#include "engine/evaluate.h"

#include <stdlib.h>

enum {
  EVAL_PAWN   = 100,
  EVAL_KNIGHT = 320,
  EVAL_BISHOP = 320,
  EVAL_ROOK   = 500,
  EVAL_QUEEN  = 900,
};

static const i32 MATERIAL[PIECE_TYPE_COUNT] = {
  [WHITE_KING]   = 0,
  [WHITE_QUEEN]  = EVAL_QUEEN,
  [WHITE_ROOK]   = EVAL_ROOK,
  [WHITE_BISHOP] = EVAL_BISHOP,
  [WHITE_KNIGHT] = EVAL_KNIGHT,
  [WHITE_PAWN]   = EVAL_PAWN,
  [BLACK_KING]   = 0,
  [BLACK_QUEEN]  = EVAL_QUEEN,
  [BLACK_ROOK]   = EVAL_ROOK,
  [BLACK_BISHOP] = EVAL_BISHOP,
  [BLACK_KNIGHT] = EVAL_KNIGHT,
  [BLACK_PAWN]   = EVAL_PAWN,
};

// simple positional bonus (a light "pst"): pawns like to advance, knights like
// the centre. everything else is just material.
static i32 pst_bonus(int piece_type, int square) {
  int rank = square / 8;
  int file = square % 8;
  if (piece_type == WHITE_PAWN) return (rank - 1) * 6;
  if (piece_type == BLACK_PAWN) return (6 - rank) * 6;
  if (piece_type == WHITE_KNIGHT || piece_type == BLACK_KNIGHT) {
    bool central = (file == 3 || file == 4) && (rank == 3 || rank == 4);
    bool nearcentre = (file >= 2 && file <= 5) && (rank >= 2 && rank <= 5);
    return central ? 16 : (nearcentre ? 4 : -4);
  }
  return 0;
}

i32 evaluate(position_t position) {
  i32 white = 0;
  i32 black = 0;
  for (int piece = 0; piece < PIECE_TYPE_COUNT; piece++) {
    bitboard_t bb = position.bitboards[piece];
    while (bb) {
      int sq = __builtin_ctzll(bb);
      bb &= bb - 1;
      if (piece < BLACK_KING) {
        white += MATERIAL[piece] + pst_bonus(piece, sq);
      } else {
        black += MATERIAL[piece] + pst_bonus(piece, sq);
      }
    }
  }
  i32 score = white - black;
  return (position.turn == WHITE_TURN) ? score : -score;
}

#ifdef TEST_MOD
#include <stdbool.h>

bool test_eval_startpos_is_balanced() {
  position_t start = position_starting();
  // symmetric starting position -> static eval should be ~0.
  return abs(evaluate(start)) < 100;
}

bool test_eval_scales_with_material() {
  position_t pos = {0};
  pos.turn = WHITE_TURN;
  // give white a queen on a1, black only a king on h8
  pos.bitboards[WHITE_QUEEN] = 1ULL;
  pos.bitboards[BLACK_KING] = (1ULL << 63);
  pos.bitboards[WHITE_KING] = (1ULL << 4);   // a5, far from the action
  pos.bitboards[BLACK_PAWN] = 0;
  i32 score = evaluate(pos);
  // white is up a queen (~900) plus a little; should be comfortably positive.
  return score > 800;
}
#endif