How to Build a Kanji Learning App in SwiftUI

import SwiftData
import Foundation

@Model
final class Kanji {
    var character: String
    var meaning: String
    var onyomi: [String]
    var kunyomi: [String]
    var strokeCount: Int
    var jlptLevel: Int        // 1 = N1 … 5 = N5
    var masteryScore: Double  // 0.0 – 1.0
    var nextReviewDate: Date
    var reviewInterval: Int   // days

    init(character: String, meaning: String, onyomi: [String],
         kunyomi: [String], strokeCount: Int, jlptLevel: Int) {
        self.character = character; self.meaning = meaning
        self.onyomi = onyomi;      self.kunyomi = kunyomi
        self.strokeCount = strokeCount; self.jlptLevel = jlptLevel
        self.masteryScore = 0.0
        self.nextReviewDate = .now
        self.reviewInterval = 1
    }
}

struct KanjiDashboardView: View {
    @Query(sort: \Kanji.jlptLevel) private var allKanji: [Kanji]
    @State private var selectedLevel = 5
    var filtered: [Kanji] { allKanji.filter { $0.jlptLevel == selectedLevel } }

    var body: some View {
        NavigationStack {
            VStack(spacing: 0) {
                Picker("JLPT Level", selection: $selectedLevel) {
                    ForEach(1...5, id: \.self) { Text("N\($0)").tag($0) }
                }
                .pickerStyle(.segmented).padding()
                List(filtered) { kanji in
                    NavigationLink(value: kanji) {
                        KanjiRowView(kanji: kanji)
                    }
                }
            }
            .navigationTitle("Kanji")
            .navigationDestination(for: Kanji.self) {
                StrokePracticeView(kanji: $0)
            }
        }
    }
}

struct StrokePracticeView: View {
    let kanji: Kanji
    @State private var strokes: [[CGPoint]] = []
    @State private var live: [CGPoint] = []
    @State private var showGuide = true

    var body: some View {
        VStack(spacing: 16) {
            Text(kanji.character)
                .font(.system(size: 80))
                .opacity(showGuide ? max(0.08, 1 - kanji.masteryScore) : 0)
            Canvas { ctx, _ in
                let style = StrokeStyle(lineWidth: 9, lineCap: .round, lineJoin: .round)
                for pts in strokes { ctx.stroke(stroke(pts), with: .color(.primary), style: style) }
                if !live.isEmpty { ctx.stroke(stroke(live), with: .color(.blue), style: style) }
            }
            .frame(width: 280, height: 280)
            .background(Color(.systemGray6))
            .clipShape(RoundedRectangle(cornerRadius: 16))
            .gesture(DragGesture(minimumDistance: 0)
                .onChanged { live.append($0.location) }
                .onEnded { _ in strokes.append(live); live = [] })
            HStack {
                Button("Clear") { strokes = []; live = [] }.buttonStyle(.bordered)
                Toggle("Guide", isOn: $showGuide)
                Spacer()
                Text("\(strokes.count) / \(kanji.strokeCount)").foregroundStyle(.secondary)
            }.padding(.horizontal)
        }
        .navigationTitle("Stroke Practice").navigationBarTitleDisplayMode(.inline)
    }

    private func stroke(_ pts: [CGPoint]) -> Path {
        var p = Path()
        guard let f = pts.first else { return p }
        p.move(to: f); pts.dropFirst().forEach { p.addLine(to: $0) }
        return p
    }
}

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