implement EncryptionProcessor class

src/main/java/consumer/EncryptionProcessor.java

 package consumer;
 
 public class EncryptionProcessor {
+    private final int shiftKey;
+
+    public EncryptionProcessor(int shiftKey) {
+        this.shiftKey = shiftKey;
+    }
+
+    public String processLine(String line) {
+        // Handle empty or null lines
+        if (line == null || line.trim().isEmpty()) {
+            return line;
+        }
+
+        return caesarCipher(line, shiftKey);
+    }
+
+    private String caesarCipher(String text, int shift) {
+        StringBuilder result = new StringBuilder();
+
+        for (char character : text.toCharArray()) {
+            if (Character.isLetter(character)) {
+                // Determine if uppercase or lowercase
+                char base = Character.isLowerCase(character) ? 'a' : 'A';
+                // Calculate new position with wrap-around
+                int originalPosition = character - base;
+                int newPosition = (originalPosition + shift) % 26;
+                // Handle negative shifts
+                if (newPosition < 0) {
+                    newPosition += 26;
+                }
+                char encryptedChar = (char) (base + newPosition);
+                result.append(encryptedChar);
+            } else {
+                // Keep non-letter characters unchanged
+                result.append(character);
+            }
+        }
+
+        return result.toString();
+    }
+
+    public int getShiftKey() {
+        return shiftKey;
+    }
 }
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