Add Stepper control

Author: colemancda

AndroidSwiftUICore/Sources/AndroidSwiftUICore/Primitives/Stepper.swift

@@ -0,0 +1,76 @@
+//
+//  Stepper.swift
+//  AndroidSwiftUICore
+//
+//  A control that increments or decrements a value. The core registers the two
+//  edge actions as callbacks; the interpreter renders a label plus − / + buttons.
+//
+
+public struct Stepper<Label: View>: View {
+
+    internal let label: Label
+    internal let onIncrement: () -> Void
+    internal let onDecrement: () -> Void
+
+    public init(
+        onIncrement: @escaping () -> Void,
+        onDecrement: @escaping () -> Void,
+        @ViewBuilder label: () -> Label
+    ) {
+        self.label = label()
+        self.onIncrement = onIncrement
+        self.onDecrement = onDecrement
+    }
+
+    public typealias Body = Never
+}
+
+public extension Stepper where Label == Text {
+
+    init<S: StringProtocol, V: Strideable>(
+        _ title: S,
+        value: Binding<V>,
+        in bounds: ClosedRange<V>,
+        step: V.Stride = 1
+    ) {
+        self.init(
+            onIncrement: {
+                let next = value.wrappedValue.advanced(by: step)
+                if next <= bounds.upperBound { value.wrappedValue = next }
+            },
+            onDecrement: {
+                let previous = value.wrappedValue.advanced(by: -step)
+                if previous >= bounds.lowerBound { value.wrappedValue = previous }
+            },
+            label: { Text(title) }
+        )
+    }
+
+    init<S: StringProtocol, V: Strideable>(
+        _ title: S,
+        value: Binding<V>,
+        step: V.Stride = 1
+    ) {
+        self.init(
+            onIncrement: { value.wrappedValue = value.wrappedValue.advanced(by: step) },
+            onDecrement: { value.wrappedValue = value.wrappedValue.advanced(by: -step) },
+            label: { Text(title) }
+        )
+    }
+}
+
+extension Stepper: PrimitiveView {
+    public func _render(in context: ResolveContext) -> RenderNode {
+        let incrementID = context.callbacks.register(.void(onIncrement))
+        let decrementID = context.callbacks.register(.void(onDecrement))
+        return RenderNode(
+            type: "Stepper",
+            id: context.path,
+            props: [
+                "onIncrement": .int(Int(incrementID)),
+                "onDecrement": .int(Int(decrementID)),
+            ],
+            children: Evaluator.resolveChildren(label, context.descending("label"))
+        )
+    }
+}