05/31 Phase 2

app/services/fx_service.py

@@ -0,0 +1,86 @@
+"""
+FX Service — fetches and caches daily USD→VND exchange rate.
+Primary source: open.er-api.com (free, no key)
+Fallback: last known rate from DB
+"""
+
+import requests
+from datetime import date, datetime
+from app.extensions import db
+from app.models.fx_rate import FxRate
+
+
+ER_API_URL = 'https://open.er-api.com/v6/latest/USD'
+REQUEST_TIMEOUT = 8  # seconds
+
+
+def get_today_rate():
+    """
+    Return today's USD→VND rate as a dict:
+    { 'rate': 25450.00, 'date': date(...), 'source': '...', 'is_stale': False }
+    """
+    today = date.today()
+
+    # 1. Check cache
+    cached = FxRate.query.filter_by(date=today).first()
+    if cached:
+        return {
+            'rate': float(cached.usd_to_vnd),
+            'date': cached.date,
+            'source': cached.source,
+            'is_stale': False,
+        }
+
+    # 2. Fetch from API
+    rate, source = _fetch_from_api()
+
+    if rate:
+        record = FxRate(
+            date=today,
+            usd_to_vnd=rate,
+            source=source,
+            fetched_at=datetime.utcnow(),
+        )
+        db.session.add(record)
+        try:
+            db.session.commit()
+        except Exception:
+            db.session.rollback()
+        return {'rate': rate, 'date': today, 'source': source, 'is_stale': False}
+
+    # 3. Fallback — last known rate
+    last = FxRate.query.order_by(FxRate.date.desc()).first()
+    if last:
+        return {
+            'rate': float(last.usd_to_vnd),
+            'date': last.date,
+            'source': last.source,
+            'is_stale': True,
+        }
+
+    # 4. Nothing available
+    return None
+
+
+def _fetch_from_api():
+    """Try open.er-api.com. Returns (rate, source) or (None, None)."""
+    try:
+        resp = requests.get(ER_API_URL, timeout=REQUEST_TIMEOUT)
+        if resp.status_code == 200:
+            data = resp.json()
+            vnd = data.get('rates', {}).get('VND')
+            if vnd:
+                return float(vnd), 'exchangerate-api'
+    except Exception:
+        pass
+    return None, None
+
+
+def get_rate_history(days=30):
+    """Return list of FxRate records for last N days, oldest first."""
+    from datetime import timedelta
+    since = date.today() - timedelta(days=days)
+    return (FxRate.query
+            .filter(FxRate.date >= since)
+            .order_by(FxRate.date.asc())
+            .all())