"""
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())