// smallobject_mid_v35.c
// Phase v11a-3: MID v3.5 HotBox implementation
//
// Design:
//   - TLS-cached page for fast allocation
//   - Refill via ColdIface when page exhausted
//   - Retire via ColdIface when page is full
//   - Stats/Learner integration for observability

#include <stdlib.h>
#include <string.h>
#include <stdint.h>
#include "box/smallobject_mid_v35_box.h"
#include "box/smallobject_segment_mid_v3_box.h"
#include "box/smallobject_cold_iface_mid_v3_box.h"
#include "box/smallobject_mid_v35_geom_box.h"  // Phase MID-V35-HOTPATH-OPT-1: geometry SSOT
#include "box/mid_v35_hotpath_env_box.h"       // Phase MID-V35-HOTPATH-OPT-1: Step 1-3 ENV gates
#include "tiny_region_id.h"  // For tiny_region_id_write_header

// SmallPageMeta is defined in smallobject_segment_mid_v3_box.h
// (included via smallobject_cold_iface_mid_v3_box.h)

// ============================================================================
// TLS Context (per-thread fast path state)
// ============================================================================

typedef struct {
    void *page[8];           // Current page per class
    uint32_t offset[8];      // Allocation offset (slot index)
    uint32_t capacity[8];    // Slots per page per class
    SmallPageMeta_MID_v3 *meta[8];  // Page metadata for retire check
} SmallMidV35TlsCtx;

static __thread SmallMidV35TlsCtx tls_mid_v35_ctx = {0};

// ============================================================================
// Slot Configuration (C5/C6/C7)
// ============================================================================
// Phase MID-V35-HOTPATH-OPT-1: Use geom_box as Single Source of Truth
// See: core/box/smallobject_mid_v35_geom_box.h

// ============================================================================
// Init
// ============================================================================

void small_mid_v35_init(void) {
    // Initialize any global state if needed
    // For v11a-3: nothing to do (TLS is zero-initialized)
}

// ============================================================================
// Alloc
// ============================================================================

void* small_mid_v35_alloc(uint32_t class_idx, size_t size) {
    (void)size;  // Unused for now
    if (class_idx < 5 || class_idx > 7) return NULL;  // Only C5-C7

    SmallMidV35TlsCtx *ctx = &tls_mid_v35_ctx;

    // ========================================================================
    // Step 3: C6 specialized fast path (constant slot size = 512)
    // ========================================================================
    if (mid_v35_c6_fastpath_enabled() && class_idx == 6) {
        void *page = ctx->page[6];
        uint32_t off = ctx->offset[6];
        if (page && off < ctx->capacity[6]) {
            // C6: slot_size = 512 (constant, compiler can optimize)
            void *base = (char*)page + off * 512;
            ctx->offset[6] = off + 1;

            // Step 2: HOT_COUNTS gate
            if (mid_v35_hot_counts_enabled() && ctx->meta[6]) {
                ctx->meta[6]->alloc_count++;
            }

            // Step 1: HEADER_PREFILL gate
            if (!mid_v35_header_prefill_enabled()) {
                tiny_region_id_write_header(base, 6);
            }

            return (char*)base + 1;
        }
        // Fall through to slow path
    }

    // ========================================================================
    // Generic fast path: allocate from TLS cached page
    // ========================================================================
    if (ctx->page[class_idx] && ctx->offset[class_idx] < ctx->capacity[class_idx]) {
        size_t slot_size = mid_v35_slot_size(class_idx);
        void *base = (char*)ctx->page[class_idx] + ctx->offset[class_idx] * slot_size;
        ctx->offset[class_idx]++;

        // Step 2: HOT_COUNTS gate - Update page metadata
        if (mid_v35_hot_counts_enabled() && ctx->meta[class_idx]) {
            ctx->meta[class_idx]->alloc_count++;
        }

        // Step 1: HEADER_PREFILL gate - Write header if not prefilled
        if (!mid_v35_header_prefill_enabled()) {
            tiny_region_id_write_header(base, class_idx);
        }

        // Return USER pointer (BASE + 1 byte header)
        return (char*)base + 1;
    }

    // ========================================================================
    // Slow path: need new page via ColdIface
    // ========================================================================
    SmallPageMeta_MID_v3 *page = small_cold_mid_v3_refill_page(class_idx);
    if (!page) {
        // Fallback to legacy or return NULL
        return NULL;
    }

    // Update TLS cache
    ctx->page[class_idx] = page->ptr;
    ctx->offset[class_idx] = 1;  // First slot already allocated
    ctx->capacity[class_idx] = mid_v35_slots_per_page(class_idx);
    ctx->meta[class_idx] = page;

    // Step 2: HOT_COUNTS gate - Record first allocation in page metadata
    if (mid_v35_hot_counts_enabled()) {
        page->alloc_count = 1;
    }

    // Step 1: HEADER_PREFILL gate - Write header for first slot if not prefilled
    if (!mid_v35_header_prefill_enabled()) {
        tiny_region_id_write_header(page->ptr, class_idx);
    }

    // Return first slot (USER pointer)
    return (char*)page->ptr + 1;
}

// ============================================================================
// Free (Simplified: just count, no freelist yet)
// ============================================================================

void small_mid_v35_free(void *ptr, uint32_t class_idx) {
    if (!ptr || class_idx < 5 || class_idx > 7) return;

    // For v11a-3: simplified free (just increment free_count)
    // In future phases: implement freelist for reuse

    // Calculate BASE from USER pointer
    void *base = (char*)ptr - 1;

    // Find page metadata via simple calculation
    // Note: Assumes 64KB pages aligned to 64KB boundary
    size_t page_size = 64 * 1024;  // 64KB
    void *page_base = (void*)((uintptr_t)base & ~(page_size - 1));

    // Check if this is the current TLS page
    SmallMidV35TlsCtx *ctx = &tls_mid_v35_ctx;
    SmallPageMeta_MID_v3 *meta = ctx->meta[class_idx];

    if (meta && meta->ptr == page_base) {
        // Free to current TLS page
        meta->free_count++;

        // Check if page is fully empty
        if (meta->free_count >= meta->capacity) {
            // Retire page via ColdIface
            small_cold_mid_v3_retire_page(meta);

            // Clear TLS cache for this class
            ctx->page[class_idx] = NULL;
            ctx->offset[class_idx] = 0;
            ctx->meta[class_idx] = NULL;
        }
    } else {
        // Different page: need RegionIdBox lookup
        // For v11a-3: simple fallback - just count the free
        // Real implementation needs proper page lookup
        // TODO: Implement cross-page free via RegionIdBox in v11b
    }
}