SwiftUI Binding for MutableStateFlow

FlowBinding.swift

// code from Chris Hatton - https://kotlinlang.slack.com/archives/C9JM6Q2UX/p1740462546873469?thread_ts=1740462525.562349&cid=C9JM6Q2UX

struct FlowBinding<FlowValue: Equatable, BoundValue: Equatable, Content>: View where Content: View {
    private let mutableStateFlow: SkieSwiftMutableStateFlow<FlowValue>
    private let content: (Binding<BoundValue>) -> Content
    private let transformOut: (FlowValue) -> BoundValue
    private let transformIn: (BoundValue) -> FlowValue
    
    // Track the source of truth internally
    @State private var currentValue: BoundValue
    @State private var lastFlowValue: FlowValue
    
    init(
        mutableStateFlow: SkieSwiftMutableStateFlow<FlowValue>,
        transformOut: @escaping (FlowValue) -> BoundValue,
        transformIn: @escaping (BoundValue) -> FlowValue,
        @SwiftUI.ViewBuilder content: @escaping (Binding<BoundValue>) -> Content
    ) {
        self.mutableStateFlow = mutableStateFlow
        self.content = content
        self.transformIn = transformIn
        self.transformOut = transformOut
        
        let initialFlowValue = mutableStateFlow.value
        self._lastFlowValue = State(initialValue: initialFlowValue)
        self._currentValue = State(initialValue: transformOut(initialFlowValue))
    }
    
    var body: some View {
        
        let binding = Binding<BoundValue>(
            get: { currentValue },
            set: { newValue in
                // Update our local value first
                currentValue = newValue
                
                // Calculate and set the new flow value
                let newFlowValue = transformIn(newValue)
                
                // Break update cycle early (even if StateFlow would do this)
                if newFlowValue != lastFlowValue {
                    lastFlowValue = newFlowValue
                    mutableStateFlow.value = newFlowValue
                }
            }
        )
        
        return content(binding)
            .collect(flow: mutableStateFlow) { newFlowValue in
                lastFlowValue = newFlowValue
                currentValue = transformOut(newFlowValue)
            }
    }
}