67 lines
3.2 KiB
PL/PgSQL
67 lines
3.2 KiB
PL/PgSQL
-- Auto-charge tuition when a student is marked present or late.
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--
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-- Idempotency is the whole problem here. The attendance UI upserts on
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-- (student_id, date) and teachers freely toggle a status — present, then absent,
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-- then present again. A naive "insert a charge on attendance" trigger bills the
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-- family once per click. So each auto-charge is bound to the attendance row that
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-- caused it via ledger_entries.attendance_id (UNIQUE), which makes the write an
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-- upsert and lets a status change back to absent *remove* the charge.
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--
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-- Manual ledger entries keep attendance_id NULL. Postgres allows unlimited NULLs
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-- in a unique index, so hand-entered charges are unaffected, and the UI can tell
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-- auto from manual by whether attendance_id is set.
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-- Per-student daily rate. NULL (the default) means "never auto-charge", so
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-- nothing starts billing until a rate is deliberately set on a student.
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ALTER TABLE public.students
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ADD COLUMN IF NOT EXISTS daily_tuition_cents INTEGER;
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ALTER TABLE public.ledger_entries
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ADD COLUMN IF NOT EXISTS attendance_id UUID REFERENCES public.attendance(id) ON DELETE CASCADE;
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-- One auto-charge per attendance record, and deleting the attendance record
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-- takes its charge with it (ON DELETE CASCADE above).
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DO $$ BEGIN
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ALTER TABLE public.ledger_entries ADD CONSTRAINT ledger_entries_attendance_id_key UNIQUE (attendance_id);
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EXCEPTION WHEN duplicate_table OR duplicate_object THEN NULL; END $$;
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-- SECURITY DEFINER because the writer is a *teacher* marking attendance, and
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-- ledger_entries is admin-write under RLS. The teacher never gains general
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-- ledger access — only this function's fixed, attendance-derived write.
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CREATE OR REPLACE FUNCTION public.sync_attendance_tuition()
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RETURNS TRIGGER LANGUAGE plpgsql SECURITY DEFINER SET search_path = public AS $$
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DECLARE
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rate INTEGER;
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BEGIN
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SELECT daily_tuition_cents INTO rate FROM public.students WHERE id = NEW.student_id;
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-- 'present' and 'late' are billable: the student attended either way.
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-- 'absent' and 'excused' are not.
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IF NEW.status IN ('present', 'late') AND rate IS NOT NULL AND rate > 0 THEN
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INSERT INTO public.ledger_entries
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(student_id, date, kind, category, amount_cents, note, created_by, attendance_id)
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VALUES
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(NEW.student_id, NEW.date, 'charge', 'tuition', rate,
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'Auto-charged from attendance (' || NEW.status || ')', NEW.recorded_by, NEW.id)
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ON CONFLICT (attendance_id) DO UPDATE
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SET amount_cents = EXCLUDED.amount_cents,
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date = EXCLUDED.date,
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note = EXCLUDED.note;
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ELSE
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-- Status moved to absent/excused, or the rate was cleared: undo the charge.
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DELETE FROM public.ledger_entries WHERE attendance_id = NEW.id;
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END IF;
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RETURN NEW;
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END $$;
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DROP TRIGGER IF EXISTS trg_attendance_tuition ON public.attendance;
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CREATE TRIGGER trg_attendance_tuition
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AFTER INSERT OR UPDATE ON public.attendance
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FOR EACH ROW EXECUTE FUNCTION public.sync_attendance_tuition();
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-- Deliberately NOT backfilled. Existing attendance records stay unbilled —
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-- retroactively generating charges against families' balances should be an
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-- explicit decision, not a side effect of deploying this migration. Re-saving an
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-- attendance record re-fires the trigger and bills that day at the current rate.
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