Binding+Debounce.swift

extension DispatchTimeInterval {
  var nanoseconds: UInt64 {
    switch self {
    case .nanoseconds(let value) where value >= 0: return UInt64(value)
    case .microseconds(let value) where value >= 0: return UInt64(value) * 1000
    case .milliseconds(let value) where value >= 0: return UInt64(value) * 1_000_000
    case .seconds(let value) where value >= 0: return UInt64(value) * 1_000_000_000
    case .never: return .zero
    default: return .zero
    }
  }
}

final class UncheckedSendable<Value>: @unchecked Sendable {
  var storage: Value
  let lock = NSRecursiveLock()

  init(_ value: Value) {
    self.storage = value
  }

  var value: Value {
    get {
      defer { self.lock.unlock() }
      self.lock.lock()
      return self.storage
    }
    set {
      defer { self.lock.unlock() }
      self.lock.lock()
      self.storage = newValue
    }
  }
}

#if canImport(SwiftUI)
import SwiftUI

extension Binding {
  struct DueValue {
    let value: Value
    let dueTime: DispatchTime
  }

  public func debounce(for dueTime: DispatchTimeInterval) -> Self {
    let lastKnownValue = UncheckedSendable<DueValue?>(nil)
    let debouncing = UncheckedSendable(false)

    return Binding {
      self.wrappedValue
    } set: { value in
      if debouncing.value {
        let newValue = DueValue(value: value, dueTime: DispatchTime.now().advanced(by: dueTime))
        lastKnownValue.value = newValue
      } else {
        debouncing.value = true
        Task {
          var timeToSleep = dueTime.nanoseconds
          var currentValue = value

          repeat {
            lastKnownValue.value = nil

            try? await Task.sleep(nanoseconds: timeToSleep)

            if let lastKnownValue = lastKnownValue.value {
              timeToSleep = DispatchTime.now().distance(to: lastKnownValue.dueTime).nanoseconds
              currentValue = lastKnownValue.value
            }
          } while lastKnownValue.value != nil
          debouncing.value = false
          self.wrappedValue = currentValue
        }
      }
    }
  }
}
#endif