import type { ApiResponse, DiscordError, DiscordRestClient } from "./types";

export interface ClientOptions {
	token: string;
	baseUrl?: string;
	fetch?: typeof fetch;
}

export function RESTClient(options: ClientOptions): DiscordRestClient {
	const baseUrl = options.baseUrl || "https://discord.com/api/v10";

	const customFetch = options.fetch ?? globalThis.fetch;

	const executeRequest = async (
		segments: string[],
		method: string,
		body?: unknown,
		query?: Record<string, unknown>,
		headers?: Record<string, string>,
	): Promise<ApiResponse<unknown>> => {
		let url = `${baseUrl}/${segments.join("/")}`;

		if (query) {
			const searchParams = new URLSearchParams();
			for (const [key, val] of Object.entries(query)) {
				if (val !== undefined && val !== null) {
					if (Array.isArray(val)) {
						for (const item of val) {
							searchParams.append(key, String(item));
						}
					} else {
						searchParams.append(key, String(val));
					}
				}
			}
			const queryString = searchParams.toString();
			if (queryString) url += `?${queryString}`;
		}

		try {
			const isFormData = typeof FormData !== "undefined" && body instanceof FormData;

			const reqHeaders: Record<string, string> = {
				Authorization: `Bot ${options.token}`,
				...headers,
			};

			if (!isFormData && !reqHeaders["Content-Type"] && body !== undefined)
				reqHeaders["Content-Type"] = "application/json";

			const res = await customFetch(url, {
				method,
				headers: reqHeaders,
				body: isFormData
					? (body as BodyInit)
					: body !== undefined
						? JSON.stringify(body)
						: undefined,
			});

			const isOk = res.ok;
			const status = res.status;

			let data: unknown = null;

			if (status !== 204) data = (await res.json().catch(() => null)) as unknown;
			if (isOk) return { ok: true, data, status };

			const errorData: DiscordError =
				data && typeof data === "object" && "message" in data
					? (data as DiscordError)
					: { message: "Unknown API Error" };

			return { ok: false, data: errorData, status };
		} catch (error) {
			const message = error instanceof Error ? error.message : "Network Error";
			return {
				ok: false,
				data: { message },
				status: 0,
			};
		}
	};

	const createProxy = (pathSegments: string[] = []): unknown => {
		const dummyTarget = () => {};

		const handler: ProxyHandler<typeof dummyTarget> = {
			apply(_target, _thisArg, argList) {
				const nextSegments = [...pathSegments, ...argList.map(String)];
				return createProxy(nextSegments);
			},

			get(_target, prop) {
				const propStr = String(prop);

				if (prop === "then") {
					const promise = executeRequest(pathSegments, "GET");
					return promise.then.bind(promise);
				}

				const lowercaseProp = propStr.toLowerCase();
				const methodMap: Record<string, string> = {
					create: "POST",
					post: "POST",
					delete: "DELETE",
					update: "PATCH",
					patch: "PATCH",
					put: "PUT",
					get: "GET",
				};

				if (lowercaseProp in methodMap) {
					const httpMethod = methodMap[lowercaseProp];
					if (!httpMethod) throw new Error(`unsupported HTTP method: ${lowercaseProp}`);

					return async (
						bodyOrOptions?: unknown,
						methodOptions?: { query?: Record<string, unknown>; headers?: Record<string, string> },
					) => {
						let body: unknown;
						let query: Record<string, unknown> | undefined;
						let headers: Record<string, string> | undefined;

						if (httpMethod === "GET" || httpMethod === "DELETE") {
							const opts = bodyOrOptions as
								| { query?: Record<string, unknown>; headers?: Record<string, string> }
								| undefined;
							query = opts?.query;
							headers = opts?.headers;
						} else {
							body = bodyOrOptions;
							query = methodOptions?.query;
							headers = methodOptions?.headers;
						}

						return executeRequest(pathSegments, httpMethod, body, query, headers);
					};
				}

				const nextSegment = prop === "me" ? "@me" : propStr;
				return createProxy([...pathSegments, nextSegment]);
			},
		};

		return new Proxy(dummyTarget, handler);
	};

	return createProxy([]) as unknown as DiscordRestClient;
}