Tasa Cero: auto-detect 'CC ' vouchers + /installment-plans API

Ingestion auto-converts CC-prefixed credit-card purchases (default 3
cuotas, push note appended). CRUD endpoints cover manual convert (e.g.
ALMACENES SIMAN), edit-with-regeneration, and unconvert; anchor deletion
tears down the plan; cuotas cannot be deferred.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/app/api/v1/endpoints/installments.py

@@ -0,0 +1,234 @@
+from datetime import datetime
+from typing import Optional
+
+from fastapi import APIRouter, Depends, HTTPException
+from pydantic import BaseModel
+from sqlmodel import Session, col, select
+
+from app.auth import get_current_user
+from app.db import get_session
+from app.models.models import (
+    InstallmentPlan,
+    InstallmentPlanCreate,
+    InstallmentPlanUpdate,
+    Transaction,
+    TransactionRead,
+    TransactionSource,
+    TransactionType,
+)
+from app.services.installments import (
+    compute_installment_amounts,
+    create_plan,
+    delete_plan,
+    regenerate_cuotas,
+)
+from app.timeutil import utcnow
+
+router = APIRouter(prefix="/installment-plans", tags=["installments"])
+
+MIN_INSTALLMENTS = 2
+MAX_INSTALLMENTS = 48
+
+
+class InstallmentPlanRead(BaseModel):
+    id: int
+    anchor_transaction_id: int
+    merchant: str
+    purchase_date: datetime
+    num_installments: int
+    first_installment_date: datetime
+    total_amount: float
+    installment_amount: float
+    last_installment_amount: float
+    currency: str
+    notes: Optional[str] = None
+    cuotas_billed: int
+    paid_amount: float
+    remaining_amount: float
+    next_cuota_date: Optional[datetime] = None
+    is_completed: bool
+
+
+class InstallmentPlanDetail(InstallmentPlanRead):
+    cuotas: list[TransactionRead] = []
+
+
+class InstallmentPlanListResponse(BaseModel):
+    plans: list[InstallmentPlanRead]
+    total_remaining: float
+
+
+def _validate_num_installments(n: int) -> None:
+    if not MIN_INSTALLMENTS <= n <= MAX_INSTALLMENTS:
+        raise HTTPException(
+            status_code=400,
+            detail=f"num_installments must be {MIN_INSTALLMENTS}-{MAX_INSTALLMENTS}",
+        )
+
+
+def _get_plan_and_anchor(
+    session: Session, plan_id: int
+) -> tuple[InstallmentPlan, Transaction]:
+    plan = session.get(InstallmentPlan, plan_id)
+    if not plan:
+        raise HTTPException(status_code=404, detail="Installment plan not found")
+    anchor = session.get(Transaction, plan.anchor_transaction_id)
+    if not anchor:
+        raise HTTPException(status_code=404, detail="Anchor transaction not found")
+    return plan, anchor
+
+
+def _to_read(
+    plan: InstallmentPlan, anchor: Transaction, cuotas: list[Transaction]
+) -> InstallmentPlanRead:
+    now = utcnow()
+    billed = [c for c in cuotas if c.date <= now]
+    future = [c for c in cuotas if c.date > now]
+    paid = float(sum(c.amount for c in billed))
+    total = float(plan.total_amount)
+    amounts = compute_installment_amounts(
+        plan.total_amount, plan.num_installments
+    )
+    return InstallmentPlanRead(
+        id=plan.id,
+        anchor_transaction_id=plan.anchor_transaction_id,
+        merchant=anchor.merchant,
+        purchase_date=anchor.date,
+        num_installments=plan.num_installments,
+        first_installment_date=plan.first_installment_date,
+        total_amount=total,
+        installment_amount=float(plan.installment_amount),
+        last_installment_amount=float(amounts[-1]),
+        currency=plan.currency.value,
+        notes=plan.notes,
+        cuotas_billed=len(billed),
+        paid_amount=paid,
+        remaining_amount=total - paid,
+        next_cuota_date=min((c.date for c in future), default=None),
+        is_completed=len(billed) == plan.num_installments,
+    )
+
+
+def _cuotas_by_plan(
+    session: Session, plan_ids: list[int]
+) -> dict[int, list[Transaction]]:
+    grouped: dict[int, list[Transaction]] = {pid: [] for pid in plan_ids}
+    if plan_ids:
+        rows = session.exec(
+            select(Transaction)
+            .where(col(Transaction.installment_plan_id).in_(plan_ids))
+            .order_by(col(Transaction.date))
+        ).all()
+        for row in rows:
+            grouped[row.installment_plan_id].append(row)
+    return grouped
+
+
+@router.get("/", response_model=InstallmentPlanListResponse)
+def list_installment_plans(
+    session: Session = Depends(get_session),
+    _user: str = Depends(get_current_user),
+):
+    plans = session.exec(select(InstallmentPlan)).all()
+    anchors = {
+        t.id: t
+        for t in session.exec(
+            select(Transaction).where(
+                col(Transaction.id).in_([p.anchor_transaction_id for p in plans])
+            )
+        ).all()
+    } if plans else {}
+    cuotas = _cuotas_by_plan(session, [p.id for p in plans])
+    reads = [
+        _to_read(p, anchors[p.anchor_transaction_id], cuotas[p.id])
+        for p in plans
+        if p.anchor_transaction_id in anchors
+    ]
+    reads.sort(key=lambda r: r.purchase_date, reverse=True)
+    return InstallmentPlanListResponse(
+        plans=reads,
+        total_remaining=sum(r.remaining_amount for r in reads),
+    )
+
+
+@router.get("/{plan_id}", response_model=InstallmentPlanDetail)
+def get_installment_plan(
+    plan_id: int,
+    session: Session = Depends(get_session),
+    _user: str = Depends(get_current_user),
+):
+    plan, anchor = _get_plan_and_anchor(session, plan_id)
+    cuotas = _cuotas_by_plan(session, [plan.id])[plan.id]
+    read = _to_read(plan, anchor, cuotas)
+    return InstallmentPlanDetail(**read.model_dump(), cuotas=cuotas)
+
+
+@router.post("/", response_model=InstallmentPlanRead, status_code=201)
+def create_installment_plan(
+    data: InstallmentPlanCreate,
+    session: Session = Depends(get_session),
+    _user: str = Depends(get_current_user),
+):
+    """Convert an existing credit-card purchase into a Tasa Cero plan."""
+    _validate_num_installments(data.num_installments)
+    anchor = session.get(Transaction, data.transaction_id)
+    if not anchor:
+        raise HTTPException(status_code=404, detail="Transaction not found")
+    if anchor.source != TransactionSource.CREDIT_CARD:
+        raise HTTPException(
+            status_code=400, detail="Only credit card transactions can be financed"
+        )
+    if anchor.transaction_type != TransactionType.COMPRA:
+        raise HTTPException(
+            status_code=400, detail="Only COMPRA transactions can be financed"
+        )
+    if anchor.installment_plan_id:
+        raise HTTPException(
+            status_code=400, detail="A cuota cannot be converted to a plan"
+        )
+    if anchor.is_installment_anchor:
+        raise HTTPException(
+            status_code=409, detail="Transaction already has an installment plan"
+        )
+    plan = create_plan(
+        session, anchor, data.num_installments, data.first_installment_date
+    )
+    session.commit()
+    session.refresh(plan)
+    cuotas = _cuotas_by_plan(session, [plan.id])[plan.id]
+    return _to_read(plan, anchor, cuotas)
+
+
+@router.patch("/{plan_id}", response_model=InstallmentPlanRead)
+def update_installment_plan(
+    plan_id: int,
+    data: InstallmentPlanUpdate,
+    session: Session = Depends(get_session),
+    _user: str = Depends(get_current_user),
+):
+    """Edit a plan; cuota rows are regenerated (per-cuota edits are lost)."""
+    plan, anchor = _get_plan_and_anchor(session, plan_id)
+    if data.num_installments is not None:
+        _validate_num_installments(data.num_installments)
+    if data.notes is not None:
+        plan.notes = data.notes
+    regenerate_cuotas(
+        session, plan, anchor, data.num_installments, data.first_installment_date
+    )
+    session.commit()
+    session.refresh(plan)
+    cuotas = _cuotas_by_plan(session, [plan.id])[plan.id]
+    return _to_read(plan, anchor, cuotas)
+
+
+@router.delete("/{plan_id}", status_code=204)
+def delete_installment_plan(
+    plan_id: int,
+    session: Session = Depends(get_session),
+    _user: str = Depends(get_current_user),
+):
+    """Unconvert: remove the plan and its cuotas; the anchor becomes a normal
+    transaction again."""
+    plan, anchor = _get_plan_and_anchor(session, plan_id)
+    delete_plan(session, plan, anchor)
+    session.commit()

backend/app/api/v1/endpoints/transactions.py

@@ -21,9 +21,19 @@ from app.models.models import (
     TransactionUpdate,
 )
 
-from app.services.budget_projection import get_cycle_range, get_previous_cycle
+from app.services.budget_projection import (
+    NOT_INSTALLMENT_ANCHOR,
+    get_cycle_range,
+    get_previous_cycle,
+)
 from app.services.csv_export import build_transactions_csv
 from app.services.exchange_rate import get_converted_amount_expr
+from app.services.installments import (
+    DEFAULT_NUM_INSTALLMENTS,
+    create_plan,
+    is_tasa_cero_merchant,
+    teardown_plan_for_anchor,
+)
 
 router = APIRouter(prefix="/transactions", tags=["transactions"])
 
@@ -130,17 +140,22 @@ def bulk_action(
     txs = session.exec(
         select(Transaction).where(col(Transaction.id).in_(req.ids))
     ).all()
+    affected = 0
     for tx in txs:
         if req.action == "delete":
+            teardown_plan_for_anchor(session, tx)
             session.delete(tx)
         elif req.action == "set_category":
             tx.category_id = req.category_id
             session.add(tx)
         elif req.action == "set_deferred":
+            if tx.installment_plan_id:
+                continue  # cuotas of a plan cannot be deferred
             tx.deferred_to_next_cycle = bool(req.deferred)
             session.add(tx)
+        affected += 1
     session.commit()
-    return {"affected": len(txs)}
+    return {"affected": affected}
 
 
 @router.get("/export")
@@ -205,7 +220,9 @@ def list_billing_cycles(
         # Count transactions in this cycle
         count_result = session.exec(
             select(func.count(), func.coalesce(func.sum(amount_crc), 0)).where(
-                Transaction.date >= start, Transaction.date < end
+                Transaction.date >= start,
+                Transaction.date < end,
+                NOT_INSTALLMENT_ANCHOR,
             )
         ).first()
         count = count_result[0] if count_result else 0
@@ -268,6 +285,20 @@ def create_transaction(
     session.commit()
     session.refresh(tx)
 
+    # Tasa Cero auto-detection: BAC prefixes financed purchases with "CC ".
+    # Default 3 cuotas starting on the purchase date; editable afterwards via
+    # /installment-plans.
+    tasa_cero_note = ""
+    if (
+        tx.source == TransactionSource.CREDIT_CARD
+        and tx.transaction_type == TransactionType.COMPRA
+        and is_tasa_cero_merchant(tx.merchant)
+    ):
+        create_plan(session, tx, DEFAULT_NUM_INSTALLMENTS, tx.date)
+        session.commit()
+        session.refresh(tx)
+        tasa_cero_note = f" — Tasa Cero {DEFAULT_NUM_INSTALLMENTS} cuotas"
+
     # Send push notification
     symbols = {Currency.CRC: "₡", Currency.USD: "$", Currency.EUR: "€"}
     symbol = symbols.get(tx.currency, tx.currency.value)
@@ -278,7 +309,7 @@ def create_transaction(
     send_push_to_all(
         session,
         title=f"{'🏦' if is_income else '💳'} {tx.merchant}",
-        body=f"{amount_str} — {tx.bank.value} {label}",
+        body=f"{amount_str} — {tx.bank.value} {label}{tasa_cero_note}",
         url="/salarios" if is_income else "/budget",
     )
 
@@ -300,6 +331,11 @@ def update_transaction(
     if not tx:
         raise HTTPException(status_code=404, detail="Transaction not found")
     update_data = data.model_dump(exclude_unset=True)
+    if update_data.get("deferred_to_next_cycle") is not None and tx.installment_plan_id:
+        raise HTTPException(
+            status_code=400,
+            detail="Cuotas of an installment plan cannot be deferred",
+        )
     for key, value in update_data.items():
         setattr(tx, key, value)
     session.add(tx)
@@ -317,5 +353,6 @@ def delete_transaction(
     tx = session.get(Transaction, transaction_id)
     if not tx:
         raise HTTPException(status_code=404, detail="Transaction not found")
+    teardown_plan_for_anchor(session, tx)
     session.delete(tx)
     session.commit()