/*
 Copyright (c) 2014, Ashley Mills
 All rights reserved.
 
 Redistribution and use in source and binary forms, with or without
 modification, are permitted provided that the following conditions are met:
 
 1. Redistributions of source code must retain the above copyright notice, this
 list of conditions and the following disclaimer.
 
 2. Redistributions in binary form must reproduce the above copyright notice,
 this list of conditions and the following disclaimer in the documentation
 and/or other materials provided with the distribution.
 
 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 POSSIBILITY OF SUCH DAMAGE.
 */

import SystemConfiguration
import Foundation

public enum ReachabilityError: Error {
    case FailedToCreateWithAddress(sockaddr_in)
    case FailedToCreateWithHostname(String)
    case UnableToSetCallback
    case UnableToSetDispatchQueue
    case UnableToGetInitialFlags
}

@available(*, unavailable, renamed: "Notification.Name.reachabilityChanged")
public let ReachabilityChangedNotification = NSNotification.Name("ReachabilityChangedNotification")

public extension Notification.Name {
    static let reachabilityChanged = Notification.Name("reachabilityChanged")
}

public class Reachability {
    
    public typealias NetworkReachable = (Reachability) -> ()
    public typealias NetworkUnreachable = (Reachability) -> ()
    
    @available(*, unavailable, renamed: "Connection")
    public enum NetworkStatus: CustomStringConvertible {
        case notReachable, reachableViaWiFi, reachableViaWWAN
        public var description: String {
            switch self {
            case .reachableViaWWAN: return "Cellular"
            case .reachableViaWiFi: return "WiFi"
            case .notReachable: return "No Connection"
            }
        }
    }
    
    public enum Connection: CustomStringConvertible {
        case none, wifi, cellular
        public var description: String {
            switch self {
            case .cellular: return "Cellular"
            case .wifi: return "WiFi"
            case .none: return "No Connection"
            }
        }
    }
    
    public var whenReachable: NetworkReachable?
    public var whenUnreachable: NetworkUnreachable?
    
    @available(*, deprecated, renamed: "allowsCellularConnection")
    public let reachableOnWWAN: Bool = true
    
    /// Set to `false` to force Reachability.connection to .none when on cellular connection (default value `true`)
    public var allowsCellularConnection: Bool
    
    // The notification center on which "reachability changed" events are being posted
    public var notificationCenter: NotificationCenter = NotificationCenter.default
    
    @available(*, deprecated, renamed: "connection.description")
    public var currentReachabilityString: String {
        return "\(connection)"
    }
    
    @available(*, unavailable, renamed: "connection")
    public var currentReachabilityStatus: Connection {
        return connection
    }
    
    public var connection: Connection {
        if flags == nil {
            try? setReachabilityFlags()
        }
        
        switch flags?.connection {
        case .none?, nil: return .none
        case .cellular?: return allowsCellularConnection ? .cellular : .none
        case .wifi?: return .wifi
        }
    }
    
    fileprivate var isRunningOnDevice: Bool = {
        #if targetEnvironment(simulator)
        return false
        #else
        return true
        #endif
    }()
    
    fileprivate var notifierRunning = false
    fileprivate let reachabilityRef: SCNetworkReachability
    fileprivate let reachabilitySerialQueue: DispatchQueue
    fileprivate(set) var flags: SCNetworkReachabilityFlags? {
        didSet {
            guard flags != oldValue else { return }
            reachabilityChanged()
        }
    }
    
    required public init(reachabilityRef: SCNetworkReachability, queueQoS: DispatchQoS = .default, targetQueue: DispatchQueue? = nil) {
        self.allowsCellularConnection = true
        self.reachabilityRef = reachabilityRef
        self.reachabilitySerialQueue = DispatchQueue(label: "uk.co.ashleymills.reachability", qos: queueQoS, target: targetQueue)
    }
    
    public convenience init?(hostname: String, queueQoS: DispatchQoS = .default, targetQueue: DispatchQueue? = nil) {
        guard let ref = SCNetworkReachabilityCreateWithName(nil, hostname) else { return nil }
        self.init(reachabilityRef: ref, queueQoS: queueQoS, targetQueue: targetQueue)
    }
    
    public convenience init?(queueQoS: DispatchQoS = .default, targetQueue: DispatchQueue? = nil) {
        var zeroAddress = sockaddr()
        zeroAddress.sa_len = UInt8(MemoryLayout<sockaddr>.size)
        zeroAddress.sa_family = sa_family_t(AF_INET)
        
        guard let ref = SCNetworkReachabilityCreateWithAddress(nil, &zeroAddress) else { return nil }
        
        self.init(reachabilityRef: ref, queueQoS: queueQoS, targetQueue: targetQueue)
    }
    
    deinit {
        stopNotifier()
    }
}

public extension Reachability {
    
    // MARK: - *** Notifier methods ***
    func startNotifier() throws {
        guard !notifierRunning else { return }
        
        let callback: SCNetworkReachabilityCallBack = { (reachability, flags, info) in
            guard let info = info else { return }
            
            let reachability = Unmanaged<Reachability>.fromOpaque(info).takeUnretainedValue()
            reachability.flags = flags
        }
        
        var context = SCNetworkReachabilityContext(version: 0, info: nil, retain: nil, release: nil, copyDescription: nil)
        context.info = UnsafeMutableRawPointer(Unmanaged<Reachability>.passUnretained(self).toOpaque())
        if !SCNetworkReachabilitySetCallback(reachabilityRef, callback, &context) {
            stopNotifier()
            throw ReachabilityError.UnableToSetCallback
        }
        
        if !SCNetworkReachabilitySetDispatchQueue(reachabilityRef, reachabilitySerialQueue) {
            stopNotifier()
            throw ReachabilityError.UnableToSetDispatchQueue
        }
        
        // Perform an initial check
        try setReachabilityFlags()
        
        notifierRunning = true
    }
    
    func stopNotifier() {
        defer { notifierRunning = false }
        
        SCNetworkReachabilitySetCallback(reachabilityRef, nil, nil)
        SCNetworkReachabilitySetDispatchQueue(reachabilityRef, nil)
    }
    
    // MARK: - *** Connection test methods ***
    @available(*, deprecated, message: "Please use `connection != .none`")
    var isReachable: Bool {
        return connection != .none
    }
    
    @available(*, deprecated, message: "Please use `connection == .cellular`")
    var isReachableViaWWAN: Bool {
        // Check we're not on the simulator, we're REACHABLE and check we're on WWAN
        return connection == .cellular
    }
    
    @available(*, deprecated, message: "Please use `connection == .wifi`")
    var isReachableViaWiFi: Bool {
        return connection == .wifi
    }
    
    var description: String {
        guard let flags = flags else { return "unavailable flags" }
        let W = isRunningOnDevice ? (flags.isOnWWANFlagSet ? "W" : "-") : "X"
        let R = flags.isReachableFlagSet ? "R" : "-"
        let c = flags.isConnectionRequiredFlagSet ? "c" : "-"
        let t = flags.isTransientConnectionFlagSet ? "t" : "-"
        let i = flags.isInterventionRequiredFlagSet ? "i" : "-"
        let C = flags.isConnectionOnTrafficFlagSet ? "C" : "-"
        let D = flags.isConnectionOnDemandFlagSet ? "D" : "-"
        let l = flags.isLocalAddressFlagSet ? "l" : "-"
        let d = flags.isDirectFlagSet ? "d" : "-"
        
        return "\(W)\(R) \(c)\(t)\(i)\(C)\(D)\(l)\(d)"
    }
}

fileprivate extension Reachability {
    
    func setReachabilityFlags() throws {
        try reachabilitySerialQueue.sync { [unowned self] in
            var flags = SCNetworkReachabilityFlags()
            if !SCNetworkReachabilityGetFlags(self.reachabilityRef, &flags) {
                self.stopNotifier()
                throw ReachabilityError.UnableToGetInitialFlags
            }
            
            self.flags = flags
        }
    }
    
    func reachabilityChanged() {
        let block = connection != .none ? whenReachable : whenUnreachable
        
        DispatchQueue.main.async { [weak self] in
            guard let self = self else { return }
            block?(self)
            self.notificationCenter.post(name: .reachabilityChanged, object: self)
        }
    }
}

extension SCNetworkReachabilityFlags {
    
    typealias Connection = Reachability.Connection
    
    var connection: Connection {
        guard isReachableFlagSet else { return .none }
        
        // If we're reachable, but not on an iOS device (i.e. simulator), we must be on WiFi
        #if targetEnvironment(simulator)
        return .wifi
        #else
        var connection = Connection.none
        
        if !isConnectionRequiredFlagSet {
            connection = .wifi
        }
        
        if isConnectionOnTrafficOrDemandFlagSet {
            if !isInterventionRequiredFlagSet {
                connection = .wifi
            }
        }
        
        if isOnWWANFlagSet {
            connection = .cellular
        }
        
        return connection
        #endif
    }
    
    var isOnWWANFlagSet: Bool {
        #if os(iOS)
        return contains(.isWWAN)
        #else
        return false
        #endif
    }
    var isReachableFlagSet: Bool {
        return contains(.reachable)
    }
    var isConnectionRequiredFlagSet: Bool {
        return contains(.connectionRequired)
    }
    var isInterventionRequiredFlagSet: Bool {
        return contains(.interventionRequired)
    }
    var isConnectionOnTrafficFlagSet: Bool {
        return contains(.connectionOnTraffic)
    }
    var isConnectionOnDemandFlagSet: Bool {
        return contains(.connectionOnDemand)
    }
    var isConnectionOnTrafficOrDemandFlagSet: Bool {
        return !intersection([.connectionOnTraffic, .connectionOnDemand]).isEmpty
    }
    var isTransientConnectionFlagSet: Bool {
        return contains(.transientConnection)
    }
    var isLocalAddressFlagSet: Bool {
        return contains(.isLocalAddress)
    }
    var isDirectFlagSet: Bool {
        return contains(.isDirect)
    }
    var isConnectionRequiredAndTransientFlagSet: Bool {
        return intersection([.connectionRequired, .transientConnection]) == [.connectionRequired, .transientConnection]
    }
}