Stage #3: Supporting decryption

src/crypto/Crypto.java

@@ -1,10 +1,107 @@
 package crypto;
 
+import java.io.File;
+import java.io.FileNotFoundException;
+import java.io.FileWriter;
+import java.io.IOException;
+import java.util.HashMap;
 import java.util.Scanner;
 
 public class Crypto {
+    interface  Strategy {
+        String encrypt(String text, int key);
+        String decrypt(String text, int key);
+    }
+    public class Xor implements Strategy{
+        @Override
+        public String encrypt(String text, int key) {
+            StringBuilder sb = new StringBuilder();
+            for (int i = 0; i < text.length(); i++) {
+                sb.append((char) (text.charAt(i) ^ key));
+            }
+            return sb.toString();
+        }
+        @Override
+        public String decrypt(String text, int key) {
+            StringBuilder sb = new StringBuilder();
+            for (int i = 0; i < text.length(); i++) {
+                sb.append((char) (text.charAt(i) ^ key));
+            }
+            return sb.toString();
+        }
+    }
+
     public static void main(String[] args) {
-        Scanner scanner = new Scanner(System.in);
-	// write your code here
+        HashMap<String, String> params = new HashMap<>();
+        for (int i = 0; i < args.length / 2; i++) {
+            params.put(args[i], args[i + 1]);
+        }
+        String operation = params.get("-mode");
+        String text = params.get("-data");
+        int key = Integer.parseInt(params.get("-key"));
+        String inputFileName = params.get("-in");
+        String outputFileName = params.get("-out");
+        String algorithm = params.get("-alg");
+        Strategy strategy;
+        //if (algorithm.isEmpty()) {
+            strategy = new Crypto().new Xor();
+        //}
+        if (operation.isEmpty()) {
+            operation = "enc";
+        }
+        if (!text.isEmpty() && !inputFileName.isEmpty()) {
+            Scanner scanner = new Scanner(System.in);
+            text = scanner.nextLine();
+            key = scanner.nextInt();
+            scanner.close();
+        }
+        if (inputFileName.isEmpty()) {
+            String result = "";
+            switch (operation) {
+                case "enc":
+                    result = strategy.encrypt(text, key);
+                    break;
+                case "dec":
+                    result = strategy.decrypt(text, key);
+                    break;
+            }
+            if (outputFileName.isEmpty()) {
+                System.out.println(result);
+            } else {
+                try {
+                    FileWriter writer = new FileWriter(new File(outputFileName));
+                    writer.write(result);
+                } catch (IOException e) {
+                    System.out.println(e);
+                }
+            }
+        } else {
+            try {
+                Scanner scanner = new Scanner(new File(inputFileName));
+                while (scanner.hasNextLine()) {
+                    String result = "";
+                    switch (operation) {
+                        case "enc":
+                            result = strategy.decrypt(scanner.nextLine(), key);
+                            break;
+                        case "dec":
+                            result = strategy.decrypt(scanner.nextLine(), key);
+                            break;
+                    }
+                    if (outputFileName.isEmpty()) {
+                        System.out.println(result);
+                    } else {
+                        try {
+                            FileWriter writer = new FileWriter(new File(outputFileName));
+                            writer.write(result);
+                        } catch (IOException e) {
+                            System.out.println(e);
+                        }
+                    }
+                }
+            } catch (FileNotFoundException e) {
+                System.out.println("Input file does not exist");
+            }
+        }
     }
-}
+}