refactor composer to use sqlalchemy, avoid string concatenations and follow conventions

api/composer/order.py

@@ -0,0 +1,38 @@
+"""ORDER BY rendering.
+
+A Pick orders by either the metric or a named dimension; both reference the
+SELECT-list *output alias* (the metric's name, or the dimension's output alias),
+not the underlying qualified column. Returns an `exp.Ordered` node.
+"""
+
+from __future__ import annotations
+
+from sqlglot import exp
+
+from api.composer.types import OrderBy, PickValidationError
+
+
+def _ordered(alias: str, direction: str) -> exp.Ordered:
+    return exp.Ordered(this=exp.column(alias, quoted=True), desc=(direction == "desc"))
+
+
+def render_order_by(
+    ob: OrderBy,
+    metric_name: str,
+    dim_select: dict[str, str],
+) -> exp.Ordered:
+    """`metric_name` is the metric SELECT alias; `dim_select` maps a dimension
+    ref → its output alias."""
+    if ob.by == "metric":
+        return _ordered(metric_name, ob.direction)
+    if ob.dimension not in dim_select:
+        raise PickValidationError(
+            f"order_by.dimension={ob.dimension!r} is not in group_by ({list(dim_select)})"
+        )
+    return _ordered(dim_select[ob.dimension], ob.direction)
+
+
+def default_order_by(metric_name: str) -> exp.Ordered:
+    """Sensible default when a grouped query gives no explicit order: largest
+    metric value first."""
+    return _ordered(metric_name, "desc")