PencilKit Handwriting Recognition & Stroke APIs

import SwiftUI
import PencilKit

struct HandwritingCheckerView: View {
    let targetWord = "heart"

    @State private var canvas = PKCanvasView()
    @State private var resultMessage: String = ""
    @State private var resultColor: Color = .clear
    @State private var isChecking = false

    private let recognizer: PKStrokeRecognizer = {
        var r = PKStrokeRecognizer()
        r.preferredLanguages = [Locale.Language(identifier: "en")]
        return r
    }()

    var body: some View {
        VStack(spacing: 16) {
            Text("Write: \"\(targetWord)\"")
                .font(.title2.bold())

            CanvasWrapper(canvas: canvas)
                .frame(height: 200)
                .clipShape(RoundedRectangle(cornerRadius: 12))
                .overlay(
                    RoundedRectangle(cornerRadius: 12)
                        .stroke(Color.secondary, lineWidth: 1)
                )

            if !resultMessage.isEmpty {
                Text(resultMessage)
                    .font(.headline)
                    .foregroundStyle(.white)
                    .padding(.horizontal, 20)
                    .padding(.vertical, 10)
                    .background(resultColor, in: RoundedRectangle(cornerRadius: 8))
            }

            HStack(spacing: 12) {
                Button("Check") {
                    Task { await checkHandwriting() }
                }
                .buttonStyle(.borderedProminent)
                .disabled(isChecking)

                Button("Clear") {
                    canvas.drawing = PKDrawing()
                    resultMessage = ""
                }
                .buttonStyle(.bordered)
            }
        }
        .padding()
    }

    @MainActor
    private func checkHandwriting() async {
        guard !canvas.drawing.strokes.isEmpty else {
            resultMessage = "Write something first!"
            resultColor = .orange
            return
        }
        isChecking = true
        defer { isChecking = false }

        let drawing = canvas.drawing
        // Collect all stroke IDs from the current drawing
        let strokeIDs = drawing.strokes.map(\.id)

        do {
            // recognizedText returns the single best interpretation
            let recognized = try await recognizer.recognizedText(
                for: drawing,
                strokeIDs: strokeIDs
            )
            let trimmed = recognized.trimmingCharacters(in: .whitespacesAndNewlines).lowercased()
            if trimmed == targetWord.lowercased() {
                resultMessage = "✅ Correct! (\"\(recognized)\")"
                resultColor = .green
            } else {
                resultMessage = "❌ Got \"\(recognized)\" — try again"
                resultColor = .red
            }
        } catch {
            resultMessage = "Recognition failed: \(error.localizedDescription)"
            resultColor = .orange
        }
    }
}

// UIViewRepresentable wrapper so PKCanvasView works in SwiftUI
struct CanvasWrapper: UIViewRepresentable {
    let canvas: PKCanvasView
    func makeUIView(context: Context) -> PKCanvasView {
        canvas.backgroundColor = UIColor.secondarySystemBackground
        canvas.tool = PKInkingTool(.pen, color: .label, width: 5)
        return canvas
    }
    func updateUIView(_ uiView: PKCanvasView, context: Context) {}
}

#Preview {
    HandwritingCheckerView()
}