// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
// This module is browser compatible.

import { parseMediaType } from "./parse_media_type.ts";
import { type DBEntry } from "./_util.ts";
import { db, type KeyOfDb } from "./_db.ts";

/**
 * Given a media type or header value, identify the encoding charset. If the
 * charset cannot be determined, the function returns `undefined`.
 *
 * @example
 * ```ts
 * import { getCharset } from "@std/media-types/get_charset";
 *
 * getCharset("text/plain"); // "UTF-8"
 * getCharset("application/foo"); // undefined
 * getCharset("application/news-checkgroups"); // "US-ASCII"
 * getCharset("application/news-checkgroups; charset=UTF-8"); // "UTF-8"
 * ```
 */
export function getCharset(type: string): string | undefined {
  try {
    const [mediaType, params] = parseMediaType(type);
    if (params && params["charset"]) {
      return params["charset"];
    }
    const entry = db[mediaType as KeyOfDb] as DBEntry;
    if (entry && entry.charset) {
      return entry.charset;
    }
    if (mediaType.startsWith("text/")) {
      return "UTF-8";
    }
  } catch {
    // just swallow errors, returning undefined
  }
  return undefined;
}