package yaokong;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.util.Objects;

public abstract class WaitForAck {
	protected final InputStream inputStream;
	protected final OutputStream outputStream;

	protected WaitForAck(InputStream inputStream, OutputStream outputStream) {
		this.inputStream = Objects.requireNonNull(inputStream, "inputStream");
		this.outputStream = Objects.requireNonNull(outputStream, "outputStream");
	}

	// 在超时内等待下位机返回指定指令的确认帧
	protected boolean waitForAck(byte expectedCommand) throws IOException {
		long deadline = System.currentTimeMillis() + 1000L;
		while (System.currentTimeMillis() < deadline) {
			if (inputStream.available() > 0) {
				byte[] response = readResponse();
				if (response != null && parseResponse(response, expectedCommand)) {
					return true;
				}
			}
			try {
				Thread.sleep(10L);
			} catch (InterruptedException interruptedException) {
				Thread.currentThread().interrupt();
				break;
			}
		}
		return false;
	}

	// 从输入流读取完整响应帧并校验帧头帧尾
	private byte[] readResponse() throws IOException {
		ByteArrayOutputStream buffer = new ByteArrayOutputStream();
		while (true) {
			int value = inputStream.read();
			if (value == -1) {
				return buffer.size() == 0 ? null : buffer.toByteArray();
			}

			buffer.write(value);

			if (buffer.size() == 1 && buffer.toByteArray()[0] != BluetoothProtocol.FRAME_HEADER[0]) {
				buffer.reset();
				continue;
			}

			if (buffer.size() == 2) {
				byte[] header = buffer.toByteArray();
				if (header[0] != BluetoothProtocol.FRAME_HEADER[0] || header[1] != BluetoothProtocol.FRAME_HEADER[1]) {
					buffer.reset();
					continue;
				}
			}

			if ((byte) value == BluetoothProtocol.FRAME_FOOTER) {
				return buffer.toByteArray();
			}
		}
	}

	// 解析确认帧并校验CRC与指令号
	private boolean parseResponse(byte[] response, byte expectedCommand) {
		if (response.length < 7) {
			return false;
		}

		if (response[0] != BluetoothProtocol.FRAME_HEADER[0] || response[1] != BluetoothProtocol.FRAME_HEADER[1]) {
			return false;
		}

		if (response[2] != BluetoothProtocol.CMD_RESPONSE) {
			return false;
		}

		ByteBuffer wrapper = ByteBuffer.wrap(response).order(ByteOrder.LITTLE_ENDIAN);
		wrapper.position(3);
		int payloadLength = wrapper.getShort() & 0xFFFF;
		int frameLength = 2 + 1 + 2 + payloadLength + 2 + 1;

		if (response.length < frameLength) {
			return false;
		}

		if (payloadLength < 2) {
			return false;
		}

		int crcOffset = 2 + 1 + 2 + payloadLength;
		int calculatedCrc = CRC16.calculateCRC16(response, 2, 1 + 2 + payloadLength);
		int receivedCrc = ByteBuffer.wrap(response, crcOffset, 2).order(ByteOrder.LITTLE_ENDIAN).getShort() & 0xFFFF;

		if (calculatedCrc != receivedCrc) {
			return false;
		}

		byte ackCommand = response[2 + 1 + 2];
		byte status = response[2 + 1 + 2 + 1];

		if (ackCommand != expectedCommand) {
			return false;
		}

		return status == BluetoothProtocol.ERROR_SUCCESS;
	}
}