From fc3f6a6f9472366a6a78fffbf3e0985f063b7d83 Mon Sep 17 00:00:00 2001
From: Khalim Conn-Kowlessar <kconnkowlessar@gmail.com>
Date: Tue, 7 Jul 2026 11:43:03 +0000
Subject: [PATCH] =?UTF-8?q?Built-form=20filter=20resolves=20with=20the=20s?=
 =?UTF-8?q?ame=20precedence=20as=20property=20type=20=F0=9F=9F=A9?=
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Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
---
 backend/app/modelling/property_filters.py | 62 +++++++++++++++++++++++
 1 file changed, 62 insertions(+)

diff --git a/backend/app/modelling/property_filters.py b/backend/app/modelling/property_filters.py
index 5f29e33ac..a09aedb94 100644
--- a/backend/app/modelling/property_filters.py
+++ b/backend/app/modelling/property_filters.py
@@ -67,6 +67,15 @@ def resolve_filtered_property_ids(
             if row.id is not None and types.get(row.id) in wanted
         ]
 
+    if filters.built_forms is not None:
+        wanted_forms = set(filters.built_forms)
+        forms = _resolved_built_forms(session, candidates)
+        candidates = [
+            row
+            for row in candidates
+            if row.id is not None and forms.get(row.id) in wanted_forms
+        ]
+
     return [
         FilteredProperty(property_id=row.id, postcode=row.postcode)
         for row in candidates
@@ -88,6 +97,59 @@ _PROPERTY_TYPE_CODES: dict[str, str] = {
     "4": "Park home",
 }
 
+_BUILT_FORM_CODES: dict[str, str] = {
+    "1": "Detached",
+    "2": "Semi-Detached",
+    "3": "End-Terrace",
+    "4": "Mid-Terrace",
+    "5": "Enclosed End-Terrace",
+    "6": "Enclosed Mid-Terrace",
+}
+
+
+def _resolved_built_forms(
+    session: Session, candidates: list[PropertyRow]
+) -> dict[int, str]:
+    """Each property's effective built_form per the ADR-0056 precedence:
+    override (building_part 0) → lodged EPC → predicted EPC → legacy column."""
+    property_ids = [row.id for row in candidates if row.id is not None]
+    by_legacy_column = {
+        row.id: row.built_form
+        for row in candidates
+        if row.id is not None and row.built_form is not None
+    }
+    overrides = session.exec(
+        select(PropertyOverrideRow)
+        .where(col(PropertyOverrideRow.property_id).in_(property_ids))
+        .where(PropertyOverrideRow.building_part == 0)
+        .where(PropertyOverrideRow.override_component == "built_form_type")
+    ).all()
+    by_override = {o.property_id: o.override_value for o in overrides}
+
+    epcs = session.exec(
+        select(EpcPropertyModel)
+        .where(col(EpcPropertyModel.property_id).in_(property_ids))
+        .where(col(EpcPropertyModel.source).in_(("lodged", "predicted")))
+    ).all()
+    by_epc_source: dict[str, dict[int, str]] = {"lodged": {}, "predicted": {}}
+    for epc in epcs:
+        if epc.property_id is not None and epc.built_form:
+            value = epc.built_form
+            by_epc_source[epc.source][epc.property_id] = _BUILT_FORM_CODES.get(
+                value, value
+            )
+
+    resolved: dict[int, str] = {}
+    for pid in property_ids:
+        resolved[pid] = (
+            by_override.get(pid)
+            or by_epc_source["lodged"].get(pid)
+            or by_epc_source["predicted"].get(pid)
+            or by_legacy_column.get(pid)
+            or _UNKNOWN
+        )
+    return resolved
+
 
 def _resolved_property_types(
     session: Session, candidates: list[PropertyRow]