import Redis from 'ioredis';
import { bindThis } from '@/decorators.js';

// redis通すとDateのインスタンスはstringに変換されるので
type Serialized<T> = {
	[K in keyof T]:
		T[K] extends Date
			? string
			: T[K] extends (Date | null)
				? (string | null)
				: T[K] extends Record<string, any>
					? Serialized<T[K]>
					: T[K];
};

export class RedisKVCache<T> {
	private redisClient: Redis.Redis;
	private name: string;
	private lifetime: number;
	private memoryCache: MemoryKVCache<T>;

	constructor(redisClient: RedisKVCache<never>['redisClient'], name: RedisKVCache<never>['name'], lifetime: RedisKVCache<never>['lifetime'], memoryCacheLifetime: number) {
		this.redisClient = redisClient;
		this.name = name;
		this.lifetime = lifetime;
		this.memoryCache = new MemoryKVCache(memoryCacheLifetime);
	}

	@bindThis
	public async set(key: string, value: T): Promise<void> {
		this.memoryCache.set(key, value);
		if (this.lifetime === Infinity) {
			await this.redisClient.set(
				`kvcache:${this.name}:${key}`,
				JSON.stringify(value),
			);
		} else {
			await this.redisClient.set(
				`kvcache:${this.name}:${key}`,
				JSON.stringify(value),
				'ex', Math.round(this.lifetime / 1000),
			);
		}
	}

	@bindThis
	public async get(key: string): Promise<Serialized<T> | T | undefined> {
		const memoryCached = this.memoryCache.get(key);
		if (memoryCached !== undefined) return memoryCached;

		const cached = await this.redisClient.get(`kvcache:${this.name}:${key}`);
		if (cached == null) return undefined;
		return JSON.parse(cached);
	}

	@bindThis
	public async delete(key: string): Promise<void> {
		this.memoryCache.delete(key);
		await this.redisClient.del(`kvcache:${this.name}:${key}`);
	}

	/**
 * キャッシュがあればそれを返し、無ければfetcherを呼び出して結果をキャッシュ&返します
 * optional: キャッシュが存在してもvalidatorでfalseを返すとキャッシュ無効扱いにします
 */
	@bindThis
	public async fetch(key: string, fetcher: () => Promise<T>, validator?: (cachedValue: Serialized<T> | T) => boolean): Promise<Serialized<T> | T> {
		const cachedValue = await this.get(key);
		if (cachedValue !== undefined) {
			if (validator) {
				if (validator(cachedValue)) {
					// Cache HIT
					return cachedValue;
				}
			} else {
				// Cache HIT
				return cachedValue;
			}
		}

		// Cache MISS
		const value = await fetcher();
		this.set(key, value);
		return value;
	}
}

// TODO: メモリ節約のためあまり参照されないキーを定期的に削除できるようにする？

export class MemoryKVCache<T> {
	public cache: Map<string, { date: number; value: T; }>;
	private lifetime: number;

	constructor(lifetime: MemoryKVCache<never>['lifetime']) {
		this.cache = new Map();
		this.lifetime = lifetime;
	}

	@bindThis
	public set(key: string, value: T): void {
		this.cache.set(key, {
			date: Date.now(),
			value,
		});
	}

	@bindThis
	public get(key: string): T | undefined {
		const cached = this.cache.get(key);
		if (cached == null) return undefined;
		if ((Date.now() - cached.date) > this.lifetime) {
			this.cache.delete(key);
			return undefined;
		}
		return cached.value;
	}

	@bindThis
	public delete(key: string) {
		this.cache.delete(key);
	}

	/**
	 * キャッシュがあればそれを返し、無ければfetcherを呼び出して結果をキャッシュ&返します
	 * optional: キャッシュが存在してもvalidatorでfalseを返すとキャッシュ無効扱いにします
	 */
	@bindThis
	public async fetch(key: string, fetcher: () => Promise<T>, validator?: (cachedValue: T) => boolean): Promise<T> {
		const cachedValue = this.get(key);
		if (cachedValue !== undefined) {
			if (validator) {
				if (validator(cachedValue)) {
					// Cache HIT
					return cachedValue;
				}
			} else {
				// Cache HIT
				return cachedValue;
			}
		}

		// Cache MISS
		const value = await fetcher();
		this.set(key, value);
		return value;
	}

	/**
	 * キャッシュがあればそれを返し、無ければfetcherを呼び出して結果をキャッシュ&返します
	 * optional: キャッシュが存在してもvalidatorでfalseを返すとキャッシュ無効扱いにします
	 */
	@bindThis
	public async fetchMaybe(key: string, fetcher: () => Promise<T | undefined>, validator?: (cachedValue: T) => boolean): Promise<T | undefined> {
		const cachedValue = this.get(key);
		if (cachedValue !== undefined) {
			if (validator) {
				if (validator(cachedValue)) {
					// Cache HIT
					return cachedValue;
				}
			} else {
				// Cache HIT
				return cachedValue;
			}
		}

		// Cache MISS
		const value = await fetcher();
		if (value !== undefined) {
			this.set(key, value);
		}
		return value;
	}
}

export class MemoryCache<T> {
	private cachedAt: number | null = null;
	private value: T | undefined;
	private lifetime: number;

	constructor(lifetime: MemoryCache<never>['lifetime']) {
		this.lifetime = lifetime;
	}

	@bindThis
	public set(value: T): void {
		this.cachedAt = Date.now();
		this.value = value;
	}

	@bindThis
	public get(): T | undefined {
		if (this.cachedAt == null) return undefined;
		if ((Date.now() - this.cachedAt) > this.lifetime) {
			this.value = undefined;
			this.cachedAt = null;
			return undefined;
		}
		return this.value;
	}

	@bindThis
	public delete() {
		this.value = undefined;
		this.cachedAt = null;
	}

	/**
	 * キャッシュがあればそれを返し、無ければfetcherを呼び出して結果をキャッシュ&返します
	 * optional: キャッシュが存在してもvalidatorでfalseを返すとキャッシュ無効扱いにします
	 */
	@bindThis
	public async fetch(fetcher: () => Promise<T>, validator?: (cachedValue: T) => boolean): Promise<T> {
		const cachedValue = this.get();
		if (cachedValue !== undefined) {
			if (validator) {
				if (validator(cachedValue)) {
					// Cache HIT
					return cachedValue;
				}
			} else {
				// Cache HIT
				return cachedValue;
			}
		}

		// Cache MISS
		const value = await fetcher();
		this.set(value);
		return value;
	}

	/**
	 * キャッシュがあればそれを返し、無ければfetcherを呼び出して結果をキャッシュ&返します
	 * optional: キャッシュが存在してもvalidatorでfalseを返すとキャッシュ無効扱いにします
	 */
	@bindThis
	public async fetchMaybe(fetcher: () => Promise<T | undefined>, validator?: (cachedValue: T) => boolean): Promise<T | undefined> {
		const cachedValue = this.get();
		if (cachedValue !== undefined) {
			if (validator) {
				if (validator(cachedValue)) {
					// Cache HIT
					return cachedValue;
				}
			} else {
				// Cache HIT
				return cachedValue;
			}
		}

		// Cache MISS
		const value = await fetcher();
		if (value !== undefined) {
			this.set(value);
		}
		return value;
	}
}