Add auditable config

README.md

@@ -37,6 +37,20 @@ Config config = ConfigFactory.configLoader()
         .load()
 ```
 
+Loads configuration files:
+- from classpath directory: `config`
+- with config base name: `application` (it's a default value)
+- with default profile: `local` (can be overridden with args `--profile=$PROFILE`)
+- overrides configuration values using args `--config-value.$NAME=$VALUE`
+
+```
+// Sample config files layout:
+src/main/resources/config
+  application.yml
+  application-local.yml
+  application-prod.yml
+```
+
 Explore the API, there is much more to configure.
 
 #### Config merging order

src/main/java/com/coditory/quark/config/AuditableConfig.java

@@ -0,0 +1,92 @@
+package com.coditory.quark.config;
+
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.stream.Collectors;
+
+import static com.coditory.quark.config.ConfigRemoveOptions.removeEmptyParents;
+
+public class AuditableConfig extends ConfigDecorator {
+    private static final Object USED_MARKER = new Object();
+    private Config unreadConfig;
+
+    public static AuditableConfig of(Config config) {
+        if (config instanceof AuditableConfig) {
+            return (AuditableConfig) config;
+        }
+        return new AuditableConfig(config);
+    }
+
+    AuditableConfig(Config config) {
+        super(config);
+        this.unreadConfig = config.copy();
+    }
+
+    @Override
+    public Config getSubConfig(String path) {
+        markAsRead(path);
+        return super.getSubConfig(path);
+    }
+
+    @Override
+    public Config getSubConfigOrEmpty(String path) {
+        markAsRead(path);
+        return super.getSubConfigOrEmpty(path);
+    }
+
+    @Override
+    public Config getSubConfig(String path, Config defaultValue) {
+        markAsRead(path);
+        return super.getSubConfig(path, defaultValue);
+    }
+
+    @Override
+    public Optional<Config> getSubConfigOptional(String path) {
+        markAsRead(path);
+        return super.getSubConfigOptional(path);
+    }
+
+    @Override
+    public <T> Optional<List<T>> getListAsOptional(Class<T> type, String path) {
+        markAsRead(path);
+        return super.getListAsOptional(type, path);
+    }
+
+    @Override
+    public <T> Optional<T> getAsOptional(Class<T> type, String path) {
+        markAsRead(path);
+        return super.getAsOptional(type, path);
+    }
+
+    public AuditableConfig markAsRead(String path) {
+        if (unreadConfig.contains(path)) {
+            unreadConfig = unreadConfig.withValue(path, USED_MARKER);
+        }
+        return this;
+    }
+
+    public Config getUnusedProperties() {
+        return unreadConfig.filterValues(
+                (path, value) -> !Objects.equals(value, USED_MARKER),
+                removeEmptyParents()
+        );
+    }
+
+    public void throwErrorOnUnusedProperties() {
+        Map<String, Object> properties = unreadConfig.toFlatMap().entrySet().stream()
+                .filter(entry -> entry.getValue() != USED_MARKER)
+                .collect(Collectors.toMap(Entry::getKey, Entry::getValue));
+        if (!properties.isEmpty()) {
+            int limit = 5;
+            List<String> names = properties.keySet().stream().sorted().toList();
+            String limitedNames = names.stream().limit(5).collect(Collectors.joining("\n"));
+            if (names.size() > limit) {
+                limitedNames = limitedNames + "\n...";
+            }
+            throw new ConfigUnusedPropertiesException("Detected unused config properties:\n" + limitedNames);
+        }
+    }
+}