/*
 * Binary protocol encoder/decoder for video-node.
 *
 * Frame layout (TCP):
 *   [u16 message_type][u32 payload_length][payload...]
 *
 * CONTROL_REQUEST payload:
 *   [u16 request_id][u16 command][command-specific...]
 *
 * CONTROL_RESPONSE payload:
 *   [u16 request_id][u16 status][command-specific...]
 *
 * str8 encoding: [u8 length][bytes...] — not NUL-terminated on wire.
 */

export const FRAME_HEADER_SIZE     = 6;
export const MSG_CONTROL_REQUEST   = 0x0002;
export const MSG_CONTROL_RESPONSE  = 0x0003;

export const CMD_ENUM_DEVICES      = 0x0003;
export const CMD_ENUM_CONTROLS     = 0x0004;
export const CMD_GET_CONTROL       = 0x0005;
export const CMD_SET_CONTROL       = 0x0006;

export const STATUS_OK             = 0x0000;

/* -------------------------------------------------------------------------
 * Low-level buffer helpers
 * ------------------------------------------------------------------------- */

function read_str8(buf, offset) {
	const len = buf.readUInt8(offset);
	const value = buf.toString('utf8', offset + 1, offset + 1 + len);
	return { value, size: 1 + len };
}

function read_i64(buf, offset) {
	/* Little-endian i64: low 4 bytes first, high 4 bytes second.
	 * Returns a JS number — safe for the int32 values V4L2 uses in practice. */
	const lo = buf.readUInt32LE(offset);
	const hi = buf.readInt32LE(offset + 4);
	return hi * 0x100000000 + lo;
}

/* -------------------------------------------------------------------------
 * Frame builder
 * ------------------------------------------------------------------------- */

export function build_frame(msg_type, payload) {
	const frame = Buffer.allocUnsafe(FRAME_HEADER_SIZE + payload.length);
	frame.writeUInt16LE(msg_type, 0);
	frame.writeUInt32LE(payload.length, 2);
	payload.copy(frame, FRAME_HEADER_SIZE);
	return frame;
}

/* -------------------------------------------------------------------------
 * Request encoders — return a complete TCP frame Buffer.
 * request_id must be provided by the caller (u16).
 * ------------------------------------------------------------------------- */

export function encode_enum_devices(request_id) {
	const p = Buffer.allocUnsafe(4);
	p.writeUInt16LE(request_id, 0);
	p.writeUInt16LE(CMD_ENUM_DEVICES, 2);
	return build_frame(MSG_CONTROL_REQUEST, p);
}

export function encode_enum_controls(request_id, device_index) {
	const p = Buffer.allocUnsafe(6);
	p.writeUInt16LE(request_id, 0);
	p.writeUInt16LE(CMD_ENUM_CONTROLS, 2);
	p.writeUInt16LE(device_index, 4);
	return build_frame(MSG_CONTROL_REQUEST, p);
}

export function encode_get_control(request_id, device_index, control_id) {
	const p = Buffer.allocUnsafe(10);
	p.writeUInt16LE(request_id, 0);
	p.writeUInt16LE(CMD_GET_CONTROL, 2);
	p.writeUInt16LE(device_index, 4);
	p.writeUInt32LE(control_id, 6);
	return build_frame(MSG_CONTROL_REQUEST, p);
}

export function encode_set_control(request_id, device_index, control_id, value) {
	const p = Buffer.allocUnsafe(14);
	p.writeUInt16LE(request_id, 0);
	p.writeUInt16LE(CMD_SET_CONTROL, 2);
	p.writeUInt16LE(device_index, 4);
	p.writeUInt32LE(control_id, 6);
	p.writeInt32LE(value, 10);
	return build_frame(MSG_CONTROL_REQUEST, p);
}

/* -------------------------------------------------------------------------
 * Response decoders — take a payload Buffer (without frame header).
 * All throw on malformed data.
 * ------------------------------------------------------------------------- */

export function decode_response_header(payload) {
	return {
		request_id: payload.readUInt16LE(0),
		status:     payload.readUInt16LE(2),
	};
}

export function decode_enum_devices_response(payload) {
	const hdr = decode_response_header(payload);
	if (hdr.status !== STATUS_OK) { return { ...hdr, media: [], standalone: [] }; }

	let pos = 4;
	const media_count = payload.readUInt16LE(pos); pos += 2;
	const media = [];

	for (let i = 0; i < media_count; i++) {
		let s;
		s = read_str8(payload, pos); pos += s.size; const path     = s.value;
		s = read_str8(payload, pos); pos += s.size; const driver   = s.value;
		s = read_str8(payload, pos); pos += s.size; const model    = s.value;
		s = read_str8(payload, pos); pos += s.size; const bus_info = s.value;
		const vcount = payload.readUInt8(pos); pos++;

		const video_nodes = [];
		for (let j = 0; j < vcount; j++) {
			s = read_str8(payload, pos); pos += s.size; const vpath       = s.value;
			s = read_str8(payload, pos); pos += s.size; const entity_name = s.value;
			const entity_type  = payload.readUInt32LE(pos); pos += 4;
			const entity_flags = payload.readUInt32LE(pos); pos += 4;
			const device_caps  = payload.readUInt32LE(pos); pos += 4;
			const pad_flags    = payload.readUInt8(pos);    pos++;
			const is_capture   = payload.readUInt8(pos);    pos++;
			video_nodes.push({ path: vpath, entity_name, entity_type,
				entity_flags, device_caps, pad_flags, is_capture: !!is_capture });
		}

		media.push({ path, driver, model, bus_info, video_nodes });
	}

	const standalone_count = payload.readUInt16LE(pos); pos += 2;
	const standalone = [];
	for (let i = 0; i < standalone_count; i++) {
		let s;
		s = read_str8(payload, pos); pos += s.size; const path = s.value;
		s = read_str8(payload, pos); pos += s.size; const name = s.value;
		standalone.push({ path, name });
	}

	return { ...hdr, media, standalone };
}

export function decode_enum_controls_response(payload) {
	const hdr = decode_response_header(payload);
	if (hdr.status !== STATUS_OK) { return { ...hdr, controls: [] }; }

	let pos = 4;
	const count = payload.readUInt16LE(pos); pos += 2;
	const controls = [];

	for (let i = 0; i < count; i++) {
		const id    = payload.readUInt32LE(pos); pos += 4;
		const type  = payload.readUInt8(pos);    pos++;
		const flags = payload.readUInt32LE(pos); pos += 4;
		const s = read_str8(payload, pos);       pos += s.size;
		const name  = s.value;
		const min   = payload.readInt32LE(pos);  pos += 4;
		const max   = payload.readInt32LE(pos);  pos += 4;
		const step  = payload.readInt32LE(pos);  pos += 4;
		const def   = payload.readInt32LE(pos);  pos += 4;
		const cur   = payload.readInt32LE(pos);  pos += 4;
		const menu_count = payload.readUInt8(pos); pos++;

		const menu_items = [];
		for (let j = 0; j < menu_count; j++) {
			const midx   = payload.readUInt32LE(pos); pos += 4;
			const ms = read_str8(payload, pos);        pos += ms.size;
			const mval   = read_i64(payload, pos);     pos += 8;
			menu_items.push({ index: midx, name: ms.value, int_value: mval });
		}

		controls.push({ id, type, flags, name, min, max, step,
			default_val: def, current_val: cur, menu_items });
	}

	return { ...hdr, controls };
}

export function decode_get_control_response(payload) {
	const hdr = decode_response_header(payload);
	const value = (hdr.status === STATUS_OK) ? payload.readInt32LE(4) : 0;
	return { ...hdr, value };
}

export function decode_set_control_response(payload) {
	return decode_response_header(payload);
}