//
//  CentralController.swift
//  CovidSafe
//
//  Copyright © 2020 Australian Government. All rights reserved.
//
import Foundation
import CoreData
import CoreBluetooth
import UIKit

struct CentralWriteData: Codable {
    var modelC: String // phone model of central
    var rssi: Double
    var txPower: Double?
    var msg: String // tempID
    var org: String
    var v: Int
}

class CentralController: NSObject {
    enum CentralError: Error {
        case centralAlreadyOn
        case centralAlreadyOff
    }
    var centralDidUpdateStateCallback: ((CBManagerState) -> Void)?
    var characteristicDidReadValue: ((EncounterRecord) -> Void)?
    private let restoreIdentifierKey = "com.joelkek.tracer.central"
    private var central: CBCentralManager?
    private var recoveredPeripherals: [CBPeripheral] = []
    private var queue: DispatchQueue
    
    // This dict is to keep track of discovered android devices, so that i do not connect to the same android device multiple times within the same BluetraceConfig.CentralScanInterval
    private var discoveredAndroidPeriManufacturerToUUIDMap = [Data: UUID]()
    
    // This dict has 2 purpose
    // 1. To store all the EncounterRecord, because the RSSI and TxPower is gotten at the didDiscoverPeripheral delegate, but the characterstic value is gotten at didUpdateValueForCharacteristic delegate
    // 2. Use to check for duplicated iphones peripheral being discovered, so that i dont connect to the same iphone again in the same scan window
    private var scannedPeripherals = [UUID: (peripheral: CBPeripheral, encounter: EncounterRecord)]() // stores the peripherals encountered within one scan interval
    var timerForScanning: Timer?
    
    public init(queue: DispatchQueue) {
        self.queue = queue
        super.init()
    }
    
    func turnOn() {
        DLog("CC requested to be turnOn")
        guard central == nil else {
            return
        }
        central = CBCentralManager(delegate: self, queue: self.queue, options: [CBCentralManagerOptionRestoreIdentifierKey: restoreIdentifierKey, CBCentralManagerOptionShowPowerAlertKey: 1])
    }
    
    func turnOff() {
        DLog("CC turnOff")
        guard central != nil else {
            return
        }
        central?.stopScan()
        central = nil
    }
    
    public func getState() -> CBManagerState? {
        return central?.state
    }
    
    public func getDiscoveredPeripheralsCount() -> Int {
        let COUNT_NOT_FOUND = -1
        guard let appDelegate = UIApplication.shared.delegate as? AppDelegate else {
            return COUNT_NOT_FOUND
        }
        let managedContext = appDelegate.persistentContainer.viewContext
        let fetchRequest = NSFetchRequest<Encounter>(entityName: "Encounter")
        let sortByDate = NSSortDescriptor(key: "timestamp", ascending: false)
        fetchRequest.sortDescriptors = [sortByDate]
        let fetchedResultsController = NSFetchedResultsController<Encounter>(fetchRequest: fetchRequest, managedObjectContext: managedContext, sectionNameKeyPath: nil, cacheName: nil)
        
        do {
            try fetchedResultsController.performFetch()
            return fetchedResultsController.fetchedObjects?.count ?? COUNT_NOT_FOUND
        } catch let error as NSError {
            print("Could not perform fetch. \(error), \(error.userInfo)")
            return COUNT_NOT_FOUND
        }
    }
}

extension CentralController: CBCentralManagerDelegate {
    
    func centralManager(_ central: CBCentralManager, willRestoreState dict: [String : Any]) { }
    
    func centralManagerDidUpdateState(_ central: CBCentralManager) {
        centralDidUpdateStateCallback?(central.state)
        switch central.state {
        case .poweredOn:
            DispatchQueue.main.async {
                self.timerForScanning = Timer.scheduledTimer(withTimeInterval: TimeInterval(BluetraceConfig.CentralScanInterval), repeats: true) { _ in
                    DLog("CC Starting a scan")
                    Encounter.timestamp(for: .scanningStarted)
                    
                    // for all peripherals that are not disconnected, disconnect them
                    self.scannedPeripherals.forEach { (scannedPeri) in
                        central.cancelPeripheralConnection(scannedPeri.value.peripheral)
                    }
                    // clear all peripherals, such that a new scan window can take place
                    self.scannedPeripherals = [UUID: (CBPeripheral, EncounterRecord)]()
                    self.discoveredAndroidPeriManufacturerToUUIDMap = [Data: UUID]()
                    
                    central.scanForPeripherals(withServices: [BluetraceConfig.BluetoothServiceID])
                    DispatchQueue.global().asyncAfter(deadline: .now() + .seconds(BluetraceConfig.CentralScanDuration)) {
                        DLog("CC Stopping a scan")
                        central.stopScan()
                        Encounter.timestamp(for: .scanningStopped)
                    }
                }
                self.timerForScanning?.fire()
            }
        default:
            timerForScanning?.invalidate()
        }
    }
    
    func handlePeripheralOfUncertainStatus(_ peripheral: CBPeripheral) {
        // If not connected to Peripheral, attempt connection and exit
        if peripheral.state != .connected {
            DLog("CC handlePeripheralOfUncertainStatus not connected")
            central?.connect(peripheral)
            return
        }
        // If don't know about Peripheral's services, discover services and exit
        if peripheral.services == nil {
            DLog("CC handlePeripheralOfUncertainStatus unknown services")
            peripheral.discoverServices([BluetraceConfig.BluetoothServiceID])
            return
        }
        // If Peripheral's services don't contain targetID, disconnect and remove, then exit.
        // If it does contain targetID, discover characteristics for service
        guard let service = peripheral.services?.first(where:  { $0.uuid == BluetraceConfig.BluetoothServiceID }) else {
            DLog("CC handlePeripheralOfUncertainStatus no matching Services")
            central?.cancelPeripheralConnection(peripheral)
            return
        }
        DLog("CC handlePeripheralOfUncertainStatus discoverCharacteristics")
        peripheral.discoverCharacteristics([BluetraceConfig.BluetoothServiceID], for: service)
        // If Peripheral's service's characteristics don't contain targetID, disconnect and remove, then exit.
        // If it does contain targetID, read value for characteristic
        guard let characteristic = service.characteristics?.first(where: { $0.uuid == BluetraceConfig.BluetoothServiceID}) else {
            DLog("CC handlePeripheralOfUncertainStatus no matching Characteristics")
            central?.cancelPeripheralConnection(peripheral)
            return
        }
        DLog("CC handlePeripheralOfUncertainStatus readValue")
        peripheral.readValue(for: characteristic)
        return
    }
    
    func centralManager(_ central: CBCentralManager, didDiscover peripheral: CBPeripheral, advertisementData: [String : Any], rssi RSSI: NSNumber) {
        let debugLogs = ["CentralState": BluetraceUtils.centralStateToString(central.state),
                         "peripheral": peripheral,
                         "advertisments": advertisementData as AnyObject] as AnyObject
        
        DLog("\(debugLogs)")
        
        // iphones will "mask" the peripheral's identifier for android devices, resulting in the same android device being discovered multiple times with different peripheral identifier. Hence Android is using use CBAdvertisementDataServiceDataKey data for identifying an android pheripheral
        if let manuData = advertisementData[CBAdvertisementDataManufacturerDataKey] as? Data {
            let androidIdentifierData = manuData.subdata(in: 2..<manuData.count)
            if discoveredAndroidPeriManufacturerToUUIDMap.keys.contains(androidIdentifierData) {
                DLog("Android Peripheral \(peripheral) has been discovered already in this window, will not attempt to connect to it again")
                return
            } else {
                peripheral.delegate = self
                discoveredAndroidPeriManufacturerToUUIDMap.updateValue(peripheral.identifier, forKey: androidIdentifierData)
                scannedPeripherals.updateValue((peripheral, EncounterRecord(rssi: RSSI.doubleValue, txPower: advertisementData[CBAdvertisementDataTxPowerLevelKey] as? Double)), forKey: peripheral.identifier)
                central.connect(peripheral)
            }
        } else {
            // Means not android device, i will check if the peripheral.identifier exist in the scannedPeripherals
            DLog("CBAdvertisementDataManufacturerDataKey Data not found. Peripheral is likely not android")
            if scannedPeripherals[peripheral.identifier] == nil {
                peripheral.delegate = self
                scannedPeripherals.updateValue((peripheral, EncounterRecord(rssi: RSSI.doubleValue, txPower: advertisementData[CBAdvertisementDataTxPowerLevelKey] as? Double)), forKey: peripheral.identifier)
                central.connect(peripheral)
            } else {
                DLog("iOS Peripheral \(peripheral) has been discovered already in this window, will not attempt to connect to it again")
            }
        }
    }
    
    func centralManager(_ central: CBCentralManager, didConnect peripheral: CBPeripheral) {
        let peripheralStateString = BluetraceUtils.peripheralStateToString(peripheral.state)
        DLog("CC didConnect peripheral peripheralCentral state: \(BluetraceUtils.centralStateToString(central.state)), Peripheral state: \(peripheralStateString)")
        peripheral.delegate = self
        peripheral.discoverServices([BluetraceConfig.BluetoothServiceID])
    }
    
    func centralManager(_ central: CBCentralManager, didDisconnectPeripheral peripheral: CBPeripheral, error: Error?) {
        DLog("CC didDisconnectPeripheral \(peripheral) , \(error != nil ? "error: \(error.debugDescription)" : "" )")
    }
    
    func centralManager(_ central: CBCentralManager, didFailToConnect peripheral: CBPeripheral, error: Error?) {
        DLog("CC didFailToConnect peripheral \(error != nil ? "error: \(error.debugDescription)" : "" )")
    }
}

extension CentralController: CBPeripheralDelegate {
    func peripheral(_ peripheral: CBPeripheral, didDiscoverServices error: Error?) {
        if let err = error {
            DLog("error: \(err)")
        }
        guard let service = peripheral.services?.first(where:  { $0.uuid == BluetraceConfig.BluetoothServiceID }) else { return }
        peripheral.discoverCharacteristics([BluetraceConfig.BluetoothServiceID], for: service)
    }
    
    func peripheral(_ peripheral: CBPeripheral, didDiscoverCharacteristicsFor service: CBService, error: Error?) {
        if let err = error {
            DLog("error: \(err)")
        }
        guard let characteristic = service.characteristics?.first(where: { $0.uuid == BluetraceConfig.BluetoothServiceID}) else { return }
        peripheral.readValue(for: characteristic)
        
        // Do not need to wait for a successful read before writing, because no data from the read is needed in the write
        if let currEncounter = scannedPeripherals[peripheral.identifier] {
            EncounterMessageManager.shared.getTempId { (result) in
                guard let tempId = result else {
                    DLog("broadcast msg not present")
                    return
                }
                guard let rssi = currEncounter.encounter.rssi else {
                    DLog("rssi should be present in \(currEncounter.encounter)")
                    return
                }
                
                let dataToWrite = CentralWriteData(modelC: DeviceIdentifier.getModel(),
                                                   rssi: rssi,
                                                   txPower: currEncounter.encounter.txPower,
                                                   msg: tempId,
                                                   org: BluetraceConfig.OrgID,
                                                   v: BluetraceConfig.ProtocolVersion)
                
                do {
                    let encodedData = try JSONEncoder().encode(dataToWrite)
                    peripheral.writeValue(encodedData, for: characteristic, type: .withResponse)
                } catch {
                    DLog("Error: \(error)")
                }
            }
        }
        
    }
    
    func peripheral(_ peripheral: CBPeripheral, didUpdateValueFor characteristic: CBCharacteristic, error: Error?) {
        let debugLogs = ["characteristic": characteristic as AnyObject,
                         "encounter": scannedPeripherals[peripheral.identifier] as AnyObject] as AnyObject
        
        DLog("\(debugLogs)")
        if error == nil {
            if let scannedPeri = scannedPeripherals[peripheral.identifier],
                let characteristicValue = characteristic.value {
                do {
                    let peripheralCharData = try JSONDecoder().decode(PeripheralCharacteristicsData.self, from: characteristicValue)
                    var encounterStruct = scannedPeri.encounter
                    encounterStruct.msg = peripheralCharData.msg
                    encounterStruct.update(modelP: peripheralCharData.modelP)
                    encounterStruct.org = peripheralCharData.org
                    encounterStruct.v = peripheralCharData.v
                    scannedPeripherals.updateValue((scannedPeri.peripheral, encounterStruct), forKey: peripheral.identifier)
                    encounterStruct.saveToCoreData()
                } catch {
                    DLog("Error: \(error). CharacteristicValue is \(characteristicValue)")
                }
            } else {
                DLog("Error: scannedPeripherals[peripheral.identifier] is \(String(describing: scannedPeripherals[peripheral.identifier])), characteristic.value is \(String(describing: characteristic.value))")
            }
        } else {
            DLog("Error: \(error!)")
        }
    }
    
    func peripheral(_ peripheral: CBPeripheral, didWriteValueFor characteristic: CBCharacteristic, error: Error?) {
        DLog("didWriteValueFor to peripheral: \(peripheral), for characteristics: \(characteristic). \(error != nil ? "error: \(error.debugDescription)" : "" )")
        central?.cancelPeripheralConnection(peripheral)
    }
}