'use strict';
const toBytes = s => Array.from(s).map(c => c.charCodeAt(0));
const xpiZipFilename = toBytes('META-INF/mozilla.rsa');
const oxmlContentTypes = toBytes('[Content_Types].xml');
const oxmlRels = toBytes('_rels/.rels');

module.exports = input => {
	const buf = new Uint8Array(input);

	if (!(buf && buf.length > 1)) {
		return null;
	}

	const check = (header, opts) => {
		opts = Object.assign({
			offset: 0
		}, opts);

		for (let i = 0; i < header.length; i++) {
			// If a bitmask is set
			if (opts.mask) {
				// If header doesn't equal `buf` with bits masked off
				if (header[i] !== (opts.mask[i] & buf[i + opts.offset])) {
					return false;
				}
			} else if (header[i] !== buf[i + opts.offset]) {
				return false;
			}
		}

		return true;
	};

	if (check([0xFF, 0xD8, 0xFF])) {
		return {
			ext: 'jpg',
			mime: 'image/jpeg'
		};
	}

	if (check([0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A])) {
		return {
			ext: 'png',
			mime: 'image/png'
		};
	}

	if (check([0x47, 0x49, 0x46])) {
		return {
			ext: 'gif',
			mime: 'image/gif'
		};
	}

	if (check([0x57, 0x45, 0x42, 0x50], {offset: 8})) {
		return {
			ext: 'webp',
			mime: 'image/webp'
		};
	}

	if (check([0x46, 0x4C, 0x49, 0x46])) {
		return {
			ext: 'flif',
			mime: 'image/flif'
		};
	}

	// Needs to be before `tif` check
	if (
		(check([0x49, 0x49, 0x2A, 0x0]) || check([0x4D, 0x4D, 0x0, 0x2A])) &&
		check([0x43, 0x52], {offset: 8})
	) {
		return {
			ext: 'cr2',
			mime: 'image/x-canon-cr2'
		};
	}

	if (
		check([0x49, 0x49, 0x2A, 0x0]) ||
		check([0x4D, 0x4D, 0x0, 0x2A])
	) {
		return {
			ext: 'tif',
			mime: 'image/tiff'
		};
	}

	if (check([0x42, 0x4D])) {
		return {
			ext: 'bmp',
			mime: 'image/bmp'
		};
	}

	if (check([0x49, 0x49, 0xBC])) {
		return {
			ext: 'jxr',
			mime: 'image/vnd.ms-photo'
		};
	}

	if (check([0x38, 0x42, 0x50, 0x53])) {
		return {
			ext: 'psd',
			mime: 'image/vnd.adobe.photoshop'
		};
	}

	// Zip-based file formats
	// Need to be before the `zip` check
	if (check([0x50, 0x4B, 0x3, 0x4])) {
		if (
			check([0x6D, 0x69, 0x6D, 0x65, 0x74, 0x79, 0x70, 0x65, 0x61, 0x70, 0x70, 0x6C, 0x69, 0x63, 0x61, 0x74, 0x69, 0x6F, 0x6E, 0x2F, 0x65, 0x70, 0x75, 0x62, 0x2B, 0x7A, 0x69, 0x70], {offset: 30})
		) {
			return {
				ext: 'epub',
				mime: 'application/epub+zip'
			};
		}

		// Assumes signed `.xpi` from addons.mozilla.org
		if (check(xpiZipFilename, {offset: 30})) {
			return {
				ext: 'xpi',
				mime: 'application/x-xpinstall'
			};
		}

		// https://github.com/file/file/blob/master/magic/Magdir/msooxml
		if (check(oxmlContentTypes, {offset: 30}) || check(oxmlRels, {offset: 30})) {
			const sliced = buf.subarray(4, 4 + 2000);
			const nextZipHeaderIndex = arr => arr.findIndex((el, i, arr) => arr[i] === 0x50 && arr[i + 1] === 0x4B && arr[i + 2] === 0x3 && arr[i + 3] === 0x4);
			const header2Pos = nextZipHeaderIndex(sliced);

			if (header2Pos !== -1) {
				const slicedAgain = buf.subarray(header2Pos + 8, header2Pos + 8 + 1000);
				const header3Pos = nextZipHeaderIndex(slicedAgain);

				if (header3Pos !== -1) {
					const offset = 8 + header2Pos + header3Pos + 30;

					if (check(toBytes('word/'), {offset})) {
						return {
							ext: 'docx',
							mime: 'application/vnd.openxmlformats-officedocument.wordprocessingml.document'
						};
					}

					if (check(toBytes('ppt/'), {offset})) {
						return {
							ext: 'pptx',
							mime: 'application/vnd.openxmlformats-officedocument.presentationml.presentation'
						};
					}

					if (check(toBytes('xl/'), {offset})) {
						return {
							ext: 'xlsx',
							mime: 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet'
						};
					}
				}
			}
		}
	}

	if (
		check([0x50, 0x4B]) &&
		(buf[2] === 0x3 || buf[2] === 0x5 || buf[2] === 0x7) &&
		(buf[3] === 0x4 || buf[3] === 0x6 || buf[3] === 0x8)
	) {
		return {
			ext: 'zip',
			mime: 'application/zip'
		};
	}

	if (check([0x75, 0x73, 0x74, 0x61, 0x72], {offset: 257})) {
		return {
			ext: 'tar',
			mime: 'application/x-tar'
		};
	}

	if (
		check([0x52, 0x61, 0x72, 0x21, 0x1A, 0x7]) &&
		(buf[6] === 0x0 || buf[6] === 0x1)
	) {
		return {
			ext: 'rar',
			mime: 'application/x-rar-compressed'
		};
	}

	if (check([0x1F, 0x8B, 0x8])) {
		return {
			ext: 'gz',
			mime: 'application/gzip'
		};
	}

	if (check([0x42, 0x5A, 0x68])) {
		return {
			ext: 'bz2',
			mime: 'application/x-bzip2'
		};
	}

	if (check([0x37, 0x7A, 0xBC, 0xAF, 0x27, 0x1C])) {
		return {
			ext: '7z',
			mime: 'application/x-7z-compressed'
		};
	}

	if (check([0x78, 0x01])) {
		return {
			ext: 'dmg',
			mime: 'application/x-apple-diskimage'
		};
	}

	if (check([0x33, 0x67, 0x70, 0x35]) || // 3gp5
		(
			check([0x0, 0x0, 0x0]) && check([0x66, 0x74, 0x79, 0x70], {offset: 4}) &&
				(
					check([0x6D, 0x70, 0x34, 0x31], {offset: 8}) || // MP41
					check([0x6D, 0x70, 0x34, 0x32], {offset: 8}) || // MP42
					check([0x69, 0x73, 0x6F, 0x6D], {offset: 8}) || // ISOM
					check([0x69, 0x73, 0x6F, 0x32], {offset: 8}) || // ISO2
					check([0x6D, 0x6D, 0x70, 0x34], {offset: 8}) || // MMP4
					check([0x4D, 0x34, 0x56], {offset: 8}) || // M4V
					check([0x64, 0x61, 0x73, 0x68], {offset: 8}) // DASH
				)
		)) {
		return {
			ext: 'mp4',
			mime: 'video/mp4'
		};
	}

	if (check([0x4D, 0x54, 0x68, 0x64])) {
		return {
			ext: 'mid',
			mime: 'audio/midi'
		};
	}

	// https://github.com/threatstack/libmagic/blob/master/magic/Magdir/matroska
	if (check([0x1A, 0x45, 0xDF, 0xA3])) {
		const sliced = buf.subarray(4, 4 + 4096);
		const idPos = sliced.findIndex((el, i, arr) => arr[i] === 0x42 && arr[i + 1] === 0x82);

		if (idPos !== -1) {
			const docTypePos = idPos + 3;
			const findDocType = type => Array.from(type).every((c, i) => sliced[docTypePos + i] === c.charCodeAt(0));

			if (findDocType('matroska')) {
				return {
					ext: 'mkv',
					mime: 'video/x-matroska'
				};
			}

			if (findDocType('webm')) {
				return {
					ext: 'webm',
					mime: 'video/webm'
				};
			}
		}
	}

	if (check([0x0, 0x0, 0x0, 0x14, 0x66, 0x74, 0x79, 0x70, 0x71, 0x74, 0x20, 0x20]) ||
		check([0x66, 0x72, 0x65, 0x65], {offset: 4}) ||
		check([0x66, 0x74, 0x79, 0x70, 0x71, 0x74, 0x20, 0x20], {offset: 4}) ||
		check([0x6D, 0x64, 0x61, 0x74], {offset: 4}) || // MJPEG
		check([0x77, 0x69, 0x64, 0x65], {offset: 4})) {
		return {
			ext: 'mov',
			mime: 'video/quicktime'
		};
	}

	if (
		check([0x52, 0x49, 0x46, 0x46]) &&
		check([0x41, 0x56, 0x49], {offset: 8})
	) {
		return {
			ext: 'avi',
			mime: 'video/x-msvideo'
		};
	}

	if (check([0x30, 0x26, 0xB2, 0x75, 0x8E, 0x66, 0xCF, 0x11, 0xA6, 0xD9])) {
		return {
			ext: 'wmv',
			mime: 'video/x-ms-wmv'
		};
	}

	if (check([0x0, 0x0, 0x1, 0xBA])) {
		return {
			ext: 'mpg',
			mime: 'video/mpeg'
		};
	}

	// Check for MP3 header at different starting offsets
	for (let start = 0; start < 2 && start < (buf.length - 16); start++) {
		if (
			check([0x49, 0x44, 0x33], {offset: start}) || // ID3 header
			check([0xFF, 0xE2], {offset: start, mask: [0xFF, 0xE2]}) // MPEG 1 or 2 Layer 3 header
		) {
			return {
				ext: 'mp3',
				mime: 'audio/mpeg'
			};
		}
	}

	if (
		check([0x66, 0x74, 0x79, 0x70, 0x4D, 0x34, 0x41], {offset: 4}) ||
		check([0x4D, 0x34, 0x41, 0x20])
	) {
		return {
			ext: 'm4a',
			mime: 'audio/m4a'
		};
	}

	// Needs to be before `ogg` check
	if (check([0x4F, 0x70, 0x75, 0x73, 0x48, 0x65, 0x61, 0x64], {offset: 28})) {
		return {
			ext: 'opus',
			mime: 'audio/opus'
		};
	}

	if (check([0x4F, 0x67, 0x67, 0x53])) {
		return {
			ext: 'ogg',
			mime: 'audio/ogg'
		};
	}

	if (check([0x66, 0x4C, 0x61, 0x43])) {
		return {
			ext: 'flac',
			mime: 'audio/x-flac'
		};
	}

	if (
		check([0x52, 0x49, 0x46, 0x46]) &&
		check([0x57, 0x41, 0x56, 0x45], {offset: 8})
	) {
		return {
			ext: 'wav',
			mime: 'audio/x-wav'
		};
	}

	if (check([0x23, 0x21, 0x41, 0x4D, 0x52, 0x0A])) {
		return {
			ext: 'amr',
			mime: 'audio/amr'
		};
	}

	if (check([0x25, 0x50, 0x44, 0x46])) {
		return {
			ext: 'pdf',
			mime: 'application/pdf'
		};
	}

	if (check([0x4D, 0x5A])) {
		return {
			ext: 'exe',
			mime: 'application/x-msdownload'
		};
	}

	if (
		(buf[0] === 0x43 || buf[0] === 0x46) &&
		check([0x57, 0x53], {offset: 1})
	) {
		return {
			ext: 'swf',
			mime: 'application/x-shockwave-flash'
		};
	}

	if (check([0x7B, 0x5C, 0x72, 0x74, 0x66])) {
		return {
			ext: 'rtf',
			mime: 'application/rtf'
		};
	}

	if (check([0x00, 0x61, 0x73, 0x6D])) {
		return {
			ext: 'wasm',
			mime: 'application/wasm'
		};
	}

	if (
		check([0x77, 0x4F, 0x46, 0x46]) &&
		(
			check([0x00, 0x01, 0x00, 0x00], {offset: 4}) ||
			check([0x4F, 0x54, 0x54, 0x4F], {offset: 4})
		)
	) {
		return {
			ext: 'woff',
			mime: 'font/woff'
		};
	}

	if (
		check([0x77, 0x4F, 0x46, 0x32]) &&
		(
			check([0x00, 0x01, 0x00, 0x00], {offset: 4}) ||
			check([0x4F, 0x54, 0x54, 0x4F], {offset: 4})
		)
	) {
		return {
			ext: 'woff2',
			mime: 'font/woff2'
		};
	}

	if (
		check([0x4C, 0x50], {offset: 34}) &&
		(
			check([0x00, 0x00, 0x01], {offset: 8}) ||
			check([0x01, 0x00, 0x02], {offset: 8}) ||
			check([0x02, 0x00, 0x02], {offset: 8})
		)
	) {
		return {
			ext: 'eot',
			mime: 'application/octet-stream'
		};
	}

	if (check([0x00, 0x01, 0x00, 0x00, 0x00])) {
		return {
			ext: 'ttf',
			mime: 'font/ttf'
		};
	}

	if (check([0x4F, 0x54, 0x54, 0x4F, 0x00])) {
		return {
			ext: 'otf',
			mime: 'font/otf'
		};
	}

	if (check([0x00, 0x00, 0x01, 0x00])) {
		return {
			ext: 'ico',
			mime: 'image/x-icon'
		};
	}

	if (check([0x46, 0x4C, 0x56, 0x01])) {
		return {
			ext: 'flv',
			mime: 'video/x-flv'
		};
	}

	if (check([0x25, 0x21])) {
		return {
			ext: 'ps',
			mime: 'application/postscript'
		};
	}

	if (check([0xFD, 0x37, 0x7A, 0x58, 0x5A, 0x00])) {
		return {
			ext: 'xz',
			mime: 'application/x-xz'
		};
	}

	if (check([0x53, 0x51, 0x4C, 0x69])) {
		return {
			ext: 'sqlite',
			mime: 'application/x-sqlite3'
		};
	}

	if (check([0x4E, 0x45, 0x53, 0x1A])) {
		return {
			ext: 'nes',
			mime: 'application/x-nintendo-nes-rom'
		};
	}

	if (check([0x43, 0x72, 0x32, 0x34])) {
		return {
			ext: 'crx',
			mime: 'application/x-google-chrome-extension'
		};
	}

	if (
		check([0x4D, 0x53, 0x43, 0x46]) ||
		check([0x49, 0x53, 0x63, 0x28])
	) {
		return {
			ext: 'cab',
			mime: 'application/vnd.ms-cab-compressed'
		};
	}

	// Needs to be before `ar` check
	if (check([0x21, 0x3C, 0x61, 0x72, 0x63, 0x68, 0x3E, 0x0A, 0x64, 0x65, 0x62, 0x69, 0x61, 0x6E, 0x2D, 0x62, 0x69, 0x6E, 0x61, 0x72, 0x79])) {
		return {
			ext: 'deb',
			mime: 'application/x-deb'
		};
	}

	if (check([0x21, 0x3C, 0x61, 0x72, 0x63, 0x68, 0x3E])) {
		return {
			ext: 'ar',
			mime: 'application/x-unix-archive'
		};
	}

	if (check([0xED, 0xAB, 0xEE, 0xDB])) {
		return {
			ext: 'rpm',
			mime: 'application/x-rpm'
		};
	}

	if (
		check([0x1F, 0xA0]) ||
		check([0x1F, 0x9D])
	) {
		return {
			ext: 'Z',
			mime: 'application/x-compress'
		};
	}

	if (check([0x4C, 0x5A, 0x49, 0x50])) {
		return {
			ext: 'lz',
			mime: 'application/x-lzip'
		};
	}

	if (check([0xD0, 0xCF, 0x11, 0xE0, 0xA1, 0xB1, 0x1A, 0xE1])) {
		return {
			ext: 'msi',
			mime: 'application/x-msi'
		};
	}

	if (check([0x06, 0x0E, 0x2B, 0x34, 0x02, 0x05, 0x01, 0x01, 0x0D, 0x01, 0x02, 0x01, 0x01, 0x02])) {
		return {
			ext: 'mxf',
			mime: 'application/mxf'
		};
	}

	if (check([0x47], {offset: 4}) && (check([0x47], {offset: 192}) || check([0x47], {offset: 196}))) {
		return {
			ext: 'mts',
			mime: 'video/mp2t'
		};
	}

	if (check([0x42, 0x4C, 0x45, 0x4E, 0x44, 0x45, 0x52])) {
		return {
			ext: 'blend',
			mime: 'application/x-blender'
		};
	}

	if (check([0x42, 0x50, 0x47, 0xFB])) {
		return {
			ext: 'bpg',
			mime: 'image/bpg'
		};
	}

	return null;
};