Combine key scanning logic in one class

pass/Models/QRKeyScanner.swift

@@ -0,0 +1,73 @@
+//
+//  QRKeyScanner.swift
+//  pass
+//
+//  Created by Danny Moesch on 19.08.20.
+//  Copyright © 2020 Bob Sun. All rights reserved.
+//
+
+struct QRKeyScanner {
+    enum Result: Equatable {
+        case lookingForStart
+        case wrongKeyType(ScannableKeyType)
+        case completed
+        case scanned(Int)
+
+        var message: String {
+            switch self {
+            case .lookingForStart:
+                return "LookingForStartingFrame.".localize()
+            case let .wrongKeyType(keyType):
+                return "Scan\(keyType.visibility)Key.".localize()
+            case .completed:
+                return "Done".localize()
+            case let .scanned(count):
+                return "ScannedQrCodes(%d)".localize(count)
+            }
+        }
+
+        var unrolled: (accepted: Bool, message: String) {
+            if self == .completed {
+                return (true, message)
+            }
+            return (false, message)
+        }
+    }
+
+    private var segments = [String]()
+    private var previousResult = Result.lookingForStart
+
+    let keyType: ScannableKeyType
+
+    init(keyType: ScannableKeyType) {
+        self.keyType = keyType
+    }
+
+    var scannedKey: String {
+        segments.joined()
+    }
+
+    mutating func add(segment: String) -> Result {
+        // Skip duplicated segments.
+        guard segment != segments.last else {
+            return previousResult
+        }
+
+        // Check whether we have found the first block.
+        guard !segments.isEmpty || segment.contains(keyType.headerStart) else {
+            // Check whether we are scanning the wrong key type.
+            if let counterKeyType = keyType.counterType, segment.contains(counterKeyType.headerStart) {
+                previousResult = .wrongKeyType(counterKeyType)
+            }
+            return previousResult
+        }
+
+        // Update the list of scanned segments and return.
+        segments.append(segment)
+        if segment.starts(with: keyType.footerStart), segment.hasSuffix(keyType.footerEnd) {
+            return .completed
+        }
+        previousResult = .scanned(segments.count)
+        return previousResult
+    }
+}