Convert USD and EUR to CRC in analytics endpoints

All three analytics endpoints (by-category, monthly-trend, daily-spending)
now convert foreign currency amounts to CRC using current exchange rates.
EUR/CRC rate derived from ExchangeRate-API (USD-based cross rate).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

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

@@ -10,6 +10,7 @@ from app.auth import get_current_user
 from app.db import get_session
 from app.models.models import Category, Transaction
 from app.services.budget_projection import get_cycle_range
+from app.services.exchange_rate import get_current_rate, get_eur_crc_rate
 
 router = APIRouter(prefix="/analytics", tags=["analytics"])
 
@@ -37,6 +38,17 @@ class DailySpending(BaseModel):
     count: int
 
 
+def _get_crc_multipliers(session: Session) -> dict[str, float]:
+    """Return multipliers to convert each currency to CRC."""
+    usd_rate = get_current_rate(session)
+    eur_rate = get_eur_crc_rate()
+    return {
+        "CRC": 1.0,
+        "USD": usd_rate.sell_rate if usd_rate else 0.0,
+        "EUR": eur_rate if eur_rate else 0.0,
+    }
+
+
 @router.get("/by-category", response_model=list[CategorySpending])
 def spending_by_category(
     cycle_year: Optional[int] = None,
@@ -44,10 +56,18 @@ def spending_by_category(
     session: Session = Depends(get_session),
     _user: str = Depends(get_current_user),
 ):
+    rates = _get_crc_multipliers(session)
+
     query = (
         select(
             Transaction.category_id,
-            func.sum(Transaction.amount).label("total"),
+            func.sum(
+                case(
+                    (Transaction.currency == "USD", Transaction.amount * rates["USD"]),
+                    (Transaction.currency == "EUR", Transaction.amount * rates["EUR"]),
+                    else_=Transaction.amount,
+                )
+            ).label("total"),
             func.count().label("count"),
         )
         .where(Transaction.transaction_type == "COMPRA")
@@ -88,7 +108,12 @@ def monthly_trend(
     session: Session = Depends(get_session),
     _user: str = Depends(get_current_user),
 ):
-    """Monthly spending totals using billing cycle boundaries (18th-18th)."""
+    """Monthly spending totals using billing cycle boundaries (18th-18th).
+
+    total_crc includes all currencies converted to CRC at current rates.
+    total_usd is the raw USD amount (unconverted) for display purposes.
+    """
+    rates = _get_crc_multipliers(session)
     now = datetime.now()
     results = []
     month_names = [
@@ -106,8 +131,9 @@ def monthly_trend(
                 func.coalesce(
                     func.sum(
                         case(
-                            (Transaction.currency == "CRC", Transaction.amount),
+                            (Transaction.currency == "USD", Transaction.amount * rates["USD"]),
-                            else_=0,
+                            (Transaction.currency == "EUR", Transaction.amount * rates["EUR"]),
+                            else_=Transaction.amount,
                         )
                     ),
                     0,
@@ -163,10 +189,18 @@ def daily_spending(
     session: Session = Depends(get_session),
     _user: str = Depends(get_current_user),
 ):
+    rates = _get_crc_multipliers(session)
+
     query = (
         select(
             func.date(Transaction.date).label("day"),
-            func.sum(Transaction.amount).label("total"),
+            func.sum(
+                case(
+                    (Transaction.currency == "USD", Transaction.amount * rates["USD"]),
+                    (Transaction.currency == "EUR", Transaction.amount * rates["EUR"]),
+                    else_=Transaction.amount,
+                )
+            ).label("total"),
             func.count().label("count"),
         )
         .where(Transaction.transaction_type == "COMPRA")

backend/app/services/exchange_rate.py

@@ -23,6 +23,10 @@ _cache: dict[str, tuple[ExchangeRate, datetime]] = {}
 _last_known: ExchangeRate | None = None  # survives cache expiry — always holds the last successful rate
 CACHE_TTL = timedelta(hours=1)
 
+# EUR/CRC mid-market rate cache
+_eur_crc_cache: dict[str, tuple[float, datetime]] = {}
+_last_known_eur_crc: float | None = None
+
 
 def _fetch_bccr_rate(indicator: int, date_str: str) -> float | None:
     """Fetch a single indicator from BCCR API."""
@@ -167,6 +171,45 @@ def get_current_rate(session: Session) -> ExchangeRate | None:
     return None
 
 
+def _fetch_eur_crc_mid() -> float | None:
+    """Derive EUR/CRC mid-market rate from ExchangeRate-API (USD-based).
+
+    EUR/CRC = CRC_per_USD / EUR_per_USD
+    """
+    try:
+        resp = httpx.get(EXCHANGERATE_API_URL, timeout=10)
+        resp.raise_for_status()
+        data = resp.json()
+        if data.get("result") == "success":
+            crc = data["rates"].get("CRC")
+            eur = data["rates"].get("EUR")
+            if crc and eur:
+                return float(crc) / float(eur)
+    except Exception:
+        pass
+    return None
+
+
+def get_eur_crc_rate() -> float | None:
+    """Get current EUR→CRC mid-market rate (cached 1 hour)."""
+    global _last_known_eur_crc
+
+    cached = _eur_crc_cache.get("current")
+    if cached and datetime.utcnow() - cached[1] < CACHE_TTL:
+        return cached[0]
+
+    rate = _fetch_eur_crc_mid()
+    if rate is not None:
+        _eur_crc_cache["current"] = (rate, datetime.utcnow())
+        _last_known_eur_crc = rate
+        return rate
+
+    if _last_known_eur_crc:
+        return _last_known_eur_crc
+
+    return None
+
+
 def get_rate_history(session: Session, days: int = 30) -> list[ExchangeRate]:
     """Get historical exchange rates."""
     cutoff = datetime.utcnow() - timedelta(days=days)