#if defined(__linux__)
#define _DEFAULT_SOURCE
#endif

#include "hybbx/chess.h"
#include "hybbx/session.h"
#include "hybbx/service.h"
#include "hybbx/log.h"
#include "hybbx/util.h"
#include "hybbx/config.h"

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>

static chess_game_t g_games[CHESS_GAME_MAX];
static unsigned g_max_games = CHESS_DEFAULT_MAX;

/* ── Board init ────────────────────────────────────────────── */

static void board_init(chess_board_t *b)
{
    static const char back[] = "RNBQKBNR";
    unsigned f;

    memset(b, 0, sizeof(*b));
    for (f = 0; f < 8; f++) {
        b->sq[0][f] = back[f];
        b->sq[1][f] = 'P';
        b->sq[6][f] = 'p';
        b->sq[7][f] = (char)tolower((unsigned char)back[f]);
    }
    for (unsigned r = 2; r < 6; r++)
        for (f = 0; f < 8; f++)
            b->sq[r][f] = CHESS_EMPTY;
}

void hybbx_chess_init(void)
{
    memset(g_games, 0, sizeof(g_games));
    g_max_games = CHESS_DEFAULT_MAX;
}

void hybbx_chess_shutdown(void)
{
    unsigned i;
    for (i = 0; i < g_max_games; i++)
        g_games[i].active = 0;
}

void hybbx_chess_config_apply(const struct hybbx_config *config)
{
    unsigned val;

    if (config != NULL) {
        val = hybbx_config_get_uint(config, "chess", "max_games",
                                     CHESS_DEFAULT_MAX, 1, CHESS_GAME_MAX);
    } else {
        val = CHESS_DEFAULT_MAX;
    }
    g_max_games = val;
    hybbx_log_info("[chess] max_games=%u", g_max_games);
}

unsigned hybbx_chess_max_games(void)
{
    return g_max_games;
}

/* ── Helpers ───────────────────────────────────────────────── */

static int parse_square(const char *s, unsigned *rank, unsigned *file)
{
    if (s == NULL || strlen(s) < 2)
        return 0;
    if (s[0] < 'a' || s[0] > 'h' || s[1] < '1' || s[1] > '8')
        return 0;
    *file = (unsigned)(s[0] - 'a');
    *rank = (unsigned)(s[1] - '1');
    return 1;
}

static chess_color_t piece_color(char p)
{
    if (p == CHESS_EMPTY) return CHESS_COLOR_NONE;
    return (p >= 'A' && p <= 'Z') ? CHESS_WHITE : CHESS_BLACK;
}

static char piece_upper(char p)
{
    return (char)toupper((unsigned char)p);
}

static int in_bounds(unsigned r, unsigned f)
{
    return r < 8 && f < 8;
}

/* ── Check detection ───────────────────────────────────────── */

static int square_attacked_by(const chess_board_t *b, unsigned rank,
                              unsigned file, chess_color_t by)
{
    unsigned r, f;
    int dr, df;
    char pawn, knight, bishop, rook, queen, king;

    if (by == CHESS_WHITE) {
        pawn = 'P'; knight = 'N'; bishop = 'B';
        rook = 'R'; queen = 'Q'; king = 'K';
    } else {
        pawn = 'p'; knight = 'n'; bishop = 'b';
        rook = 'r'; queen = 'q'; king = 'k';
    }

    /* Pawn attacks */
    if (by == CHESS_WHITE) {
        if (rank > 0 && file > 0 && b->sq[rank - 1][file - 1] == pawn) return 1;
        if (rank > 0 && file < 7 && b->sq[rank - 1][file + 1] == pawn) return 1;
    } else {
        if (rank < 7 && file > 0 && b->sq[rank + 1][file - 1] == pawn) return 1;
        if (rank < 7 && file < 7 && b->sq[rank + 1][file + 1] == pawn) return 1;
    }

    /* Knight */
    {
        static const int kr[] = {2,2,-2,-2,1,1,-1,-1};
        static const int kf[] = {1,-1,1,-1,2,-2,2,-2};
        for (unsigned i = 0; i < 8; i++) {
            int nr = (int)rank + kr[i], nf = (int)file + kf[i];
            if (nr >= 0 && nr < 8 && nf >= 0 && nf < 8)
                if (b->sq[nr][nf] == knight) return 1;
        }
    }

    /* Sliding: bishop/queen diagonals */
    {
        static const int drs[] = {1,1,-1,-1};
        static const int dfs[] = {1,-1,1,-1};
        for (unsigned d = 0; d < 4; d++) {
            dr = drs[d]; df = dfs[d];
            r = rank; f = file;
            while (1) {
                r = (unsigned)((int)r + dr);
                f = (unsigned)((int)f + df);
                if (!in_bounds(r, f)) break;
                if (b->sq[r][f] != CHESS_EMPTY) {
                    if (b->sq[r][f] == bishop || b->sq[r][f] == queen) return 1;
                    break;
                }
            }
        }
    }

    /* Sliding: rook/queen straights */
    {
        static const int drs[] = {1,-1,0,0};
        static const int dfs[] = {0,0,1,-1};
        for (unsigned d = 0; d < 4; d++) {
            dr = drs[d]; df = dfs[d];
            r = rank; f = file;
            while (1) {
                r = (unsigned)((int)r + dr);
                f = (unsigned)((int)f + df);
                if (!in_bounds(r, f)) break;
                if (b->sq[r][f] != CHESS_EMPTY) {
                    if (b->sq[r][f] == rook || b->sq[r][f] == queen) return 1;
                    break;
                }
            }
        }
    }

    /* King */
    {
        static const int drs[] = {1,1,1,0,0,-1,-1,-1};
        static const int dfs[] = {1,0,-1,1,-1,1,0,-1};
        for (unsigned d = 0; d < 8; d++) {
            int nr = (int)rank + drs[d], nf = (int)file + dfs[d];
            if (nr >= 0 && nr < 8 && nf >= 0 && nf < 8)
                if (b->sq[nr][nf] == king) return 1;
        }
    }

    return 0;
}

static int find_king(const chess_board_t *b, chess_color_t color,
                     unsigned *kr, unsigned *kf)
{
    char king = (color == CHESS_WHITE) ? 'K' : 'k';
    for (unsigned r = 0; r < 8; r++)
        for (unsigned f = 0; f < 8; f++)
            if (b->sq[r][f] == king) { *kr = r; *kf = f; return 1; }
    return 0;
}

static int is_in_check(const chess_board_t *b, chess_color_t side)
{
    unsigned kr, kf;
    chess_color_t opp = (side == CHESS_WHITE) ? CHESS_BLACK : CHESS_WHITE;
    if (!find_king(b, side, &kr, &kf)) return 0;
    return square_attacked_by(b, kr, kf, opp);
}

/* ── Move legality ─────────────────────────────────────────── */

static int pseudo_legal_pawn(const chess_board_t *b, unsigned fr,
                             unsigned ff, unsigned tr, unsigned tf,
                             chess_color_t side)
{
    int dir = (side == CHESS_WHITE) ? 1 : -1;
    int start_rank = (side == CHESS_WHITE) ? 1 : 6;
    int dr = (int)tr - (int)fr;
    int df = (int)tf - (int)ff;

    if (df == 0) {
        if (dr == dir && b->sq[tr][tf] == CHESS_EMPTY) return 1;
        if (dr == 2 * dir && (int)fr == start_rank &&
            b->sq[fr + (unsigned)dir][ff] == CHESS_EMPTY &&
            b->sq[tr][tf] == CHESS_EMPTY) return 1;
    }
    if ((df == 1 || df == -1) && dr == dir) {
        if (b->sq[tr][tf] != CHESS_EMPTY) return 1;
    }
    return 0;
}

static int pseudo_legal_knight(unsigned fr, unsigned ff, unsigned tr,
                               unsigned tf)
{
    int dr = abs((int)tr - (int)fr);
    int df = abs((int)tf - (int)ff);
    return (dr == 2 && df == 1) || (dr == 1 && df == 2);
}

static int sliding_clear(const chess_board_t *b, unsigned fr, unsigned ff,
                         unsigned tr, unsigned tf)
{
    int dr = 0, df = 0;
    unsigned r, f;

    if ((int)tr > (int)fr) dr = 1;
    else if ((int)tr < (int)fr) dr = -1;
    if ((int)tf > (int)ff) df = 1;
    else if ((int)tf < (int)ff) df = -1;

    r = (unsigned)((int)fr + dr);
    f = (unsigned)((int)ff + df);
    while (r != tr || f != tf) {
        if (!in_bounds(r, f) || b->sq[r][f] != CHESS_EMPTY) return 0;
        r = (unsigned)((int)r + dr);
        f = (unsigned)((int)f + df);
    }
    return 1;
}

static int pseudo_legal(const chess_board_t *b, unsigned fr, unsigned ff,
                        unsigned tr, unsigned tf, chess_color_t side)
{
    char piece = b->sq[fr][ff];
    int dr = abs((int)tr - (int)fr);
    int df = abs((int)tf - (int)ff);
    chess_color_t target_color;

    if (piece == CHESS_EMPTY) return 0;
    if (piece_color(piece) != side) return 0;

    target_color = piece_color(b->sq[tr][tf]);
    if (target_color == side) return 0;

    switch (piece_upper(piece)) {
    case 'P': return pseudo_legal_pawn(b, fr, ff, tr, tf, side);
    case 'N': return pseudo_legal_knight(fr, ff, tr, tf);
    case 'B':
        if (dr != df || dr == 0) return 0;
        return sliding_clear(b, fr, ff, tr, tf);
    case 'R':
        if (fr != tr && ff != tf) return 0;
        return sliding_clear(b, fr, ff, tr, tf);
    case 'Q':
        if (fr != tr && ff != tf && dr != df) return 0;
        return sliding_clear(b, fr, ff, tr, tf);
    case 'K':
        return dr <= 1 && df <= 1 && (dr + df > 0);
    }
    return 0;
}

static int has_any_legal_move(chess_board_t *b, chess_color_t side);

static int is_legal_move(chess_board_t *b, unsigned fr, unsigned ff,
                         unsigned tr, unsigned tf, chess_color_t side)
{
    chess_board_t tmp;

    if (!pseudo_legal(b, fr, ff, tr, tf, side)) return 0;

    memcpy(&tmp, b, sizeof(tmp));
    tmp.sq[tr][tf] = tmp.sq[fr][ff];
    tmp.sq[fr][ff] = CHESS_EMPTY;

    /* Auto-promote to queen */
    if (piece_upper(tmp.sq[tr][tf]) == 'P') {
        if ((side == CHESS_WHITE && tr == 7) ||
            (side == CHESS_BLACK && tr == 0)) {
            tmp.sq[tr][tf] = (side == CHESS_WHITE) ? 'Q' : 'q';
        }
    }

    return !is_in_check(&tmp, side);
}

static int has_any_legal_move(chess_board_t *b, chess_color_t side)
{
    for (unsigned fr = 0; fr < 8; fr++)
        for (unsigned ff = 0; ff < 8; ff++) {
            if (piece_color(b->sq[fr][ff]) != side) continue;
            for (unsigned tr = 0; tr < 8; tr++)
                for (unsigned tf = 0; tf < 8; tf++)
                    if (is_legal_move(b, fr, ff, tr, tf, side))
                        return 1;
        }
    return 0;
}

/* ── SAN notation (simplified) ─────────────────────────────── */

static void make_san(char *out, size_t outlen, char piece,
                     unsigned ff, unsigned tr, unsigned tf,
                     int capture, int check, int mate, char promote)
{
    char *p = out;
    size_t room = outlen;

    if (piece_upper(piece) == 'P') {
        if (capture) {
            int n = snprintf(p, room, "%cx%c%d", 'a' + ff, 'a' + tf, tr + 1);
            p += n; room -= (size_t)n;
        } else {
            int n = snprintf(p, room, "%c%d", 'a' + tf, tr + 1);
            p += n; room -= (size_t)n;
        }
    } else {
        int n = snprintf(p, room, "%c%c%d", piece_upper(piece),
                         'a' + tf, tr + 1);
        p += n; room -= (size_t)n;
    }
    if (promote) {
        snprintf(p, room, "=%c", piece_upper(promote));
    } else if (mate) {
        snprintf(p, room, "#");
    } else if (check) {
        snprintf(p, room, "+");
    }
}

/* ── Game management ───────────────────────────────────────── */

chess_game_t *hybbx_chess_get_game(unsigned index)
{
    if (index >= CHESS_GAME_MAX) return NULL;
    return &g_games[index];
}

chess_game_t *hybbx_chess_create_game(struct hybbx_session *white,
                                      const char *white_name)
{
    unsigned i;
    for (i = 0; i < g_max_games; i++) {
        if (!g_games[i].active) {
            memset(&g_games[i], 0, sizeof(g_games[i]));
            g_games[i].active = 1;
            hybbx_strlcpy(g_games[i].white_name, white_name,
                          sizeof(g_games[i].white_name));
            g_games[i].white_session = white;
            board_init(&g_games[i].board);
            g_games[i].turn = CHESS_WHITE;
            g_games[i].move_number = 1;
            snprintf(g_games[i].game_id, sizeof(g_games[i].game_id),
                     "G%u", i + 1);
            hybbx_log_info("[chess] game %s created by %s",
                           g_games[i].game_id, white_name);
            return &g_games[i];
        }
    }
    return NULL;
}

chess_game_t *hybbx_chess_find_open_game(void)
{
    unsigned i;
    for (i = 0; i < g_max_games; i++)
        if (g_games[i].active && g_games[i].black_session == NULL)
            return &g_games[i];
    return NULL;
}

chess_game_t *hybbx_chess_find_game_by_id(const char *id)
{
    unsigned i;
    if (id == NULL) return NULL;
    for (i = 0; i < g_max_games; i++)
        if (g_games[i].active && strcasecmp(g_games[i].game_id, id) == 0)
            return &g_games[i];
    return NULL;
}

int hybbx_chess_join_game(chess_game_t *game, struct hybbx_session *black,
                          const char *black_name)
{
    if (game == NULL || game->black_session != NULL) return 0;
    game->black_session = black;
    hybbx_strlcpy(game->black_name, black_name, sizeof(game->black_name));
    hybbx_log_info("[chess] %s joined game %s as black", black_name,
                   game->game_id);
    return 1;
}

int hybbx_chess_add_spectator(chess_game_t *game,
                              struct hybbx_session *spec)
{
    unsigned i;
    if (game == NULL || spec == NULL) return 0;
    if (hybbx_chess_is_player(game, spec)) return 0;
    for (i = 0; i < game->spectator_count; i++)
        if (game->spectators[i] == spec) return 1;
    if (game->spectator_count >= CHESS_SPECTATOR_MAX) return 0;
    game->spectators[game->spectator_count++] = spec;
    return 1;
}

void hybbx_chess_remove_spectator(chess_game_t *game,
                                  struct hybbx_session *spec)
{
    unsigned i;
    if (game == NULL || spec == NULL) return;
    for (i = 0; i < game->spectator_count; i++) {
        if (game->spectators[i] == spec) {
            game->spectators[i] = game->spectators[--game->spectator_count];
            return;
        }
    }
}

int hybbx_chess_is_player(const chess_game_t *game,
                          const struct hybbx_session *session)
{
    if (game == NULL || session == NULL) return 0;
    return game->white_session == session || game->black_session == session;
}

int hybbx_chess_is_spectator(const chess_game_t *game,
                             const struct hybbx_session *session)
{
    unsigned i;
    if (game == NULL || session == NULL) return 0;
    for (i = 0; i < game->spectator_count; i++)
        if (game->spectators[i] == session) return 1;
    return 0;
}

chess_color_t hybbx_chess_player_color(const chess_game_t *game,
                                       const struct hybbx_session *session)
{
    if (game == NULL || session == NULL) return CHESS_COLOR_NONE;
    if (game->white_session == session) return CHESS_WHITE;
    if (game->black_session == session) return CHESS_BLACK;
    return CHESS_COLOR_NONE;
}

/* ── Move execution ────────────────────────────────────────── */

int hybbx_chess_make_move(chess_game_t *game, const char *from,
                          const char *to, char promote, char *err,
                          size_t errlen)
{
    unsigned fr, ff, tr, tf;
    char piece, captured;
    int check, mate;
    chess_color_t side, opp;

    if (game == NULL || game->result != CHESS_RESULT_NONE) {
        if (err) snprintf(err, errlen, "Game is over.");
        return 0;
    }

    side = game->turn;

    if (!parse_square(from, &fr, &ff)) {
        if (err) snprintf(err, errlen, "Invalid square: %s", from);
        return 0;
    }
    if (!parse_square(to, &tr, &tf)) {
        if (err) snprintf(err, errlen, "Invalid square: %s", to);
        return 0;
    }

    piece = game->board.sq[fr][ff];
    if (piece_color(piece) != side) {
        if (err) snprintf(err, errlen, "Not your piece.");
        return 0;
    }

    if (!is_legal_move(&game->board, fr, ff, tr, tf, side)) {
        if (err) snprintf(err, errlen, "Illegal move.");
        return 0;
    }

    captured = game->board.sq[tr][tf];
    game->board.sq[tr][tf] = piece;
    game->board.sq[fr][ff] = CHESS_EMPTY;

    /* Pawn promotion */
    if (piece_upper(piece) == 'P') {
        if ((side == CHESS_WHITE && tr == 7) ||
            (side == CHESS_BLACK && tr == 0)) {
            char pp = promote ? (char)toupper((unsigned char)promote) : 'Q';
            game->board.sq[tr][tf] = (side == CHESS_WHITE) ? pp :
                                      (char)tolower((unsigned char)pp);
        }
    }

    opp = (side == CHESS_WHITE) ? CHESS_BLACK : CHESS_WHITE;
    check = is_in_check(&game->board, opp);
    mate = check && !has_any_legal_move(&game->board, opp);

    make_san(game->last_move_san, sizeof(game->last_move_san), piece,
             ff, tr, tf, captured != CHESS_EMPTY, check, mate, promote);

    if (mate) {
        game->result = (side == CHESS_WHITE) ? CHESS_WHITE_WINS :
                                                CHESS_BLACK_WINS;
    } else if (!has_any_legal_move(&game->board, opp)) {
        game->result = CHESS_DRAW_STALEMATE;
    }

    game->turn = opp;
    if (opp == CHESS_WHITE) game->move_number++;
    game->tick_counter = 0;

    hybbx_log_info("[chess] %s: %s %s", game->game_id,
                   (side == CHESS_WHITE) ? game->white_name : game->black_name,
                   game->last_move_san);
    return 1;
}

/* ── Resign / Draw ─────────────────────────────────────────── */

void hybbx_chess_resign(chess_game_t *game, struct hybbx_session *who)
{
    if (game == NULL || game->result != CHESS_RESULT_NONE) return;
    if (game->white_session == who)
        game->result = CHESS_BLACK_WINS;
    else if (game->black_session == who)
        game->result = CHESS_WHITE_WINS;
}

void hybbx_chess_offer_draw(chess_game_t *game, struct hybbx_session *who)
{
    (void)who;
    if (game == NULL || game->result != CHESS_RESULT_NONE) return;
    game->result = CHESS_DRAW_AGREEMENT;
}

/* ── Board rendering ───────────────────────────────────────── */

void hybbx_chess_render_board(const chess_board_t *board,
                              struct hybbx_session *session,
                              const char *label)
{
    static const char *glyph = ".KQRBNPkqrbnp";
    char line[96];
    unsigned r, f;

    if (label && label[0])
        hybbx_session_write_line(session, label);

    hybbx_session_write_line(session,
        "  +---+---+---+---+---+---+---+---+");

    for (r = 0; r < 8; r++) {
        unsigned rank = 7 - r;
        int n = snprintf(line, sizeof(line), "%u |", rank + 1);
        for (f = 0; f < 8; f++) {
            char p = board->sq[rank][f];
            const char *ch;
            switch (p) {
            case 'K': ch = "K"; break; case 'Q': ch = "Q"; break;
            case 'R': ch = "R"; break; case 'B': ch = "B"; break;
            case 'N': ch = "N"; break; case 'P': ch = "P"; break;
            case 'k': ch = "k"; break; case 'q': ch = "q"; break;
            case 'r': ch = "r"; break; case 'b': ch = "b"; break;
            case 'n': ch = "n"; break; case 'p': ch = "p"; break;
            default:  ch = "."; break;
            }
            n += snprintf(line + n, sizeof(line) - (size_t)n, " %s |", ch);
        }
        hybbx_session_write_line(session, line);
        hybbx_session_write_line(session,
            "  +---+---+---+---+---+---+---+---+");
    }
    hybbx_session_write_line(session,
        "    a   b   c   d   e   f   g   h");
}

void hybbx_chess_send_board(chess_game_t *game,
                            struct hybbx_session *session)
{
    char label[96];
    const char *turn_name;

    if (game == NULL || session == NULL) return;

    turn_name = (game->turn == CHESS_WHITE) ? game->white_name :
                                                game->black_name;

    if (game->result != CHESS_RESULT_NONE) {
        const char *result_str;
        switch (game->result) {
        case CHESS_WHITE_WINS:     result_str = "1-0 White wins"; break;
        case CHESS_BLACK_WINS:     result_str = "0-1 Black wins"; break;
        case CHESS_DRAW_STALEMATE: result_str = "1/2-1/2 Stalemate"; break;
        case CHESS_DRAW_AGREEMENT: result_str = "1/2-1/2 Draw"; break;
        default:                   result_str = "Game over"; break;
        }
        snprintf(label, sizeof(label), "[%s] %s vs %s  %s  Move %u",
                 game->game_id, game->white_name, game->black_name,
                 result_str, game->move_number);
    } else {
        snprintf(label, sizeof(label),
                 "[%s] %s(W) vs %s(B)  %s to move  %s  Move %u",
                 game->game_id, game->white_name, game->black_name,
                 turn_name,
                 game->last_move_san[0] ? game->last_move_san : "",
                 game->move_number);
    }

    hybbx_chess_render_board(&game->board, session, label);
}

/* ── 15-second broadcast tick ──────────────────────────────── */

void hybbx_chess_tick(struct hybbx_service *service)
{
    unsigned i, j;

    (void)service;

    for (i = 0; i < g_max_games; i++) {
        chess_game_t *g = &g_games[i];

        if (!g->active) continue;
        if (g->black_session == NULL) continue;

        g->tick_counter++;
        if (g->tick_counter < CHESS_REFRESH_SEC) continue;
        g->tick_counter = 0;

        if (g->white_session)
            hybbx_chess_send_board(g, g->white_session);
        if (g->black_session)
            hybbx_chess_send_board(g, g->black_session);
        for (j = 0; j < g->spectator_count; j++)
            hybbx_chess_send_board(g, g->spectators[j]);
    }
}