feat(data): enhance DataStore with metrics tracking and configuration validation

jans-cedarling/cedarling/src/data/config.rs

@@ -7,7 +7,7 @@ use std::time::Duration;
 
 /// Configuration for the DataStore component.
 ///
-/// Controls storage limits, TTL behavior, and capacity management.
+/// Controls storage limits, TTL behavior, capacity management, and metrics.
 ///
 /// ## TTL Semantics
 ///
@@ -47,6 +47,8 @@ pub struct DataStoreConfig {
     /// Maximum allowed TTL.
     /// `None` means no upper limit on TTL values (uses 10 years).
     pub max_ttl: Option<Duration>,
+    /// Enable metrics tracking (access counts, timestamps)
+    pub enable_metrics: bool,
 }
 
 impl Default for DataStoreConfig {
@@ -56,10 +58,43 @@ impl Default for DataStoreConfig {
             max_entry_size: 1_048_576, // 1MB
             default_ttl: None,
             max_ttl: Some(Duration::from_secs(3600)), // 1 hour
+            enable_metrics: true,
         }
     }
 }
 
+/// Error returned when DataStoreConfig validation fails.
+#[derive(Debug, thiserror::Error)]
+pub enum ConfigValidationError {
+    /// default_ttl exceeds max_ttl
+    #[error("default_ttl ({default:?}) exceeds max_ttl ({max:?})")]
+    DefaultTtlExceedsMax {
+        /// The default TTL value that exceeds the maximum
+        default: Duration,
+        /// The maximum TTL value
+        max: Duration,
+    },
+}
+
+impl DataStoreConfig {
+    /// Validate the configuration for consistency.
+    ///
+    /// # Errors
+    ///
+    /// Returns `ConfigValidationError` if:
+    /// - `default_ttl` exceeds `max_ttl` (when both are Some)
+    pub fn validate(&self) -> Result<(), ConfigValidationError> {
+        // Check if default_ttl exceeds max_ttl
+        if let (Some(default), Some(max)) = (self.default_ttl, self.max_ttl) {
+            if default > max {
+                return Err(ConfigValidationError::DefaultTtlExceedsMax { default, max });
+            }
+        }
+
+        Ok(())
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -71,5 +106,74 @@ mod tests {
         assert_eq!(config.max_entry_size, 1_048_576);
         assert_eq!(config.default_ttl, None);
         assert_eq!(config.max_ttl, Some(Duration::from_secs(3600)));
+        assert!(config.enable_metrics);
+    }
+
+    #[test]
+    fn test_valid_config() {
+        let config = DataStoreConfig {
+            default_ttl: Some(Duration::from_secs(300)),
+            max_ttl: Some(Duration::from_secs(3600)),
+            ..Default::default()
+        };
+        assert!(
+            matches!(config.validate(), Ok(_)),
+            "expected DataStoreConfig::validate() to succeed when default_ttl is less than max_ttl"
+        );
+    }
+
+    #[test]
+    fn test_default_ttl_exceeds_max() {
+        let config = DataStoreConfig {
+            default_ttl: Some(Duration::from_secs(7200)), // 2 hours
+            max_ttl: Some(Duration::from_secs(3600)),     // 1 hour
+            ..Default::default()
+        };
+        assert!(
+            matches!(
+                config.validate(),
+                Err(ConfigValidationError::DefaultTtlExceedsMax { .. })
+            ),
+            "expected DataStoreConfig::validate() to return ConfigValidationError when default_ttl exceeds max_ttl"
+        );
+    }
+
+    #[test]
+    fn test_none_ttls_are_valid() {
+        let config = DataStoreConfig {
+            default_ttl: None,
+            max_ttl: None,
+            ..Default::default()
+        };
+        assert!(
+            matches!(config.validate(), Ok(_)),
+            "expected DataStoreConfig::validate() to succeed when both TTL values are None"
+        );
+    }
+
+    #[test]
+    fn test_only_default_ttl_is_valid() {
+        let config = DataStoreConfig {
+            default_ttl: Some(Duration::from_secs(300)),
+            max_ttl: None,
+            ..Default::default()
+        };
+        assert!(
+            matches!(config.validate(), Ok(_)),
+            "expected DataStoreConfig::validate() to succeed when only default_ttl is set"
+        );
+    }
+
+    #[test]
+    fn test_only_max_ttl_is_valid() {
+        let config = DataStoreConfig {
+            default_ttl: None,
+            max_ttl: Some(Duration::from_secs(3600)),
+            ..Default::default()
+        };
+        assert!(
+            matches!(config.validate(), Ok(_)),
+            "expected DataStoreConfig::validate() to succeed when only max_ttl is set"
+        );
     }
 }