import Dispatch

/**
 Waits on all provided promises.

 `when` rejects as soon as one of the provided promises rejects. `join` waits on all provided promises, then rejects if any of those promises rejected, otherwise it fulfills with values from the provided promises.

     join(promise1, promise2, promise3).then { results in
         //…
     }.catch { error in
         switch error {
         case Error.Join(let promises):
             //…
         }
     }

 - Returns: A new promise that resolves once all the provided promises resolve.
 - SeeAlso: `PromiseKit.Error.join`
*/
@available(*, deprecated: 4.0, message: "Use when(resolved:)")
public func join<T>(_ promises: Promise<T>...) -> Promise<[T]> {
    return join(promises)
}

/// Waits on all provided promises.
@available(*, deprecated: 4.0, message: "Use when(resolved:)")
public func join(_ promises: [Promise<Void>]) -> Promise<Void> {
    return join(promises).then(on: zalgo) { (_: [Void]) in return Promise(value: ()) }
}

/// Waits on all provided promises.
@available(*, deprecated: 4.0, message: "Use when(resolved:)")
public func join<T>(_ promises: [Promise<T>]) -> Promise<[T]> {
    guard !promises.isEmpty else { return Promise(value: []) }
  
    var countdown = promises.count
    let barrier = DispatchQueue(label: "org.promisekit.barrier.join", attributes: .concurrent)
    var rejected = false

    return Promise { fulfill, reject in
        for promise in promises {
            promise.state.pipe { resolution in
                barrier.sync(flags: .barrier) {
                    if case .rejected(_, let token) = resolution {
                        token.consumed = true  // the parent Error.Join consumes all
                        rejected = true
                    }
                    countdown -= 1
                    if countdown == 0 {
                        if rejected {
                            reject(PMKError.join(promises))
                        } else {
                            fulfill(promises.map{ $0.value! })
                        }
                    }
                }
            }
        }
    }
}