feat: selection Coordinate and weighted distance

hef/selection.py

@@ -1 +1,37 @@
 """Nearest-match selection of a catalog record for a knob coordinate."""
+
+from __future__ import annotations
+
+import math
+from dataclasses import dataclass
+
+from hef.catalog import Record
+
+SELECTOR_MODES = frozenset({"none", "audio", "video", "av"})
+CONTENT_MODES = frozenset({"audio", "video", "av"})
+
+
+@dataclass(frozen=True)
+class Coordinate:
+    left: int
+    right: int
+    dark: int
+    light: int
+
+
+@dataclass(frozen=True)
+class Weights:
+    brain: float = 1.0
+    mood: float = 1.0
+
+
+def distance(a: Coordinate, b: Coordinate, weights: Weights = Weights()) -> float:
+    """Weighted Euclidean distance; brain plane and mood plane weighted separately."""
+    brain_sq = (a.left - b.left) ** 2 + (a.right - b.right) ** 2
+    mood_sq = (a.dark - b.dark) ** 2 + (a.light - b.light) ** 2
+    return math.sqrt(weights.brain * brain_sq + weights.mood * mood_sq)
+
+
+def record_coordinate(record: Record) -> Coordinate:
+    """The (left, right, dark, light) coordinate of a catalog record."""
+    return Coordinate(record.left, record.right, record.dark, record.light)