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//

//  RequestTaskMap.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.

//

import Foundation

/// A type that maintains a two way, one to one map of `URLSessionTask`s to `Request`s.

struct RequestTaskMap {

    private typealias Events = (completed: Bool, metricsGathered: Bool)

    private var tasksToRequests: [URLSessionTask: Request]

    private var requestsToTasks: [Request: URLSessionTask]

    private var taskEvents: [URLSessionTask: Events]

    var requests: [Request] {

        Array(tasksToRequests.values)

    }

    init(tasksToRequests: [URLSessionTask: Request] = [:],

         requestsToTasks: [Request: URLSessionTask] = [:],

         taskEvents: [URLSessionTask: (completed: Bool, metricsGathered: Bool)] = [:]) {

        self.tasksToRequests = tasksToRequests

        self.requestsToTasks = requestsToTasks

        self.taskEvents = taskEvents

    }

    subscript(_ request: Request) -> URLSessionTask? {

        get { requestsToTasks[request] }

        set {

            guard let newValue = newValue else {

                guard let task = requestsToTasks[request] else {

                    fatalError("RequestTaskMap consistency error: no task corresponding to request found.")

                }

                requestsToTasks.removeValue(forKey: request)

                tasksToRequests.removeValue(forKey: task)

                taskEvents.removeValue(forKey: task)

                return

            }

            requestsToTasks[request] = newValue

            tasksToRequests[newValue] = request

            taskEvents[newValue] = (completed: false, metricsGathered: false)

        }

    }

    subscript(_ task: URLSessionTask) -> Request? {

        get { tasksToRequests[task] }

        set {

            guard let newValue = newValue else {

                guard let request = tasksToRequests[task] else {

                    fatalError("RequestTaskMap consistency error: no request corresponding to task found.")

                }

                tasksToRequests.removeValue(forKey: task)

                requestsToTasks.removeValue(forKey: request)

                taskEvents.removeValue(forKey: task)

                return

            }

            tasksToRequests[task] = newValue

            requestsToTasks[newValue] = task

            taskEvents[task] = (completed: false, metricsGathered: false)

        }

    }

    var count: Int {

        precondition(tasksToRequests.count == requestsToTasks.count,

                     "RequestTaskMap.count invalid, requests.count: \(tasksToRequests.count) != tasks.count: \(requestsToTasks.count)")

        return tasksToRequests.count

    }

    var eventCount: Int {

        precondition(taskEvents.count == count, "RequestTaskMap.eventCount invalid, count: \(count) != taskEvents.count: \(taskEvents.count)")

        return taskEvents.count

    }

    var isEmpty: Bool {

        precondition(tasksToRequests.isEmpty == requestsToTasks.isEmpty,

                     "RequestTaskMap.isEmpty invalid, requests.isEmpty: \(tasksToRequests.isEmpty) != tasks.isEmpty: \(requestsToTasks.isEmpty)")

        return tasksToRequests.isEmpty

    }

    var isEventsEmpty: Bool {

        precondition(taskEvents.isEmpty == isEmpty, "RequestTaskMap.isEventsEmpty invalid, isEmpty: \(isEmpty) != taskEvents.isEmpty: \(taskEvents.isEmpty)")

        return taskEvents.isEmpty

    }

    mutating func disassociateIfNecessaryAfterGatheringMetricsForTask(_ task: URLSessionTask) -> Bool {

        guard let events = taskEvents[task] else {

            fatalError("RequestTaskMap consistency error: no events corresponding to task found.")

        }

        switch (events.completed, events.metricsGathered) {

        case (_, true): fatalError("RequestTaskMap consistency error: duplicate metricsGatheredForTask call.")

        case (false, false): taskEvents[task] = (completed: false, metricsGathered: true); return false

        case (true, false): self[task] = nil; return true

        }

    }

    mutating func disassociateIfNecessaryAfterCompletingTask(_ task: URLSessionTask) -> Bool {

        guard let events = taskEvents[task] else {

            fatalError("RequestTaskMap consistency error: no events corresponding to task found.")

        }

        switch (events.completed, events.metricsGathered) {

        case (true, _): fatalError("RequestTaskMap consistency error: duplicate completionReceivedForTask call.")

        #if os(Linux) // Linux doesn't gather metrics, so unconditionally remove the reference and return true.

        default: self[task] = nil; return true

        #else

        case (false, false):

            if #available(macOS 10.12, iOS 10, watchOS 7, tvOS 10, *) {

                taskEvents[task] = (completed: true, metricsGathered: false); return false

            } else {

                // watchOS < 7 doesn't gather metrics, so unconditionally remove the reference and return true.

                self[task] = nil; return true

            }

        case (false, true):

            self[task] = nil; return true

        #endif

        }

    }

}