import SwiftUI

struct OtpPreviewView: View {
    let seed: String

    @State private var code     = ""
    @State private var progress = 0.0   // 0.0 – 1.0 within the current 30s window
    @State private var timer: Timer?

    var body: some View {
        HStack(spacing: 12) {
            VStack(alignment: .leading, spacing: 2) {
                Text("Current OTP")
                    .font(.caption2)
                    .foregroundStyle(.secondary)
                Text(formatted(code))
                    .font(.system(size: 22, weight: .semibold, design: .monospaced))
                    .foregroundStyle(.primary)
            }

            Spacer()

            ZStack {
                Circle()
                    .stroke(Color(.systemFill), lineWidth: 3)
                Circle()
                    .trim(from: 0, to: progress)
                    .stroke(progressColor, style: StrokeStyle(lineWidth: 3, lineCap: .round))
                    .rotationEffect(.degrees(-90))
                    .animation(.linear(duration: 0.8), value: progress)
                Text("\(Int(progress * 30))")
                    .font(.caption2.monospacedDigit())
                    .foregroundStyle(.secondary)
            }
            .frame(width: 36, height: 36)
        }
        .padding(.horizontal, 16)
        .padding(.vertical, 10)
        .background(.regularMaterial, in: RoundedRectangle(cornerRadius: 12))
        .contentShape(Rectangle())
        .onTapGesture { UIPasteboard.general.string = code }
        .onAppear { refresh(); startTimer() }
        .onDisappear { timer?.invalidate(); timer = nil }
    }

    private var progressColor: Color {
        progress < 0.33 ? .red : progress < 0.6 ? .orange : .green
    }

    private func formatted(_ otp: String) -> String {
        guard otp.count == 6 else { return otp }
        return "\(otp.prefix(3)) \(otp.suffix(3))"
    }

    private func refresh() {
        code = (try? Totp.generate(seed)) ?? Totp.generate(seed)
        let seconds = Int(Date().timeIntervalSince1970) % 30
        progress = Double(30 - seconds) / 30.0
    }

    private func startTimer() {
        timer?.invalidate()
        timer = Timer.scheduledTimer(withTimeInterval: 1, repeats: true) { _ in refresh() }
    }
}

#Preview {
    OtpPreviewView(seed: "JBSWY3DPEHPK3PXP")
        .padding()
}