TempTrack-iOS/TempTrack/Bluetooth/DeviceInfo.swift

import Foundation

struct DeviceInfo {

    /**
     The maximum factor by which the device clock can run
     */
    private let maximumTimeDilationFactor: Double = 0.01


    /// The number of bytes recorded by the tracker
    let numberOfRecordedBytes: Int
    
    /// The number of measurements already performed
    let numberOfStoredMeasurements: Int
    
    /// The interval between measurements (in seconds)
    let measurementInterval: Int
    
    let sensor0: TemperatureSensor?
    
    let sensor1: TemperatureSensor?
    
    // MARK: Device time
    
    let wakeupReason: DeviceWakeCause

    let time: DeviceTime
    
    // MARK: Storage
    
    let storageSize: Int
    
    /// The maximum number of bytes which can be requested
    let transferBlockSize: Int
    
    var storageFillRatio: Double {
        Double(numberOfRecordedBytes) / Double(storageSize)
    }
    
    var storageFillPercentage: Int {
        Int((storageFillRatio * 100).rounded())
    }

    var currentMeasurementStartTime: Date {
        time.nextMeasurement.addingTimeInterval(-Double(numberOfStoredMeasurements * measurementInterval))
    }

    func estimatedTimeDilation(to previous: DeviceTime?) -> (start: Date, dilation: Double) {
        let trivialResult = (start: currentMeasurementStartTime, dilation: 1.0)
        guard let previous else {
            log.info("No previous device time to compare")
            return trivialResult
        }
        // Check if device was restarted in between
        guard time.secondsSincePowerOn >= previous.secondsSincePowerOn else {
            log.info("Device restarted (runtime decreased from \(previous.secondsSincePowerOn) to \(time.secondsSincePowerOn))")
            return trivialResult
        }
        let newMeasurementCount = time.totalNumberOfMeasurements - previous.totalNumberOfMeasurements
        guard newMeasurementCount >= 0 else {
            log.info("Device restarted (measurements decreased from \(previous.totalNumberOfMeasurements) to \(time.totalNumberOfMeasurements))")
            return trivialResult
        }
        guard newMeasurementCount > 0 else {
            log.warning("No new measurements to calculate time difference")
            return trivialResult
        }

        // Check that no measurements are missing

        // Calculate the difference between the expected time for the next measurement and the device time
        let deviceTimeDifference = Double(newMeasurementCount * measurementInterval)
        let expectedNextMeasurement = previous.nextMeasurement.addingTimeInterval(deviceTimeDifference)
        let timeDifference = time.nextMeasurement.timeIntervalSince(expectedNextMeasurement)

        let realTimeDifference = time.nextMeasurement.timeIntervalSince(previous.nextMeasurement)
        let timeDilation = realTimeDifference / deviceTimeDifference

        log.info("Device time dilation \(timeDilation) (difference \(timeDifference))")

        guard abs(timeDilation - 1.0) < maximumTimeDilationFactor else {
            log.warning("Device time too different from expected value (difference \(timeDifference) s)")
            return (currentMeasurementStartTime, 1.0)
        }
        return (previous.nextMeasurement, timeDilation)
    }
}

extension DeviceInfo {
    
    init(info: Data) throws {
        let date = Date()

        var data = info
        
        self.numberOfRecordedBytes = try data.decodeTwoByteInteger()
        let secondsUntilNextMeasurement = try data.decodeTwoByteInteger()
        self.measurementInterval = try data.decodeTwoByteInteger()
        self.numberOfStoredMeasurements = try data.decodeTwoByteInteger()
        let totalNumberOfMeasurements = try data.decodeFourByteInteger()
        self.transferBlockSize = try data.decodeTwoByteInteger()
        self.storageSize = try data.decodeTwoByteInteger()
        let secondsSincePowerOn = try data.decodeFourByteInteger()

        self.time = .init(
            date: date,
            secondsSincePowerOn: secondsSincePowerOn,
            totalNumberOfMeasurements: totalNumberOfMeasurements,
            secondsUntilNextMeasurement: secondsUntilNextMeasurement)
        let _ = try data.decodeFourByteInteger()
        self.sensor0 = try data.decodeSensor()
        self.sensor1 = try data.decodeSensor()
        self.wakeupReason = .init(rawValue: try data.getByte()) ?? .WAKEUP_UNDEFINED
    }
}

extension DeviceInfo {
    
    static var mock: DeviceInfo {
        .init(
            numberOfRecordedBytes: 123,
            numberOfStoredMeasurements: 234,
            measurementInterval: 60,
            sensor0: .init(address: [0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08], value: .value(21.0), date: .now.addingTimeInterval(-2)),
            sensor1: .init(address: [0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09], value: .value(19.0), date: .now.addingTimeInterval(-4)),
            wakeupReason: .WAKEUP_EXT0,
            time: .mock,
            storageSize: 10000,
            transferBlockSize: 180)
    }
}