feat(api): group GIAS school types and religions for parents

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

backend/school_groups.py

@@ -0,0 +1,104 @@
+"""Parent-facing groups over GIAS establishment types and religious characters.
+
+The 34 GIAS establishment types describe governance and funding, which for a
+mainstream state school barely changes what a parent experiences. The search
+filter offers six groups a parent recognises instead, and a faith filter in
+place of the faith signal that "Voluntary aided" and "Voluntary controlled"
+only half carry. See
+docs/superpowers/specs/2026-10-02-school-type-groups-and-faith-filter-design.md.
+
+Groups are defined over GIAS codes and looked up by the translated name,
+because the DataFrame the API filters carries names only: the codes are
+replaced at load (data_loader.translate_gias_code_columns), the legacy-name
+mart fallback never had them, and test fixtures are written in names.
+"""
+
+from typing import Optional
+
+import pandas as pd
+
+from .gias_codes import RELIGIOUS_CHARACTER, SCHOOL_TYPE
+
+# (key, label, GIAS TypeOfEstablishment codes), in the order shown.
+TYPE_GROUPS: tuple[tuple[str, str, frozenset[int]], ...] = (
+    # Academy sponsor led, Academy converter, Free schools, University technical
+    # college, Studio schools, City technology college. UTCs and studio schools
+    # are legally academies, and a family considering one searches by name.
+    ("academy", "State school: academy or free school", frozenset({28, 34, 35, 40, 41, 6})),
+    # Community, Voluntary aided, Voluntary controlled, Foundation, LA nursery.
+    ("council", "State school: council-run", frozenset({1, 2, 3, 5, 15})),
+    ("independent", "Independent (fee-paying)", frozenset({11})),
+    # Every special type, independent ones included (usually funded by the
+    # council through an EHCP, so SEND provision to a parent, not private
+    # school), and Special post 16 institutions.
+    ("special", "Special school (SEND)", frozenset({7, 8, 10, 12, 32, 33, 36, 44})),
+    # Further education, Sixth form centres, the 16-19 academies and free schools.
+    ("post16", "Sixth form or college", frozenset({18, 31, 39, 45, 46})),
+    # Pupil referral units and AP academies and free schools. Last: parents do
+    # not apply to these; the local authority places children there.
+    ("alternative", "Alternative provision", frozenset({14, 38, 42, 43})),
+)
+
+# In no group, so reachable only under "Any school type": Secure units,
+# Miscellaneous, Higher education institutions, Online provider, Institution
+# funded by other government department, Academy secure 16 to 19.
+UNOFFERED_TYPE_CODES: frozenset[int] = frozenset({24, 27, 29, 49, 56, 57})
+
+# (key, label, GIAS ReligiousCharacter codes), in the order shown. A joint
+# school is in every faith its label names; a generic "Christian" beside a
+# named church adds nothing.
+FAITH_GROUPS: tuple[tuple[str, str, frozenset[int]], ...] = (
+    # Does not apply, None, and 99 (a blank label).
+    ("none", "No religious character", frozenset({0, 6, 99})),
+    ("church_of_england", "Church of England",
+     frozenset({2, 9, 10, 11, 12, 13, 19, 20, 30, 31, 32, 33, 34, 41, 48})),
+    ("roman_catholic", "Roman Catholic", frozenset({3, 11, 13, 35, 48})),
+    # 28 "Inter- / non- denominational" is how GIAS files Christian schools
+    # tied to no one church.
+    ("other_christian", "Other Christian",
+     frozenset({4, 8, 9, 10, 12, 14, 15, 16, 17, 18, 19, 22, 26, 28, 30, 33,
+                37, 38, 39, 40, 41, 44, 45, 46, 47})),
+    ("jewish", "Jewish", frozenset({5, 36, 43})),
+    ("muslim", "Muslim", frozenset({7, 42, 49})),
+    ("other_faith", "Other faith", frozenset({21, 24, 25, 29})),
+)
+
+TYPE_GROUP_KEYS: frozenset[str] = frozenset(k for k, _, _ in TYPE_GROUPS)
+FAITH_KEYS: frozenset[str] = frozenset(k for k, _, _ in FAITH_GROUPS)
+
+
+def _key(name: str) -> str:
+    return name.strip().lower()
+
+
+_TYPE_GROUP_BY_NAME: dict[str, str] = {
+    _key(SCHOOL_TYPE[code]): key
+    for key, _, codes in TYPE_GROUPS
+    for code in codes
+    if code in SCHOOL_TYPE
+}
+
+_FAITHS_BY_NAME: dict[str, tuple[str, ...]] = {}
+for _faith, _, _codes in FAITH_GROUPS:
+    for _code in sorted(_codes):
+        if _code in RELIGIOUS_CHARACTER:
+            _name = _key(RELIGIOUS_CHARACTER[_code])
+            _FAITHS_BY_NAME[_name] = _FAITHS_BY_NAME.get(_name, ()) + (_faith,)
+
+
+def type_group_for(name: object) -> Optional[str]:
+    """The type group of a GIAS establishment type name, or None."""
+    if not isinstance(name, str):
+        return None
+    return _TYPE_GROUP_BY_NAME.get(_key(name))
+
+
+def faith_groups_for(name: object) -> tuple[str, ...]:
+    """The faith groups of a GIAS religious character name.
+
+    A missing or blank name is "No religious character". A name the
+    dictionary does not know has no faith, so it matches no faith option.
+    """
+    if not isinstance(name, str):
+        return ("none",) if name is None or pd.isna(name) else ()
+    return _FAITHS_BY_NAME.get(_key(name), ())