thi-ng/umbrella

import { DB } from "./generated.js";

/**
 * Decodes list of extensions, taking compressible flag into account.
 *
 * @internal
 */
const __ext = (val: string) => val.substring(~~(val[0] === "1")).split(",");

const __group = (mime: string) => {
    const [prefix, suffix] = mime.split("/");
    const group = DB[prefix];
    return group ? group[suffix] : undefined;
};

// https://www.iana.org/assignments/media-types/

export const MIME_TYPES = ((defs: any) => {
    const res: Record<string, string[]> = {};
    for (let groupID in defs) {
        const group = defs[groupID];
        for (let type in group) {
            const mime = groupID + "/" + type;
            for (let e of __ext(group[type])) {
                const isLowPri = e[0] === "*";
                const ext = isLowPri ? e.substring(1) : e;
                let coll = res[ext];
                !coll && (coll = res[ext] = []);
                isLowPri ? coll.push(mime) : coll.unshift(mime);
            }
        }
    }
    return res;
})(DB);

/**
 * Returns preferred MIME type for given file extension `ext`, or if no match is
 * available, the `fallback` MIME type (default: `application/octet-stream`).
 * `ext` is converted to lowercase first.
 *
 * @remarks
 * Since v0.2.0 the extension can be given as either `".ext"` or `"ext"`.
 * Previously, only the latter was supported.
 *
 * Also see {@link preferredExtension} for reverse operation.
 *
 * @param ext -
 * @param fallback -
 */
export const preferredType = (ext: string, fallback = MIME_TYPES.bin[0]) => {
    ext = ext.toLowerCase();
    const type = MIME_TYPES[ext[0] === "." ? ext.substring(1) : ext];
    return type ? type[0] : fallback;
};

/**
 * Reverse lookup to {@link preferredType}. Takes MIME type string and returns
 * preferred file extension (or failing that) returns `fallback` (default:
 * "bin").
 *
 * @param mime -
 * @param fallback -
 */
export const preferredExtension = (mime: string, fallback = "bin") => {
    const group = __group(mime);
    const ext = group ? __ext(group) : undefined;
    return ext
        ? ext.find((x) => x[0] !== "*") || ext[0].substring(1)
        : fallback;
};

/**
 * Returns all known file extensions for given MIME type or undefined if
 * unknown.
 *
 * @param mime
 */
export const extensionsForType = (mime: string) => {
    const group = __group(mime);
    const ext = group ? __ext(group) : undefined;
    return ext
        ? ext.map((x) => (x[0] === "*" ? x.substring(1) : x))
        : undefined;
};

/**
 * Returns true if the given MIME type can be compressed (or served using
 * gzip/brotli encoding).
 *
 * @remarks
 * Note: Information here is included as is. Some of these judgements in the
 * original mime-db project (or their sources of information) are highly
 * questionable...
 *
 * @param mime
 */
export const isCompressible = (mime: string) => !!(__group(mime)?.[0] === "1");

export * from "./presets.js";