/*
Copyright (C) 2015 Apple Inc. All Rights Reserved.
See LICENSE.txt for this sample’s licensing information

Abstract:
This file shows an example of implementing the OperationCondition protocol.
*/

import Foundation

/// A generic condition for describing kinds of operations that may not execute concurrently.
struct MutuallyExclusive<T>: OperationCondition {
    static var name: String {
        return "MutuallyExclusive<\(T.self)>"
    }

    static var isMutuallyExclusive: Bool {
        return true
    }
    
    init() { }
    
    func dependencyForOperation(operation: EarthquakeOperation) -> Operation? {
        return nil
    }
    
    func evaluateForOperation(operation: EarthquakeOperation, completion: (OperationConditionResult) -> Void) {
        completion(.Satisfied)
    }
}

/**
    The purpose of this enum is to simply provide a non-constructible
    type to be used with `MutuallyExclusive<T>`.
*/
enum Alert { }

/// A condition describing that the targeted operation may present an alert.
typealias AlertPresentation = MutuallyExclusive<Alert>