refactor: separate metric definition from metric value and share comp…

plexe/internal/models/entities/metric.py

@@ -22,6 +22,8 @@
 
 from enum import Enum
 from functools import total_ordering
+from typing import Optional
+from weakref import WeakValueDictionary
 
 
 class ComparisonMethod(Enum):
@@ -98,31 +100,138 @@ def compare(self, value1: float, value2: float) -> int:
             raise ValueError("Invalid comparison method.")
 
 
-# todo: this class is a mess as it mixes concerns of a metric and a metric value; needs refactoring
+# Internal cache for sharing MetricComparator instances across all metrics
+# This ensures only one comparator object exists per unique (method, target, epsilon) combination
+_comparator_cache: WeakValueDictionary = WeakValueDictionary()
+
+
+def _get_shared_comparator(comparison_method: ComparisonMethod, target: Optional[float] = None, epsilon: float = 1e-9) -> MetricComparator:
+    """
+    Get or create a shared MetricComparator instance.
+
+    This function ensures that identical comparators are reused across all Metric instances,
+    reducing memory usage and ensuring consistency.
+
+    :param comparison_method: The comparison method.
+    :param target: Optional target value for TARGET_IS_BETTER.
+    :param epsilon: Tolerance for floating-point comparisons.
+    :return: A shared MetricComparator instance.
+    """
+    # Create a cache key from the comparator parameters
+    cache_key = (comparison_method, target, epsilon)
+
+    # Try to get existing comparator from cache
+    if cache_key in _comparator_cache:
+        return _comparator_cache[cache_key]
+
+    # Create new comparator and cache it
+    comparator = MetricComparator(comparison_method, target, epsilon)
+    _comparator_cache[cache_key] = comparator
+    return comparator
+
+
+class _MetricDefinition:
+    """
+    Internal class representing a metric type definition.
+
+    This separates the metric definition (what it is) from the metric value (a measurement).
+    Metric definitions are immutable and can be shared across multiple metric values.
+
+    This is an internal implementation detail - users should not interact with this class directly.
+    """
+
+    def __init__(self, name: str, comparator: MetricComparator):
+        """
+        Initialize a metric definition.
+
+        :param name: The name of the metric.
+        :param comparator: The shared comparator instance.
+        """
+        self._name = name
+        self._comparator = comparator
+
+    @property
+    def name(self) -> str:
+        """The name of the metric."""
+        return self._name
+
+    @property
+    def comparator(self) -> MetricComparator:
+        """The shared comparator instance."""
+        return self._comparator
+
+    def __eq__(self, other) -> bool:
+        """Check if two metric definitions are equal."""
+        if not isinstance(other, _MetricDefinition):
+            return False
+        return (
+            self.name == other.name
+            and self.comparator.comparison_method == other.comparator.comparison_method
+            and self.comparator.target == other.comparator.target
+        )
+
+    def __hash__(self) -> int:
+        """Hash the metric definition."""
+        return hash((self.name, self.comparator.comparison_method, self.comparator.target))
+
+
 @total_ordering
 class Metric:
     """
     Represents a metric with a name, a value, and a comparator for determining which metric is better.
 
+    This class internally separates the metric definition (type) from the metric value (measurement),
+    and automatically shares comparator instances to reduce memory usage.
+
     Attributes:
         name (str): The name of the metric (e.g., 'accuracy', 'loss').
         value (float): The numeric value of the metric.
-        comparator (MetricComparator): The comparison logic for the metric.
+        comparator (MetricComparator): The comparison logic for the metric (shared instance).
     """
 
     def __init__(self, name: str, value: float = None, comparator: MetricComparator = None, is_worst: bool = False):
         """
         Initializes a Metric object.
 
+        The comparator instance is automatically shared with other metrics that have the same
+        comparison method, target, and epsilon values, reducing memory usage.
+
         :param name: The name of the metric.
         :param value: The numeric value of the metric.
         :param comparator: An instance of MetricComparator for comparison logic.
         :param is_worst: Indicates if the metric value is the worst possible value.
         """
-        self.name = name
+        # Store the metric value (dynamic, instance-specific)
         self.value = value
-        self.comparator = comparator
         self.is_worst = is_worst or value is None
+
+        # Get or create a shared comparator instance
+        if comparator is not None:
+            # Use the shared comparator cache to ensure we reuse identical comparators
+            # This is the key optimization: identical comparators are shared across all metrics
+            shared_comparator = _get_shared_comparator(
+                comparison_method=comparator.comparison_method,
+                target=comparator.target,
+                epsilon=comparator.epsilon
+            )
+        else:
+            # If no comparator provided, raise an error as it's required for a valid metric
+            # This maintains the same behavior as before
+            raise ValueError("Metric requires a comparator. Provide a MetricComparator instance.")
+
+        # Create internal metric definition (separates type from value)
+        # This is the key separation: definition (what it is) vs value (measurement)
+        self._definition = _MetricDefinition(name=name, comparator=shared_comparator)
+
+    @property
+    def name(self) -> str:
+        """The name of the metric (for backward compatibility)."""
+        return self._definition.name
+
+    @property
+    def comparator(self) -> MetricComparator:
+        """The shared comparator instance (for backward compatibility)."""
+        return self._definition.comparator
 
     def __gt__(self, other) -> bool:
         """
@@ -141,17 +250,18 @@ def __gt__(self, other) -> bool:
         if other.is_worst:
             return True
 
-        if self.name != other.name:
-            raise ValueError("Cannot compare metrics with different names.")
-
-        if self.comparator.comparison_method != other.comparator.comparison_method:
-            raise ValueError("Cannot compare metrics with different comparison methods.")
-
-        if (
-            self.comparator.comparison_method == ComparisonMethod.TARGET_IS_BETTER
-            and self.comparator.target != other.comparator.target
-        ):
-            raise ValueError("Cannot compare 'TARGET_IS_BETTER' metrics with different target values.")
+        # Compare using definitions - this is cleaner and ensures consistency
+        if self._definition != other._definition:
+            # Provide detailed error message for backward compatibility
+            if self.name != other.name:
+                raise ValueError("Cannot compare metrics with different names.")
+            if self.comparator.comparison_method != other.comparator.comparison_method:
+                raise ValueError("Cannot compare metrics with different comparison methods.")
+            if (
+                self.comparator.comparison_method == ComparisonMethod.TARGET_IS_BETTER
+                and self.comparator.target != other.comparator.target
+            ):
+                raise ValueError("Cannot compare 'TARGET_IS_BETTER' metrics with different target values.")
 
         return self.comparator.compare(self.value, other.value) < 0
 
@@ -171,9 +281,9 @@ def __eq__(self, other) -> bool:
         if self.is_worst or other.is_worst:
             return False
 
+        # Use definition equality for cleaner comparison
         return (
-            self.name == other.name
-            and self.comparator.comparison_method == other.comparator.comparison_method
+            self._definition == other._definition
             and self.comparator.compare(self.value, other.value) == 0
         )