/** @type {Set<string>} */

const VALID_CACHE_CONTROL_DIRECTIVES = new Set([

'max-age',

'public',

'private',

'no-cache',

'no-store',

'must-revalidate',

'proxy-revalidate',

's-maxage',

'immutable',

'stale-while-revalidate',

'stale-if-error',

'no-transform',

'only-if-cached',

'max-stale',

'min-fresh'

]);

const CONTENT_TYPE_PATTERN =

/^(application|audio|example|font|haptics|image|message|model|multipart|text|video|x-[a-z]+)\/[-+.\w]+$/i;

/** @type {Record<string, (value: string) => void>} */

const HEADER_VALIDATORS = {

'cache-control': (value) => {

const error_suffix = `(While parsing "${value}".)`;

const parts = value.split(',').map((part) => part.trim());

if (parts.some((part) => !part)) {

throw new Error(`\`cache-control\` header contains empty directives. ${error_suffix}`);

}

const directives = parts.map((part) => part.split('=')[0].toLowerCase());

const invalid = directives.find((directive) => !VALID_CACHE_CONTROL_DIRECTIVES.has(directive));

if (invalid) {

throw new Error(

`Invalid cache-control directive "${invalid}". Did you mean one of: ${[...VALID_CACHE_CONTROL_DIRECTIVES].join(', ')}? ${error_suffix}`

);

}

},

'content-type': (value) => {

const type = value.split(';')[0].trim();

const error_suffix = `(While parsing "${value}".)`;

if (!CONTENT_TYPE_PATTERN.test(type)) {

throw new Error(`Invalid content-type value "${type}". ${error_suffix}`);

}

}

};

/**

* @param {Record<string, string>} headers

*/

export function validateHeaders(headers) {

}