AsyncTimerSequence.swift

//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift Async Algorithms open source project
//
// Copyright (c) 2022 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
//
//===----------------------------------------------------------------------===//

/// An `AsyncSequence` that produces elements at regular intervals.
@available(macOS 13.0, iOS 16.0, watchOS 9.0, tvOS 16.0, *)
public struct AsyncTimerSequence<C: Clock>: AsyncSequence {
  public typealias Element = C.Instant

  /// The iterator for an `AsyncTimerSequence` instance.
  public struct Iterator: AsyncIteratorProtocol {
    var clock: C?
    let interval: C.Instant.Duration
    let tolerance: C.Instant.Duration?
    var last: C.Instant?

    init(interval: C.Instant.Duration, tolerance: C.Instant.Duration?, clock: C) {
      self.clock = clock
      self.interval = interval
      self.tolerance = tolerance
    }

    public mutating func next() async -> C.Instant? {
      guard let clock = self.clock else {
        return nil
      }

      let next = (self.last ?? clock.now).advanced(by: self.interval)
      do {
        try await clock.sleep(until: next, tolerance: self.tolerance)
      } catch {
        self.clock = nil
        return nil
      }
      let now = clock.now
      self.last = next
      return now
    }
  }

  let clock: C
  let interval: C.Instant.Duration
  let tolerance: C.Instant.Duration?

  /// Create an `AsyncTimerSequence` with a given repeating interval.
  public init(interval: C.Instant.Duration, tolerance: C.Instant.Duration? = nil, clock: C) {
    self.clock = clock
    self.interval = interval
    self.tolerance = tolerance
  }

  public func makeAsyncIterator() -> Iterator {
    Iterator(interval: interval, tolerance: tolerance, clock: clock)
  }
}

@available(macOS 13.0, iOS 16.0, watchOS 9.0, tvOS 16.0, *)
extension AsyncTimerSequence {
  /// Create an `AsyncTimerSequence` with a given repeating interval.
  public static func repeating(every interval: C.Instant.Duration, tolerance: C.Instant.Duration? = nil, clock: C) -> AsyncTimerSequence<C> {
    return AsyncTimerSequence(interval: interval, tolerance: tolerance, clock: clock)
  }
}

@available(macOS 13.0, iOS 16.0, watchOS 9.0, tvOS 16.0, *)
extension AsyncTimerSequence where C == SuspendingClock {
  /// Create an `AsyncTimerSequence` with a given repeating interval.
  public static func repeating(every interval: Duration, tolerance: Duration? = nil) -> AsyncTimerSequence<SuspendingClock> {
    return AsyncTimerSequence(interval: interval, tolerance: tolerance, clock: SuspendingClock())
  }
}

@available(macOS 13.0, iOS 16.0, watchOS 9.0, tvOS 16.0, *)
extension AsyncTimerSequence: Sendable { }

@available(*, unavailable)
extension AsyncTimerSequence.Iterator: Sendable { }