/*
class to parse the .mid file format
(depends on stream.js)
*/

const Stream = require("./stream.js");



module.exports = function MidiFile (data) {
	function readChunk (stream) {
		const id = stream.readString(4);
		const length = stream.readInt32();

		return {
			id,
			length,
			data: stream.read(length),
		};
	}

	let lastEventTypeByte;

	function readEvent (stream) {
		const event = {};
		event.deltaTime = stream.readVarInt();
		let eventTypeByte = stream.readInt8();
		if ((eventTypeByte & 0xf0) === 0xf0) {
			// system / meta event
			if (eventTypeByte === 0xff) {
				// meta event
				event.type = "meta";
				const subtypeByte = stream.readInt8();
				const length = stream.readVarInt();

				switch (subtypeByte) {
				case 0x00:
					event.subtype = "sequenceNumber";
					if (length !== 2)
						throw new Error("Expected length for sequenceNumber event is 2, got " + length);
					event.number = stream.readInt16();

					return event;
				case 0x01:
					event.subtype = "text";
					event.text = stream.readString(length);

					return event;
				case 0x02:
					event.subtype = "copyrightNotice";
					event.text = stream.readString(length);

					return event;
				case 0x03:
					event.subtype = "trackName";
					event.text = stream.readString(length);

					return event;
				case 0x04:
					event.subtype = "instrumentName";
					event.text = stream.readString(length);

					return event;
				case 0x05:
					event.subtype = "lyrics";
					event.text = stream.readString(length);

					return event;
				case 0x06:
					event.subtype = "marker";
					event.text = stream.readString(length);

					return event;
				case 0x07:
					event.subtype = "cuePoint";
					event.text = stream.readString(length);

					return event;
				case 0x20:
					event.subtype = "midiChannelPrefix";
					if (length !== 1)
						throw new Error("Expected length for midiChannelPrefix event is 1, got " + length);
					event.channel = stream.readInt8();

					return event;
				case 0x2f:
					event.subtype = "endOfTrack";
					if (length !== 0)
						throw new Error("Expected length for endOfTrack event is 0, got " + length);

					return event;
				case 0x51:
					event.subtype = "setTempo";
					if (length !== 3)
						throw new Error("Expected length for setTempo event is 3, got " + length);
					event.microsecondsPerBeat = (
						(stream.readInt8() << 16) +
							(stream.readInt8() << 8) +
							stream.readInt8()
					);

					return event;
				case 0x54:
					event.subtype = "smpteOffset";
					if (length !== 5)
						throw new Error("Expected length for smpteOffset event is 5, got " + length);
					const hourByte = stream.readInt8();
					event.frameRate = {
						0x00: 24, 0x20: 25, 0x40: 29, 0x60: 30,
					}[hourByte & 0x60];
					event.hour = hourByte & 0x1f;
					event.min = stream.readInt8();
					event.sec = stream.readInt8();
					event.frame = stream.readInt8();
					event.subframe = stream.readInt8();

					return event;
				case 0x58:
					event.subtype = "timeSignature";
					if (length !== 4)
						throw new Error("Expected length for timeSignature event is 4, got " + length);
					event.numerator = stream.readInt8();
					event.denominator = Math.pow(2, stream.readInt8());
					event.metronome = stream.readInt8();
					event.thirtyseconds = stream.readInt8();

					return event;
				case 0x59:
					event.subtype = "keySignature";
					if (length !== 2)
						throw new Error("Expected length for keySignature event is 2, got " + length);
					event.key = stream.readInt8(true);
					event.scale = stream.readInt8();

					return event;
				case 0x7f:
					event.subtype = "sequencerSpecific";
					event.data = stream.readString(length);

					return event;
				default:
					// console.log("Unrecognised meta event subtype: " + subtypeByte);
					event.subtype = "unknown";
					event.data = stream.readString(length);

					return event;
				}

				//event.data = stream.readString(length);
				//return event;
			}
			else if (eventTypeByte === 0xf0) {
				event.type = "sysEx";
				const length = stream.readVarInt();
				event.data = stream.readString(length);

				return event;
			}
			else if (eventTypeByte === 0xf7) {
				event.type = "dividedSysEx";
				const length = stream.readVarInt();
				event.data = stream.readString(length);

				return event;
			}
			else
				throw new Error("Unrecognised MIDI event type byte: " + eventTypeByte);
		}
		else {
			/* channel event */
			let param1;
			if ((eventTypeByte & 0x80) === 0) {
				/* running status - reuse lastEventTypeByte as the event type.
					eventTypeByte is actually the first parameter
				*/
				param1 = eventTypeByte;
				eventTypeByte = lastEventTypeByte;
			}
			else {
				param1 = stream.readInt8();
				lastEventTypeByte = eventTypeByte;
			}

			const eventType = eventTypeByte >> 4;
			event.channel = eventTypeByte & 0x0f;
			event.type = "channel";

			switch (eventType) {
			case 0x08:
				event.subtype = "noteOff";
				event.noteNumber = param1;
				event.velocity = stream.readInt8();

				return event;
			case 0x09:
				event.noteNumber = param1;
				event.velocity = stream.readInt8();
				if (event.velocity === 0)
					event.subtype = "noteOff";
				else
					event.subtype = "noteOn";

				return event;
			case 0x0a:
				event.subtype = "noteAftertouch";
				event.noteNumber = param1;
				event.amount = stream.readInt8();

				return event;
			case 0x0b:
				event.subtype = "controller";
				event.controllerType = param1;
				event.value = stream.readInt8();

				return event;
			case 0x0c:
				event.subtype = "programChange";
				event.programNumber = param1;

				return event;
			case 0x0d:
				event.subtype = "channelAftertouch";
				event.amount = param1;

				return event;
			case 0x0e:
				event.subtype = "pitchBend";
				event.value = param1 + (stream.readInt8() << 7);

				return event;
			default:
				throw new Error("Unrecognised MIDI event type: " + eventType);

				/*
				console.log("Unrecognised MIDI event type: " + eventType);
				stream.readInt8();
				event.subtype = 'unknown';
				return event;
				*/
			}
		}
	}


	let source = data;
	if (typeof data === "string")
		source = data.split("").map(c => c.charCodeAt(0));

	const stream = new Stream(source);
	const headerChunk = readChunk(stream);
	if (headerChunk.id !== "MThd" || headerChunk.length !== 6)
		throw new Error("Bad .mid file - header not found");

	const headerStream = new Stream(headerChunk.data);
	const formatType = headerStream.readInt16();
	const trackCount = headerStream.readInt16();
	const timeDivision = headerStream.readInt16();

	let ticksPerBeat;
	if (timeDivision & 0x8000)
		throw new Error("Expressing time division in SMTPE frames is not supported yet");
	else
		ticksPerBeat = timeDivision;


	const header = {
		formatType,
		trackCount,
		ticksPerBeat,
	};
	const tracks = [];
	for (let i = 0; i < header.trackCount; i++) {
		tracks[i] = [];
		const trackChunk = readChunk(stream);
		if (trackChunk.id !== "MTrk")
			throw new Error("Unexpected chunk - expected MTrk, got " + trackChunk.id);

		const trackStream = new Stream(trackChunk.data);
		while (!trackStream.eof()) {
			const event = readEvent(trackStream);
			tracks[i].push(event);
		}
	}

	return {
		header,
		tracks,
	};
};