/*
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 weakifiedReachability = Unmanaged<ReachabilityWeakifier>.fromOpaque(info).takeUnretainedValue()
            weakifiedReachability.reachability?.flags = flags
        }

        let weakifiedReachability = ReachabilityWeakifier(reachability: self)

        var context = SCNetworkReachabilityContext(
            version: 0,
            info: UnsafeMutableRawPointer(Unmanaged<ReachabilityWeakifier>.passUnretained(weakifiedReachability).toOpaque()),
            retain: { (info: UnsafeRawPointer) -> UnsafeRawPointer in
                return UnsafeRawPointer(Unmanaged<ReachabilityWeakifier>.fromOpaque(info).retain().toOpaque())
            },
            release: { (info: UnsafeRawPointer) -> Void in
                Unmanaged<ReachabilityWeakifier>.fromOpaque(info).release()
            },
            copyDescription: { (info: UnsafeRawPointer) -> Unmanaged<CFString> in
                let weakifiedReachability = Unmanaged<ReachabilityWeakifier>.fromOpaque(info).takeUnretainedValue()
                let description = weakifiedReachability.reachability?.description ?? "nil"
                return Unmanaged.passRetained(description as CFString)
            }
        )

        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]
    }
}

/**
 The `ReachabilityWeakifier` class wraps the `Reachability` class in a weak
 manner in order to break retain cycles when interacting with CoreFoundation
 APIs. CoreFoundation-style callbacks expect a pair or retain/release in
 addition to the typical info paramter.

 If we passed `SCNetworkReachabilitySetCallback` a direct reference to our
 `Reachability` class without also providing corresponding retain/release
 callbacks, then a race condition can lead to crashes when:
   - `Reachability` is deallocated on thread X
   - A `SCNetworkReachability` callback(s) is already in flight on thread Y

 If we passed `Reachability` directly but also provided retain/release
 callbacks as required by CoreFoundation, we would avoid race condition
 crashes, but create a retain cycle which would only be broken after calling
 `stopNotifier()`.

 By both providing retain/release callbacks and wrapping `Reachability` in
 a weak wrapper, we:
   - fix the race condition crashes by interacting correctly with CoreFoundation
     APIs. See "Memory Management Programming Guide for Core Foundation".
   - Don't alter the public API of `Reachability.swift`
   - Don't introduce any retain cycles thereby still allowing for automatic
     stopping of the notifier on `deinit`.
 */
private class ReachabilityWeakifier {
    weak var reachability: Reachability?
    init(reachability: Reachability) {
        self.reachability = reachability
    }
}