Extract interfaces and add javadocs

Author: malczuuu

src/main/java/io/github/malczuuu/problem4j/core/JsonEscape.java

@@ -3,8 +3,15 @@
 import java.util.HashMap;
 import java.util.Map;
 
+/**
+ * Utility class for escaping strings for safe inclusion in JSON.
+ *
+ * <p>Replaces control characters, special characters, and Unicode ranges with appropriate escape
+ * sequences to produce valid JSON string literals.
+ */
 final class JsonEscape {
 
+  /** Mapping of characters to their JSON escape sequences. */
   private static final Map<Character, String> REPLACEMENTS = new HashMap<>();
 
   static {
@@ -18,6 +25,18 @@ final class JsonEscape {
     REPLACEMENTS.put('/', "\\/");
   }
 
+  /** Private constructor to prevent instantiation. */
+  private JsonEscape() {}
+
+  /**
+   * Escapes the given string for inclusion in JSON.
+   *
+   * <p>Replaces control characters, special characters, and certain Unicode ranges with appropriate
+   * escape sequences.
+   *
+   * @param value the string to escape
+   * @return the escaped string
+   */
   static String escape(String value) {
     StringBuilder result = new StringBuilder();
 
@@ -34,24 +53,56 @@ static String escape(String value) {
     return result.toString();
   }
 
+  /**
+   * Determines if the character should be replaced using a predefined escape sequence.
+   *
+   * @param character the character to check
+   * @return true if the character has a predefined replacement
+   */
   private static boolean shouldBeReplaced(char character) {
     return REPLACEMENTS.containsKey(character);
   }
 
+  /**
+   * Appends the JSON escape sequence for a character that has a predefined replacement.
+   *
+   * @param result the StringBuilder to append to
+   * @param character the character to escape
+   */
   private static void replace(StringBuilder result, char character) {
     result.append(REPLACEMENTS.get(character));
   }
 
+  /**
+   * Determines if the character should be escaped using a Unicode hexadecimal escape.
+   *
+   * <p>Characters that are control characters or in certain Unicode ranges are escaped.
+   *
+   * @param character the character to check
+   * @return true if the character should be represented as a Unicode escape
+   */
   private static boolean shouldBeHexed(char character) {
     return character <= '\u001F'
         || character >= '\u007F' && character <= '\u009F'
         || character >= '\u2000' && character <= '\u20FF';
   }
 
+  /**
+   * Appends the Unicode hexadecimal escape sequence for the given character to the result.
+   *
+   * <p>The escape sequence is in the format {@code "\\uXXXX"}, where {@code "XXXX"} is the
+   * uppercase hexadecimal representation of the character code, padded with leading zeros to four
+   * digits.
+   *
+   * @param result the StringBuilder to append the escape sequence to
+   * @param character the character to be escaped
+   */
   private static void hex(StringBuilder result, char character) {
-    String hexedCharacter = Integer.toHexString(character);
+    String hexedCharacter = Integer.toHexString(character).toUpperCase();
     result.append("\\u");
-    result.append("0".repeat(4 - hexedCharacter.length()));
-    result.append(hexedCharacter.toUpperCase());
+    for (int i = 0; i < 4 - hexedCharacter.length(); i++) {
+      result.append('0');
+    }
+    result.append(hexedCharacter);
   }
 }