import { ref, Ref } from "vue";

// 分页器的可选参数
export interface PagerOptions {
	current?: number;
	size?: number;
	total?: number;
}

// Loader 的参数
export interface LoaderParams {
	current: number;
	size: number;
}

// Loader 的返回值
export interface LoaderRes<T> {
	current?: number;
	size?: number;
	total: number;
	records: Array<T>;
}

// Loader
export type LoaderTyp<T> = (params: LoaderParams) => Promise<LoaderRes<T>>;

const PAGER_DEF_VALUE = () => ({
	PAGE_INDEX: 0,
	PAGE_SIZE: 10,
	TOTAL: -1,
	RECORDS: []
});

export enum PagerState {
	// 分页器处于初始状态
	INIT,
	// 闲置
	IDLE,
	// 加载数据中
	LOADING,
	// 没有更多数据
	NO_MORE,
	// 网络异常
	NETWORK_ERR
}

// 分页器
export class Pager<T> {
	current = PAGER_DEF_VALUE().PAGE_INDEX;

	size = PAGER_DEF_VALUE().PAGE_SIZE;

	total = PAGER_DEF_VALUE().TOTAL;

	records: Ref<Array<T>> = ref(PAGER_DEF_VALUE().RECORDS);

	loader: LoaderTyp<T>;

	// 状态
	state: Ref<PagerState> = ref(PagerState.INIT);

	constructor(loader: LoaderTyp<T>, options?: PagerOptions) {
		this.loader = loader;

		const pageDef = PAGER_DEF_VALUE();
		this.current = options?.current || pageDef.PAGE_INDEX;
		this.size = options?.size || pageDef.PAGE_SIZE;
		this.total = options?.total || pageDef.TOTAL;
		this.records.value = pageDef.RECORDS;
	}

	// 是否还存在数据
	isNoMore = () => this.total > 0 && this.total <= this.current * this.size;

	// 无数据
	// isEmpty = this.state.value === PagerState.IDLE && this.records.value.length <= 0

	// 获取记录列表
	#_getNextRecodes = async (): Promise<Array<T>> => {
		const res = await this.loader({ current: this.current + 1, size: this.size });
		this.current += 1;
		this.total = res.total || 0;
		return res.records || [];
	};

	getNextRecodes = async (): Promise<Array<T>> => {
		if (this.state.value === PagerState.LOADING) {
			return [];
		}

		if (this.isNoMore()) {
			this.state.value = PagerState.NO_MORE;
			return [];
		}

		this.state.value = PagerState.LOADING;
		try {
			const resp: Array<T> = await this.#_getNextRecodes();
			return resp;
		} finally {
			this.state.value = PagerState.IDLE;
		}
	};

	// 加载下一页数据
	nextPage = async () => {
		const records = await this.getNextRecodes();
		this.records.value.push(...records);
		return this.records;
	};

	// 加载更多
	loadMore = this.nextPage;

	// 重置数据
	reInit = (options?: PagerOptions) => {
		const pageDef = PAGER_DEF_VALUE();
		this.current = options?.current || pageDef.PAGE_INDEX;
		this.total = options?.total || pageDef.TOTAL;

		this.state.value = PagerState.INIT;
	};

	// 重新加载
	reload = async () => {
		if (this.state.value === PagerState.LOADING || this.state.value === PagerState.NO_MORE) {
			return;
		}

		this.reInit();
		const records = await this.getNextRecodes();
		this.records.value = records;
		return this.records;
	};

	// 刷新
	refresh = this.reload;

	async refreshWithChangeLoader(loader?: LoaderTyp<T>) {
		loader && (this.loader = loader);
		await this.reload();
	}
}

export default Pager;