Prevents user button smashing.

SingleTaskButton.swift

/// A button that ensures only a single async task executes at a time.
///
/// `SingleTaskButton` prevents double-execution of async operations by tracking the active task
/// and disabling itself while the operation is in progress. This is essential for critical
/// operations like purchases, payments, or irreversible actions where duplicate execution
/// would be harmful.
///
/// ## Example
/// ```swift
/// SingleTaskButton {
///     try await store.purchaseProduct(product)
/// } label: {
///     Text("Purchase")
/// }
/// ```
///
/// ## Features
/// - Guarantees only one task runs at a time (no race conditions)
/// - Self-disables during operation (visual feedback)
/// - Supports throwing async functions
/// - Generic over label content
///
/// ## Use Cases
/// - Financial transactions (purchases, payments)
/// - Irreversible destructive actions (permanent delete)
/// - Operations with side effects (sending emails, notifications)
struct SingleTaskButton<Label: View>: View {

    /// The async action to perform when the button is tapped.
    let action: () async throws -> Void

    /// The button's label content.
    @ViewBuilder let label: Label

    /// Tracks the currently running task to prevent re-entry.
    @State private var task: Task<Void, Never>?

    var body: some View {
        Button {
            // Prevent creating a new task if one is already running
            guard task == nil else { return }

            task = Task {
                defer { task = nil }
                // Silently handle errors - callers should handle errors in their action
                try? await action()
            }
        } label: {
            label
        }
        .disabled(task != nil)
    }
}