/* logic/reader/page_cache.c — 解压页磁盘缓存实现，见 page_cache.h 的纪律说明。 */
#include "logic/reader/page_cache.h"

#include <ctype.h>
#include <dirent.h>
#include <errno.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <sys/stat.h>
#include <unistd.h>

typedef struct cache_entry {
    char               path[MR_CACHE_FILE_MAX];
    long long          size;
    unsigned long long used;      /* LRU 计数（越大越新） */
} cache_entry;

static pthread_mutex_t g_lock = PTHREAD_MUTEX_INITIALIZER;
static char            g_dir[MR_CACHE_DIR_MAX];
static int             g_ready;
static cache_entry     g_idx[MR_CACHE_MAX_PAGES];
static int             g_n;
static long long       g_bytes;
static unsigned long long g_tick;

/* ============================================================ */
/* 目录推导                                                      */
/* ============================================================ */
int mr_cache_dir_from_data(const char *data_dir, char *out, int outsz)
{
    if (!data_dir || !data_dir[0] || !out || outsz <= 0) return -1;

    size_t n = strlen(data_dir);
    while (n > 1 && data_dir[n - 1] == '/') n--;
    if (n >= (size_t)outsz) return -1;
    memcpy(out, data_dir, n);
    out[n] = '\0';

    /* 末段是 "data" 时换成 "cache"（数据目录 → 同级缓存目录）。 */
    char *slash = strrchr(out, '/');
    if (slash && strcmp(slash + 1, "data") == 0) *slash = '\0';

    n = strlen(out);
    if (n == 0) {
        if (outsz < 7) return -1;
        memcpy(out, "/cache", 7);
        return 0;
    }
    int w = snprintf(out + n, (size_t)(outsz - (int)n), "/cache");
    if (w <= 0 || w >= outsz - (int)n) {
        out[0] = '\0';
        return -1;
    }
    return 0;
}

int mr_cache_is_page_name(const char *name)
{
    return name && strncmp(name, MR_CACHE_PREFIX, strlen(MR_CACHE_PREFIX)) == 0;
}

const char *mr_cache_dir(void)
{
    return g_ready ? g_dir : "";
}

int mr_cache_ready(void)
{
    return g_ready;
}

/* ============================================================ */
/* 索引（调用方持锁）                                            */
/* ============================================================ */
static int idx_find_locked(const char *path)
{
    for (int i = 0; i < g_n; i++)
        if (strcmp(g_idx[i].path, path) == 0) return i;
    return -1;
}

static void idx_remove_locked(int i)
{
    if (i < 0 || i >= g_n) return;
    g_bytes -= g_idx[i].size;
    g_idx[i] = g_idx[g_n - 1];
    g_n--;
}

static void idx_evict_locked(void)
{
    if (g_n <= 0) return;
    int oldest = 0;
    for (int i = 1; i < g_n; i++)
        if (g_idx[i].used < g_idx[oldest].used) oldest = i;
    unlink(g_idx[oldest].path);
    idx_remove_locked(oldest);
}

/* 腾出 len 字节：页数或字节先到上限就淘汰最旧。单条 len 本身超过
 * MR_CACHE_MAX_BYTES 时会清空其它条目、让这一条独占（文档化的一次性溢出，
 * 上限由页源单页 64MiB 约束）——大页仍可读，不因预算拒绝落缓存。 */
static void make_room_locked(long long len)
{
    while (g_n > 0 && (g_n >= MR_CACHE_MAX_PAGES ||
                       g_bytes + len > MR_CACHE_MAX_BYTES))
        idx_evict_locked();
}

static void idx_add_locked(const char *path, long long size)
{
    if (g_n >= MR_CACHE_MAX_PAGES) return;
    cache_entry *e = &g_idx[g_n++];
    snprintf(e->path, sizeof e->path, "%s", path);
    e->size = size;
    g_tick++;
    e->used = g_tick;
    g_bytes += size;
}

/* 上一进程遗留的解压页：索引在内存里，磁盘上的 mrpage_* 全是孤儿。 */
static void clean_orphans_locked(void)
{
    DIR *d = opendir(g_dir);
    if (!d) return;
    size_t plen = strlen(MR_CACHE_PREFIX);
    struct dirent *de;
    while ((de = readdir(d)) != NULL) {
        if (strncmp(de->d_name, MR_CACHE_PREFIX, plen) != 0) continue;
        char full[MR_CACHE_FILE_MAX];
        int w = snprintf(full, sizeof full, "%s/%s", g_dir, de->d_name);
        if (w > 0 && w < (int)sizeof full) unlink(full);
    }
    closedir(d);
}

/* ============================================================ */
/* 生命周期                                                      */
/* ============================================================ */
/* 逐级建目录（数据目录的父级可能还不存在；只建到缓存目录为止）。 */
static int mkdir_p(const char *path)
{
    char tmp[MR_CACHE_DIR_MAX];
    size_t n = strlen(path);
    if (n == 0 || n >= sizeof tmp) return -1;
    memcpy(tmp, path, n + 1);
    for (size_t i = 1; i <= n; i++) {
        if (tmp[i] != '/' && tmp[i] != '\0') continue;
        char ch = tmp[i];
        tmp[i] = '\0';
        if (mkdir(tmp, 0755) != 0 && errno != EEXIST) {
            struct stat st;
            if (stat(tmp, &st) != 0 || !S_ISDIR(st.st_mode)) return -1;
        }
        tmp[i] = ch;
    }
    return 0;
}

int mr_cache_init(const char *data_dir)
{
    char dir[MR_CACHE_DIR_MAX];
    if (mr_cache_dir_from_data(data_dir, dir, (int)sizeof dir) != 0) return -1;

    pthread_mutex_lock(&g_lock);
    if (g_ready && strcmp(g_dir, dir) == 0) {
        pthread_mutex_unlock(&g_lock);
        return 0;
    }

    g_ready = 0;
    g_n = 0;
    g_bytes = 0;
    g_dir[0] = '\0';

    if (mkdir_p(dir) != 0) {
        pthread_mutex_unlock(&g_lock);
        return -1;
    }
    struct stat st;
    if (stat(dir, &st) != 0 || !S_ISDIR(st.st_mode)) {
        pthread_mutex_unlock(&g_lock);
        return -1;
    }
    snprintf(g_dir, sizeof g_dir, "%s", dir);
    clean_orphans_locked();
    g_tick = 0;
    g_ready = 1;
    pthread_mutex_unlock(&g_lock);
    return 0;
}

void mr_cache_shutdown(void)
{
    pthread_mutex_lock(&g_lock);
    g_ready = 0;
    g_n = 0;
    g_bytes = 0;
    g_tick = 0;
    g_dir[0] = '\0';
    pthread_mutex_unlock(&g_lock);
}

/* ============================================================ */
/* 键 / 命中 / 写入                                              */
/* ============================================================ */
static unsigned long long hash_bytes(unsigned long long h, const void *p, size_t n)
{
    const unsigned char *b = (const unsigned char *)p;
    for (size_t i = 0; i < n; i++) {
        h ^= (unsigned long long)b[i];
        h *= 1099511628211ULL;
    }
    return h;
}

static unsigned long long cache_hash(const char *archive, long long mtime,
                                     long long size, const char *entry, int page)
{
    char num[64];
    unsigned long long h = 1469598103934665603ULL;
    h = hash_bytes(h, archive, strlen(archive) + 1);
    int n = snprintf(num, sizeof num, "%lld", mtime);
    h = hash_bytes(h, num, (size_t)n + 1);
    n = snprintf(num, sizeof num, "%lld", size);
    h = hash_bytes(h, num, (size_t)n + 1);
    h = hash_bytes(h, entry, strlen(entry) + 1);
    n = snprintf(num, sizeof num, "%d", page);
    h = hash_bytes(h, num, (size_t)n + 1);
    return h;
}

/* 保留图片扩展名：解码入口按 .jpg/.jpeg 区分「解码期缩解」路径。 */
static void entry_ext(const char *entry, char *out, int outsz)
{
    const char *dot = entry ? strrchr(entry, '.') : NULL;
    const char *ext = dot ? dot + 1 : "";
    if ((strcasecmp(ext, "jpg") == 0) || (strcasecmp(ext, "jpeg") == 0) ||
        (strcasecmp(ext, "png") == 0) || (strcasecmp(ext, "bmp") == 0)) {
        int i = 0;
        for (; ext[i] && i < outsz - 1; i++) out[i] = (char)tolower((unsigned char)ext[i]);
        out[i] = '\0';
        return;
    }
    snprintf(out, (size_t)outsz, "img");
}

int mr_cache_path(const char *archive, long long mtime, long long size,
                  const char *entry, int page_index, char *out, int outsz)
{
    if (!out || outsz <= 0) return -1;
    out[0] = '\0';
    if (!archive || !archive[0] || !entry || !entry[0]) return -1;

    char ext[8];
    entry_ext(entry, ext, (int)sizeof ext);

    pthread_mutex_lock(&g_lock);
    if (!g_ready) {
        pthread_mutex_unlock(&g_lock);
        return -1;
    }
    unsigned long long h = cache_hash(archive, mtime, size, entry, page_index);
    int n = snprintf(out, (size_t)outsz, "%s/%s%016llx.%s", g_dir, MR_CACHE_PREFIX, h, ext);
    pthread_mutex_unlock(&g_lock);
    if (n <= 0 || n >= outsz) {
        out[0] = '\0';
        return -1;
    }
    return 0;
}

int mr_cache_touch(const char *path)
{
    if (!path || !path[0]) return 0;

    pthread_mutex_lock(&g_lock);
    if (!g_ready) {
        pthread_mutex_unlock(&g_lock);
        return 0;
    }
    int i = idx_find_locked(path);
    /* 命中也要 stat 校验（P2-1 纵深防御）：外部清理、掉电残留、或别的 LRU 误删
     * 都会让索引指向不存在的文件；假命中会让页源返回死路径且永不自愈。缺失或
     * 尺寸不符就从索引移除、按未命中处理，让调用方重新解压。 */
    struct stat st;
    int exists = stat(path, &st) == 0 && S_ISREG(st.st_mode) && st.st_size > 0;
    if (i >= 0) {
        if (!exists || (long long)st.st_size != g_idx[i].size) {
            idx_remove_locked(i);
            pthread_mutex_unlock(&g_lock);
            return 0;
        }
        g_tick++;
        g_idx[i].used = g_tick;
        pthread_mutex_unlock(&g_lock);
        return 1;
    }
    /* 索引里没有（外部写入/索引满）：磁盘上有就算命中，能装进索引就装。 */
    if (exists && g_n < MR_CACHE_MAX_PAGES && strlen(path) < MR_CACHE_FILE_MAX)
        idx_add_locked(path, (long long)st.st_size);
    pthread_mutex_unlock(&g_lock);
    return exists ? 1 : 0;
}

int mr_cache_store(const char *path, const void *data, size_t len)
{
    if (!path || !path[0] || !data || len == 0) return 0;
    if (strlen(path) >= MR_CACHE_FILE_MAX) return 0;

    char tmp[MR_CACHE_FILE_MAX + 8];
    int w = snprintf(tmp, sizeof tmp, "%s.part", path);
    if (w <= 0 || w >= (int)sizeof tmp) return 0;

    pthread_mutex_lock(&g_lock);
    if (!g_ready) {
        pthread_mutex_unlock(&g_lock);
        return 0;
    }
    int i = idx_find_locked(path);
    if (i >= 0) idx_remove_locked(i);
    make_room_locked((long long)len);
    pthread_mutex_unlock(&g_lock);      /* 写盘不持锁：大页不阻塞并发读者 */

    FILE *f = fopen(tmp, "wb");
    int ok = f && fwrite(data, 1, len, f) == len;
    if (f && fclose(f) != 0) ok = 0;
    if (!ok) {
        unlink(tmp);
        return 0;
    }
    if (rename(tmp, path) != 0) {
        unlink(tmp);
        return 0;
    }

    pthread_mutex_lock(&g_lock);
    if (g_ready) {
        i = idx_find_locked(path);
        if (i >= 0) idx_remove_locked(i);
        make_room_locked((long long)len);   /* 写盘期间可能被别的线程填满 */
        idx_add_locked(path, (long long)len);
        g_tick++;
    }
    pthread_mutex_unlock(&g_lock);
    return 1;
}

int mr_cache_count(void)
{
    pthread_mutex_lock(&g_lock);
    int n = g_n;
    pthread_mutex_unlock(&g_lock);
    return n;
}

long long mr_cache_bytes(void)
{
    pthread_mutex_lock(&g_lock);
    long long b = g_bytes;
    pthread_mutex_unlock(&g_lock);
    return b;
}