BluetoothGatt — 什么是它、方法及 Android 中 BLE 的 GATT 协议

// 创建 BluetoothGatt 连接
import android.bluetooth.*

class GattConnector(private val context: Context) {

    private var bluetoothGatt: BluetoothGatt? = null

    fun connect(device: BluetoothDevice): BluetoothGatt? {
        // 关闭已有连接（如果存在）
        close()

        bluetoothGatt = device.connectGatt(
            context,
            false,  // autoConnect = false ( )
            object : BluetoothGattCallback() {
                override fun onConnectionStateChange(
                    gatt: BluetoothGatt, status: Int, newState: Int
                ) {
                    when (newState) {
                        BluetoothProfile.STATE_CONNECTED -> {
                            // 2. 连接已建立 → 发现
                            gatt.discoverServices()
                        }
                        BluetoothProfile.STATE_DISCONNECTED -> {
                            // 3. 连接丢失
                            close()
                        }
                    }
                }

                override fun onServicesDiscovered(
                    gatt: BluetoothGatt, status: Int
                ) {
                    if (status == BluetoothGatt.GATT_SUCCESS) {
                        // 4. 已接收 GATT 层次结构
                        onGattReady(gatt)
                    }
                }
            },
            BluetoothDevice.TRANSPORT_LE
        )
        return bluetoothGatt
    }

    private fun onGattReady(gatt: BluetoothGatt) {
        // GATT 准备好进行读写操作
    }

    fun close() {
        bluetoothGatt?.disconnect()
        bluetoothGatt?.close()
        bluetoothGatt = null
    }
}

// 服务发现和特征搜索
class GattServiceExplorer {

    // 按 UUID 查找服务
    fun findService(gatt: BluetoothGatt, uuid: UUID): BluetoothGattService? {
        return gatt.services?.firstOrNull { it.uuid == uuid }
    }

    // 在服务中查找特征
    fun findCharacteristic(
        service: BluetoothGattService,
        uuid: UUID
    ): BluetoothGattCharacteristic? {
        return service.characteristics?.firstOrNull { it.uuid == uuid }
    }

    // 获取所有支持的特征操作
    fun getCharacteristicProperties(chars: BluetoothGattCharacteristic): List<String> {
        val props = mutableListOf<String>()
        with(chars.properties) {
            if (and(BluetoothGattCharacteristic.PROPERTY_READ) != 0) props.add("READ")
            if (and(BluetoothGattCharacteristic.PROPERTY_WRITE) != 0) props.add("WRITE")
            if (and(BluetoothGattCharacteristic.PROPERTY_WRITE_NO_RESPONSE) != 0) props.add("WRITE_NO_RESP")
            if (and(BluetoothGattCharacteristic.PROPERTY_NOTIFY) != 0) props.add("NOTIFY")
            if (and(BluetoothGattCharacteristic.PROPERTY_INDICATE) != 0) props.add("INDICATE")
        }
        return props
    }

    // 记录完整 GATT 层次结构
    fun dumpGattTree(gatt: BluetoothGatt) {
        gatt.services?.forEach { service ->
            print("Service: ${service.uuid}")
            service.characteristics?.forEach { char ->
                print("  Characteristic: ${char.uuid}, properties: ${char.properties}")
                char.descriptors?.forEach { desc ->
                    print("    Descriptor: ${desc.uuid}")
                }
            }
        }
    }
}

// 通过 BluetoothGatt 读取特征和描述符
class GattReader {

    fun readHeartRate(gatt: BluetoothGatt) {
        // 心率服务 UUID = 0x180D
        val service = gatt.getService(UUID.fromString("0000180D-0000-1000-8000-00805F9B34FB"))
            ?: return
        // 心率测量 UUID = 0x2A37
        val characteristic = service.getCharacteristic(
            UUID.fromString("00002A37-0000-1000-8000-00805F9B34FB")
        ) ?: return

        if (hasProperty(characteristic, BluetoothGattCharacteristic.PROPERTY_READ)) {
            gatt.readCharacteristic(characteristic)
        }
    }

    fun readDescriptor(gatt: BluetoothGatt, characteristic: BluetoothGattCharacteristic) {
        // CCCD（0x2902）
        val cccd = characteristic.getDescriptor(
            UUID.fromString("00002902-0000-1000-8000-00805F9B34FB")
        )
        cccd?.let { gatt.readDescriptor(it) }
    }

    // 在 onCharacteristicRead 回调中处理数据：
    fun parseHeartRate(value: ByteArray): Int {
        // BLE 心率：字节 = 标志位，第二 = bpm
        return if (value.isNotEmpty()) value[1].toInt() and 0xFF else 0
    }

    private fun hasProperty(char: BluetoothGattCharacteristic, prop: Int): Boolean {
        return char.properties and prop != 0
    }
}

// 在 Android API 33+ 上写入 BLE 特征
class GattWriter {

    // 带响应的写入（withResponse）
    fun writeWithResponse(gatt: BluetoothGatt, characteristic: BluetoothGattCharacteristic, data: ByteArray) {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.TIRAMISU) {
            // API 33+：writeCharacteristic
            val request = BluetoothGattCharacteristicWriteRequest(
                characteristic,
                data,
                BluetoothGattCharacteristicWriteRequest.WRITE_TYPE_DEFAULT,
                @android.annotation.RequiresPermission(android.Manifest.permission.BLUETOOTH_CONNECT)
            )
            gatt.writeCharacteristic(request)
        } else {
            // API < 33:   (deprecated)
            characteristic.setValue(data)
            gatt.writeCharacteristic(characteristic)
        }
    }

    // 无响应写入（最大速度）
    fun writeWithoutResponse(gatt: BluetoothGatt, characteristic: BluetoothGattCharacteristic, data: ByteArray) {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.TIRAMISU) {
            val request = BluetoothGattCharacteristicWriteRequest(
                characteristic,
                data,
                BluetoothGattCharacteristicWriteRequest.WRITE_TYPE_NO_RESPONSE,
                @android.annotation.RequiresPermission(android.Manifest.permission.BLUETOOTH_CONNECT)
            )
            gatt.writeCharacteristic(request)
        } else {
            characteristic.setValue(data)
            characteristic.writeType = BluetoothGattCharacteristic.WRITE_TYPE_NO_RESPONSE
            gatt.writeCharacteristic(characteristic)
        }
    }

    // onCharacteristicWrite 回调（API 33+）
    private val writeCallback = object : BluetoothGattCallback() {
        override fun onCharacteristicWrite(
            gatt: BluetoothGatt,
            characteristic: BluetoothGattCharacteristic,
            value: ByteArray,
            status: Int,
            callbackType: Int
        ) {
            if (status == BluetoothGatt.GATT_SUCCESS) {
                print("Write success: ${value.size} bytes")
            }
        }
    }
}

// 正确的 BLE 通知订阅
class GattNotificationManager {

    // 1. 启用通知
    fun enableNotification(gatt: BluetoothGatt, characteristic: BluetoothGattCharacteristic) {
        // 步骤 1：Android 本地订阅
        val success = gatt.setCharacteristicNotification(characteristic, true)
        if (!success) {
            print("订阅失败")
            return
        }

        // 步骤 2：在 BLE 设备上写入 CCCD（0x2902）
        val cccdDescriptor = characteristic.getDescriptor(
            UUID.fromString("00002902-0000-1000-8000-00805F9B34FB")
        ) ?: return

        // 0x0100 = 通知，0x0200 = 指示
        val cccdValue = if (characteristic.properties
            and BluetoothGattCharacteristic.PROPERTY_NOTIFY != 0) {
            BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE  // [0x01， 0x00]
        } else {
            BluetoothGattDescriptor.ENABLE_INDICATION_VALUE     // [0x02， 0x00]
        }

        cccdDescriptor.setValue(cccdValue)
        gatt.writeDescriptor(cccdDescriptor)
    }

    // 2. 特征发现
    fun disableNotification(gatt: BluetoothGatt, characteristic: BluetoothGattCharacteristic) {
        gatt.setCharacteristicNotification(characteristic, false)
        val cccdDescriptor = characteristic.getDescriptor(
            UUID.fromString("00002902-0000-1000-8000-00805F9B34FB")
        ) ?: return
        cccdDescriptor.setValue(BluetoothGattDescriptor.DISABLE_NOTIFICATION_VALUE)
        gatt.writeDescriptor(cccdDescriptor)
    }

    // 3. 通知回调
    private val notificationCallback = object : BluetoothGattCallback() {
        override fun onCharacteristicChanged(
            gatt: BluetoothGatt,
            characteristic: BluetoothGattCharacteristic,
            value: ByteArray,
            callbackType: Int
        ) {
            // 来自 BLE 外设的新值
            print("Notification: ${value.size} bytes")
        }
    }
}

// 在 Kotlin 中使用协程的完整 GATT 客户端
class GattClient(context: Context) {

    private val context = context.applicationContext
    private var gatt: BluetoothGatt? = null

    // 使用协程连接
    suspend fun connect(device: BluetoothDevice): Boolean =
        suspendCoroutine { continuation ->
            gatt = device.connectGatt(
                context, false,
                object : BluetoothGattCallback() {
                    override fun onConnectionStateChange(
                        gatt: BluetoothGatt, status: Int, newState: Int
                    ) {
                        if (newState == BluetoothProfile.STATE_CONNECTED) {
                            gatt.discoverServices()
                        } else {
                            continuation.resume(false)
                        }
                    }

                    override fun onServicesDiscovered(gatt: BluetoothGatt, status: Int) {
                        continuation.resume(status == BluetoothGatt.GATT_SUCCESS)
                    }
                },
                BluetoothDevice.TRANSPORT_LE
            )
        }

    // 通过协程读取特征
    suspend fun readCharacteristicValue(char: BluetoothGattCharacteristic): ByteArray? =
        suspendCoroutine { continuation ->
            gatt?.let { gatt ->
                // 保存特征标签用于回调识别
                gatt.setCharacteristic(char, null)  // 适用于 API < 33
                gatt.readCharacteristic(char)
            }
        }

    // 关闭连接
    fun release() {
        gatt?.disconnect()
        gatt?.close()
        gatt = null
    }
}