import { UnsupportedMediaTypeError } from '@/errors/response-errors/unsupported-media-type.error';

const JSON_MEDIA_TYPE = 'application/json';

/**
 * The media type, plus the string the legacy validator reports: lower-cased, parameters sorted by
 * name, `boundary` left out.
 */
function readMediaType(header: string): { mediaType: string; reported: string } {
	const [rawMediaType, ...parameterParts] = header.split(';');
	const mediaType = rawMediaType.trim().toLowerCase();
	const parameters = new Map<string, string>();

	for (const part of parameterParts) {
		const separator = part.indexOf('=');
		if (separator === -1) continue;

		const name = part.slice(0, separator).trim().toLowerCase();
		if (name === 'boundary') continue;

		const value = part.slice(separator + 1);
		parameters.set(name, name === 'charset' ? value.toLowerCase() : value);
	}

	const reported = [...parameters.entries()]
		.sort(([a], [b]) => (a < b ? -1 : 1))
		.reduce((out, [name, value]) => `${out}; ${name}=${value}`, mediaType);

	return { mediaType, reported };
}

/**
 * The legacy validator accepted only JSON. It reported a header that names no media type — absent,
 * empty, or whitespace — as the literal `undefined`, and rejected it only when the body was
 * required. Migrated routes keep both behaviours and the messages that came with them.
 */
export function assertJsonContentType(header: string | undefined, bodyRequired: boolean): void {
	const { mediaType, reported } = readMediaType(header ?? '');

	if (mediaType === '') {
		if (bodyRequired) throw new UnsupportedMediaTypeError('unsupported media type undefined');
		return;
	}

	if (mediaType !== JSON_MEDIA_TYPE) {
		throw new UnsupportedMediaTypeError(`unsupported media type ${reported}`);
	}
}