
   if(finished) {
     lock_release(&lock);
     return MOVE_NONE;
   }
   m = this->get_next_move();
   if(m == MOVE_NONE)
     finished = true;
   lock_release(&lock);
   
   return m;
}

 
/// MovePicker::number_of_moves() simply returns the numOfMoves member
/// variable.  It is intended to be used in positions where the side to move
/// is in check, for detecting checkmates or situations where there is only
/// a single reply to check.

int MovePicker::number_of_moves() const {
  return numOfMoves;
}


/// MovePicker::score_captures(), MovePicker::score_noncaptures(),
/// MovePicker::score_evasions() and MovePicker::score_qcaptures() assign a
/// numerical move ordering score to each move in a move list.  The moves
/// with highest scores will be picked first by
/// MovePicker::pick_move_from_list().

void MovePicker::score_captures() {
  // Winning and equal captures in the main search are ordered by MVV/LVA.
  // Suprisingly, this appears to perform slightly better than SEE based
  // move ordering.  The reason is probably that in a position with a winning
  // capture, capturing a more valuable (but sufficiently defended) piece
  // first usually doesn't hurt.  The opponent will have to recapture, and
  // the hanging piece will still be hanging (except in the unusual cases
  // where it is possible to recapture with the hanging piece).  Exchanging
  // big pieces before capturing a hanging piece probably helps to reduce
  // the subtree size.
  for(int i = 0; i < numOfMoves; i++) {
    int seeValue = pos->see(moves[i].move);
    if(seeValue >= 0) {
      if(move_promotion(moves[i].move))
        moves[i].score = QueenValueMidgame;
      else 
        moves[i].score =
          int(pos->midgame_value_of_piece_on(move_to(moves[i].move))) -
          int(pos->type_of_piece_on(move_from(moves[i].move)));
    }
    else
      moves[i].score = seeValue;
        
  }
}

void MovePicker::score_noncaptures() {
  for(int i = 0; i < numOfMoves; i++) {
    Move m = moves[i].move;
    if(m == killer1)
      moves[i].score = HistoryMax + 2;
    else if(m == killer2)
      moves[i].score = HistoryMax + 1;
    else
      moves[i].score = H.move_ordering_score(pos->piece_on(move_from(m)), m);
  }
}

void MovePicker::score_evasions() {
  for(int i = 0; i < numOfMoves; i++) {
    Move m = moves[i].move;
    if(m == ttMove)
      moves[i].score = 2*HistoryMax;
    else if(!pos->square_is_empty(move_to(m))) {
      int seeScore = pos->see(m);
      moves[i].score = (seeScore >= 0)? seeScore + HistoryMax : seeScore;
    }
    else
      moves[i].score = H.move_ordering_score(pos->piece_on(move_from(m)), m);
  }
}

void MovePicker::score_qcaptures() {
  // Use MVV/LVA ordering.
  for(int i = 0; i < numOfMoves; i++) {
    Move m = moves[i].move;
    if(move_promotion(m))
      moves[i].score = QueenValueMidgame;
    else
      moves[i].score =
        int(pos->midgame_value_of_piece_on(move_to(m))) -
        int(pos->midgame_value_of_piece_on(move_to(m))) / 64;
  }
}


/// MovePicker::pick_move_from_list() picks the move with the biggest score
/// from a list of generated moves (moves[] or badCaptures[], depending on
/// the current move generation phase).  It takes care not to return the
/// transposition table move if that has already been serched previously.
/// While picking captures in the PH_GOOD_CAPTURES phase (i.e. while picking
/// non-losing captures in the main search), it moves all captures with
/// negative SEE values to the badCaptures[] array.

Move MovePicker::pick_move_from_list() {
  int bestScore = -10000000;
  int bestIndex;
  Move move;

  switch(PhaseTable[phaseIndex]) {

  case PH_GOOD_CAPTURES:
    assert(!pos->is_check());
    assert(movesPicked >= 0);
    while(movesPicked < numOfMoves) {
      bestScore = -10000000;
      bestIndex = -1;
      for(int i = movesPicked; i < numOfMoves; i++) {
        if(moves[i].score < 0) {
          // Losing capture, move it to the badCaptures[] array
          assert(numOfBadCaptures < 63);
          badCaptures[numOfBadCaptures++] = moves[i];
          moves[i--] = moves[--numOfMoves];
        }
        else if(moves[i].score > bestScore) {
          bestIndex = i;
          bestScore = moves[i].score;
        }
      }
      if(bestIndex != -1) { // Found a good capture
        MoveStack tmp = moves[movesPicked];
        moves[movesPicked] = moves[bestIndex];
        moves[bestIndex] = tmp;
        move = moves[movesPicked++].move;
        if(move != ttMove && move != mateKiller &&
           pos->move_is_legal(move, pinned))
          return move;
      }
    }
    break;

  case PH_NONCAPTURES:
    assert(!pos->is_check());
    assert(movesPicked >= 0);
    while(movesPicked < numOfMoves) {
      bestScore = -10000000;

      // If this is a PV node or we have only picked a few moves, scan
      // the entire move list for the best move.  If many moves have already
      // been searched and it is not a PV node, we are probably failing low
      // anyway, so we just pick the first move from the list.
      if(pvNode || movesPicked < 12) {
        bestIndex = -1;
        for(int i = movesPicked; i < numOfMoves; i++)
          if(moves[i].score > bestScore) {
            bestIndex = i;
            bestScore = moves[i].score;
          }
      }
      else
        bestIndex = movesPicked;

      if(bestIndex != -1) {
        MoveStack tmp = moves[movesPicked];
        moves[movesPicked] = moves[bestIndex];
        moves[bestIndex] = tmp;
        move = moves[movesPicked++].move;
        if(move != ttMove && move != mateKiller &&
           pos->move_is_legal(move, pinned))
          return move;
      }
    }
    break;

  case PH_EVASIONS:
    assert(pos->is_check());
    assert(movesPicked >= 0);
    while(movesPicked < numOfMoves) {
      bestScore = -10000000;
      bestIndex = -1;
      for(int i = movesPicked; i < numOfMoves; i++)
        if(moves[i].score > bestScore) {
          bestIndex = i;
          bestScore = moves[i].score;
        }

      if(bestIndex != -1) {
        MoveStack tmp = moves[movesPicked];
        moves[movesPicked] = moves[bestIndex];
        moves[bestIndex] = tmp;
        move = moves[movesPicked++].move;
        return move;
      }
    }
    break;

  case PH_BAD_CAPTURES:
    assert(!pos->is_check());
    assert(badCapturesPicked >= 0);
    // It's probably a good idea to use SEE move ordering here, instead
    // of just picking the first move.  FIXME
    while(badCapturesPicked < numOfBadCaptures) {
      move = badCaptures[badCapturesPicked++].move;
      if(move != ttMove && move != mateKiller && 
         pos->move_is_legal(move, pinned))
        return move;
    }
    break;

  case PH_QCAPTURES:
    assert(!pos->is_check());
    assert(movesPicked >= 0);
    while(movesPicked < numOfMoves) {
      bestScore = -10000000;
      if(movesPicked < 4) {
        bestIndex = -1;
        for(int i = movesPicked; i < numOfMoves; i++)
          if(moves[i].score > bestScore) {
            bestIndex = i;
            bestScore = moves[i].score;
          }
      }
      else
        bestIndex = movesPicked;

      if(bestIndex != -1) {
        MoveStack tmp = moves[movesPicked];
        moves[movesPicked] = moves[bestIndex];
        moves[bestIndex] = tmp;

        move = moves[movesPicked++].move;
        // Remember to change the line below if we decide to hash the qsearch!
        // Maybe also postpone the legality check until after futility pruning?
        if(/* move != ttMove && */ pos->move_is_legal(move, pinned))
          return move;
      }
    }
    break;

  case PH_QCHECKS:
    assert(!pos->is_check());
    assert(movesPicked >= 0);
    // Perhaps we should do something better than just picking the first
    // move here?  FIXME
    while(movesPicked < numOfMoves) {
      move = moves[movesPicked++].move;
      // Remember to change the line below if we decide to hash the qsearch!
      if(/* move != ttMove && */ pos->move_is_legal(move, pinned))
        return move;
    }
    break;

  default:
    break;
  }

  return MOVE_NONE;
}


/// MovePicker::init_phase_table() initializes the PhaseTable[],
/// MainSearchPhaseIndex, EvasionPhaseIndex, QsearchWithChecksPhaseIndex
/// and QsearchWithoutChecksPhaseIndex variables.  It is only called once
/// during program startup, and never again while the program is running.

void MovePicker::init_phase_table() {
  int i = 0;

  // Main search
  MainSearchPhaseIndex = i - 1;
  PhaseTable[i++] = PH_TT_MOVE;
  PhaseTable[i++] = PH_MATE_KILLER;
  PhaseTable[i++] = PH_GOOD_CAPTURES;
  // PH_KILLER_1 and PH_KILLER_2 are not yet used.
  // PhaseTable[i++] = PH_KILLER_1;
  // PhaseTable[i++] = PH_KILLER_2;
  PhaseTable[i++] = PH_NONCAPTURES;
  PhaseTable[i++] = PH_BAD_CAPTURES;
  PhaseTable[i++] = PH_STOP;

  // Check evasions
  EvasionsPhaseIndex = i - 1;
  PhaseTable[i++] = PH_EVASIONS;
  PhaseTable[i++] = PH_STOP;

  // Quiescence search with checks
  QsearchWithChecksPhaseIndex = i - 1;
  PhaseTable[i++] = PH_QCAPTURES;
  PhaseTable[i++] = PH_QCHECKS;
  PhaseTable[i++] = PH_STOP;

  // Quiescence search without checks
  QsearchWithoutChecksPhaseIndex = i - 1;
  PhaseTable[i++] = PH_QCAPTURES;
  PhaseTable[i++] = PH_STOP;
}