DataView.prototype.getString = function(offset, length) {
	text = '';
	let end = offset + length;
	for (let i = offset; i < end; i++) {
		text += String.fromCharCode(this.getUint8(i));
	}
	return text;
}


class MP4Tree {
	constructor(data) {
		this.data = new DataView(data);
		this.codecs = [];
		this.idx = 0;
		this.parse_codecs();
	}

	parse_codecs() {
		this.parse_into('moov', 8);
		while (this.idx < this.data.byteLength) {
			if (!this.parse_until('trak')) {
				break;
			}
			const curr_track_end = this.idx + this.read_next_head().len;
			this.idx += 8
			this.parse_into('mdia', 8);
			this.parse_into('minf', 8);
			const track_type_head = this.read_next_head().name;
			if (track_type_head == 'smhd' || track_type_head == 'vmhd') {
				this.parse_into('stbl', 8);
				this.parse_into('stsd', 16);
				const media_sample = this.read_next_head().name;
				if (media_sample == 'avc1') {
					this.parse_avc1();
				} else if (media_sample == 'mp4a') {
					this.parse_mp4a();
				}
			}
			this.idx = curr_track_end;
		}
	}
	
	parse_avc1() {
		this.parse_into('avc1', 86);
		console.log(this.read_next_head());
	}

	parse_mp4a() {
		this.parse_into('mp4a', 36);
		console.log(this.read_next_head());
	}

	get_mime() {
		return 'video/mp4; codecs="' + this.get_codec_string() + '"';
	}

	get_codec_string() {
		return this.codecs.join(', ');
	}

	parse_into(name, header_offset) {
		this.parse_until(name);
		this.idx += header_offset;
	}

	parse_until(name) {
		let curr_head = null;
		while (this.idx + 8 < this.data.byteLength) {
			curr_head = this.read_next_head();
			if (curr_head.name == name) {
				return true;
			} else {
				this.idx += curr_head.len;
			}
		}
		return false;
	}
	
	read_next_head() {
		return {"len": this.data.getUint32(this.idx), "name": this.data.getString(this.idx + 4, 4)};
	}
}