import { type Kysely, sql } from "kysely";
import type { DB } from "./types.ts";

/**
 * PG 缓存后端:移植 MP app/runtime/cache.py 的内存后端(MemoryBackend + _MemoryTLRUCache)与 @cached 装饰器语义,
 * 只把存储从进程内存换成 PG UNLOGGED 表 kv_cache(迁移 0042),三进程共享。行为对照(docs/porting/moviepilot-tmdb-cache.md):
 * - region 分区;set 时每个 key 独立 TTL(秒),ttl ≤ 0 = 删除该 key;未给 ttl 用后端缺省(DEFAULT_CACHE_TTL 365 天);
 * - maxsize 按 region 计条数,超出时先删已过期、再删最久未用(TLRU);get 命中刷新"最近使用";
 * - get 未命中 / 已过期返回 null;clear(region) 清一个区;items(region) 列出未过期条目;
 * - cached():skipNone / skipEmpty / skipIf 不写缓存,emptyTtl + emptyIf 空结果短 TTL,fresh 跳过读缓存。
 * 与 MP 的差异只在存储介质:值用 JSON(jsonb)而不是 pickle;过期行由定时任务 sweep() 物理删除。
 */

/** MP DEFAULT_CACHE_TTL(秒) */
export const DEFAULT_CACHE_TTL = 365 * 24 * 60 * 60;
/** MP DEFAULT_CACHE_SIZE */
export const DEFAULT_CACHE_SIZE = 1024;

// biome-ignore lint/suspicious/noExplicitAny: 测试会传入隔离 schema 的实例
type AnyDb = Kysely<DB> | Kysely<any>;

export interface SetOptions {
  /** 秒;缺省 DEFAULT_CACHE_TTL;≤ 0 删除该 key */
  ttl?: number;
  /** region 条数上限;缺省 DEFAULT_CACHE_SIZE */
  maxsize?: number;
}

export class PgCache {
  constructor(private readonly db: AnyDb) {}

  /** MemoryBackend.set */
  async set(region: string, key: string, value: unknown, opts: SetOptions = {}): Promise<void> {
    const ttl = opts.ttl ?? DEFAULT_CACHE_TTL;
    if (ttl <= 0) {
      await this.delete(region, key);
      return;
    }
    await sql`insert into kv_cache (region, key, value, expires_at, updated_at, accessed_at)
      values (${region}, ${key}, ${JSON.stringify(value ?? null)}::jsonb, now() + make_interval(secs => ${ttl}), now(), now())
      on conflict (region, key) do update set value = excluded.value, expires_at = excluded.expires_at,
        updated_at = excluded.updated_at, accessed_at = excluded.accessed_at`.execute(this.db);
    await this.evict(region, opts.maxsize ?? DEFAULT_CACHE_SIZE);
  }

  /** TLRUCache 写入时的淘汰:先删已过期,再按最近使用从旧到新删到 maxsize */
  private async evict(region: string, maxsize: number): Promise<void> {
    await sql`delete from kv_cache where region = ${region} and expires_at <= now()`.execute(this.db);
    await sql`delete from kv_cache where region = ${region} and key in (
        select key from kv_cache where region = ${region}
         order by accessed_at desc, updated_at desc offset ${Math.max(1, Math.floor(maxsize))})`.execute(this.db);
  }

  /** MemoryBackend.get:未命中 / 过期返回 null;命中刷新最近使用时间 */
  async get<T = unknown>(region: string, key: string): Promise<T | null> {
    const r = await sql<{ value: T }>`update kv_cache set accessed_at = now()
      where region = ${region} and key = ${key} and expires_at > now() returning value`.execute(this.db);
    return r.rows.length ? (r.rows[0]!.value as T) : null;
  }

  /** 续期:未过期的条目把 expires_at 推到 now + ttl(只延长不缩短);返回是否有行被续期 */
  async renew(region: string, key: string, ttl: number): Promise<boolean> {
    if (ttl <= 0) return false;
    const r = await sql`update kv_cache set expires_at = greatest(expires_at, now() + make_interval(secs => ${ttl}))
      where region = ${region} and key = ${key} and expires_at > now()`.execute(this.db);
    return Number(r.numAffectedRows ?? 0) > 0;
  }

  async exists(region: string, key: string): Promise<boolean> {
    const r =
      await sql`select 1 from kv_cache where region = ${region} and key = ${key} and expires_at > now()`.execute(
        this.db,
      );
    return r.rows.length > 0;
  }

  async delete(region: string, key: string): Promise<void> {
    await sql`delete from kv_cache where region = ${region} and key = ${key}`.execute(this.db);
  }

  /** 清一个区,返回删除行数 */
  async clear(region: string): Promise<number> {
    const r = await sql`delete from kv_cache where region = ${region}`.execute(this.db);
    return Number(r.numAffectedRows ?? 0);
  }

  /** MemoryBackend.items:未过期条目(附过期时间与大小,管理界面用),按 key 排序 */
  async items<T = unknown>(
    region: string,
    limit = 5000,
  ): Promise<{ key: string; value: T; expiresAt: Date; updatedAt: Date; bytes: number }[]> {
    const r = await sql<{ key: string; value: T; expires_at: Date; updated_at: Date; bytes: number }>`
      select key, value, expires_at, updated_at, pg_column_size(value)::int as bytes
        from kv_cache where region = ${region} and expires_at > now() order by key limit ${limit}`.execute(this.db);
    return r.rows.map((x) => ({
      key: x.key,
      value: x.value,
      expiresAt: x.expires_at,
      updatedAt: x.updated_at,
      bytes: Number(x.bytes),
    }));
  }

  /** 未过期条目数(len(region_cache)) */
  async count(region: string): Promise<number> {
    const r = await sql<{ n: number }>`select count(*)::int as n from kv_cache
      where region = ${region} and expires_at > now()`.execute(this.db);
    return Number(r.rows[0]?.n ?? 0);
  }

  /** 删除全部过期行(存储换成 PG 后需要的物理清理;cache.sweep 定时任务) */
  async sweep(): Promise<number> {
    const r = await sql`delete from kv_cache where expires_at <= now()`.execute(this.db);
    return Number(r.numAffectedRows ?? 0);
  }
}

/** MP @cached 的参数 */
export interface CachedOptions<T> {
  region: string;
  maxsize?: number;
  /** 秒 */
  ttl?: number;
  /** 缺省 true:结果为 null / undefined 不缓存 */
  skipNone?: boolean;
  /** 缺省 false:结果为假值(空数组 / 空对象 / 空串…)不缓存 */
  skipEmpty?: boolean;
  /** 返回真值时不缓存(如业务失败的响应) */
  skipIf?: (v: T) => boolean;
  /** 空结果的独立 TTL(秒) */
  emptyTtl?: number;
  /** 判断空结果;缺省按假值 */
  emptyIf?: (v: T) => boolean;
  /** MP fresh():true 时不读缓存(仍写) */
  fresh?: boolean;
}

const isFalsy = (v: unknown) =>
  !v || (Array.isArray(v) && v.length === 0) || (typeof v === "object" && Object.keys(v as object).length === 0);

/** MP @cached 的调用体:命中直接返回;否则执行 fn,按 should_cache / get_cache_ttl 写入 */
export async function cachedCall<T>(
  cache: PgCache,
  key: string,
  o: CachedOptions<T>,
  fn: () => Promise<T>,
): Promise<T> {
  const should = (v: T | null | undefined) => {
    if ((o.skipNone ?? true) && (v === null || v === undefined)) return false;
    if (o.skipEmpty && isFalsy(v)) return false;
    if (o.skipIf && v !== null && v !== undefined && o.skipIf(v)) return false;
    return true;
  };
  if (!o.fresh) {
    const hit = await cache.get<T>(o.region, key);
    if (should(hit)) return hit as T;
  }
  const result = await fn();
  if (!should(result)) return result;
  let ttl = o.ttl;
  if (o.emptyTtl !== undefined) {
    if (result === null || result === undefined) ttl = o.emptyTtl;
    else if (o.emptyIf) ttl = o.emptyIf(result) ? o.emptyTtl : o.ttl;
    else ttl = isFalsy(result) ? o.emptyTtl : o.ttl;
  }
  await cache.set(o.region, key, result, {
    ...(ttl !== undefined ? { ttl } : {}),
    ...(o.maxsize ? { maxsize: o.maxsize } : {}),
  });
  return result;
}

const caches = new WeakMap<object, PgCache>();

/** 同一个 Kysely 实例共用一个 PgCache */
export function pgCacheFor(db: AnyDb): PgCache {
  let c = caches.get(db);
  if (!c) {
    c = new PgCache(db);
    caches.set(db, c);
  }
  return c;
}