import type {
	Headers,
	HttpResponse,
	ResponseBuilder,
	StatusCode,
} from "../contracts/typegen/http/index.ts";
import {
	FORM_CONTENT_TYPE,
	HTML_CONTENT_TYPE,
	JSON_CONTENT_TYPE,
	TEXT_CONTENT_TYPE,
	mediaType,
} from "../contracts/typegen/http/index.ts";
import type { RequestContext } from "../contracts/typegen/http/request.ts";
import { toFormFields } from "./form.ts";
import { existsSync, statSync } from "node:fs";
import { readFile } from "node:fs/promises";
import { extname, resolve } from "node:path";

/** Creates an HTML response. */
export function html(
	body: string,
	status: StatusCode = 200,
): HttpResponse<string> {
	return { status, headers: { "content-type": HTML_CONTENT_TYPE }, body };
}

/** Creates a JSON response. */
export function json(
	body: unknown,
	status: StatusCode = 200,
): HttpResponse<unknown> {
	return { status, headers: { "content-type": JSON_CONTENT_TYPE }, body };
}

/** Creates a plain text response. */
export function text(
	body: string,
	status: StatusCode = 200,
): HttpResponse<string> {
	return { status, headers: { "content-type": TEXT_CONTENT_TYPE }, body };
}

/** Creates a redirect response. */
export function redirect(
	location: string,
	status: StatusCode = 302,
): HttpResponse<never> {
	return { status, headers: { location }, body: undefined as never };
}

/** Creates a `404` response. */
export function notFound(message = "Not Found"): HttpResponse<string> {
	return text(message, 404);
}

/** Creates a response builder bound to a status code and a set of headers. */
export function createResponseBuilder(
	initialStatus: StatusCode = 200,
	initialHeaders: Headers = {},
): ResponseBuilder {
	let status = initialStatus;
	const headers: Headers = { ...initialHeaders };
	const builder: ResponseBuilder = {
		html(body, code) {
			return {
				status: code ?? status,
				headers: { ...headers, "content-type": HTML_CONTENT_TYPE },
				body,
			};
		},
		json(body, code) {
			return {
				status: code ?? status,
				headers: { ...headers, "content-type": JSON_CONTENT_TYPE },
				body,
			};
		},
		text(body, code) {
			return {
				status: code ?? status,
				headers: { ...headers, "content-type": TEXT_CONTENT_TYPE },
				body,
			};
		},
		redirect(location, code) {
			return {
				status: code ?? 302,
				headers: { ...headers, location },
				body: undefined as never,
			};
		},
		status(code) {
			status = code as StatusCode;
			return builder;
		},
		header(name, value) {
			headers[name.toLowerCase()] = value;
			return builder;
		},
		send(body) {
			return { status, headers: { ...headers }, body };
		},
	};
	return builder;
}

/** Parses the body of a fetch `Request` according to its content type. */
export async function parseRequestBody(request: Request): Promise<unknown> {
	const type = mediaType(request.headers.get("content-type") ?? "");
	if (request.method === "GET" || request.method === "HEAD") return undefined;
	if (type === "application/json") {
		const raw = await request.text();
		if (!raw) return undefined;
		try {
			return JSON.parse(raw);
		} catch (cause) {
			throw new Error(`Invalid JSON body: ${(cause as Error).message}`, {
				cause,
			});
		}
	}
	if (type === FORM_CONTENT_TYPE) {
		const form = await request.formData();
		const result: Record<string, unknown> = {};
		for (const [key, value] of form.entries()) {
			result[key] = typeof value === "string" ? value : value.name;
		}
		return result;
	}
	if (type === "text/plain") {
		return await request.text();
	}
	if (
		type === "" ||
		type === "multipart/form-data" ||
		type === "application/octet-stream"
	) {
		const buffer = await request.arrayBuffer();
		return buffer.byteLength === 0 ? undefined : buffer;
	}
	return await request.text();
}

/** Parses a query string into a plain object. */
export function parseQuery(search: string): Record<string, string> {
	const params = new URLSearchParams(search);
	const result: Record<string, string> = {};
	for (const [key, value] of params.entries()) {
		result[key] = value;
	}
	return result;
}

/** Lower-cases every header name of a header record. */
export function normalizeHeaders(
	headers: Record<string, string>,
): Record<string, string> {
	const result: Record<string, string> = {};
	for (const [name, value] of Object.entries(headers)) {
		result[name.toLowerCase()] = value;
	}
	return result;
}

/** Content type of a file extension. */
export function contentTypeOf(extension: string): string {
	switch (extension) {
		case ".html":
		case ".htm":
			return "text/html; charset=utf-8";
		case ".css":
			return "text/css; charset=utf-8";
		case ".js":
		case ".mjs":
			return "text/javascript; charset=utf-8";
		case ".json":
			return "application/json; charset=utf-8";
		case ".svg":
			return "image/svg+xml";
		case ".png":
			return "image/png";
		case ".jpg":
		case ".jpeg":
			return "image/jpeg";
		case ".webp":
			return "image/webp";
		case ".ico":
			return "image/x-icon";
		case ".txt":
			return "text/plain; charset=utf-8";
		case ".woff2":
			return "font/woff2";
		default:
			return "application/octet-stream";
	}
}

/** Serves a file of a static root. */
export async function serveStaticFile(
	root: string,
	path: string,
): Promise<HttpResponse | undefined> {
	const relative = decodeURIComponent(path.split("?")[0] ?? "");
	const target = resolve(
		root,
		`.${relative.startsWith("/") ? relative : `/${relative}`}`,
	);
	if (!target.startsWith(resolve(root))) return undefined;
	if (!existsSync(target)) return undefined;
	if (!statSync(target).isFile()) return undefined;

	const file = await readFile(target);
	return {
		status: 200,
		headers: { "content-type": contentTypeOf(extname(target)) },
		body: new Uint8Array(file),
	};
}

/** Builds the request context handed to controllers. */
export function createRequestContext(request: Request): RequestContext {
	const url = new URL(request.url);
	const headers = normalizeHeaders(
		Object.fromEntries(request.headers.entries()),
	);
	const context: RequestContext = {
		method: request.method as RequestContext["method"],
		url: request.url,
		path: url.pathname,
		params: {},
		query: parseQuery(url.search),
		body: undefined,
		form: toFormFields(undefined),
		headers,
		signal: request.signal,
		locals: {},
		raw: request,
		respond: createResponseBuilder(),
	};
	return context;
}