Add DragGesture and the long press gesture

Author: colemancda

AndroidSwiftUICore/Sources/AndroidSwiftUICore/Gesture.swift

@@ -0,0 +1,109 @@
+//
+//  Gesture.swift
+//  AndroidSwiftUICore
+//
+//  Continuous gestures. A drag reports through the fixed string callback rather
+//  than growing the bridge with a two-number entry point: the interpreter sends
+//  "<phase>;<startX>,<startY>;<x>,<y>" in points, which rebuilds a Value here.
+//
+
+import Foundation
+
+/// A gesture recognized on a view. `.gesture(_:)` currently accepts `DragGesture`.
+public protocol Gesture {}
+
+public struct DragGesture: Gesture {
+
+    /// The state of a drag as it is recognized.
+    public struct Value {
+        public var startLocation: CGPoint
+        public var location: CGPoint
+        public var translation: CGSize
+    }
+
+    /// How far the touch must move before the drag is recognized.
+    public var minimumDistance: Double
+
+    internal var changedAction: ((Value) -> Void)?
+    internal var endedAction: ((Value) -> Void)?
+
+    public init(minimumDistance: Double = 10) {
+        self.minimumDistance = minimumDistance
+    }
+
+    public func onChanged(_ action: @escaping (Value) -> Void) -> DragGesture {
+        var copy = self
+        copy.changedAction = action
+        return copy
+    }
+
+    public func onEnded(_ action: @escaping (Value) -> Void) -> DragGesture {
+        var copy = self
+        copy.endedAction = action
+        return copy
+    }
+}
+
+internal extension DragGesture.Value {
+
+    /// Rebuilds a value from the interpreter's `"<phase>;<sx>,<sy>;<x>,<y>"`.
+    init?(payload: String) {
+        let fields = payload.split(separator: ";")
+        guard fields.count == 3 else { return nil }
+        let start = fields[1].split(separator: ",").compactMap { Double($0) }
+        let current = fields[2].split(separator: ",").compactMap { Double($0) }
+        guard start.count == 2, current.count == 2 else { return nil }
+        self.startLocation = CGPoint(x: start[0], y: start[1])
+        self.location = CGPoint(x: current[0], y: current[1])
+        self.translation = CGSize(width: current[0] - start[0], height: current[1] - start[1])
+    }
+}
+
+// MARK: - Modifiers
+
+public struct _GestureModifier: RenderModifier, _CallbackModifier {
+
+    let gesture: DragGesture
+
+    public var _modifierNode: ModifierNode { ModifierNode(kind: "drag") }
+
+    public func _callbackNode(in context: ResolveContext) -> ModifierNode {
+        let changed = gesture.changedAction
+        let ended = gesture.endedAction
+        let id = context.callbacks.register(.string { payload in
+            guard let value = DragGesture.Value(payload: payload) else { return }
+            if payload.hasPrefix("ended") {
+                ended?(value)
+            } else {
+                changed?(value)
+            }
+        })
+        return ModifierNode(kind: "drag", args: [
+            "action": .int(Int(id)),
+            "minimumDistance": .double(gesture.minimumDistance),
+        ])
+    }
+}
+
+public struct _LongPressModifier: RenderModifier, _CallbackModifier {
+
+    let action: () -> Void
+
+    public var _modifierNode: ModifierNode { ModifierNode(kind: "longPress") }
+
+    public func _callbackNode(in context: ResolveContext) -> ModifierNode {
+        let id = context.callbacks.register(.void(action))
+        return ModifierNode(kind: "longPress", args: ["action": .int(Int(id))])
+    }
+}
+
+public extension View {
+
+    func gesture(_ gesture: DragGesture) -> ModifiedContent<Self, _GestureModifier> {
+        modifier(_GestureModifier(gesture: gesture))
+    }
+
+    func onLongPressGesture(perform action: @escaping () -> Void) -> ModifiedContent<Self, _LongPressModifier> {
+        modifier(_LongPressModifier(action: action))
+    }
+}