/*
 * 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

/* 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;
}

/* 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;

    if (engine_state != READY)
        return ENGINE_ERROR_NOT_INITIALISED;
    if (!is_base64_id(position_id, L_POSITIONID) || !PositionFromID(pos->board, position_id))
        return ENGINE_ERROR_POSITION_ID;
    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));
    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;
    out->equity = evaluated ? normalized_equity(m->rScore, &pos->cube) : 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, avec les filtres « normaux ». */
    if (FindnSaveBestMoves(&list, die1, die2, (ConstTanBoard) pos.board, NULL, FALSE, 0.0f,
                           &pos.cube, &context, aaamfMoveFilterSettings[0]) < 0)
        return ENGINE_ERROR_INTERNAL;

    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 anglais des décisions, dans l'ordre de l'énumération cubedecision. */
static const char *const cube_decision_names[] = {
    "double_take", "double_pass", "no_double_take", "too_good_take", "too_good_pass",
    "double_beaver", "no_double_beaver", "redouble_take", "redouble_pass",
    "no_redouble_take", "too_good_redouble_take", "too_good_redouble_pass",
    "no_redouble_beaver", "no_double_dead_cube", "no_redouble_dead_cube",
    "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[4];
    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->decision = cube_decision_names[decision];
    return ENGINE_OK;
}