/*
 * Entertain plugin — chess.c
 * Chess game engine: board, moves, check/checkmate, SAN, tick broadcast.
 */
#include "entertain_chess.h"
#include "hybbx/session.h"
#include "hybbx/log.h"
#include "hybbx/util.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;

/* ── Session slot tracking (future use) ────────────────────── */

#define SESS_MAX 256u
static struct { uint64_t id; unsigned slot; } g_sess[SESS_MAX];

unsigned chess_session_slot(const struct hybbx_session *s)
{
    uint64_t sid; unsigned i;
    if (!s) return 0;
    sid = hybbx_session_id(s);
    for (i = 0; i < SESS_MAX; i++)
        if (g_sess[i].id == sid) return g_sess[i].slot;
    return 0;
}

void chess_session_set_slot(struct hybbx_session *s, unsigned slot)
{
    uint64_t sid; unsigned i, fi = SESS_MAX;
    if (!s) return;
    sid = hybbx_session_id(s);
    for (i = 0; i < SESS_MAX; i++) {
        if (g_sess[i].id == sid) { g_sess[i].slot = slot; return; }
        if (g_sess[i].id == 0 && fi == SESS_MAX) fi = i;
    }
    if (slot > 0 && fi < SESS_MAX) { g_sess[fi].id = sid; g_sess[fi].slot = slot; }
}

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

static void board_init(chess_board_t *b)
{
    static const char bk[] = "RNBQKBNR";
    unsigned f;
    memset(b, 0, sizeof(*b));
    for (f = 0; f < 8; f++) {
        b->sq[0][f] = bk[f];
        b->sq[1][f] = 'P';
        b->sq[6][f] = 'p';
        b->sq[7][f] = (char)tolower((unsigned char)bk[f]);
    }
    for (unsigned r = 2; r < 6; r++)
        for (f = 0; f < 8; f++)
            b->sq[r][f] = CHESS_EMPTY;
}

/* ── Lifecycle ─────────────────────────────────────────────── */

void chess_init(unsigned max_games)
{
    unsigned i;
    memset(g_games, 0, sizeof(g_games));
    memset(g_sess, 0, sizeof(g_sess));
    if (max_games == 0 || max_games > CHESS_GAME_MAX)
        max_games = CHESS_DEFAULT_MAX;
    g_max_games = max_games;
    for (i = 0; i < g_max_games; i++) {
        g_games[i].active = 1;
        snprintf(g_games[i].game_id, sizeof(g_games[i].game_id), "G%u", i + 1);
    }
}

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

unsigned chess_max_games(void) { return g_max_games; }

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

static int parse_sq(const char *s, unsigned *r, unsigned *f)
{
    if (!s || strlen(s) < 2 || s[0] < 'a' || s[0] > 'h' ||
        s[1] < '1' || s[1] > '8')
        return 0;
    *f = (unsigned)(s[0] - 'a');
    *r = (unsigned)(s[1] - '1');
    return 1;
}

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

static char pup(char p) { return (char)toupper((unsigned char)p); }
static int inb(unsigned r, unsigned f) { return r < 8 && f < 8; }

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

static int sq_attacked(const chess_board_t *b, unsigned rk, unsigned fl,
                       chess_color_t by)
{
    unsigned r, f;
    char P, N, B, R, Q, K;
    if (by == CHESS_WHITE) { P='P'; N='N'; B='B'; R='R'; Q='Q'; K='K'; }
    else                   { P='p'; N='n'; B='b'; R='r'; Q='q'; K='k'; }

    /* Pawn */
    if (by == CHESS_WHITE) {
        if (rk > 0 && fl > 0 && b->sq[rk-1][fl-1] == P) return 1;
        if (rk > 0 && fl < 7 && b->sq[rk-1][fl+1] == P) return 1;
    } else {
        if (rk < 7 && fl > 0 && b->sq[rk+1][fl-1] == P) return 1;
        if (rk < 7 && fl < 7 && b->sq[rk+1][fl+1] == P) 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)rk + kr[i], nf = (int)fl + kf[i];
            if (nr >= 0 && nr < 8 && nf >= 0 && nf < 8)
                if (b->sq[nr][nf] == N) return 1;
        }
    }

    /* Bishop/Queen diagonals */
    {
        static const int dr[] = {1,1,-1,-1}, df[] = {1,-1,1,-1};
        for (unsigned d = 0; d < 4; d++) {
            r = rk; f = fl;
            while (1) {
                r = (unsigned)((int)r + dr[d]);
                f = (unsigned)((int)f + df[d]);
                if (!inb(r, f)) break;
                if (b->sq[r][f] != CHESS_EMPTY) {
                    if (b->sq[r][f] == B || b->sq[r][f] == Q) return 1;
                    break;
                }
            }
        }
    }

    /* Rook/Queen straights */
    {
        static const int dr[] = {1,-1,0,0}, df[] = {0,0,1,-1};
        for (unsigned d = 0; d < 4; d++) {
            r = rk; f = fl;
            while (1) {
                r = (unsigned)((int)r + dr[d]);
                f = (unsigned)((int)f + df[d]);
                if (!inb(r, f)) break;
                if (b->sq[r][f] != CHESS_EMPTY) {
                    if (b->sq[r][f] == R || b->sq[r][f] == Q) return 1;
                    break;
                }
            }
        }
    }

    /* King */
    {
        static const int dr[] = {1,1,1,0,0,-1,-1,-1};
        static const int df[] = {1,0,-1,1,-1,1,0,-1};
        for (unsigned d = 0; d < 8; d++) {
            int nr = (int)rk + dr[d], nf = (int)fl + df[d];
            if (nr >= 0 && nr < 8 && nf >= 0 && nf < 8)
                if (b->sq[nr][nf] == K) return 1;
        }
    }

    return 0;
}

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

static int 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 sq_attacked(b, kr, kf, opp);
}

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

static int pseudo_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 = (side == CHESS_WHITE) ? 1 : 6;
    int dr = (int)tr - (int)fr, 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 &&
            b->sq[fr+(unsigned)dir][ff] == CHESS_EMPTY &&
            b->sq[tr][tf] == CHESS_EMPTY) return 1;
    }
    if ((df == 1 || df == -1) && dr == dir && b->sq[tr][tf] != CHESS_EMPTY)
        return 1;
    return 0;
}

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

static int slide_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 (!inb(r,f) || b->sq[r][f] != CHESS_EMPTY) return 0;
        r = (unsigned)((int)r+dr); f = (unsigned)((int)f+df);
    }
    return 1;
}

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

static int pseudo_legal(const chess_board_t *b, unsigned fr, unsigned ff,
                        unsigned tr, unsigned tf, chess_color_t side)
{
    char pc = b->sq[fr][ff];
    int dr = abs((int)tr-(int)fr), df = abs((int)tf-(int)ff);
    if (pc == CHESS_EMPTY || pcol(pc) != side) return 0;
    if (pcol(b->sq[tr][tf]) == side) return 0;
    switch (pup(pc)) {
    case 'P': return pseudo_pawn(b, fr, ff, tr, tf, side);
    case 'N': return pseudo_knight(fr, ff, tr, tf);
    case 'B': return dr==df && dr>0 && slide_clear(b, fr, ff, tr, tf);
    case 'R': return (fr==tr||ff==tf) && slide_clear(b, fr, ff, tr, tf);
    case 'Q': return ((fr==tr||ff==tf)||(dr==df)) && slide_clear(b, fr, ff, tr, tf);
    case 'K': return dr<=1 && df<=1 && (dr+df>0);
    }
    return 0;
}

static int is_legal(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;
    if (pup(tmp.sq[tr][tf]) == 'P' &&
        ((side == CHESS_WHITE && tr == 7) || (side == CHESS_BLACK && tr == 0)))
        tmp.sq[tr][tf] = (side == CHESS_WHITE) ? 'Q' : 'q';
    return !in_check(&tmp, side);
}

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

/* ── SAN ───────────────────────────────────────────────────── */

static void make_san(char *out, size_t len, char pc, unsigned ff,
                     unsigned tr, unsigned tf, int cap, int chk,
                     int mate, char promo)
{
    int n;
    if (pup(pc) == 'P') {
        if (cap) n = snprintf(out, len, "%cx%c%d", 'a'+(int)ff, 'a'+(int)tf, (int)(tr+1));
        else     n = snprintf(out, len, "%c%d", 'a'+(int)tf, (int)(tr+1));
    } else {
        n = snprintf(out, len, "%c%c%d", pup(pc), 'a'+(int)tf, (int)(tr+1));
    }
    if (promo) snprintf(out+n, len-(size_t)n, "=%c", pup(promo));
    else if (mate) snprintf(out+n, len-(size_t)n, "#");
    else if (chk) snprintf(out+n, len-(size_t)n, "+");
}

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

chess_game_t *chess_get_game(unsigned i)
{
    return (i < CHESS_GAME_MAX && g_games[i].active) ? &g_games[i] : NULL;
}

chess_game_t *chess_create_game(struct hybbx_session *white, const char *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, name, CHESS_NAME_MAX);
            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, name);
            return &g_games[i];
        }
    }
    return NULL;
}

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

chess_game_t *chess_find_game_by_id(const char *id)
{
    if (!id) return NULL;
    for (unsigned 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 chess_join_game(chess_game_t *g, struct hybbx_session *black, const char *name)
{
    if (!g || g->black_session) return 0;
    g->black_session = black;
    hybbx_strlcpy(g->black_name, name, CHESS_NAME_MAX);
    hybbx_log_info("[chess] %s joined %s as black", name, g->game_id);
    return 1;
}

int chess_add_spectator(chess_game_t *g, struct hybbx_session *spec)
{
    unsigned i;
    if (!g || !spec) return 0;
    if (chess_is_player(g, spec)) return 0;
    for (i = 0; i < g->spectator_count; i++)
        if (g->spectators[i] == spec) return 1;
    if (g->spectator_count >= CHESS_SPECTATOR_MAX) return 0;
    g->spectators[g->spectator_count++] = spec;
    return 1;
}

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

int chess_is_player(const chess_game_t *g, const struct hybbx_session *s)
{
    return g && s && (g->white_session == s || g->black_session == s);
}

int chess_is_spectator(const chess_game_t *g, const struct hybbx_session *s)
{
    unsigned i;
    if (!g || !s) return 0;
    for (i = 0; i < g->spectator_count; i++)
        if (g->spectators[i] == s) return 1;
    return 0;
}

chess_color_t chess_player_color(const chess_game_t *g, const struct hybbx_session *s)
{
    if (!g || !s) return CHESS_COLOR_NONE;
    if (g->white_session == s) return CHESS_WHITE;
    if (g->black_session == s) return CHESS_BLACK;
    return CHESS_COLOR_NONE;
}

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

int chess_make_move(chess_game_t *g, 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 (!g || g->result != CHESS_RESULT_NONE) {
        if (err) snprintf(err, errlen, "Game is over.");
        return 0;
    }
    side = g->turn;
    if (!parse_sq(from, &fr, &ff)) { if (err) snprintf(err, errlen, "Bad square: %s", from); return 0; }
    if (!parse_sq(to, &tr, &tf))   { if (err) snprintf(err, errlen, "Bad square: %s", to); return 0; }

    piece = g->board.sq[fr][ff];
    if (pcol(piece) != side) { if (err) snprintf(err, errlen, "Not your piece."); return 0; }
    if (!is_legal(&g->board, fr, ff, tr, tf, side)) { if (err) snprintf(err, errlen, "Illegal move."); return 0; }

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

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

    opp = (side == CHESS_WHITE) ? CHESS_BLACK : CHESS_WHITE;
    check = in_check(&g->board, opp);
    mate = check && !has_any_legal(&g->board, opp);

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

    if (mate) g->result = (side == CHESS_WHITE) ? CHESS_WHITE_WINS : CHESS_BLACK_WINS;
    else if (!has_any_legal(&g->board, opp)) g->result = CHESS_DRAW_STALEMATE;

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

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

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

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

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

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

static void render_board(const chess_board_t *b, struct hybbx_session *s,
                         const char *label)
{
    char line[96];
    unsigned r, f;
    static const char *gc = ".KQRBNPkqrbnp";
    (void)gc;

    if (label && label[0]) hybbx_session_write_line(s, label);
    hybbx_session_write_line(s, "  +---+---+---+---+---+---+---+---+");
    for (r = 0; r < 8; r++) {
        unsigned rk = 7 - r;
        int n = snprintf(line, sizeof(line), "%u |", rk + 1);
        for (f = 0; f < 8; f++) {
            char p = b->sq[rk][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(s, line);
        hybbx_session_write_line(s, "  +---+---+---+---+---+---+---+---+");
    }
    hybbx_session_write_line(s, "    a   b   c   d   e   f   g   h");
}

void chess_send_board(chess_game_t *g, struct hybbx_session *s)
{
    char label[160];
    const char *turn;
    if (!g || !s) return;
    turn = (g->turn == CHESS_WHITE) ? g->white_name : g->black_name;
    if (g->result != CHESS_RESULT_NONE) {
        const char *rs;
        switch (g->result) {
        case CHESS_WHITE_WINS:     rs = "1-0 White wins"; break;
        case CHESS_BLACK_WINS:     rs = "0-1 Black wins"; break;
        case CHESS_DRAW_STALEMATE: rs = "1/2 Stalemate"; break;
        case CHESS_DRAW_AGREEMENT: rs = "1/2 Draw"; break;
        default:                   rs = "Over"; break;
        }
        snprintf(label, sizeof(label), "[%s] %s vs %s  %s  Move %u",
                 g->game_id, g->white_name, g->black_name, rs, g->move_number);
    } else {
        snprintf(label, sizeof(label), "[%s] %s(W) vs %s(B)  %s to move  %s  Move %u",
                 g->game_id, g->white_name, g->black_name, turn,
                 g->last_move_san[0] ? g->last_move_san : "", g->move_number);
    }
    render_board(&g->board, s, label);
}

/* ── Tick — 15s board broadcast ────────────────────────────── */

void 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 || !g->black_session) continue;
        g->tick_counter++;
        if (g->tick_counter < CHESS_REFRESH_SEC) continue;
        g->tick_counter = 0;
        if (g->white_session)  chess_send_board(g, g->white_session);
        if (g->black_session)  chess_send_board(g, g->black_session);
        for (j = 0; j < g->spectator_count; j++)
            chess_send_board(g, g->spectators[j]);
    }
}