/*
 * portal.c — Save/resume machine state to JSON files
 *
 * Port of the Python portal_save/portal_resume system.
 * Serializes environment bindings and full continuations.
 */
#include "lumbda.h"
#include <fcntl.h>

/* ═══════════════════════════════════════════════════════════════════════════
 * Portal checkpoint — thread-local signal for mid-execution save
 *
 * MOAD-0002: Module-level global — intentional coupling. Checked in the VM
 * hot loop (OP_JUMP, OP_TAIL_CALL) so passing it as a parameter would add
 * overhead to every iteration.
 * ═══════════════════════════════════════════════════════════════════════════ */

__thread const char *g_portal_checkpoint_path = NULL;

/* ═══════════════════════════════════════════════════════════════════════════
 * xoshiro256** — deterministic, portable PRNG shared with Python and asm.
 * Portal serializes these 4 words so simulations continue across processes
 * with a bit-identical random stream. Reference: Blackman & Vigna 2018.
 * ═══════════════════════════════════════════════════════════════════════════ */

static uint64_t g_rng_state[4] = {0, 0, 0, 0};

static uint64_t rng_rotl(uint64_t x, int k) {
    return (x << k) | (x >> (64 - k));
}

static uint64_t rng_splitmix64_step(uint64_t *z) {
    *z += 0x9e3779b97f4a7c15ULL;
    uint64_t r = *z;
    r = (r ^ (r >> 30)) * 0xbf58476d1ce4e5b9ULL;
    r = (r ^ (r >> 27)) * 0x94d049bb133111ebULL;
    return r ^ (r >> 31);
}

static void rng_seed(uint64_t k) {
    uint64_t z = k;
    for (int i = 0; i < 4; i++) g_rng_state[i] = rng_splitmix64_step(&z);
}

static uint64_t rng_next(void) {
    uint64_t result = rng_rotl(g_rng_state[1] * 5, 7) * 9;
    uint64_t t = g_rng_state[1] << 17;
    g_rng_state[2] ^= g_rng_state[0];
    g_rng_state[3] ^= g_rng_state[1];
    g_rng_state[1] ^= g_rng_state[2];
    g_rng_state[0] ^= g_rng_state[3];
    g_rng_state[2] ^= t;
    g_rng_state[3] = rng_rotl(g_rng_state[3], 45);
    return result;
}

void rng_get_halves(uint32_t out[8]) {
    for (int i = 0; i < 4; i++) {
        out[2 * i]     = (uint32_t)(g_rng_state[i] & 0xffffffffULL);
        out[2 * i + 1] = (uint32_t)(g_rng_state[i] >> 32);
    }
}

void rng_set_halves(const uint32_t in[8]) {
    for (int i = 0; i < 4; i++) {
        g_rng_state[i] = ((uint64_t)in[2 * i + 1] << 32) | (uint64_t)in[2 * i];
    }
}

/* ═══════════════════════════════════════════════════════════════════════════
 * Minimal JSON writer — writes directly to FILE*
 * ═══════════════════════════════════════════════════════════════════════════ */

static void json_write_string(FILE *fp, const char *s) {
    fputc('"', fp);
    for (const char *p = s; *p; p++) {
        switch (*p) {
            case '"':  fputs("\\\"", fp); break;
            case '\\': fputs("\\\\", fp); break;
            case '\n': fputs("\\n", fp); break;
            case '\r': fputs("\\r", fp); break;
            case '\t': fputs("\\t", fp); break;
            default:
                if ((unsigned char)*p < 0x20)
                    fprintf(fp, "\\u%04x", (unsigned)*p);
                else
                    fputc(*p, fp);
        }
    }
    fputc('"', fp);
}

static void json_write_value(FILE *fp, Value v);

static void json_write_env_bindings(FILE *fp, Env *env, bool global_only) {
    /* Write user-defined bindings as a JSON object */
    fputc('{', fp);
    bool first = true;
    for (size_t i = 0; i < env->nbuckets; i++) {
        EnvBinding *b = env->buckets[i];
        while (b) {
            if (global_only) {
                /* Skip builtins for global env — only save user values */
                if (IS_BUILTIN(b->val)) { b = b->next; continue; }
                if (IS_MACRO(b->val)) { b = b->next; continue; }
            }
            if (!first) fputc(',', fp);
            first = false;
            json_write_string(fp, sym_name(b->sym));
            fputc(':', fp);
            json_write_value(fp, b->val);
            b = b->next;
        }
    }
    fputc('}', fp);
}

static void json_write_value(FILE *fp, Value v) {
    if (IS_NIL(v)) {
        fputs("{\"t\":\"nil\"}", fp);
    } else if (IS_VOID(v)) {
        fputs("{\"t\":\"void\"}", fp);
    } else if (IS_TRUE(v)) {
        fputs("{\"t\":\"bool\",\"v\":true}", fp);
    } else if (IS_FALSE(v)) {
        fputs("{\"t\":\"bool\",\"v\":false}", fp);
    } else if (IS_EOF(v)) {
        fputs("{\"t\":\"eof\"}", fp);
    } else if (IS_INT(v)) {
        fprintf(fp, "%lld", (long long)as_int(v));
    } else if (IS_DOUBLE(v)) {
        double d = as_double(v);
        if (isinf(d)) fprintf(fp, "{\"t\":\"float\",\"v\":\"%s\"}", d > 0 ? "+inf" : "-inf");
        else if (isnan(d)) fputs("{\"t\":\"float\",\"v\":\"nan\"}", fp);
        else fprintf(fp, "{\"t\":\"float\",\"v\":%.17g}", d);
    } else if (IS_RATIONAL(v)) {
        Rational *r = AS_RATIONAL(v);
        fprintf(fp, "{\"t\":\"frac\",\"n\":%lld,\"d\":%lld}",
                (long long)r->num, (long long)r->den);
    } else if (IS_SYM(v)) {
        fputs("{\"t\":\"sym\",\"v\":", fp);
        json_write_string(fp, sym_name(v));
        fputc('}', fp);
    } else if (IS_STRING(v)) {
        ULString *s = AS_STRING(v);
        fputs(s->mutable ? "{\"t\":\"mstr\",\"v\":" : "{\"t\":\"str\",\"v\":", fp);
        json_write_string(fp, s->data);
        fputc('}', fp);
    } else if (IS_CHAR(v)) {
        fprintf(fp, "{\"t\":\"char\",\"v\":%d}", AS_CHAR(v));
    } else if (IS_PAIR(v)) {
        fputs("{\"t\":\"pair\",\"car\":", fp);
        json_write_value(fp, CAR(v));
        fputs(",\"cdr\":", fp);
        json_write_value(fp, CDR(v));
        fputc('}', fp);
    } else if (IS_VECTOR(v)) {
        ULVector *vec = AS_VECTOR(v);
        fputs("{\"t\":\"vec\",\"v\":[", fp);
        for (size_t i = 0; i < vec->len; i++) {
            if (i > 0) fputc(',', fp);
            json_write_value(fp, vec->data[i]);
        }
        fputs("]}", fp);
    } else if (IS_HASHTABLE(v)) {
        ULHashTable *ht = AS_HASHTABLE(v);
        fputs("{\"t\":\"hash\",\"entries\":[", fp);
        bool first = true;
        for (size_t i = 0; i < ht->nbuckets; i++) {
            HTEntry *e = ht->buckets[i];
            while (e) {
                if (!first) fputc(',', fp);
                first = false;
                fputc('[', fp);
                json_write_value(fp, e->key);
                fputc(',', fp);
                json_write_value(fp, e->value);
                fputc(']', fp);
                e = e->next;
            }
        }
        fputs("]}", fp);
    } else if (IS_PROC(v)) {
        /* Serialize procedure body as source text */
        Proc *p = AS_PROC(v);
        fputs("{\"t\":\"proc\"", fp);
        if (p->name) { fputs(",\"name\":", fp); json_write_string(fp, p->name); }
        fputs(",\"params\":[", fp);
        for (int i = 0; i < p->nparams; i++) {
            if (i > 0) fputc(',', fp);
            json_write_string(fp, sym_name(p->params[i]));
        }
        fputs("]", fp);
        if (!IS_NIL(p->rest)) {
            fputs(",\"rest\":", fp);
            json_write_string(fp, sym_name(p->rest));
        }
        fputs(",\"body\":[", fp);
        for (int i = 0; i < p->body.count; i++) {
            if (i > 0) fputc(',', fp);
            char *s = show(p->body.exprs[i], false);
            json_write_string(fp, s);
            ul_free(s);
        }
        fputs("]}", fp);
    } else if (IS_COMPILED_PROC(v)) {
        /* For compiled procs, we save minimal info */
        CompiledProc *cp = AS_COMPILED_PROC(v);
        fputs("{\"t\":\"cproc\"", fp);
        if (cp->name) { fputs(",\"name\":", fp); json_write_string(fp, cp->name); }
        fputs(",\"params\":[", fp);
        for (int i = 0; i < cp->nparams; i++) {
            if (i > 0) fputc(',', fp);
            json_write_string(fp, sym_name(cp->params[i]));
        }
        fputs("]", fp);
        if (!IS_NIL(cp->rest)) {
            fputs(",\"rest\":", fp);
            json_write_string(fp, sym_name(cp->rest));
        }
        fputs("}", fp);
    } else if (IS_CONTINUATION(v)) {
        fputs("{\"t\":\"cont_marker\"}", fp);
    } else if (IS_BUILTIN(v)) {
        fputs("{\"t\":\"builtin\"}", fp);
    } else {
        fputs("{\"t\":\"opaque\"}", fp);
    }
}

/* ═══════════════════════════════════════════════════════════════════════════
 * portal_save — write env + optional continuation to JSON
 * ═══════════════════════════════════════════════════════════════════════════ */

void portal_save(Env *env, const char *path, FullCont *continuation) {
    FILE *fp = fopen(path, "w");
    if (!fp) {
        lisp_error("portal_save: cannot open %s", path);
        return;
    }

    fputs("{\"format\":\"lumbda-portal-v1\",\n", fp);

    /* RNG state — xoshiro256** as 8 × u32 halves (low, high, low, high, ...) */
    {
        uint32_t halves[8];
        rng_get_halves(halves);
        fputs("\"rng\":{\"algo\":\"xoshiro256**\",\"state\":[", fp);
        for (int i = 0; i < 8; i++) {
            if (i > 0) fputc(',', fp);
            fprintf(fp, "%u", halves[i]);
        }
        fputs("]},\n", fp);
    }

    /* Environment bindings (user-defined only from global) */
    fputs("\"env\":", fp);
    json_write_env_bindings(fp, env, (env->global == env));
    fputs(",\n", fp);

    /* Continuation */
    if (continuation) {
        fputs("\"continuation\":{\"t\":\"cont\",\n", fp);
        fprintf(fp, "\"ip\":%d,\n", continuation->ip);
        fprintf(fp, "\"n_instrs\":%d,\n", continuation->n_instrs);

        /* Stack */
        fputs("\"stack\":[", fp);
        for (int i = 0; i < continuation->stack_len; i++) {
            if (i > 0) fputc(',', fp);
            json_write_value(fp, continuation->stack[i]);
        }
        fputs("],\n", fp);

        /* Environment */
        fputs("\"env\":", fp);
        json_write_env_bindings(fp, continuation->env, false);
        fputs(",\n", fp);

        /* Frames */
        fprintf(fp, "\"nframes\":%d,\n", continuation->nframes);
        fputs("\"frames\":[", fp);
        for (int i = 0; i < continuation->nframes; i++) {
            if (i > 0) fputc(',', fp);
            VMFrame *f = &continuation->frames[i];
            fputs("{", fp);
            fprintf(fp, "\"ip\":%d,\"n_instrs\":%d,", f->ip, f->n_instrs);
            fputs("\"stack\":[", fp);
            for (int j = 0; j < f->stack_len; j++) {
                if (j > 0) fputc(',', fp);
                json_write_value(fp, f->stack[j]);
            }
            fputs("],\"env\":", fp);
            json_write_env_bindings(fp, f->env, false);
            fputc('}', fp);
        }
        fputs("]\n", fp);

        fputc('}', fp);
    } else {
        fputs("\"continuation\":null", fp);
    }

    fputs("\n}\n", fp);
    fclose(fp);
}

/* ═══════════════════════════════════════════════════════════════════════════
 * Minimal JSON reader — for portal_resume
 *
 * Supports: objects, arrays, strings, numbers, true, false, null
 * ═══════════════════════════════════════════════════════════════════════════ */

typedef enum {
    JT_NULL, JT_BOOL, JT_INT, JT_FLOAT, JT_STRING, JT_ARRAY, JT_OBJECT
} JsonType;

typedef struct JsonNode JsonNode;

typedef struct JsonKV {
    char *key;
    JsonNode *value;
    struct JsonKV *next;
} JsonKV;

struct JsonNode {
    JsonType type;
    union {
        bool bval;
        int64_t ival;
        double fval;
        char *sval;
        struct { JsonNode **items; int count; } array;
        JsonKV *object;  /* linked list of key-value pairs */
    };
};

static void skip_ws(const char **p) {
    while (**p == ' ' || **p == '\t' || **p == '\n' || **p == '\r') (*p)++;
}

static JsonNode *json_parse(const char **p);

static char *json_parse_string(const char **p) {
    if (**p != '"') return NULL;
    (*p)++; /* skip opening " */
    int cap = 256;
    char *buf = (char *)ul_malloc(cap);
    int len = 0;
    while (**p && **p != '"') {
        if (len + 8 >= cap) { cap *= 2; buf = (char *)ul_realloc(buf, cap); }
        if (**p == '\\') {
            (*p)++;
            switch (**p) {
                case '"': buf[len++] = '"'; break;
                case '\\': buf[len++] = '\\'; break;
                case 'n': buf[len++] = '\n'; break;
                case 'r': buf[len++] = '\r'; break;
                case 't': buf[len++] = '\t'; break;
                case '/': buf[len++] = '/'; break;
                case 'u': {
                    (*p)++;
                    char hex[5] = {0};
                    for (int i = 0; i < 4 && **p; i++) hex[i] = *(*p)++;
                    int code = (int)strtol(hex, NULL, 16);
                    if (code < 0x80) buf[len++] = (char)code;
                    else { buf[len++] = '?'; }
                    continue; /* skip the (*p)++ below */
                }
                default: buf[len++] = **p;
            }
        } else {
            buf[len++] = **p;
        }
        (*p)++;
    }
    if (**p == '"') (*p)++; /* skip closing " */
    buf[len] = '\0';
    return buf;
}

static JsonNode *json_make_node(JsonType type) {
    JsonNode *n = (JsonNode *)ul_malloc(sizeof(JsonNode));
    memset(n, 0, sizeof(JsonNode));
    n->type = type;
    return n;
}

static JsonNode *json_parse(const char **p) {
    skip_ws(p);
    if (**p == '\0') return NULL;

    if (**p == '"') {
        JsonNode *n = json_make_node(JT_STRING);
        n->sval = json_parse_string(p);
        return n;
    }
    if (**p == '{') {
        (*p)++;
        JsonNode *n = json_make_node(JT_OBJECT);
        n->object = NULL;
        skip_ws(p);
        if (**p == '}') { (*p)++; return n; }
        JsonKV *tail = NULL;
        while (1) {
            skip_ws(p);
            char *key = json_parse_string(p);
            skip_ws(p);
            if (**p == ':') (*p)++;
            JsonNode *val = json_parse(p);
            JsonKV *kv = (JsonKV *)ul_malloc(sizeof(JsonKV));
            kv->key = key;
            kv->value = val;
            kv->next = NULL;
            if (!tail) n->object = kv;
            else tail->next = kv;
            tail = kv;
            skip_ws(p);
            if (**p == ',') (*p)++;
            else break;
        }
        skip_ws(p);
        if (**p == '}') (*p)++;
        return n;
    }
    if (**p == '[') {
        (*p)++;
        JsonNode *n = json_make_node(JT_ARRAY);
        int cap = 16;
        n->array.items = (JsonNode **)ul_malloc(sizeof(JsonNode *) * cap);
        n->array.count = 0;
        skip_ws(p);
        if (**p == ']') { (*p)++; return n; }
        while (1) {
            if (n->array.count >= cap) {
                cap *= 2;
                n->array.items = (JsonNode **)ul_realloc(n->array.items, sizeof(JsonNode *) * cap);
            }
            n->array.items[n->array.count++] = json_parse(p);
            skip_ws(p);
            if (**p == ',') (*p)++;
            else break;
        }
        skip_ws(p);
        if (**p == ']') (*p)++;
        return n;
    }
    if (strncmp(*p, "true", 4) == 0) {
        *p += 4;
        JsonNode *n = json_make_node(JT_BOOL);
        n->bval = true;
        return n;
    }
    if (strncmp(*p, "false", 5) == 0) {
        *p += 5;
        JsonNode *n = json_make_node(JT_BOOL);
        n->bval = false;
        return n;
    }
    if (strncmp(*p, "null", 4) == 0) {
        *p += 4;
        return json_make_node(JT_NULL);
    }
    /* Number */
    {
        char *end;
        double d = strtod(*p, &end);
        if (end != *p) {
            /* Check if it's actually an integer */
            bool is_int = true;
            for (const char *c = *p; c < end; c++) {
                if (*c == '.' || *c == 'e' || *c == 'E') { is_int = false; break; }
            }
            *p = end;
            if (is_int && d >= -140737488355328LL && d <= 140737488355327LL) {
                JsonNode *n = json_make_node(JT_INT);
                n->ival = (int64_t)d;
                return n;
            }
            JsonNode *n = json_make_node(JT_FLOAT);
            n->fval = d;
            return n;
        }
    }
    /* Skip unknown */
    (*p)++;
    return json_make_node(JT_NULL);
}

static JsonNode *json_obj_get(JsonNode *obj, const char *key) {
    if (!obj || obj->type != JT_OBJECT) return NULL;
    for (JsonKV *kv = obj->object; kv; kv = kv->next) {
        if (kv->key && strcmp(kv->key, key) == 0) return kv->value;
    }
    return NULL;
}

static const char *json_str(JsonNode *n) {
    if (!n || n->type != JT_STRING) return NULL;
    return n->sval;
}

static int64_t json_int(JsonNode *n) {
    if (!n) return 0;
    if (n->type == JT_INT) return n->ival;
    if (n->type == JT_FLOAT) return (int64_t)n->fval;
    return 0;
}

static void json_free(JsonNode *n) {
    if (!n) return;
    switch (n->type) {
        case JT_STRING: ul_free(n->sval); break;
        case JT_ARRAY:
            for (int i = 0; i < n->array.count; i++) json_free(n->array.items[i]);
            ul_free(n->array.items);
            break;
        case JT_OBJECT: {
            JsonKV *kv = n->object;
            while (kv) {
                JsonKV *next = kv->next;
                ul_free(kv->key);
                json_free(kv->value);
                ul_free(kv);
                kv = next;
            }
            break;
        }
        default: break;
    }
    ul_free(n);
}

/* ═══════════════════════════════════════════════════════════════════════════
 * Deserialize a JSON value node into a Lisp Value
 * ═══════════════════════════════════════════════════════════════════════════ */

static Value json_to_value(JsonNode *n, Env *base_env) {
    if (!n || n->type == JT_NULL) return VAL_NIL;
    if (n->type == JT_INT) return VAL_INT(n->ival);
    if (n->type == JT_FLOAT) return make_double(n->fval);

    if (n->type != JT_OBJECT) return VAL_NIL;

    const char *t = json_str(json_obj_get(n, "t"));
    if (!t) return VAL_NIL;

    if (strcmp(t, "nil") == 0) return VAL_NIL;
    if (strcmp(t, "void") == 0) return VAL_VOID;
    if (strcmp(t, "eof") == 0) return VAL_EOF;
    if (strcmp(t, "bool") == 0) {
        JsonNode *v = json_obj_get(n, "v");
        return (v && v->type == JT_BOOL && v->bval) ? VAL_TRUE : VAL_FALSE;
    }
    if (strcmp(t, "float") == 0) {
        JsonNode *v = json_obj_get(n, "v");
        if (v && v->type == JT_STRING) {
            if (strcmp(v->sval, "+inf") == 0) return make_double(INFINITY);
            if (strcmp(v->sval, "-inf") == 0) return make_double(-INFINITY);
            if (strcmp(v->sval, "nan") == 0) return make_double(NAN);
        }
        if (v && v->type == JT_FLOAT) return make_double(v->fval);
        if (v && v->type == JT_INT) return make_double((double)v->ival);
        return make_double(0.0);
    }
    if (strcmp(t, "frac") == 0) {
        int64_t num = json_int(json_obj_get(n, "n"));
        int64_t den = json_int(json_obj_get(n, "d"));
        return rational_normalize(num, den);
    }
    if (strcmp(t, "sym") == 0) {
        const char *v = json_str(json_obj_get(n, "v"));
        return v ? intern(v) : VAL_NIL;
    }
    if (strcmp(t, "str") == 0) {
        const char *v = json_str(json_obj_get(n, "v"));
        return v ? make_string_from_cstr(v) : make_string_from_cstr("");
    }
    if (strcmp(t, "mstr") == 0) {
        const char *v = json_str(json_obj_get(n, "v"));
        return v ? make_string(v, strlen(v), true) : make_string("", 0, true);
    }
    if (strcmp(t, "char") == 0) {
        return VAL_CHAR((int)json_int(json_obj_get(n, "v")));
    }
    if (strcmp(t, "pair") == 0) {
        Value car = json_to_value(json_obj_get(n, "car"), base_env);
        Value cdr = json_to_value(json_obj_get(n, "cdr"), base_env);
        return cons(car, cdr);
    }
    if (strcmp(t, "vec") == 0) {
        JsonNode *arr = json_obj_get(n, "v");
        if (!arr || arr->type != JT_ARRAY) return make_vector(0, VAL_NIL);
        Value vec = make_vector(arr->array.count, VAL_NIL);
        for (int i = 0; i < arr->array.count; i++) {
            AS_VECTOR(vec)->data[i] = json_to_value(arr->array.items[i], base_env);
        }
        return vec;
    }
    if (strcmp(t, "hash") == 0) {
        Value ht = make_hashtable();
        JsonNode *entries = json_obj_get(n, "entries");
        if (entries && entries->type == JT_ARRAY) {
            for (int i = 0; i < entries->array.count; i++) {
                JsonNode *pair = entries->array.items[i];
                if (pair && pair->type == JT_ARRAY && pair->array.count >= 2) {
                    Value k = json_to_value(pair->array.items[0], base_env);
                    Value v = json_to_value(pair->array.items[1], base_env);
                    ht_set(AS_HASHTABLE(ht), k, v);
                }
            }
        }
        return ht;
    }
    if (strcmp(t, "proc") == 0) {
        /* Reconstruct a Proc from serialized body source */
        const char *name = json_str(json_obj_get(n, "name"));
        JsonNode *params_arr = json_obj_get(n, "params");
        const char *rest_str = json_str(json_obj_get(n, "rest"));
        JsonNode *body_arr = json_obj_get(n, "body");

        int nparams = (params_arr && params_arr->type == JT_ARRAY) ? params_arr->array.count : 0;
        Value *params = (Value *)ul_malloc_values(sizeof(Value) * (nparams > 0 ? nparams : 1));
        for (int i = 0; i < nparams; i++) {
            params[i] = intern(json_str(params_arr->array.items[i]));
        }
        Value rest = rest_str ? intern(rest_str) : VAL_NIL;

        int nbody = (body_arr && body_arr->type == JT_ARRAY) ? body_arr->array.count : 0;
        ExprList body;
        body.count = nbody;
        body.exprs = (Value *)ul_malloc_values(sizeof(Value) * (nbody > 0 ? nbody : 1));
        for (int i = 0; i < nbody; i++) {
            const char *src = json_str(body_arr->array.items[i]);
            if (src) {
                int count;
                Value *parsed = read_all(src, &count, false);
                body.exprs[i] = count > 0 ? parsed[0] : VAL_VOID;
                ul_free(parsed);
            } else {
                body.exprs[i] = VAL_VOID;
            }
        }

        Proc *p = make_proc(params, nparams, rest, body, base_env, name);
        ul_free(params);
        return VAL_PTR(p);
    }
    if (strcmp(t, "builtin") == 0 || strcmp(t, "opaque") == 0 ||
        strcmp(t, "cproc") == 0 || strcmp(t, "cont_marker") == 0) {
        /* These can't be fully reconstructed — return void */
        return VAL_VOID;
    }

    return VAL_NIL;
}

/* ═══════════════════════════════════════════════════════════════════════════
 * portal_resume — load machine state from JSON file
 * ═══════════════════════════════════════════════════════════════════════════ */

bool portal_resume(const char *path, Env *base_env, Env **out_env, FullCont **out_cont) {
    FILE *fp = fopen(path, "r");
    if (!fp) return false;

    fseek(fp, 0, SEEK_END);
    long sz = ftell(fp);
    fseek(fp, 0, SEEK_SET);

    char *src = (char *)ul_malloc(sz + 1);
    size_t nread = fread(src, 1, sz, fp);
    src[nread] = '\0';
    fclose(fp);

    const char *p = src;
    JsonNode *root = json_parse(&p);
    ul_free(src);

    if (!root || root->type != JT_OBJECT) {
        json_free(root);
        return false;
    }

    /* Check format */
    const char *fmt = json_str(json_obj_get(root, "format"));
    if (!fmt || strcmp(fmt, "lumbda-portal-v1") != 0) {
        json_free(root);
        return false;
    }

    /* Restore RNG state if present (absent = pre-RNG portal file, skip) */
    JsonNode *rng_node = json_obj_get(root, "rng");
    if (rng_node && rng_node->type == JT_OBJECT) {
        JsonNode *state_arr = json_obj_get(rng_node, "state");
        if (state_arr && state_arr->type == JT_ARRAY && state_arr->array.count == 8) {
            uint32_t halves[8];
            for (int i = 0; i < 8; i++) {
                halves[i] = (uint32_t)json_int(state_arr->array.items[i]);
            }
            rng_set_halves(halves);
        }
    }

    /* Merge environment bindings into base_env */
    JsonNode *env_node = json_obj_get(root, "env");
    if (env_node && env_node->type == JT_OBJECT) {
        for (JsonKV *kv = env_node->object; kv; kv = kv->next) {
            if (!kv->key) continue;
            Value sym = intern(kv->key);
            Value val = json_to_value(kv->value, base_env);
            /* Only set if non-void (skip builtins that couldn't be serialized) */
            if (!IS_VOID(val)) {
                env_define(base_env, sym, val);
            }
        }
    }

    *out_env = base_env;

    /* Continuation — for now, we mark it present but don't fully
     * reconstruct bytecode (that requires code serialization).
     * The continuation is stored so callers know one was saved. */
    JsonNode *cont_node = json_obj_get(root, "continuation");
    if (cont_node && cont_node->type == JT_OBJECT) {
        /* A continuation was saved. We can't fully restore it without
         * reconstructing the bytecode instructions, but we signal its presence. */
        *out_cont = (FullCont *)ul_malloc(sizeof(FullCont));
        (*out_cont)->hdr.type = OBJ_CONTINUATION;
        (*out_cont)->nframes = 0;
        (*out_cont)->frames = NULL;
        (*out_cont)->stack = NULL;
        (*out_cont)->stack_len = 0;
        (*out_cont)->ip = (int)json_int(json_obj_get(cont_node, "ip"));
        (*out_cont)->instrs = NULL;
        (*out_cont)->n_instrs = 0;
        (*out_cont)->env = base_env;
        (*out_cont)->vm_id = NULL;
    } else {
        *out_cont = NULL;
    }

    json_free(root);
    return true;
}

/* ═══════════════════════════════════════════════════════════════════════════
 * portal-checkpoint! builtin — signals VM to save at next safe point
 * ═══════════════════════════════════════════════════════════════════════════ */

static Value builtin_portal_checkpoint(Value *args, int nargs, Env *env) {
    (void)env;
    if (nargs < 1 || !IS_STRING(args[0]))
        lisp_error("portal-checkpoint!: expected string path");
    g_portal_checkpoint_path = ul_strdup(AS_STRING(args[0])->data);
    return VAL_VOID;
}

static Value builtin_random_seed_bang(Value *args, int nargs, Env *env) {
    (void)env;
    if (nargs != 1) lisp_error("random-seed!: expected 1 arg");
    rng_seed((uint64_t)as_number_int(args[0]));
    return VAL_VOID;
}

static Value builtin_random(Value *args, int nargs, Env *env) {
    (void)args; (void)env;
    if (nargs != 0) lisp_error("random: expected 0 args");
    return make_double((double)(rng_next() >> 11) / (double)(1ULL << 53));
}

static Value builtin_random_int(Value *args, int nargs, Env *env) {
    (void)env;
    if (nargs != 1) lisp_error("random-int: expected 1 arg");
    int64_t n = as_number_int(args[0]);
    if (n <= 0) lisp_error("random-int: n must be positive, got %lld", (long long)n);
    return VAL_INT((int64_t)(rng_next() % (uint64_t)n));
}

static Value builtin_random_state(Value *args, int nargs, Env *env) {
    (void)args; (void)env;
    if (nargs != 0) lisp_error("random-state: expected 0 args");
    uint32_t halves[8];
    rng_get_halves(halves);
    Value list = VAL_NIL;
    for (int i = 7; i >= 0; i--) {
        list = cons(VAL_INT((int64_t)halves[i]), list);
    }
    return list;
}

static Value builtin_random_state_bang(Value *args, int nargs, Env *env) {
    (void)env;
    if (nargs != 1) lisp_error("random-state!: expected 1 arg (list of 8 ints)");
    uint32_t halves[8];
    Value lst = args[0];
    for (int i = 0; i < 8; i++) {
        if (!IS_PAIR(lst)) lisp_error("random-state!: list too short");
        halves[i] = (uint32_t)as_number_int(CAR(lst));
        lst = CDR(lst);
    }
    rng_set_halves(halves);
    return VAL_VOID;
}

/* Opt-in kernel entropy seed. See docs/tickets/0002-os-entropy-seed.md. */
static Value builtin_random_seed_from_os(Value *args, int nargs, Env *env) {
    (void)args; (void)env;
    if (nargs != 0) lisp_error("random-seed-from-os!: expected 0 args");
    int fd = open("/dev/urandom", O_RDONLY);
    if (fd < 0) lisp_error("random-seed-from-os!: cannot open /dev/urandom");
    uint64_t k = 0;
    ssize_t n = read(fd, &k, sizeof k);
    close(fd);
    if (n != (ssize_t)sizeof k)
        lisp_error("random-seed-from-os!: short read from /dev/urandom");
    rng_seed(k);
    return VAL_VOID;
}

void register_portal_builtins(Env *env) {
    env_define(env, intern("portal-checkpoint!"), VAL_BUILTIN(builtin_portal_checkpoint));
    env_define(env, intern("portal-save!"), VAL_BUILTIN(builtin_portal_checkpoint));
    env_define(env, intern("random-seed!"), VAL_BUILTIN(builtin_random_seed_bang));
    env_define(env, intern("random-seed-from-os!"), VAL_BUILTIN(builtin_random_seed_from_os));
    env_define(env, intern("random"), VAL_BUILTIN(builtin_random));
    env_define(env, intern("random-int"), VAL_BUILTIN(builtin_random_int));
    env_define(env, intern("random-state"), VAL_BUILTIN(builtin_random_state));
    env_define(env, intern("random-state!"), VAL_BUILTIN(builtin_random_state_bang));
    /* Default seed = 0 so (random) without (random-seed!) is deterministic
     * and non-zero. All three impls agree on this startup state. */
    rng_seed(0);
}