"""
FX Service — fetches and caches daily USD→VND exchange rate.

Source priority:
1. DB cache (same day, fresh)
2. yfinance (USDVND=X forex ticker — most reliable)
3. open.er-api.com (free REST API fallback)
4. Last known DB rate (stale fallback)

Force-refresh: if cached rate is > 1 day old, re-fetch regardless.
"""

import logging
import requests
from datetime import date, datetime, timedelta
from app.extensions import db
from app.models.fx_rate import FxRate

log = logging.getLogger(__name__)
REQUEST_TIMEOUT = 10


def get_today_rate():
    """
    Return today's USD→VND rate as a dict:
    { 'rate': 26350.00, 'date': date(...), 'source': '...', 'is_stale': False }
    """
    today = date.today()

    # 1. Check DB cache — only use if fetched TODAY
    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. Try all live sources in order
    fetchers = [
        _fetch_yfinance,
        _fetch_er_api,
    ]

    for fetcher in fetchers:
        rate = fetcher()
        if rate and rate > 1000:   # sanity check: VND is always >> 1000 per USD
            _save_rate(today, rate, fetcher.__name__.replace('_fetch_', ''))
            return {'rate': rate, 'date': today, 'source': fetcher.__name__, 'is_stale': False}

    # 3. Stale fallback — last known rate from DB
    last = FxRate.query.order_by(FxRate.date.desc()).first()
    if last:
        days_old = (today - last.date).days
        log.warning(f'[fx] Using stale rate from {last.date} ({days_old}d old)')
        return {
            'rate': float(last.usd_to_vnd),
            'date': last.date,
            'source': last.source,
            'is_stale': True,
        }

    return None


def force_refresh():
    """Delete today's cached rate and fetch fresh. Returns new rate dict."""
    today = date.today()
    existing = FxRate.query.filter_by(date=today).first()
    if existing:
        db.session.delete(existing)
        db.session.commit()
    return get_today_rate()


# ── Fetchers ──────────────────────────────────────────────────────────────────

def _fetch_yfinance():
    """Fetch USDVND=X via Yahoo Finance v8 chart API (direct HTTP, no yfinance needed)."""
    for subdomain in ('query1', 'query2'):
        url = (
            f'https://{subdomain}.finance.yahoo.com/v8/finance/chart/USDVND=X'
            '?range=5d&interval=1d&includePrePost=false'
        )
        try:
            resp = requests.get(url, timeout=REQUEST_TIMEOUT,
                                headers={'User-Agent': 'Mozilla/5.0', 'Accept': 'application/json'})
            if resp.status_code == 200:
                result = resp.json().get('chart', {}).get('result')
                if result:
                    closes = result[0]['indicators']['quote'][0]['close']
                    valid = [c for c in closes if c is not None]
                    if valid:
                        rate = float(valid[-1])
                        log.info(f'[fx] Yahoo v8: 1 USD = {rate:,.0f} VND')
                        return rate
        except Exception as e:
            log.warning(f'[fx] Yahoo v8 {subdomain}: {e}')
    return None


def _fetch_er_api():
    """Fetch from open.er-api.com (free, no key required)."""
    try:
        resp = requests.get(
            'https://open.er-api.com/v6/latest/USD',
            timeout=REQUEST_TIMEOUT,
            headers={'User-Agent': 'PFM/1.0'},
        )
        if resp.status_code == 200:
            data = resp.json()
            vnd = data.get('rates', {}).get('VND')
            if vnd and float(vnd) > 1000:
                log.info(f'[fx] er-api: 1 USD = {vnd:,.0f} VND')
                return float(vnd)
    except Exception as e:
        log.warning(f'[fx] er-api failed: {e}')
    return None


# ── DB helpers ────────────────────────────────────────────────────────────────

def _save_rate(rate_date, rate, source):
    try:
        # Upsert — delete existing for this date first
        existing = FxRate.query.filter_by(date=rate_date).first()
        if existing:
            db.session.delete(existing)
            db.session.flush()

        record = FxRate(
            date=rate_date,
            usd_to_vnd=rate,
            source=source,
            fetched_at=datetime.utcnow(),
        )
        db.session.add(record)
        db.session.commit()
    except Exception as e:
        db.session.rollback()
        log.error(f'[fx] DB save failed: {e}')


def get_rate_history(days=30):
    """Return list of FxRate records for last N days, oldest first."""
    since = date.today() - timedelta(days=days)
    return (FxRate.query
            .filter(FxRate.date >= since)
            .order_by(FxRate.date.asc())
            .all())