import Foundation

final class TemperatureDataTransfer {
    
    private let startDateOfCurrentTransfer: Date
    
    private let interval: Int
    
    private var dataBuffer: Data = Data()
    
    private(set) var currentByteIndex = 0
    
    private(set) var size: Int
    
    private(set) var blockSize: Int
    
    private var numberOfRecordingsInCurrentTransfer = 0

    var measurements: [TemperatureMeasurement] = []

    /// The last temperatures to calculate relative values
    private var lastRecording: TemperatureMeasurement = .init(sensor0: .notFound, sensor1: .notFound, date: .now)
    
    private var dateOfNextRecording: Date {
        startDateOfCurrentTransfer.addingTimeInterval(TimeInterval(numberOfRecordingsInCurrentTransfer * interval))
    }
    
    var unprocessedByteCount: Int {
        dataBuffer.count
    }
    
    var remainingBytesToTransfer: Int {
        size - currentByteIndex
    }
    
    init(info: DeviceInfo) {
        self.interval = info.measurementInterval
        let recordingTime = info.numberOfStoredMeasurements * info.measurementInterval
        self.startDateOfCurrentTransfer = info.nextMeasurement.addingTimeInterval(-TimeInterval(recordingTime))
        self.size = info.numberOfRecordedBytes
        self.blockSize = info.transferBlockSize
    }
    
    func update(info: DeviceInfo) {
        self.size = info.numberOfRecordedBytes
        self.blockSize = info.transferBlockSize
    }
    
    func nextRequest() -> BluetoothRequest {
        guard remainingBytesToTransfer > 0 else {
            return .clearRecordingBuffer(byteCount: size)
        }
        let chunkSize = min(remainingBytesToTransfer, blockSize)
        return .getRecordingData(offset: currentByteIndex, count: chunkSize)
    }
    
    func add(data: Data, offset: Int, count: Int) {
        guard currentByteIndex == offset else {
            print("Discarding \(data.count) bytes at offset \(offset), expected \(currentByteIndex)")
            return
        }
        dataBuffer.append(data)
        currentByteIndex += data.count
        processBytes()
    }
    
    private func processBytes() {
        while !dataBuffer.isEmpty {
            let byte = dataBuffer.removeFirst()
            guard (byte == 0xFF) else {
                addRelative(byte: byte)
                continue
            }
            guard dataBuffer.count >= 2 else {
                // Wait for more data
                return
            }
            let temp0 = TemperatureValue(byte: dataBuffer.removeFirst())
            let temp1 = TemperatureValue(byte: dataBuffer.removeFirst())
            add(sensor0: temp0, sensor1: temp1)
        }
    }
    
    func completeTransfer() {
        processBytes()
    }
    
    private func addRelative(byte: UInt8) {
        add(sensor0: convertTemp(value: byte >> 4, relativeTo: lastRecording.sensor0),
            sensor1: convertTemp(value: byte & 0x0F, relativeTo: lastRecording.sensor1))
    }
    
    private func add(sensor0: TemperatureValue, sensor1: TemperatureValue) {
        let measurement = TemperatureMeasurement(
            sensor0: sensor0,
            sensor1: sensor1,
            date: dateOfNextRecording)
        
        numberOfRecordingsInCurrentTransfer += 1
        if measurement.sensor0.isValid {
            lastRecording.sensor0 = measurement.sensor0
        }
        if measurement.sensor1.isValid {
            lastRecording.sensor1 = measurement.sensor1
        }
        lastRecording.id = measurement.id
        measurements.append(measurement)
    }
    
    private func convertTemp(value: UInt8, relativeTo previous: TemperatureValue) -> TemperatureValue {
        if value == 0 {
            return .notFound
        }
        let newValue = previous.relativeValue - (Double(value) - 8) * 0.5
        return .value(newValue)
    }
}


private extension TemperatureValue {
    
    var relativeValue: Double {
        if case .value(let double) = self {
            return double
        }
        return 0
    }
}