import { NextResponse } from "next/server";

/**
 * JSON response helper for the public REST API. Serialises BigInt (DB ids)
 * to strings — JSON.stringify throws on BigInt otherwise — and sets CORS to
 * APP_URL so the game client / external integrations can read it.
 */
const CORS_ORIGIN = process.env.APP_URL ?? "http://localhost:3000";

export function apiJson(data: unknown, init?: ResponseInit): NextResponse {
	const body = JSON.stringify(data, (_k, v) =>
		typeof v === "bigint" ? v.toString() : v,
	);
	return new NextResponse(body, {
		status: init?.status ?? 200,
		headers: {
			"content-type": "application/json; charset=utf-8",
			"access-control-allow-origin": CORS_ORIGIN,
			"cache-control": "no-store",
			...(init?.headers ?? {}),
		},
	});
}

/** Standard error envelope. */
export function apiError(message: string, status = 400): NextResponse {
	return apiJson({ error: message }, { status });
}

/** Safe response for temporary infrastructure failures. */
export function apiUnavailable(
	message = "Service temporarily unavailable",
): NextResponse {
	return apiError(message, 503);
}

/** Parse an unsigned, non-zero database identifier without Number precision loss. */
export function positiveBigInt(raw: string | null): bigint | null {
	if (!raw || !/^\d+$/.test(raw)) return null;
	const value = BigInt(raw);
	return value > 0n ? value : null;
}

/** Clamp a ?page / ?perPage pair from search params. */
export function pagination(
	searchParams: URLSearchParams,
	defaultPer = 20,
	maxPer = 100,
) {
	const requestedPage = positiveInteger(searchParams.get("page"), 1);
	const requestedPerPage = positiveInteger(
		searchParams.get("perPage"),
		defaultPer,
	);
	const perPage = Math.min(maxPer, requestedPerPage);
	const maxSafePage = Math.floor(Number.MAX_SAFE_INTEGER / perPage) + 1;
	const page = Math.min(requestedPage, maxSafePage);
	return { page, perPage, skip: (page - 1) * perPage, take: perPage };
}

function positiveInteger(raw: string | null, fallback: number): number {
	if (!raw || !/^\d+$/.test(raw)) return fallback;
	const value = Number(raw);
	return Number.isSafeInteger(value) && value > 0 ? value : fallback;
}