M3-AP-007: Startvalidierung für Quellordner testbar gemacht

pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/config/StartConfigurationValidator.java

@@ -14,11 +14,57 @@ import java.util.List;
  * Performs mandatory field checks, numeric range validation, URI scheme validation,
  * and basic path existence checks. Throws {@link InvalidStartConfigurationException}
  * if any validation rule fails.
+ * <p>
+ * M3/AP-007: Supports injected source folder validation for testability
+ * (allows mocking of platform-dependent filesystem checks).
  */
 public class StartConfigurationValidator {
 
     private static final Logger LOG = LogManager.getLogger(StartConfigurationValidator.class);
 
+    /**
+     * Abstraction for source folder existence, type, and readability checks.
+     * <p>
+     * Separates filesystem operations from validation logic to enable
+     * platform-independent unit testing (mocking) of readability edge cases.
+     * <p>
+     * Implementation note: The default implementation uses {@code java.nio.file.Files}
+     * static methods directly; tests can substitute alternative implementations.
+     */
+    @FunctionalInterface
+    public interface SourceFolderChecker {
+        /**
+         * Checks source folder and returns validation error message, or null if valid.
+         * <p>
+         * Checks (in order):
+         * 1. Folder exists
+         * 2. Is a directory
+         * 3. Is readable
+         *
+         * @param path the source folder path
+         * @return error message string, or null if all checks pass
+         */
+        String checkSourceFolder(Path path);
+    }
+
+    private final SourceFolderChecker sourceFolderChecker;
+
+    /**
+     * Creates a validator with the default source folder checker (NIO-based).
+     */
+    public StartConfigurationValidator() {
+        this(new DefaultSourceFolderChecker());
+    }
+
+    /**
+     * Creates a validator with a custom source folder checker (primarily for testing).
+     *
+     * @param sourceFolderChecker the checker to use (must not be null)
+     */
+    public StartConfigurationValidator(SourceFolderChecker sourceFolderChecker) {
+        this.sourceFolderChecker = sourceFolderChecker;
+    }
+
     /**
      * Validates the given configuration.
      * <p>
@@ -66,12 +112,9 @@ public class StartConfigurationValidator {
             errors.add("- source.folder: must not be null");
             return;
         }
-        if (!Files.exists(sourceFolder)) {
-            errors.add("- source.folder: path does not exist: " + sourceFolder);
-        } else if (!Files.isDirectory(sourceFolder)) {
-            errors.add("- source.folder: path is not a directory: " + sourceFolder);
-        } else if (!Files.isReadable(sourceFolder)) {
-            errors.add("- source.folder: directory is not readable: " + sourceFolder);
+        String checkError = sourceFolderChecker.checkSourceFolder(sourceFolder);
+        if (checkError != null) {
+            errors.add(checkError);
         }
     }
 
@@ -197,4 +240,29 @@ public class StartConfigurationValidator {
             // If it doesn't exist yet, that's acceptable - we don't auto-create
         }
     }
+
+    /**
+     * Default NIO-based implementation of {@link SourceFolderChecker}.
+     * <p>
+     * Uses {@code java.nio.file.Files} static methods to check existence, type, and readability.
+     * <p>
+     * M3/AP-007: This separation allows unit tests to inject alternative implementations
+     * that control the outcome of readability checks without relying on actual filesystem
+     * permissions (which are platform-dependent).
+     */
+    private static class DefaultSourceFolderChecker implements SourceFolderChecker {
+        @Override
+        public String checkSourceFolder(Path path) {
+            if (!Files.exists(path)) {
+                return "- source.folder: path does not exist: " + path;
+            }
+            if (!Files.isDirectory(path)) {
+                return "- source.folder: path is not a directory: " + path;
+            }
+            if (!Files.isReadable(path)) {
+                return "- source.folder: directory is not readable: " + path;
+            }
+            return null;  // All checks passed
+        }
+    }
 }