joplin/packages/lib/mime-utils.ts

const mimeTypes = require('./mime-utils-types');

export const fromFileExtension = (ext: string) => {
	ext = ext.toLowerCase();
	for (let i = 0; i < mimeTypes.length; i++) {
		const t = mimeTypes[i];
		if (t.e.indexOf(ext) >= 0) {
			return t.t;
		}
	}
	return null;
};

export const fromFilename = (name: string) => {
	if (!name) return null;
	const splitted = name.trim().split('.');
	if (splitted.length <= 1) return null;
	return fromFileExtension(splitted[splitted.length - 1]);
};

export const toFileExtension = (mimeType: string) => {
	mimeType = mimeType.toLowerCase();
	for (let i = 0; i < mimeTypes.length; i++) {
		const t = mimeTypes[i];
		if (mimeType === t.t) {
			// Return the first file extension that is 3 characters long
			// If none exist return the first one in the list.
			for (let j = 0; j < t.e.length; j++) {
				if (t.e[j].length === 3) return t.e[j];
			}
			return t.e[0];
		}
	}
	return null;
};

export const fromDataUrl = (dataUrl: string) => {
	// Example: data:image/jpeg;base64,/9j/4AAQSkZJR.....
	const defaultMime = 'text/plain';
	const p = dataUrl.substr(0, dataUrl.indexOf(',')).split(';');
	let s = p[0];
	const result = s.split(':');
	if (result.length <= 1) return defaultMime;
	s = result[1];
	return s.indexOf('/') >= 0 ? s : defaultMime; // https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/Data_URIs
};