/*
 * engine.c -- façade du moteur d'Ustagammon sur le cœur de GNU Backgammon.
 *
 * Copyright (C) 2026 les auteurs d'Ustagammon.
 * Licence : GPLv3 ou ultérieure (voir LICENSE).
 *
 * Chaque fonction décode les identifiants de position, prépare le contexte
 * de gnubg (cubeinfo, réglages d'évaluation) comme le fait gnubg de bureau
 * pour ses commandes « hint » et « eval », puis appelle gnubg.
 */

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

#include "config.h"
#include "backgammon.h"
#include "drawboard.h"
#include "matchequity.h"
#include "matchid.h"
#include "multithread.h"
#include "positionid.h"
#include "gnubg-support.h"
#include "engine.h"

/* Nombre de castors autorisés en partie libre : valeur par défaut de gnubg. */
#define DEFAULT_BEAVERS 3

/* Seuil d'erreur « douteuse » de gnubg (arSkillLevel[SKILL_DOUBTFUL] dans
 * gnubg.c), que la commande « hint » passe à FindnSaveBestMoves. */
#define DOUBTFUL_THRESHOLD 0.03f

/* Fichier de table d'équité de match : celui de gnubg de bureau par défaut. */
#define MET_FILE "Kazaross-XG2.xml"

/* gnubg ne sait pas se réinitialiser après EvalShutdown : on retient l'état. */
static enum { NOT_STARTED, READY, STOPPED } engine_state = NOT_STARTED;

/* Une position décodée, prête pour gnubg. */
typedef struct {
    TanBoard board;
    cubeinfo cube;
    engine_match match;
} position;

/* -------------------------------------------------------- Initialisation */

/* Vérifie l'en-tête de gnubg.wd, pour éviter l'exit() de EvalInitialise. */
static int
binary_weights_ok(const char *path)
{
    float header[2];
    FILE *f = fopen(path, "rb");
    int ok;

    if (!f)
        return 0;
    ok = fread(header, sizeof header[0], 2, f) == 2
        && header[0] == WEIGHTS_MAGIC_BINARY && header[1] == WEIGHTS_VERSION_BINARY;
    fclose(f);
    return ok;
}

static engine_status
load_match_equity_table(const char *data_dir)
{
    char *path = g_build_filename(data_dir, MET_FILE, NULL);
    int ok;

    ok = g_file_test(path, G_FILE_TEST_IS_REGULAR);
    if (ok) {
        InitMatchEquity(path);
        /* En cas d'échec, gnubg se rabat sans erreur sur la table de Zadeh. */
        ok = miCurrent.szFileName && strcmp(miCurrent.szFileName, path) == 0;
    }
    g_free(path);
    return ok ? ENGINE_OK : ENGINE_ERROR_DATA;
}

static engine_status
load_neural_nets_and_bearoff(const char *data_dir)
{
    char *weights = g_build_filename(data_dir, "gnubg.wd", NULL);
    int ok = binary_weights_ok(weights);

    if (ok) {
        EvalInitialise(NULL, weights, FALSE, NULL);
        /* Bases de fin de partie : gnubg continue sans elles, pas nous. */
        ok = pbc1 && !pbc1->fHeuristic && pbc2;
    }
    g_free(weights);
    return ok ? ENGINE_OK : ENGINE_ERROR_DATA;
}

engine_status
engine_init(const char *data_dir)
{
    engine_status status;

    if (engine_state == READY)
        return ENGINE_OK;
    if (engine_state == STOPPED || !data_dir)
        return ENGINE_ERROR_NOT_INITIALISED;

    gnubg_support_set_data_dir(data_dir);
    status = load_match_equity_table(data_dir);
    if (status == ENGINE_OK)
        status = load_neural_nets_and_bearoff(data_dir);
    if (status != ENGINE_OK)
        return status;

    MT_InitThreads();
    engine_state = READY;
    return ENGINE_OK;
}

void
engine_shutdown(void)
{
    if (engine_state != READY)
        return;
    MT_Close();
    td.tld = NULL;
    EvalShutdown();
    engine_state = STOPPED;
}

const char *
engine_status_message(engine_status status)
{
    switch (status) {
    case ENGINE_OK:
        return "succès";
    case ENGINE_ERROR_NOT_INITIALISED:
        return "moteur non initialisé";
    case ENGINE_ERROR_DATA:
        return "données du moteur absentes ou invalides";
    case ENGINE_ERROR_POSITION_ID:
        return "Position ID invalide";
    case ENGINE_ERROR_MATCH_ID:
        return "Match ID invalide";
    case ENGINE_ERROR_DICE:
        return "dés invalides (chacun entre 1 et 6)";
    case ENGINE_ERROR_PLY:
        return "niveau invalide";
    case ENGINE_ERROR_TOO_MANY_MOVES:
        return "tableau de coups trop petit";
    case ENGINE_ERROR_INTERNAL:
        return "erreur interne de gnubg";
    }
    return "erreur inconnue";
}

/* ------------------------------------------------------------- Décodage */

/* Vrai si id a exactement length caractères de l'alphabet base64 de gnubg. */
static int
is_base64_id(const char *id, size_t length)
{
    size_t i;

    if (!id || strlen(id) != length)
        return 0;
    for (i = 0; i < length; i++)
        if (Base64((unsigned char) id[i]) == 255)
            return 0;
    return 1;
}

engine_status
engine_decode_match(const char *match_id, engine_match *match)
{
    unsigned int dice[2];
    int turn, resigned, doubled;
    gamestate state;

    if (!is_base64_id(match_id, L_MATCHID))
        return ENGINE_ERROR_MATCH_ID;
    if (MatchFromID(dice, &turn, &resigned, &doubled, &match->player_on_roll,
                    &match->cube_owner, &match->crawford, &match->match_length,
                    match->score, &match->cube_value, &match->jacoby, &state, match_id) != 0)
        return ENGINE_ERROR_MATCH_ID;
    return ENGINE_OK;
}

/* Code un Match ID : voir engine.h. */
engine_status
engine_encode_match(const engine_match *match, char match_id[13])
{
    const unsigned int no_dice[2] = { 0, 0 };
    int value = match->cube_value, log2 = 0;

    while (value > 1 && value % 2 == 0) {
        value /= 2;
        log2++;
    }
    if (value != 1 || log2 > 12 || match->cube_owner < -1 || match->cube_owner > 1
        || match->player_on_roll < 0 || match->player_on_roll > 1 || match->match_length < 0)
        return ENGINE_ERROR_MATCH_ID;
    snprintf(match_id, 13, "%s",
             MatchID(no_dice, match->player_on_roll, 0, 0, match->player_on_roll,
                     match->cube_owner, match->crawford, match->match_length, match->score,
                     match->cube_value, match->jacoby, GAME_PLAYING));
    return ENGINE_OK;
}

/* Décode un Position ID en plateau de gnubg. */
static engine_status
decode_board(const char *position_id, TanBoard board)
{
    if (engine_state != READY)
        return ENGINE_ERROR_NOT_INITIALISED;
    if (!is_base64_id(position_id, L_POSITIONID) || !PositionFromID(board, position_id))
        return ENGINE_ERROR_POSITION_ID;
    return ENGINE_OK;
}

/* Décode Position ID et Match ID, et prépare le cubeinfo de gnubg. */
static engine_status
decode_position(const char *position_id, const char *match_id, position *pos)
{
    engine_match *m = &pos->match;
    engine_status status;

    status = decode_board(position_id, pos->board);
    if (status != ENGINE_OK)
        return status;
    status = engine_decode_match(match_id, m);
    if (status != ENGINE_OK)
        return status;
    if (SetCubeInfo(&pos->cube, m->cube_value, m->cube_owner, m->player_on_roll,
                    m->match_length, m->score, m->crawford, m->jacoby,
                    DEFAULT_BEAVERS, VARIATION_STANDARD) != 0)
        return ENGINE_ERROR_MATCH_ID;
    return ENGINE_OK;
}

static engine_status
check_dice(int die1, int die2)
{
    if (die1 < 1 || die1 > 6 || die2 < 1 || die2 > 6)
        return ENGINE_ERROR_DICE;
    return ENGINE_OK;
}

/* Réglages prédéfinis de gnubg pour un niveau, sans bruit. */
static engine_status
eval_context_for_ply(int ply, evalcontext *context)
{
    if (ply < 0 || ply > ENGINE_MAX_PLY)
        return ENGINE_ERROR_PLY;
    *context = aecSettings[SETTINGS_0PLY + ply];
    return ENGINE_OK;
}

/* En match, gnubg calcule en chances de gain du match : on convertit. */
static float
normalized_equity(float score, const cubeinfo *cube)
{
    return cube->nMatchTo ? mwc2eq(score, cube) : score;
}

/* ------------------------------------------------------------------ Coups */

static void
fill_move(engine_move *out, const move *m, const position *pos, int evaluated)
{
    int i;

    FormatMove(out->notation, (ConstTanBoard) pos->board, m->anMove);
    snprintf(out->position_id, sizeof out->position_id, "%s", PositionIDFromKey(&m->key));
    /* gnubg numérote les cases de 0 à 23, la barre 24 et la sortie -1. */
    out->half_move_count = 0;
    for (i = 0; i < 2 * ENGINE_MAX_HALF_MOVES && m->anMove[i] >= 0; i += 2) {
        out->half_moves[i / 2].from = m->anMove[i] + 1;
        out->half_moves[i / 2].to = m->anMove[i + 1] + 1;
        out->half_move_count++;
    }
    out->ply = evaluated ? (int) m->esMove.ec.nPlies : -1;
    for (i = 0; i < ENGINE_NUM_PROBABILITIES; i++)
        out->probabilities[i] = evaluated ? m->arEvalMove[i] : 0.0f;
    /* ScoreMove a déjà converti rScore en équité normalisée en match. */
    out->equity = evaluated ? m->rScore : 0.0f;
}

engine_status
engine_legal_moves(const char *position_id, const char *match_id, int die1, int die2,
                   engine_move *moves, int max_moves, int *count)
{
    position pos;
    movelist list;
    engine_status status;
    unsigned int i;

    status = decode_position(position_id, match_id, &pos);
    if (status == ENGINE_OK)
        status = check_dice(die1, die2);
    if (status != ENGINE_OK)
        return status;

    /* La liste pointe vers un tableau interne de gnubg : rien à libérer. */
    GenerateMoves(&list, (ConstTanBoard) pos.board, die1, die2, FALSE);
    if (list.cMoves > (unsigned int) max_moves)
        return ENGINE_ERROR_TOO_MANY_MOVES;
    for (i = 0; i < list.cMoves; i++)
        fill_move(&moves[i], &list.amMoves[i], &pos, 0);
    *count = (int) list.cMoves;
    return ENGINE_OK;
}

engine_status
engine_best_moves(const char *position_id, const char *match_id, int die1, int die2, int ply,
                  engine_move *moves, int max_moves, int *count)
{
    position pos;
    movelist list;
    evalcontext context;
    engine_status status;
    unsigned int i;

    status = decode_position(position_id, match_id, &pos);
    if (status == ENGINE_OK)
        status = check_dice(die1, die2);
    if (status == ENGINE_OK)
        status = eval_context_for_ply(ply, &context);
    if (status != ENGINE_OK)
        return status;

    /*
     * Comme la commande « hint » de gnubg (hint_move dans gnubg.c), avec le
     * filtre « Normal » : fAnalyse vrai (un coup évalué moins profondément
     * ne peut pas passer devant un coup mieux évalué), puis RefreshMoveList,
     * qui classe d'abord par niveau d'évaluation et départage les égalités.
     */
    if (FindnSaveBestMoves(&list, die1, die2, (ConstTanBoard) pos.board, NULL, TRUE,
                           DOUBTFUL_THRESHOLD, &pos.cube, &context,
                           aaamfMoveFilterSettings[0]) < 0)
        return ENGINE_ERROR_INTERNAL;
    RefreshMoveList(&list, NULL);

    status = ENGINE_OK;
    if (list.cMoves > (unsigned int) max_moves)
        status = ENGINE_ERROR_TOO_MANY_MOVES;
    else {
        for (i = 0; i < list.cMoves; i++)
            fill_move(&moves[i], &list.amMoves[i], &pos, 1);
        *count = (int) list.cMoves;
    }
    g_free(list.amMoves);
    return status;
}

/* ------------------------------------------------- Évaluation et videau */

engine_status
engine_evaluate(const char *position_id, const char *match_id, int ply,
                engine_evaluation *evaluation)
{
    position pos;
    evalcontext context;
    float output[NUM_ROLLOUT_OUTPUTS];
    engine_status status;
    int i;

    status = decode_position(position_id, match_id, &pos);
    if (status == ENGINE_OK)
        status = eval_context_for_ply(ply, &context);
    if (status != ENGINE_OK)
        return status;

    if (GeneralEvaluationE(output, (ConstTanBoard) pos.board, &pos.cube, &context) < 0)
        return ENGINE_ERROR_INTERNAL;

    for (i = 0; i < ENGINE_NUM_PROBABILITIES; i++)
        evaluation->probabilities[i] = output[i];
    evaluation->cubeless_equity = output[OUTPUT_EQUITY];
    evaluation->cubeful_equity = normalized_equity(output[OUTPUT_CUBEFUL_EQUITY], &pos.cube);
    return ENGINE_OK;
}

/* Noms des décisions, dans l'ordre de l'énumération cubedecision (eval.h). */
static const char *const cube_decision_names[] = {
    "DOUBLE_TAKE", "DOUBLE_PASS", "NODOUBLE_TAKE", "TOOGOOD_TAKE", "TOOGOOD_PASS",
    "DOUBLE_BEAVER", "NODOUBLE_BEAVER", "REDOUBLE_TAKE", "REDOUBLE_PASS",
    "NO_REDOUBLE_TAKE", "TOOGOODRE_TAKE", "TOOGOODRE_PASS",
    "NO_REDOUBLE_BEAVER", "NODOUBLE_DEADCUBE", "NO_REDOUBLE_DEADCUBE",
    "NOT_AVAILABLE", "OPTIONAL_DOUBLE_TAKE", "OPTIONAL_REDOUBLE_TAKE",
    "OPTIONAL_DOUBLE_BEAVER", "OPTIONAL_DOUBLE_PASS", "OPTIONAL_REDOUBLE_PASS"
};

engine_status
engine_cube_decision(const char *position_id, const char *match_id, int ply, engine_cube *cube)
{
    position pos;
    evalcontext context;
    float output[2][NUM_ROLLOUT_OUTPUTS];
    float equities[NUM_CUBEFUL_OUTPUTS];
    cubedecision decision;
    engine_status status;
    int i;

    status = decode_position(position_id, match_id, &pos);
    if (status == ENGINE_OK)
        status = eval_context_for_ply(ply, &context);
    if (status != ENGINE_OK)
        return status;

    if (GeneralCubeDecisionE(output, (ConstTanBoard) pos.board, &pos.cube, &context, NULL) < 0)
        return ENGINE_ERROR_INTERNAL;
    /* FindCubeDecision renvoie des équités déjà normalisées. */
    decision = FindCubeDecision(equities, output, &pos.cube);
    if ((size_t) decision >= sizeof cube_decision_names / sizeof cube_decision_names[0])
        return ENGINE_ERROR_INTERNAL;

    for (i = 0; i < ENGINE_NUM_PROBABILITIES; i++)
        cube->probabilities[i] = output[0][i];
    cube->no_double = equities[OUTPUT_NODOUBLE];
    cube->double_take = equities[OUTPUT_TAKE];
    cube->double_pass = equities[OUTPUT_DROP];
    cube->optimal = equities[OUTPUT_OPTIMAL];
    cube->decision = cube_decision_names[decision];
    cube->decision_text = GetCubeRecommendation(decision);
    GetDPEq(&cube->available, NULL, &pos.cube);
    cube->should_double = decision == DOUBLE_TAKE || decision == DOUBLE_PASS
        || decision == DOUBLE_BEAVER || decision == REDOUBLE_TAKE || decision == REDOUBLE_PASS;
    cube->should_take = cube->double_take <= cube->double_pass;
    return ENGINE_OK;
}

/* ------------------------------------------------- Plateau et fin de partie */

static void
fill_side(engine_side *side, const unsigned int checkers[25])
{
    int i, on_board = 0;

    side->pip_count = 0;
    for (i = 0; i < 25; i++) {
        on_board += (int) checkers[i];
        side->pip_count += (int) checkers[i] * (i + 1);
    }
    for (i = 0; i < 24; i++)
        side->points[i] = (int) checkers[i];
    side->bar = (int) checkers[24];
    side->off = anChequers[VARIATION_STANDARD] - on_board;
}

engine_status
engine_decode_position(const char *position_id, engine_board *board)
{
    TanBoard b;
    engine_status status = decode_board(position_id, b);

    if (status != ENGINE_OK)
        return status;
    /* Dans gnubg, b[1] est le joueur au trait et b[0] son adversaire. */
    fill_side(&board->on_roll, b[1]);
    fill_side(&board->opponent, b[0]);
    SwapSides(b);
    snprintf(board->swapped_position_id, sizeof board->swapped_position_id, "%s", PositionID((ConstTanBoard) b));
    return ENGINE_OK;
}

engine_status
engine_game_result(const char *position_id, const char *match_id, engine_result *result)
{
    TanBoard b;
    engine_match match;
    engine_status status = decode_board(position_id, b);
    int i;

    if (status == ENGINE_OK)
        status = engine_decode_match(match_id, &match);
    if (status != ENGINE_OK)
        return status;

    memset(result, 0, sizeof *result);
    result->kind = GameStatus((ConstTanBoard) b, VARIATION_STANDARD);
    if (result->kind == 0)
        return ENGINE_OK;
    result->over = 1;
    /* Le gagnant est celui qui n'a plus aucune dame sur le plateau. */
    for (i = 0; i < 25 && b[1][i] == 0; i++)
        ;
    result->winner = i == 25 ? 0 : 1;
    /* Règle Jacoby : gammons et backgammons ne comptent qu'une fois le
     * videau tourné, c'est-à-dire quand il n'est plus au centre. */
    if (match.match_length == 0 && match.jacoby && match.cube_owner == -1)
        result->points = match.cube_value;
    else
        result->points = result->kind * match.cube_value;
    return ENGINE_OK;
}

/* ------------------------------------------ Saisie demi-coup par demi-coup */

/*
 * La légalité de chaque demi-coup vient de gnubg : GenerateMoves avec un seul
 * dé (le second à 0) donne exactement les demi-coups permis avec ce dé (barre
 * d'abord, case libre, règles de sortie). Celle du coup entier aussi : les
 * demi-coups doivent pouvoir se compléter en une position de la liste des
 * coups légaux, qui impose de jouer le plus de dés possible.
 */

/* Un demi-coup permis et la position où il mène. */
typedef struct {
    int from, to;           /* numérotation de gnubg : 0 à 24, -1 sortie */
    positionkey key;
} step;

/* Positions d'arrivée des coups légaux. */
typedef struct {
    positionkey *keys;
    int count;
} legal_results;

/* Les demi-coups permis avec un dé. Ils sont copiés : GenerateMoves réutilise
 * un tableau interne, que l'appel suivant écraserait. Il y en a au plus un
 * par case de départ. */
static int
single_steps(ConstTanBoard board, int die, step steps[25])
{
    movelist list;
    unsigned int i;

    GenerateMoves(&list, board, die, 0, FALSE);
    for (i = 0; i < list.cMoves && i < 25; i++) {
        steps[i].from = list.amMoves[i].anMove[0];
        steps[i].to = list.amMoves[i].anMove[1];
        steps[i].key = list.amMoves[i].key;
    }
    return (int) i;
}

static int
is_legal_result(ConstTanBoard board, const legal_results *legal)
{
    positionkey key;
    int i;

    PositionKey(board, &key);
    for (i = 0; i < legal->count; i++)
        if (EqualKeys(key, legal->keys[i]))
            return 1;
    return 0;
}

/* Les dés sans celui d'indice skip. */
static void
remove_die(const int dice[], int count, int skip, int rest[])
{
    int i, j = 0;

    for (i = 0; i < count; i++)
        if (i != skip)
            rest[j++] = dice[i];
}

/* Vrai si board peut encore mener à un coup légal avec les dés restants. */
static int
can_complete(ConstTanBoard board, const int dice[], int count, const legal_results *legal)
{
    step steps[25];
    int rest[ENGINE_MAX_HALF_MOVES];
    TanBoard next;
    int i, j, n;

    if (is_legal_result(board, legal))
        return 1;
    for (i = 0; i < count; i++) {
        if (i > 0 && dice[i] == dice[0])
            continue;       /* même valeur déjà essayée (double) */
        remove_die(dice, count, i, rest);
        n = single_steps(board, dice[i], steps);
        for (j = 0; j < n; j++) {
            PositionFromKey(next, &steps[j].key);
            if (can_complete((ConstTanBoard) next, rest, count - 1, legal))
                return 1;
        }
    }
    return 0;
}

/* Joue les demi-coups ; en cas de succès, result reçoit la position atteinte.
 * Un même demi-coup peut correspondre à plusieurs dés (une sortie avec un dé
 * plus fort que nécessaire) : chacun est essayé. */
static int
play_half_moves(ConstTanBoard board, const int dice[], int count,
                const engine_half_move *half_moves, int remaining,
                const legal_results *legal, TanBoard result)
{
    step steps[25];
    int rest[ENGINE_MAX_HALF_MOVES];
    TanBoard next;
    int i, j, n;

    if (remaining == 0) {
        if (!can_complete(board, dice, count, legal))
            return 0;
        memcpy(result, board, sizeof(TanBoard));
        return 1;
    }
    for (i = 0; i < count; i++) {
        if (i > 0 && dice[i] == dice[0])
            continue;       /* même valeur déjà essayée (double) */
        remove_die(dice, count, i, rest);
        n = single_steps(board, dice[i], steps);
        for (j = 0; j < n; j++) {
            if (steps[j].from != half_moves->from - 1 || steps[j].to != half_moves->to - 1)
                continue;
            PositionFromKey(next, &steps[j].key);
            if (play_half_moves((ConstTanBoard) next, rest, count - 1, half_moves + 1,
                                remaining - 1, legal, result))
                return 1;
        }
    }
    return 0;
}

engine_status
engine_check_half_moves(const char *position_id, int die1, int die2,
                        const engine_half_move *half_moves, int count,
                        engine_half_moves_check *check)
{
    TanBoard board, result;
    movelist list;
    legal_results legal;
    int dice[ENGINE_MAX_HALF_MOVES] = { die1, die2, die1, die2 };
    int dice_count = die1 == die2 ? 4 : 2;
    engine_status status;
    unsigned int i;

    status = decode_board(position_id, board);
    if (status == ENGINE_OK)
        status = check_dice(die1, die2);
    if (status != ENGINE_OK)
        return status;

    memset(check, 0, sizeof *check);
    if (count < 0 || count > dice_count)
        return ENGINE_OK;

    GenerateMoves(&list, (ConstTanBoard) board, die1, die2, FALSE);
    if (list.cMoves == 0)
        return ENGINE_OK;   /* aucun coup possible : rien à saisir */
    legal.count = (int) list.cMoves;
    legal.keys = g_malloc(sizeof *legal.keys * list.cMoves);
    for (i = 0; i < list.cMoves; i++)
        legal.keys[i] = list.amMoves[i].key;

    if (play_half_moves((ConstTanBoard) board, dice, dice_count, half_moves, count, &legal, result)) {
        check->valid = 1;
        check->complete = is_legal_result((ConstTanBoard) result, &legal);
        snprintf(check->position_id, sizeof check->position_id, "%s",
                 PositionID((ConstTanBoard) result));
    }
    g_free(legal.keys);
    return ENGINE_OK;
}