An AsyncSequence that iterates at most once every `interval`

AsyncIntervalSequence.swift

/// An AsyncSequence that iterates at most once every `interval`
public struct AsyncIntervalSequence<Base: AsyncSequence, C: Clock> {
    public let base: Base
    public let interval: C.Instant.Duration
    public let clock: C

    public init(_ base: Base, interval: C.Instant.Duration, clock: C) {
        self.base = base
        self.interval = interval
        self.clock = clock
    }
}

extension AsyncIntervalSequence: AsyncSequence {
    public typealias Element = Base.Element

    public struct AsyncIterator: AsyncIteratorProtocol {
        public var base: Base.AsyncIterator
        public let interval: C.Instant.Duration
        public let clock: C
        public var last: C.Instant?

        public init(_ base: Base.AsyncIterator, interval: C.Instant.Duration, clock: C) {
            self.base = base
            self.interval = interval
            self.clock = clock
        }

        public mutating func next() async throws -> Base.Element? {
            if let last {
                let next = last.advanced(by: interval)

                if clock.now < next {
                    try await Task.sleep(until: next, clock: clock)
                }
            }

            last = clock.now

            return try await base.next()
        }
    }

    public func makeAsyncIterator() -> AsyncIterator {
        AsyncIterator(base.makeAsyncIterator(), interval: interval, clock: clock)
    }
}

extension AsyncSequence {
    public func every(
        _ interval: Duration
    ) -> AsyncIntervalSequence<Self, ContinuousClock> {
        .init(self, interval: interval, clock: .continuous)
    }
}