// This source file is part of the Swift.org open source project
//
// Copyright (c) 2018 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See http://swift.org/LICENSE.txt for license information
// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//
//  XCTWaiter.swift
//

import CoreFoundation

/// Events are reported to the waiter's delegate via these methods. XCTestCase conforms to this
/// protocol and will automatically report timeouts and other unexpected events as test failures.
///
/// - Note: These methods are invoked on an arbitrary queue.
public protocol XCTWaiterDelegate: AnyObject {

    /// Invoked when not all waited on expectations are fulfilled during the timeout period. If the delegate
    /// is an XCTestCase instance, this will be reported as a test failure.
    ///
    /// - Parameter waiter: The waiter which timed out.
    /// - Parameter unfulfilledExpectations: The expectations which were unfulfilled when `waiter` timed out.
    func waiter(_ waiter: XCTWaiter, didTimeoutWithUnfulfilledExpectations unfulfilledExpectations: [XCTestExpectation])

    /// Invoked when the wait specified that fulfillment order should be enforced and an expectation
    /// has been fulfilled in the wrong order. If the delegate is an XCTestCase instance, this will be reported
    /// as a test failure.
    ///
    /// - Parameter waiter: The waiter which had an ordering violation.
    /// - Parameter expectation: The expectation which was fulfilled instead of the required expectation.
    /// - Parameter requiredExpectation: The expectation which was fulfilled instead of the required expectation.
    func waiter(_ waiter: XCTWaiter, fulfillmentDidViolateOrderingConstraintsFor expectation: XCTestExpectation, requiredExpectation: XCTestExpectation)

    /// Invoked when an expectation marked as inverted is fulfilled. If the delegate is an XCTestCase instance,
    /// this will be reported as a test failure.
    ///
    /// - Parameter waiter: The waiter which had an inverted expectation fulfilled.
    /// - Parameter expectation: The inverted expectation which was fulfilled.
    ///
    /// - SeeAlso: `XCTestExpectation.isInverted`
    func waiter(_ waiter: XCTWaiter, didFulfillInvertedExpectation expectation: XCTestExpectation)

    /// Invoked when the waiter is interrupted prior to its expectations being fulfilled or timing out.
    /// This occurs when an "outer" waiter times out, resulting in any waiters nested inside it being
    /// interrupted to allow the call stack to quickly unwind.
    ///
    /// - Parameter waiter: The waiter which was interrupted.
    /// - Parameter outerWaiter: The "outer" waiter which interrupted `waiter`.
    func nestedWaiter(_ waiter: XCTWaiter, wasInterruptedByTimedOutWaiter outerWaiter: XCTWaiter)

}

// All `XCTWaiterDelegate` methods are optional, so empty default implementations are provided
public extension XCTWaiterDelegate {
    func waiter(_ waiter: XCTWaiter, didTimeoutWithUnfulfilledExpectations unfulfilledExpectations: [XCTestExpectation]) {}
    func waiter(_ waiter: XCTWaiter, fulfillmentDidViolateOrderingConstraintsFor expectation: XCTestExpectation, requiredExpectation: XCTestExpectation) {}
    func waiter(_ waiter: XCTWaiter, didFulfillInvertedExpectation expectation: XCTestExpectation) {}
    func nestedWaiter(_ waiter: XCTWaiter, wasInterruptedByTimedOutWaiter outerWaiter: XCTWaiter) {}
}

/// Manages waiting - pausing the current execution context - for an array of XCTestExpectations. Waiters
/// can be used with or without a delegate to respond to events such as completion, timeout, or invalid
/// expectation fulfillment. XCTestCase conforms to the delegate protocol and will automatically report
/// timeouts and other unexpected events as test failures.
///
/// Waiters can be used without a delegate or any association with a test case instance. This allows test
/// support libraries to provide convenience methods for waiting without having to pass test cases through
/// those APIs.
open class XCTWaiter {

    /// Values returned by a waiter when it completes, times out, or is interrupted due to another waiter
    /// higher in the call stack timing out.
    public enum Result: Int {
        case completed = 1
        case timedOut
        case incorrectOrder
        case invertedFulfillment
        case interrupted
    }

    private enum State: Equatable {
        case ready
        case waiting(state: Waiting)
        case finished(state: Finished)

        struct Waiting: Equatable {
            var enforceOrder: Bool
            var expectations: [XCTestExpectation]
            var fulfilledExpectations: [XCTestExpectation]
        }

        struct Finished: Equatable {
            let result: Result
            let fulfilledExpectations: [XCTestExpectation]
            let unfulfilledExpectations: [XCTestExpectation]
        }

        var allExpectations: [XCTestExpectation] {
            switch self {
            case .ready:
                return []
            case let .waiting(waitingState):
                return waitingState.expectations
            case let .finished(finishedState):
                return finishedState.fulfilledExpectations + finishedState.unfulfilledExpectations
            }
        }
    }

    internal static let subsystemQueue = DispatchQueue(label: "org.swift.XCTest.XCTWaiter")

    private var state = State.ready
    internal var timeout: TimeInterval = 0
    internal var waitSourceLocation: SourceLocation?
    private weak var manager: WaiterManager<XCTWaiter>?
    private var runLoop: RunLoop?

    private weak var _delegate: XCTWaiterDelegate?
    private let delegateQueue = DispatchQueue(label: "org.swift.XCTest.XCTWaiter.delegate")

    /// The waiter delegate will be called with various events described in the `XCTWaiterDelegate` protocol documentation.
    ///
    /// - SeeAlso: `XCTWaiterDelegate`
    open var delegate: XCTWaiterDelegate? {
        get {
            return XCTWaiter.subsystemQueue.sync { _delegate }
        }
        set {
            dispatchPrecondition(condition: .notOnQueue(XCTWaiter.subsystemQueue))
            XCTWaiter.subsystemQueue.async { self._delegate = newValue }
        }
    }

    /// Returns an array containing the expectations that were fulfilled, in that order, up until the waiter
    /// stopped waiting. Expectations fulfilled after the waiter stopped waiting will not be in the array.
    /// The array will be empty until the waiter has started waiting, even if expectations have already been
    /// fulfilled.
    open var fulfilledExpectations: [XCTestExpectation] {
        return XCTWaiter.subsystemQueue.sync {
            let fulfilledExpectations: [XCTestExpectation]

            switch state {
            case .ready:
                fulfilledExpectations = []
            case let .waiting(waitingState):
                fulfilledExpectations = waitingState.fulfilledExpectations
            case let .finished(finishedState):
                fulfilledExpectations = finishedState.fulfilledExpectations
            }

            // Sort by fulfillment token before returning, since it is the true fulfillment order.
            // The waiter being notified by the expectation isn't guaranteed to happen in the same order.
            return fulfilledExpectations.sorted { $0.queue_fulfillmentToken < $1.queue_fulfillmentToken }
        }
    }

    /// Initializes a waiter with an optional delegate.
    public init(delegate: XCTWaiterDelegate? = nil) {
        _delegate = delegate
    }

    /// Wait on an array of expectations for up to the specified timeout, and optionally specify whether they
    /// must be fulfilled in the given order. May return early based on fulfillment of the waited on expectations.
    ///
    /// - Parameter expectations: The expectations to wait on.
    /// - Parameter timeout: The maximum total time duration to wait on all expectations.
    /// - Parameter enforceOrder: Specifies whether the expectations must be fulfilled in the order
    ///   they are specified in the `expectations` Array. Default is false.
    /// - Parameter file: The file name to use in the error message if
    ///   expectations are not fulfilled before the given timeout. Default is the file
    ///   containing the call to this method. It is rare to provide this
    ///   parameter when calling this method.
    /// - Parameter line: The line number to use in the error message if the
    ///   expectations are not fulfilled before the given timeout. Default is the line
    ///   number of the call to this method in the calling file. It is rare to
    ///   provide this parameter when calling this method.
    ///
    /// - Note: Whereas Objective-C XCTest determines the file and line
    ///   number of the "wait" call using symbolication, this implementation
    ///   opts to take `file` and `line` as parameters instead. As a result,
    ///   the interface to these methods are not exactly identical between
    ///   these environments. To ensure compatibility of tests between
    ///   swift-corelibs-xctest and Apple XCTest, it is not recommended to pass
    ///   explicit values for `file` and `line`.
    @discardableResult
    open func wait(for expectations: [XCTestExpectation], timeout: TimeInterval, enforceOrder: Bool = false, file: StaticString = #file, line: Int = #line) -> Result {
        precondition(Set(expectations).count == expectations.count, "API violation - each expectation can appear only once in the 'expectations' parameter.")

        self.timeout = timeout
        waitSourceLocation = SourceLocation(file: file, line: line)
        let runLoop = RunLoop.current

        XCTWaiter.subsystemQueue.sync {
            precondition(state == .ready, "API violation - wait(...) has already been called on this waiter.")

            let previouslyWaitedOnExpectations = expectations.filter { $0.queue_hasBeenWaitedOn }
            let previouslyWaitedOnExpectationDescriptions = previouslyWaitedOnExpectations.map { $0.queue_expectationDescription }.joined(separator: "`, `")
            precondition(previouslyWaitedOnExpectations.isEmpty, "API violation - expectations can only be waited on once, `\(previouslyWaitedOnExpectationDescriptions)` have already been waited on.")

            let waitingState = State.Waiting(
                enforceOrder: enforceOrder,
                expectations: expectations,
                fulfilledExpectations: expectations.filter { $0.queue_isFulfilled }
            )
            queue_configureExpectations(expectations)
            state = .waiting(state: waitingState)
            self.runLoop = runLoop

            queue_validateExpectationFulfillment(dueToTimeout: false)
        }

        let manager = WaiterManager<XCTWaiter>.current
        manager.startManaging(self, timeout: timeout)
        self.manager = manager

        // Begin the core wait loop.
        let timeoutTimestamp = CFAbsoluteTimeGetCurrent() + timeout
        while !isFinished {
            let remaining = timeoutTimestamp - CFAbsoluteTimeGetCurrent()
            if remaining <= 0 {
                break
            }
            primitiveWait(using: runLoop, duration: remaining)
        }

        manager.stopManaging(self)
        self.manager = nil

        let result: Result = XCTWaiter.subsystemQueue.sync {
            queue_validateExpectationFulfillment(dueToTimeout: true)

            for expectation in expectations {
                expectation.cleanUp()
                expectation.queue_didFulfillHandler = nil
            }

            guard case let .finished(finishedState) = state else { fatalError("Unexpected state: \(state)") }
            return finishedState.result
        }

        delegateQueue.sync {
            // DO NOT REMOVE ME
            // This empty block, executed synchronously, ensures that inflight delegate callbacks from the
            // internal queue have been processed before wait returns.
        }

        return result
    }

    /// Convenience API to create an XCTWaiter which then waits on an array of expectations for up to the specified timeout, and optionally specify whether they
    /// must be fulfilled in the given order. May return early based on fulfillment of the waited on expectations. The waiter
    /// is discarded when the wait completes.
    ///
    /// - Parameter expectations: The expectations to wait on.
    /// - Parameter timeout: The maximum total time duration to wait on all expectations.
    /// - Parameter enforceOrder: Specifies whether the expectations must be fulfilled in the order
    ///   they are specified in the `expectations` Array. Default is false.
    /// - Parameter file: The file name to use in the error message if
    ///   expectations are not fulfilled before the given timeout. Default is the file
    ///   containing the call to this method. It is rare to provide this
    ///   parameter when calling this method.
    /// - Parameter line: The line number to use in the error message if the
    ///   expectations are not fulfilled before the given timeout. Default is the line
    ///   number of the call to this method in the calling file. It is rare to
    ///   provide this parameter when calling this method.
    open class func wait(for expectations: [XCTestExpectation], timeout: TimeInterval, enforceOrder: Bool = false, file: StaticString = #file, line: Int = #line) -> Result {
        return XCTWaiter().wait(for: expectations, timeout: timeout, enforceOrder: enforceOrder, file: file, line: line)
    }

    deinit {
        for expectation in state.allExpectations {
            expectation.cleanUp()
        }
    }

    private func queue_configureExpectations(_ expectations: [XCTestExpectation]) {
        dispatchPrecondition(condition: .onQueue(XCTWaiter.subsystemQueue))

        for expectation in expectations {
            expectation.queue_didFulfillHandler = { [weak self, unowned expectation] in
                self?.expectationWasFulfilled(expectation)
            }
            expectation.queue_hasBeenWaitedOn = true
        }
    }

    private func queue_validateExpectationFulfillment(dueToTimeout: Bool) {
        dispatchPrecondition(condition: .onQueue(XCTWaiter.subsystemQueue))
        guard case let .waiting(waitingState) = state else { return }

        let validatableExpectations = waitingState.expectations.map { ValidatableXCTestExpectation(expectation: $0) }
        let validationResult = XCTWaiter.validateExpectations(validatableExpectations, dueToTimeout: dueToTimeout, enforceOrder: waitingState.enforceOrder)

        switch validationResult {
        case .complete:
            queue_finish(result: .completed, cancelPrimitiveWait: !dueToTimeout)

        case .fulfilledInvertedExpectation(let invertedValidationExpectation):
            queue_finish(result: .invertedFulfillment, cancelPrimitiveWait: true) { delegate in
                delegate.waiter(self, didFulfillInvertedExpectation: invertedValidationExpectation.expectation)
            }

        case .violatedOrderingConstraints(let validationExpectation, let requiredValidationExpectation):
            queue_finish(result: .incorrectOrder, cancelPrimitiveWait: true) { delegate in
                delegate.waiter(self, fulfillmentDidViolateOrderingConstraintsFor: validationExpectation.expectation, requiredExpectation: requiredValidationExpectation.expectation)
            }

        case .timedOut(let unfulfilledValidationExpectations):
            queue_finish(result: .timedOut, cancelPrimitiveWait: false) { delegate in
                delegate.waiter(self, didTimeoutWithUnfulfilledExpectations: unfulfilledValidationExpectations.map { $0.expectation })
            }

        case .incomplete:
            break

        }
    }

    private func queue_finish(result: Result, cancelPrimitiveWait: Bool, delegateBlock: ((XCTWaiterDelegate) -> Void)? = nil) {
        dispatchPrecondition(condition: .onQueue(XCTWaiter.subsystemQueue))
        guard case let .waiting(waitingState) = state else { preconditionFailure("Unexpected state: \(state)") }

        let unfulfilledExpectations = waitingState.expectations.filter { !waitingState.fulfilledExpectations.contains($0) }

        state = .finished(state: State.Finished(
            result: result,
            fulfilledExpectations: waitingState.fulfilledExpectations,
            unfulfilledExpectations: unfulfilledExpectations
        ))

        if cancelPrimitiveWait {
            self.cancelPrimitiveWait()
        }

        if let delegateBlock = delegateBlock, let delegate = _delegate {
            delegateQueue.async {
                delegateBlock(delegate)
            }
        }
    }

    private func expectationWasFulfilled(_ expectation: XCTestExpectation) {
        XCTWaiter.subsystemQueue.sync {
            // If already finished, do nothing
            guard case var .waiting(waitingState) = state else { return }

            waitingState.fulfilledExpectations.append(expectation)
            queue_validateExpectationFulfillment(dueToTimeout: false)
        }
    }

}

private extension XCTWaiter {
    func primitiveWait(using runLoop: RunLoop, duration timeout: TimeInterval) {
        // The contract for `primitiveWait(for:)` explicitly allows waiting for a shorter period than requested
        // by the `timeout` argument. Only run for a short time in case `cancelPrimitiveWait()` was called and
        // issued `CFRunLoopStop` just before we reach this point.
        let timeIntervalToRun = min(0.1, timeout)

        // RunLoop.run(mode:before:) should have @discardableResult <rdar://problem/45371901>
        _ = runLoop.run(mode: .default, before: Date(timeIntervalSinceNow: timeIntervalToRun))
    }

    func cancelPrimitiveWait() {
        guard let runLoop = runLoop else { return }
        CFRunLoopStop(runLoop.getCFRunLoop())
    }
}

extension XCTWaiter: Equatable {
    public static func == (lhs: XCTWaiter, rhs: XCTWaiter) -> Bool {
        return lhs === rhs
    }
}

extension XCTWaiter: CustomStringConvertible {
    public var description: String {
        return XCTWaiter.subsystemQueue.sync {
            let expectationsString = state.allExpectations.map { "'\($0.queue_expectationDescription)'" }.joined(separator: ", ")

            return "<XCTWaiter expectations: \(expectationsString)>"
        }
    }
}

extension XCTWaiter: ManageableWaiter {
    var isFinished: Bool {
        return XCTWaiter.subsystemQueue.sync {
            switch state {
            case .ready, .waiting: return false
            case .finished: return true
            }
        }
    }

    func queue_handleWatchdogTimeout() {
        dispatchPrecondition(condition: .onQueue(XCTWaiter.subsystemQueue))

        queue_validateExpectationFulfillment(dueToTimeout: true)
        manager!.queue_handleWatchdogTimeout(of: self)
        cancelPrimitiveWait()
    }

    func queue_interrupt(for interruptingWaiter: XCTWaiter) {
        dispatchPrecondition(condition: .onQueue(XCTWaiter.subsystemQueue))

        queue_finish(result: .interrupted, cancelPrimitiveWait: true) { delegate in
            delegate.nestedWaiter(self, wasInterruptedByTimedOutWaiter: interruptingWaiter)
        }
    }
}