// Box: Unified Backend (Phase 12)
// Purpose: Unified entry point for SuperSlab allocation (shared pool + legacy fallback)

#include "ss_unified_backend_box.h"
#include "ss_legacy_backend_box.h"
#include "hakmem_tiny_superslab.h"
#include "hakmem_shared_pool.h"
#include "hakmem_tiny_config.h"
#include "ss_allocation_box.h"
#include <stdio.h>
#include <stdlib.h>

// ============================================================================
// Shared Pool Backend
// ============================================================================

/*
 * Shared pool backend for hak_tiny_alloc_superslab_box().
 *
 * Phase 12-2:
 *  - Uses SharedSuperSlabPool (g_shared_pool) to obtain a SuperSlab/slab
 *    for the requested class_idx.
 *  - This backend EXPRESSLY owns only:
 *      - choosing (ss, slab_idx) via shared_pool_acquire_slab()
 *      - initializing that slab's TinySlabMeta via superslab_init_slab()
 *    and nothing else; all callers must go through hak_tiny_alloc_superslab_box().
 *
 *  - For now this is a minimal, conservative implementation:
 *      - One linear bump-run is carved from the acquired slab using tiny_block_stride_for_class().
 *      - No complex per-slab freelist or refill policy yet (Phase 12-3+).
 *      - If shared_pool_acquire_slab() fails, we fall back to legacy backend.
 */
void* hak_tiny_alloc_superslab_backend_shared(int class_idx)
{
    if (class_idx < 0 || class_idx >= TINY_NUM_CLASSES_SS) {
        return NULL;
    }

    SuperSlab* ss = NULL;
    int slab_idx = -1;

    if (shared_pool_acquire_slab(class_idx, &ss, &slab_idx) != 0 || !ss) {
        // Shared pool could not provide a slab; caller may choose to fall back.
        return NULL;
    }

    TinySlabMeta* meta = &ss->slabs[slab_idx];

    // Defensive: shared_pool must either hand us an UNASSIGNED slab or one
    // already bound to this class. Anything else is a hard bug.
    if (meta->class_idx != 255 && meta->class_idx != (uint8_t)class_idx) {
#if !HAKMEM_BUILD_RELEASE
        fprintf(stderr,
                "[HAKMEM][SS_SHARED] BUG: acquire_slab mismatch: cls=%d meta->class_idx=%u slab_idx=%d ss=%p\n",
                class_idx, (unsigned)meta->class_idx, slab_idx, (void*)ss);
#endif
        return NULL;
    }

    // Initialize slab geometry once for this class.
    if (meta->capacity == 0) {
        size_t block_size = g_tiny_class_sizes[class_idx];
        // owner_tid_low is advisory; we can use 0 in this backend.
        superslab_init_slab(ss, slab_idx, block_size, 0);
        meta = &ss->slabs[slab_idx];

        // CRITICAL FIX: Always set class_idx after init to avoid C0/C7 confusion.
        // New SuperSlabs start with meta->class_idx=0 (mmap zero-init).
        // Must explicitly set to requested class, not just when class_idx==255.
        meta->class_idx = (uint8_t)class_idx;
    }

    // Final contract check before computing addresses.
    if (meta->class_idx != (uint8_t)class_idx ||
        meta->capacity == 0 ||
        meta->used > meta->capacity) {
#if !HAKMEM_BUILD_RELEASE
        fprintf(stderr,
                "[HAKMEM][SS_SHARED] BUG: invalid slab meta before alloc: "
                "cls=%d slab_idx=%d meta_cls=%u used=%u cap=%u ss=%p\n",
                class_idx, slab_idx,
                (unsigned)meta->class_idx,
                (unsigned)meta->used,
                (unsigned)meta->capacity,
                (void*)ss);
#endif
        return NULL;
    }

    // Simple bump allocation within this slab.
    if (meta->used >= meta->capacity) {
        // Slab exhausted: in minimal Phase12-2 backend we do not loop;
        // caller or future logic must acquire another slab.
        return NULL;
    }

    size_t stride = tiny_block_stride_for_class(class_idx);
    size_t offset = (size_t)meta->used * stride;

    // Phase 12-2 minimal geometry:
    //  - slab 0 data offset via SUPERSLAB_SLAB0_DATA_OFFSET
    //  - subsequent slabs at fixed SUPERSLAB_SLAB_USABLE_SIZE strides.
    size_t slab_base_off = SUPERSLAB_SLAB0_DATA_OFFSET
                         + (size_t)slab_idx * SUPERSLAB_SLAB_USABLE_SIZE;
    uint8_t* base = (uint8_t*)ss + slab_base_off + offset;

    meta->used++;
    atomic_fetch_add_explicit(&ss->total_active_blocks, 1, memory_order_relaxed);

    hak_tiny_ss_hint_record(class_idx, ss, slab_idx);

    return (void*)base;
}

// ============================================================================
// Unified Entry Point
// ============================================================================

/*
 * Box API entry:
 *  - Single front-door for tiny-side Superslab allocations.
 *
 * Phase 27 policy (Unified backend line):
 *  - デフォルト: Shared Pool backend のみを使用（legacy backend は利用しない）。
 *  - 回帰/デバッグ用途でのみ、ENV で legacy fallback を明示的に有効化できる。
 *
 * ENV:
 *   HAKMEM_TINY_SS_SHARED=0              → 強制的に legacy backend のみを使用（過去挙動の回帰確認用）
 *   HAKMEM_TINY_SS_LEGACY_FALLBACK=0     → shared 失敗時の legacy fallback を無効化（デフォルト: 1, 有効）
 *   HAKMEM_TINY_SS_C23_UNIFIED=1         → C2/C3 限定で legacy fallback を無効化（Shared Pool のみで運転）
 *   HAKMEM_TINY_SS_LEGACY_HINT=1         → shared→legacy 間の軽量な hint Box を有効化
 */
void* hak_tiny_alloc_superslab_box(int class_idx)
{
    static int g_ss_shared_mode = -1;
    static int g_ss_legacy_fallback = -1;
    static int g_ss_c23_unified = -1;

    if (__builtin_expect(g_ss_shared_mode == -1, 0)) {
        const char* e = getenv("HAKMEM_TINY_SS_SHARED");
        // デフォルト: shared 有効。ENV=0 のときのみ legacy 専用に切り替え。
        g_ss_shared_mode = (e && *e == '0') ? 0 : 1;
    }
    if (__builtin_expect(g_ss_legacy_fallback == -1, 0)) {
        const char* e = getenv("HAKMEM_TINY_SS_LEGACY_FALLBACK");
        // デフォルト: legacy fallback 有効。
        //   ENV=0 のときのみ fallback 無効（完全 Unified backend モード）。
        g_ss_legacy_fallback = (e && *e == '0') ? 0 : 1;
    }
    if (__builtin_expect(g_ss_c23_unified == -1, 0)) {
        const char* e = getenv("HAKMEM_TINY_SS_C23_UNIFIED");
        // ENV=1 のときだけ C2/C3 を「ほぼ完全 Unified」モードに切り替える。
        g_ss_c23_unified = (e && *e && *e != '0') ? 1 : 0;
    }

    // shared OFF 時は legacy のみ（強制回帰モード）
    if (!g_ss_shared_mode) {
        return hak_tiny_alloc_superslab_backend_legacy(class_idx);
    }

    int legacy_fallback = g_ss_legacy_fallback;
    if ((class_idx == 2 || class_idx == 3) && g_ss_c23_unified == 1) {
        // C2/C3 は専用の Shared Pool 実験モード:
        //   - ENV=1 のときだけ legacy fallback を OFF にする。
        legacy_fallback = 0;
    }

    // Unified backend ライン: Shared Pool backend を唯一の正経路とする。
    void* p = hak_tiny_alloc_superslab_backend_shared(class_idx);
    if (p != NULL || !legacy_fallback) {
        // shared 成功、または legacy fallback 無効 → そのまま返す（NULLも許容）
        return p;
    }

    // オプション: shared 失敗時に、軽量な hint Box を一度だけ試す
    void* hint = hak_tiny_alloc_superslab_backend_hint(class_idx);
    if (hint != NULL) {
        return hint;
    }

    // shared 失敗時のみ legacy backend へフォールバック（回帰/デバッグ用）
    return hak_tiny_alloc_superslab_backend_legacy(class_idx);
}