//
//  NetworkReachabilityManager.swift
//
//  Copyright (c) 2014-2018 Alamofire Software Foundation (http://alamofire.org/)
//
//  Permission is hereby granted, free of charge, to any person obtaining a copy
//  of this software and associated documentation files (the "Software"), to deal
//  in the Software without restriction, including without limitation the rights
//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//  copies of the Software, and to permit persons to whom the Software is
//  furnished to do so, subject to the following conditions:
//
//  The above copyright notice and this permission notice shall be included in
//  all copies or substantial portions of the Software.
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
//  THE SOFTWARE.
//

#if !os(watchOS)

    import Foundation
    import SystemConfiguration

    /// The `NetworkReachabilityManager` class listens for reachability changes of hosts and addresses for both WWAN and
    /// WiFi network interfaces.
    ///
    /// Reachability can be used to determine background information about why a network operation failed, or to retry
    /// network requests when a connection is established. It should not be used to prevent a user from initiating a network
    /// request, as it's possible that an initial request may be required to establish reachability.
    open class NetworkReachabilityManager {
        /// Defines the various states of network reachability.
        ///
        /// - unknown:      It is unknown whether the network is reachable.
        /// - notReachable: The network is not reachable.
        /// - reachable:    The network is reachable.
        public enum NetworkReachabilityStatus {
            case unknown
            case notReachable
            case reachable(ConnectionType)
        }

        /// Defines the various connection types detected by reachability flags.
        ///
        /// - ethernetOrWiFi: The connection type is either over Ethernet or WiFi.
        /// - wwan:           The connection type is a WWAN connection.
        public enum ConnectionType {
            case ethernetOrWiFi
            case wwan
        }

        /// A closure executed when the network reachability status changes. The closure takes a single argument: the
        /// network reachability status.
        public typealias Listener = (NetworkReachabilityStatus) -> Void

        // MARK: - Properties

        /// Whether the network is currently reachable.
        open var isReachable: Bool { return isReachableOnWWAN || isReachableOnEthernetOrWiFi }

        /// Whether the network is currently reachable over the WWAN interface.
        open var isReachableOnWWAN: Bool { return networkReachabilityStatus == .reachable(.wwan) }

        /// Whether the network is currently reachable over Ethernet or WiFi interface.
        open var isReachableOnEthernetOrWiFi: Bool { return networkReachabilityStatus == .reachable(.ethernetOrWiFi) }

        /// The current network reachability status.
        open var networkReachabilityStatus: NetworkReachabilityStatus {
            guard let flags = self.flags else { return .unknown }
            return networkReachabilityStatusForFlags(flags)
        }

        /// The dispatch queue to execute the `listener` closure on.
        open var listenerQueue: DispatchQueue = DispatchQueue.main

        /// A closure executed when the network reachability status changes.
        open var listener: Listener?

        open var flags: SCNetworkReachabilityFlags? {
            var flags = SCNetworkReachabilityFlags()

            if SCNetworkReachabilityGetFlags(reachability, &flags) {
                return flags
            }

            return nil
        }

        private let reachability: SCNetworkReachability
        open var previousFlags: SCNetworkReachabilityFlags

        // MARK: - Initialization

        /// Creates a `NetworkReachabilityManager` instance with the specified host.
        ///
        /// - parameter host: The host used to evaluate network reachability.
        ///
        /// - returns: The new `NetworkReachabilityManager` instance.
        public convenience init?(host: String) {
            guard let reachability = SCNetworkReachabilityCreateWithName(nil, host) else { return nil }
            self.init(reachability: reachability)
        }

        /// Creates a `NetworkReachabilityManager` instance that monitors the address 0.0.0.0.
        ///
        /// Reachability treats the 0.0.0.0 address as a special token that causes it to monitor the general routing
        /// status of the device, both IPv4 and IPv6.
        ///
        /// - returns: The new `NetworkReachabilityManager` instance.
        public convenience init?() {
            var address = sockaddr_in()
            address.sin_len = UInt8(MemoryLayout<sockaddr_in>.size)
            address.sin_family = sa_family_t(AF_INET)

            guard let reachability = withUnsafePointer(to: &address, { pointer in
                pointer.withMemoryRebound(to: sockaddr.self, capacity: MemoryLayout<sockaddr>.size) {
                    return SCNetworkReachabilityCreateWithAddress(nil, $0)
                }
            }) else { return nil }

            self.init(reachability: reachability)
        }

        private init(reachability: SCNetworkReachability) {
            self.reachability = reachability
            self.previousFlags = SCNetworkReachabilityFlags()
        }

        deinit {
            stopListening()
        }

        // MARK: - Listening

        /// Starts listening for changes in network reachability status.
        ///
        /// - returns: `true` if listening was started successfully, `false` otherwise.
        @discardableResult
        open func startListening() -> Bool {
            var context = SCNetworkReachabilityContext(version: 0, info: nil, retain: nil, release: nil, copyDescription: nil)
            context.info = Unmanaged.passUnretained(self).toOpaque()

            let callbackEnabled = SCNetworkReachabilitySetCallback(
                reachability,
                { _, flags, info in
                    let reachability = Unmanaged<NetworkReachabilityManager>.fromOpaque(info!).takeUnretainedValue()
                    reachability.notifyListener(flags)
                },
                &context
            )

            let queueEnabled = SCNetworkReachabilitySetDispatchQueue(reachability, listenerQueue)

            listenerQueue.async {
                self.previousFlags = SCNetworkReachabilityFlags()
                self.notifyListener(self.flags ?? SCNetworkReachabilityFlags())
            }

            return callbackEnabled && queueEnabled
        }

        /// Stops listening for changes in network reachability status.
        open func stopListening() {
            SCNetworkReachabilitySetCallback(reachability, nil, nil)
            SCNetworkReachabilitySetDispatchQueue(reachability, nil)
        }

        // MARK: - Internal - Listener Notification

        func notifyListener(_ flags: SCNetworkReachabilityFlags) {
            guard previousFlags != flags else { return }
            previousFlags = flags

            listener?(networkReachabilityStatusForFlags(flags))
        }

        // MARK: - Internal - Network Reachability Status

        func networkReachabilityStatusForFlags(_ flags: SCNetworkReachabilityFlags) -> NetworkReachabilityStatus {
            guard isNetworkReachable(with: flags) else { return .notReachable }

            var networkStatus: NetworkReachabilityStatus = .reachable(.ethernetOrWiFi)

            #if os(iOS)
                if flags.contains(.isWWAN) { networkStatus = .reachable(.wwan) }
            #endif

            return networkStatus
        }

        func isNetworkReachable(with flags: SCNetworkReachabilityFlags) -> Bool {
            let isReachable = flags.contains(.reachable)
            let needsConnection = flags.contains(.connectionRequired)
            let canConnectAutomatically = flags.contains(.connectionOnDemand) || flags.contains(.connectionOnTraffic)
            let canConnectWithoutUserInteraction = canConnectAutomatically && !flags.contains(.interventionRequired)

            return isReachable && (!needsConnection || canConnectWithoutUserInteraction)
        }
    }

    // MARK: -

    extension NetworkReachabilityManager.NetworkReachabilityStatus: Equatable {}

    /// Returns whether the two network reachability status values are equal.
    ///
    /// - parameter lhs: The left-hand side value to compare.
    /// - parameter rhs: The right-hand side value to compare.
    ///
    /// - returns: `true` if the two values are equal, `false` otherwise.
    public func == (
        lhs: NetworkReachabilityManager.NetworkReachabilityStatus,
        rhs: NetworkReachabilityManager.NetworkReachabilityStatus)
        -> Bool {
        switch (lhs, rhs) {
        case (.unknown, .unknown):
            return true
        case (.notReachable, .notReachable):
            return true
        case let (.reachable(lhsConnectionType), .reachable(rhsConnectionType)):
            return lhsConnectionType == rhsConnectionType
        default:
            return false
        }
    }

#endif
