Implement bank transfer app flows

Thijooree iOS/ViewModels/LockViewModel.swift

@@ -0,0 +1,85 @@
+import Foundation
+import Observation
+
+@Observable
+final class LockViewModel {
+    private static let maxAttempts       = 5
+    private static let lockoutDuration   = 30.0
+
+    var pinDigits:   [Int] = []
+    var hintMessage  = ""
+    var isVerifying  = false
+
+    private let autoUnlock: Bool
+    private(set) var pinLength: Int
+
+    init() {
+        self.autoUnlock = UserDefaults.standard.bool(forKey: "auto_unlock_pin")
+        self.pinLength  = max(4, UserDefaults.standard.integer(forKey: "pin_length"))
+    }
+
+    // MARK: - Display
+
+    var dotsDisplay: String {
+        let n     = pinDigits.count
+        let total = autoUnlock ? pinLength : max(n, 4)
+        return String(repeating: "●", count: n)
+             + String(repeating: "○", count: max(total - n, 0))
+    }
+
+    // MARK: - Lockout
+
+    var lockoutRemaining: TimeInterval {
+        let fails = UserDefaults.standard.integer(forKey: "lock_fail_count")
+        guard fails >= Self.maxAttempts else { return 0 }
+        let lastFail = UserDefaults.standard.double(forKey: "lock_last_fail_time")
+        let elapsed  = Date().timeIntervalSince1970 - lastFail
+        return max(0, Self.lockoutDuration - elapsed)
+    }
+
+    var isLockedOut: Bool { lockoutRemaining > 0 }
+
+    func resetFailures() {
+        UserDefaults.standard.removeObject(forKey: "lock_fail_count")
+        UserDefaults.standard.removeObject(forKey: "lock_last_fail_time")
+    }
+
+    @discardableResult
+    func incrementFailures() -> Int {
+        let fails = UserDefaults.standard.integer(forKey: "lock_fail_count") + 1
+        UserDefaults.standard.set(fails, forKey: "lock_fail_count")
+        UserDefaults.standard.set(Date().timeIntervalSince1970, forKey: "lock_last_fail_time")
+        return fails
+    }
+
+    // MARK: - Key handling
+
+    // Returns true when PIN should be submitted
+    func handleKey(_ key: String) -> Bool {
+        guard !isVerifying else { return false }
+        switch key {
+        case "⌫":
+            if !pinDigits.isEmpty { pinDigits.removeLast() }
+        case "✓":
+            if pinDigits.count >= 4 { return true }
+        default:
+            if let d = Int(key), pinDigits.count < 8 {
+                pinDigits.append(d)
+                if autoUnlock && pinDigits.count == pinLength { return true }
+            }
+        }
+        return false
+    }
+
+    func currentPin() -> String { pinDigits.map(String.init).joined() }
+    func clearPin()             { pinDigits = [] }
+
+    func failureHint() -> String {
+        let fails     = incrementFailures()
+        let remaining = Self.maxAttempts - fails
+        if remaining <= 0 {
+            return "Too many attempts. Try again in \(Int(Self.lockoutDuration))s."
+        }
+        return "\(remaining) attempt\(remaining == 1 ? "" : "s") remaining"
+    }
+}