// tiny_c7_ultra_segment.c - C7 ULTRA 専用セグメント管理（UF-3）

#include "box/tiny_c7_ultra_segment_box.h"

#include <errno.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>

// 2MiB セグメントを 64KiB ページに分割（C7 専用、pow2 で mask しやすく）
#define TINY_C7_ULTRA_SEG_SIZE  ((size_t)(2 * 1024 * 1024))
#define TINY_C7_ULTRA_PAGE_SIZE ((size_t)(64 * 1024))
#define TINY_C7_ULTRA_PAGE_SHIFT 16  // 64KiB = 2^16 (for O(1) bit shift instead of division)

static __thread tiny_c7_ultra_segment_t* g_ultra_seg;

static inline void tiny_c7_ultra_segment_clear(tiny_c7_ultra_segment_t* seg) {
    if (!seg) return;
    seg->base = NULL;
    seg->seg_size = 0;
    seg->page_size = 0;
    seg->num_pages = 0;
    seg->pages = NULL;
}

tiny_c7_ultra_segment_t* tiny_c7_ultra_segment_acquire(void) {
    if (g_ultra_seg) {
        return g_ultra_seg;
    }

    tiny_c7_ultra_segment_t* seg =
        (tiny_c7_ultra_segment_t*)calloc(1, sizeof(tiny_c7_ultra_segment_t));
    if (!seg) {
        return NULL;
    }
    seg->seg_size = TINY_C7_ULTRA_SEG_SIZE;
    seg->page_size = TINY_C7_ULTRA_PAGE_SIZE;
    seg->num_pages = (uint32_t)(seg->seg_size / seg->page_size);

    seg->pages = (tiny_c7_ultra_page_meta_t*)calloc(seg->num_pages,
                                                    sizeof(tiny_c7_ultra_page_meta_t));
    if (!seg->pages) {
        free(seg);
        return NULL;
    }

    void* base = mmap(NULL, seg->seg_size, PROT_READ | PROT_WRITE,
                      MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
    if (base == MAP_FAILED) {
        int saved = errno;
        free(seg->pages);
        free(seg);
        (void)saved;
        return NULL;
    }

    seg->base = base;
    g_ultra_seg = seg;
    return seg;
}

void tiny_c7_ultra_segment_release(tiny_c7_ultra_segment_t* seg) {
    if (!seg) return;
    if (seg->base && seg->seg_size) {
        munmap(seg->base, seg->seg_size);
    }
    free(seg->pages);
    if (seg == g_ultra_seg) {
        g_ultra_seg = NULL;
    }
    free(seg);
}

tiny_c7_ultra_segment_t* tiny_c7_ultra_segment_from_ptr(void* p) {
    tiny_c7_ultra_segment_t* seg = g_ultra_seg;
    if (!seg || !seg->base || seg->seg_size == 0) return NULL;
    uintptr_t base = (uintptr_t)seg->base;
    uintptr_t addr = (uintptr_t)p;
    if (addr < base || addr >= base + seg->seg_size) {
        return NULL;
    }
    return seg;
}

tiny_c7_ultra_page_meta_t* tiny_c7_ultra_page_of(void* p,
                                                 tiny_c7_ultra_segment_t** out_seg,
                                                 uint32_t* out_page_idx) {
    tiny_c7_ultra_segment_t* seg = tiny_c7_ultra_segment_from_ptr(p);
    if (!seg) {
        return NULL;
    }
    uintptr_t base = (uintptr_t)seg->base;
    uintptr_t addr = (uintptr_t)p;
    size_t offset = (size_t)(addr - base);
    // Phase PERF-ULTRA-REFILL-OPT-1a: Replace division with bit shift for O(1) lookup
    uint32_t idx = (uint32_t)(offset >> TINY_C7_ULTRA_PAGE_SHIFT);
    if (idx >= seg->num_pages) {
        return NULL;
    }
    if (out_seg) {
        *out_seg = seg;
    }
    if (out_page_idx) {
        *out_page_idx = idx;
    }
    return &seg->pages[idx];
}