rudeshark.net/packages/firefish-js/src/api.ts

import { Endpoints } from "./api.types";

const MK_API_ERROR = Symbol();

export type APIError = {
	id: string;
	code: string;
	message: string;
	kind: "client" | "server";
	info: Record<string, any>;
};

export function isAPIError(reason: any): reason is APIError {
	return reason[MK_API_ERROR] === true;
}

export type FetchLike = (
	input: string,
	init?: {
		method?: string;
		body?: string;
		credentials?: RequestCredentials;
		cache?: RequestCache;
	},
) => Promise<{
	status: number;
	json(): Promise<any>;
}>;

type IsNeverType<T> = [T] extends [never] ? true : false;

type StrictExtract<Union, Cond> = Cond extends Union ? Union : never;

type IsCaseMatched<
	E extends keyof Endpoints,
	P extends Endpoints[E]["req"],
	C extends number,
> = IsNeverType<
	StrictExtract<Endpoints[E]["res"]["$switch"]["$cases"][C], [P, any]>
> extends false
	? true
	: false;

type GetCaseResult<
	E extends keyof Endpoints,
	P extends Endpoints[E]["req"],
	C extends number,
> = StrictExtract<Endpoints[E]["res"]["$switch"]["$cases"][C], [P, any]>[1];

export class APIClient {
	public origin: string;
	public credential: string | null | undefined;
	public fetch: FetchLike;

	constructor(opts: {
		origin: APIClient["origin"];
		credential?: APIClient["credential"];
		fetch?: APIClient["fetch"] | null | undefined;
	}) {
		this.origin = opts.origin;
		this.credential = opts.credential;
		// ネイティブ関数をそのまま変数に代入して使おうとするとChromiumではIllegal invocationエラーが発生するため、
		// 環境で実装されているfetchを使う場合は無名関数でラップして使用する
		this.fetch = opts.fetch || ((...args) => fetch(...args));
	}

	public request<E extends keyof Endpoints, P extends Endpoints[E]["req"]>(
		endpoint: E,
		params: P = {} as P,
		credential?: string | null | undefined,
	): Promise<
		Endpoints[E]["res"] extends {
			$switch: { $cases: [any, any][]; $default: any };
		}
			? IsCaseMatched<E, P, 0> extends true
				? GetCaseResult<E, P, 0>
				: IsCaseMatched<E, P, 1> extends true
				? GetCaseResult<E, P, 1>
				: IsCaseMatched<E, P, 2> extends true
				? GetCaseResult<E, P, 2>
				: IsCaseMatched<E, P, 3> extends true
				? GetCaseResult<E, P, 3>
				: IsCaseMatched<E, P, 4> extends true
				? GetCaseResult<E, P, 4>
				: IsCaseMatched<E, P, 5> extends true
				? GetCaseResult<E, P, 5>
				: IsCaseMatched<E, P, 6> extends true
				? GetCaseResult<E, P, 6>
				: IsCaseMatched<E, P, 7> extends true
				? GetCaseResult<E, P, 7>
				: IsCaseMatched<E, P, 8> extends true
				? GetCaseResult<E, P, 8>
				: IsCaseMatched<E, P, 9> extends true
				? GetCaseResult<E, P, 9>
				: Endpoints[E]["res"]["$switch"]["$default"]
			: Endpoints[E]["res"]
	> {
		const promise = new Promise((resolve, reject) => {
			this.fetch(`${this.origin}/api/${endpoint}`, {
				method: "POST",
				body: JSON.stringify({
					...params,
					i: credential !== undefined ? credential : this.credential,
				}),
				credentials: "omit",
				cache: "no-cache",
			})
				.then(async (res) => {
					const body = res.status === 204 ? null : await res.json();

					if (res.status === 200) {
						resolve(body);
					} else if (res.status === 204) {
						resolve(null);
					} else {
						reject({
							[MK_API_ERROR]: true,
							...body.error,
						});
					}
				})
				.catch(reject);
		});

		return promise as any;
	}
}