// smallobject_hotbox_v5.c - SmallObject HotBox v5 Full Implementation (Phase v5-2)
//
// Phase v5-2: C6-only full implementation with segment-based allocation

#include <stdlib.h>
#include <stdbool.h>
#include <string.h>
#include "box/smallsegment_v5_box.h"
#include "box/smallobject_hotbox_v5_box.h"
#include "box/smallobject_cold_iface_v5.h"
#include "box/smallobject_v5_env_box.h"
#include "tiny_region_id.h"  // For HEADER_MAGIC and HEADER_CLASS_MASK

#ifndef likely
#define likely(x)   __builtin_expect(!!(x), 1)
#define unlikely(x) __builtin_expect(!!(x), 0)
#endif

// TLS context
static __thread SmallHeapCtxV5 g_small_heap_ctx_v5;
static __thread int g_small_heap_ctx_v5_init = 0;

SmallHeapCtxV5* small_heap_ctx_v5(void) {
    // Phase v5-4/v5-5/v5-6: Lazy initialization of cached ENV flags
    if (unlikely(!g_small_heap_ctx_v5_init)) {
        g_small_heap_ctx_v5.header_mode = (uint8_t)small_heap_v5_header_mode();
        g_small_heap_ctx_v5.tls_cache_enabled = small_heap_v5_tls_cache_enabled();
        g_small_heap_ctx_v5.c6_cached_block = NULL;  // Initialize cache to empty
        g_small_heap_ctx_v5.batch_enabled = small_heap_v5_batch_enabled();
        g_small_heap_ctx_v5.c6_batch.count = 0;  // Initialize batch to empty
        for (int i = 0; i < SMALL_V5_BATCH_CAP; i++) {
            g_small_heap_ctx_v5.c6_batch.slots[i] = NULL;
        }
        g_small_heap_ctx_v5_init = 1;
    }
    return &g_small_heap_ctx_v5;
}

// Forward declarations for pool v1 fallback
extern void* hak_pool_try_alloc(size_t size, uintptr_t site_id);
extern void hak_pool_free(void* ptr, size_t size, uintptr_t site_id);

// ============================================================================
// Helper: Slow path (refill from partial or cold)
// ============================================================================

static SmallPageMetaV5* alloc_slow_v5(SmallHeapCtxV5* ctx, uint32_t class_idx) {
    SmallClassHeapV5* h = &ctx->cls[class_idx];
    SmallPageMetaV5* cur = h->current;

    // If current exists but is exhausted, move to full list only
    // (exhausted pages are fully allocated, not partially free)
    if (cur && !cur->free_list) {
        SMALL_PAGE_V5_PUSH_FULL(h, cur);
        h->current = NULL;
    }

    // Try to pop from partial list (pages with some free blocks)
    SmallPageMetaV5* from_partial = SMALL_PAGE_V5_POP_PARTIAL(h);
    if (from_partial) {
        h->current = from_partial;
        return from_partial;
    }

    // Refill from cold interface (allocates new page)
    SmallPageMetaV5* page = small_cold_v5_refill_page(ctx, class_idx);
    if (!page) return NULL;

    h->current = page;
    return page;
}

// ============================================================================
// Phase v5-2: Fast alloc (C6-only full implementation)
// ============================================================================

void* small_alloc_fast_v5(size_t size, uint32_t class_idx, SmallHeapCtxV5* ctx) {
    (void)size;  // Not used in fast path

    // C6-only check
    if (unlikely(class_idx != SMALL_HEAP_V5_C6_CLASS_IDX)) {
        // Fallback to pool v1 for non-C6 classes
        return hak_pool_try_alloc(size, 0);
    }

    // Phase v5-5: TLS cache hit path (C6 only)
    if (unlikely(ctx->tls_cache_enabled)) {
        void* cached = ctx->c6_cached_block;
        if (likely(cached != NULL)) {
            ctx->c6_cached_block = NULL;  // Consume cache slot
            // NOTE: cached is BASE pointer (same as freelist format), convert to USER pointer
            // This is consistent with the free path which stores (ptr - 1) as BASE
            // Header mode handling (same logic as freelist path)
            uint8_t* header_ptr = (uint8_t*)cached;
            uint8_t desired_header = (uint8_t)(HEADER_MAGIC | (class_idx & HEADER_CLASS_MASK));

            if (ctx->header_mode == SMALL_HEAP_V5_HEADER_MODE_LIGHT) {
                // light mode: only write if invalid
                uint8_t existing = *header_ptr;
                if (existing != desired_header) {
                    *header_ptr = desired_header;
                }
            } else {
                // full mode: always write header
                *header_ptr = desired_header;
            }
            return header_ptr + 1;
        }
    }

    // Phase v5-6: Batch alloc path (C6 only, after cache)
    if (ctx->batch_enabled && class_idx == SMALL_HEAP_V5_C6_CLASS_IDX && ctx->c6_batch.count > 0) {
        uint8_t idx = --ctx->c6_batch.count;
        void* b = ctx->c6_batch.slots[idx];
        ctx->c6_batch.slots[idx] = NULL;
        // b is BASE pointer, return based on header mode
        if (ctx->header_mode == SMALL_HEAP_V5_HEADER_MODE_LIGHT) {
            return (uint8_t*)b + 1;
        } else {
            // full mode: write header
            uint8_t* header_ptr = (uint8_t*)b;
            uint8_t desired_header = (uint8_t)(HEADER_MAGIC | (class_idx & HEADER_CLASS_MASK));
            *header_ptr = desired_header;
            return header_ptr + 1;
        }
    }

    // Cache miss - proceed to existing page_meta path
    SmallClassHeapV5* h = &ctx->cls[SMALL_HEAP_V5_C6_CLASS_IDX];
    SmallPageMetaV5* page = h->current;

    // Fast path: Try current page freelist
    if (likely(page && page->free_list)) {
        void* blk = page->free_list;
        void* next = NULL;
        memcpy(&next, blk, sizeof(void*));
        page->free_list = next;
        page->used++;

        // Phase v5-4: Header mode handling
        uint8_t* header_ptr = (uint8_t*)blk;
        uint8_t desired_header = (uint8_t)(HEADER_MAGIC | (class_idx & HEADER_CLASS_MASK));

        if (ctx->header_mode == SMALL_HEAP_V5_HEADER_MODE_LIGHT) {
            // light mode: only write header if it's invalid/incorrect
            // This saves redundant writes when blocks are recycled
            uint8_t existing = *header_ptr;
            if (existing != desired_header) {
                *header_ptr = desired_header;
            }
        } else {
            // full mode: always write header (safety first)
            *header_ptr = desired_header;
        }
        return header_ptr + 1;
    }

    // Slow path: Current exhausted or NULL
    page = alloc_slow_v5(ctx, class_idx);
    if (unlikely(!page || !page->free_list)) {
        // Cold refill failed, fallback to pool v1
        return hak_pool_try_alloc(size, 0);
    }

    // Allocate from newly acquired page
    void* blk = page->free_list;
    void* next = NULL;
    memcpy(&next, blk, sizeof(void*));
    page->free_list = next;
    page->used++;

    // Phase v5-4: Header mode handling (same logic as fast path)
    uint8_t* header_ptr = (uint8_t*)blk;
    uint8_t desired_header = (uint8_t)(HEADER_MAGIC | (class_idx & HEADER_CLASS_MASK));

    if (ctx->header_mode == SMALL_HEAP_V5_HEADER_MODE_LIGHT) {
        // light mode: only write if invalid
        uint8_t existing = *header_ptr;
        if (existing != desired_header) {
            *header_ptr = desired_header;
        }
    } else {
        // full mode: always write header
        *header_ptr = desired_header;
    }
    return header_ptr + 1;
}

// ============================================================================
// Helper: Determine page location in heap lists (Phase v5-3)
// ============================================================================

static inline page_loc_t get_page_location(SmallClassHeapV5* h, SmallPageMetaV5* page,
                                           SmallPageMetaV5** prev_out) {
    if (prev_out) *prev_out = NULL;
    if (!h || !page) return LOC_NONE;

    // Check current (O(1))
    if (h->current == page) {
        return LOC_CURRENT;
    }

    // Check partial list (typically 0-1 pages in v5-3)
    SmallPageMetaV5* prev = NULL;
    for (SmallPageMetaV5* p = h->partial_head; p; prev = p, p = p->next) {
        if (p == page) {
            if (prev_out) *prev_out = prev;
            return LOC_PARTIAL;
        }
    }

    // Check full list
    prev = NULL;
    for (SmallPageMetaV5* p = h->full_head; p; prev = p, p = p->next) {
        if (p == page) {
            if (prev_out) *prev_out = prev;
            return LOC_FULL;
        }
    }

    return LOC_NONE;
}

// ============================================================================
// Phase v5-3: Fast free (C6-only O(1) implementation)
// ============================================================================

void small_free_fast_v5(void* ptr, uint32_t class_idx, SmallHeapCtxV5* ctx) {
    if (unlikely(!ptr)) {
        return;
    }

    // C6-only check
    if (unlikely(class_idx != SMALL_HEAP_V5_C6_CLASS_IDX)) {
        hak_pool_free(ptr, 0, 0);
        return;
    }

    // Phase v5-3: O(1) segment lookup (no list search)
    SmallPageMetaV5* page = small_segment_v5_page_meta_of(ptr);
    if (unlikely(!page)) {
        // Not in v5 segment, fallback to pool v1
        hak_pool_free(ptr, 0, 0);
        return;
    }

    SmallClassHeapV5* h = &ctx->cls[SMALL_HEAP_V5_C6_CLASS_IDX];

    // Phase v5-5: TLS cache refill path (before pushing to freelist)
    if (unlikely(ctx->tls_cache_enabled)) {
        if (ctx->c6_cached_block == NULL) {
            // Cache is empty, refill it with this block
            // NOTE: ptr is USER pointer, convert to BASE pointer for cache storage
            // (consistent with freelist storage format)
            void* base = (uint8_t*)ptr - 1;
            ctx->c6_cached_block = base;

            // IMPORTANT: Do NOT decrement page->used here!
            // The cached block is still logically "allocated" until it's:
            // - consumed during alloc (at which point it becomes allocated again)
            // - evicted to freelist (at which point page->used is decremented)
            // This prevents premature page retirement while holding a cached reference
            return;
        }
        // Cache full - evict cached block to freelist first, then cache this one
        else {
            void* evicted = ctx->c6_cached_block;
            // Evicted block is BASE pointer, convert to USER pointer for freelist push
            void* evicted_user = (uint8_t*)evicted + 1;

            // Look up the page for the evicted block (might be different from current page)
            SmallPageMetaV5* evicted_page = small_segment_v5_page_meta_of(evicted_user);
            if (evicted_page) {
                // Push evicted block to its page's freelist
                void* evicted_head = evicted_page->free_list;
                memcpy(evicted_user, &evicted_head, sizeof(void*));
                evicted_page->free_list = evicted_user;
                if (evicted_page->used > 0) {
                    evicted_page->used--;
                }
                // Note: We don't handle empty page transition here for evicted page
                // to keep this path fast. Empty pages will be handled on next alloc/free.
            }

            // Now cache the new block
            void* base = (uint8_t*)ptr - 1;
            ctx->c6_cached_block = base;
            return;
        }
    }

    // Phase v5-6: Batch free path (C6 only, after cache, before freelist)
    SmallV5Batch* batch = &ctx->c6_batch;
    if (ctx->batch_enabled && class_idx == SMALL_HEAP_V5_C6_CLASS_IDX && batch->count < SMALL_V5_BATCH_CAP) {
        // ptr is USER pointer, convert to BASE pointer for batch storage
        void* base = (uint8_t*)ptr - 1;
        batch->slots[batch->count++] = base;
        return;
    }

    // Cache disabled or batch full - push to freelist (standard path)
    void* head = page->free_list;
    memcpy(ptr, &head, sizeof(void*));
    page->free_list = ptr;
    if (page->used > 0) {
        page->used--;
    }

    // Handle empty page (used == 0)
    if (page->used == 0) {
        // Fast path: if this is current, just keep it
        if (h->current == page) {
            return;
        }

        // Determine location and unlink (rare path)
        SmallPageMetaV5* prev = NULL;
        page_loc_t loc = get_page_location(h, page, &prev);
        if (loc != LOC_NONE && loc != LOC_CURRENT) {
            SMALL_PAGE_V5_UNLINK(h, loc, prev, page);
        }

        // Promote to current if empty
        if (!h->current) {
            h->current = page;
            page->next = NULL;
            return;
        }

        // Try partial (limit 1)
        if (h->partial_count < SMALL_HEAP_V5_C6_PARTIAL_LIMIT) {
            SMALL_PAGE_V5_PUSH_PARTIAL(h, page);
            return;
        }

        // Retire to cold
        small_cold_v5_retire_page(ctx, page);
        return;
    }

    // Page not empty - handle full→partial transition
    if (h->current != page) {
        SmallPageMetaV5* prev = NULL;
        page_loc_t loc = get_page_location(h, page, &prev);
        if (loc == LOC_FULL && page->free_list) {
            // Move from full to partial
            SMALL_PAGE_V5_UNLINK(h, loc, prev, page);
            if (h->partial_count < SMALL_HEAP_V5_C6_PARTIAL_LIMIT) {
                SMALL_PAGE_V5_PUSH_PARTIAL(h, page);
            } else {
                SMALL_PAGE_V5_PUSH_FULL(h, page);
            }
        } else if (!h->current) {
            // No current, promote this
            if (loc != LOC_NONE) {
                SMALL_PAGE_V5_UNLINK(h, loc, prev, page);
            }
            h->current = page;
            page->next = NULL;
        }
    }
}

// ============================================================================
// Helper: C6 block size query
// ============================================================================

uint32_t small_heap_v5_c6_block_size(void) {
    return SMALL_HEAP_V5_C6_BLOCK_SIZE;
}