WealthySmart/backend/app/services/exchange_rate.py

import asyncio
import logging
import xml.etree.ElementTree as ET
from datetime import datetime, timedelta

import httpx
from sqlalchemy import case
from sqlmodel import Session, col, select

from app.config import settings
from app.db import engine
from app.models.models import ExchangeRate

logger = logging.getLogger(__name__)

# Scheduled refresh interval — 4x/day
REFRESH_INTERVAL_SECONDS = 6 * 3600

# BCCR indicators: 317 = buy, 318 = sell
BCCR_URL = "https://gee.bccr.fi.cr/Indicadores/Suscripciones/WS/wsindicadoreseconomicos.asmx/ObtenerIndicadoresEconomicos"

# Fallback APIs (no API key required, all support CRC)
EXCHANGERATE_API_URL = "https://open.er-api.com/v6/latest/USD"
CURRENCY_API_URL = "https://cdn.jsdelivr.net/npm/@fawazahmed0/currency-api@latest/v1/currencies/usd.json"
CURRENCY_API_FALLBACK_URL = "https://latest.currency-api.pages.dev/v1/currencies/usd.json"
FLOATRATES_URL = "https://www.floatrates.com/daily/usd.json"

# Typical buy/sell spread for USD/CRC (~0.5% each side of mid-market)
_SPREAD = 0.005

_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)

# Generic X/CRC mid-market rate cache (by currency code)
_xcrc_cache: dict[str, tuple[float, datetime]] = {}
_last_known_xcrc: dict[str, float] = {}

# CoinGecko ids for supported crypto codes
_COINGECKO_IDS = {"BTC": "bitcoin", "XMR": "monero"}
COINGECKO_URL = "https://api.coingecko.com/api/v3/simple/price"


def _fetch_bccr_rate(indicator: int, date_str: str) -> float | None:
    """Fetch a single indicator from BCCR API."""
    try:
        params = {
            "Indicador": str(indicator),
            "FechaInicio": date_str,
            "FechaFinal": date_str,
            "Nombre": settings.BCCR_API_EMAIL or "WealthySmart",
            "SubNiveles": "N",
            "CorreoElectronico": settings.BCCR_API_EMAIL or "no-reply@example.com",
            "Token": settings.BCCR_API_TOKEN or "",
        }
        resp = httpx.get(BCCR_URL, params=params, timeout=10)
        resp.raise_for_status()

        root = ET.fromstring(resp.text)
        for datos in root.iter():
            if datos.tag.endswith("NUM_VALOR"):
                return float(datos.text.strip().replace(",", "."))
    except Exception:
        pass
    return None


def _fetch_bccr() -> tuple[float, float] | None:
    """Try BCCR official API. Returns (buy, sell) or None."""
    today = datetime.now().strftime("%d/%m/%Y")
    buy = _fetch_bccr_rate(317, today)
    sell = _fetch_bccr_rate(318, today)
    if buy is not None and sell is not None:
        return (buy, sell)
    return None


def _mid_to_buy_sell(mid: float) -> tuple[float, float]:
    """Convert a mid-market rate to approximate buy/sell with a spread."""
    return (mid * (1 - _SPREAD), mid * (1 + _SPREAD))


def _fetch_exchangerate_api() -> tuple[float, float] | None:
    """Try ExchangeRate-API (open.er-api.com). No key required."""
    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")
            if crc:
                return _mid_to_buy_sell(float(crc))
    except Exception:
        pass
    return None


def _fetch_currency_api() -> tuple[float, float] | None:
    """Try fawazahmed0/currency-api (CDN-hosted). No key required."""
    for url in (CURRENCY_API_URL, CURRENCY_API_FALLBACK_URL):
        try:
            resp = httpx.get(url, timeout=10)
            resp.raise_for_status()
            data = resp.json()
            crc = data.get("usd", {}).get("crc")
            if crc:
                return _mid_to_buy_sell(float(crc))
        except Exception:
            continue
    return None


def _fetch_floatrates() -> tuple[float, float] | None:
    """Try FloatRates. No key required."""
    try:
        resp = httpx.get(FLOATRATES_URL, timeout=10)
        resp.raise_for_status()
        data = resp.json()
        crc_data = data.get("crc")
        if crc_data and "rate" in crc_data:
            return _mid_to_buy_sell(float(crc_data["rate"]))
    except Exception:
        pass
    return None


def _fetch_rate_from_apis() -> tuple[float, float] | None:
    """Try all sources in order: BCCR → ExchangeRate-API → currency-api → FloatRates."""
    for fetcher in (_fetch_bccr, _fetch_exchangerate_api, _fetch_currency_api, _fetch_floatrates):
        result = fetcher()
        if result is not None:
            return result
    return None


def _remember(rate: ExchangeRate) -> ExchangeRate:
    """Store rate in both TTL cache and permanent last-known holder."""
    global _last_known
    _cache["current"] = (rate, datetime.utcnow())
    _last_known = rate
    return rate


def get_current_rate(session: Session) -> ExchangeRate | None:
    """Get current USD/CRC rate. Never returns None once a rate has been fetched."""
    global _last_known

    # 1. Fresh memory cache (< 1 hour)
    cached = _cache.get("current")
    if cached and datetime.utcnow() - cached[1] < CACHE_TTL:
        return cached[0]

    # 2. Fresh DB rate (< 1 hour)
    one_hour_ago = datetime.utcnow() - CACHE_TTL
    db_rate = session.exec(
        select(ExchangeRate)
        .where(ExchangeRate.fetched_at > one_hour_ago)
        .order_by(col(ExchangeRate.fetched_at).desc())
    ).first()
    if db_rate:
        return _remember(db_rate)

    # 3. Try all API sources
    result = _fetch_rate_from_apis()
    if result is not None:
        buy, sell = result
        rate = ExchangeRate(date=datetime.utcnow(), buy_rate=buy, sell_rate=sell)
        session.add(rate)
        session.commit()
        session.refresh(rate)
        return _remember(rate)

    # 4. Stale DB rate (any age)
    fallback = session.exec(
        select(ExchangeRate).order_by(col(ExchangeRate.fetched_at).desc())
    ).first()
    if fallback:
        return _remember(fallback)

    # 5. Last known in-memory rate (survives even if DB is empty)
    if _last_known:
        return _last_known

    return None


def _fetch_fiat_crc_mid(code: str) -> float | None:
    """Derive {code}/CRC mid-market rate from ExchangeRate-API (USD-based).

    X/CRC = CRC_per_USD / X_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")
            x = data["rates"].get(code)
            if crc and x:
                return float(crc) / float(x)
    except Exception:
        pass
    return None


def _fetch_crypto_crc(code: str) -> float | None:
    """Fetch {code}/CRC spot from CoinGecko."""
    coin_id = _COINGECKO_IDS.get(code)
    if not coin_id:
        return None
    try:
        resp = httpx.get(
            COINGECKO_URL,
            params={"ids": coin_id, "vs_currencies": "crc"},
            timeout=10,
        )
        resp.raise_for_status()
        data = resp.json()
        price = data.get(coin_id, {}).get("crc")
        if price:
            return float(price)
    except Exception:
        pass
    return None


def get_crc_rate(code: str) -> float | None:
    """Get current {code}→CRC rate (cached 1 hour). Fiat via ExchangeRate-API, crypto via CoinGecko."""
    if code == "CRC":
        return 1.0

    cached = _xcrc_cache.get(code)
    if cached and datetime.utcnow() - cached[1] < CACHE_TTL:
        return cached[0]

    if code in _COINGECKO_IDS:
        rate = _fetch_crypto_crc(code)
    else:
        rate = _fetch_fiat_crc_mid(code)

    if rate is not None:
        _xcrc_cache[code] = (rate, datetime.utcnow())
        _last_known_xcrc[code] = rate
        return rate

    return _last_known_xcrc.get(code)


def get_crc_multipliers(session: Session) -> dict[str, float]:
    """Return {currency_code: CRC_multiplier} for every supported currency."""
    from app.models.models import Currency

    multipliers: dict[str, float] = {"CRC": 1.0}

    usd_rate = get_current_rate(session)
    if usd_rate:
        multipliers["USD"] = usd_rate.sell_rate

    for code in (c.value for c in Currency):
        if code in multipliers:
            continue
        rate = get_crc_rate(code)
        if rate is not None:
            multipliers[code] = rate

    return multipliers


def get_converted_amount_expr(session: Session):
    """Return a SQLAlchemy expression converting Transaction.amount to CRC.

    Builds a CASE that multiplies by the per-currency CRC rate; CRC passes through.
    Missing rates fall back to 1.0 (treat as CRC) rather than 0.0 so a transient
    API outage does not silently zero out foreign-currency totals.
    """
    from app.models.models import Transaction

    multipliers = get_crc_multipliers(session)
    whens = [
        (Transaction.currency == code, Transaction.amount * mult)
        for code, mult in multipliers.items()
        if code != "CRC"
    ]
    if not whens:
        return Transaction.amount
    return case(*whens, else_=Transaction.amount)


def _refresh_usd_rate() -> bool:
    """Force-fetch USD/CRC from APIs and persist to DB. Returns True on success."""
    fetched = _fetch_rate_from_apis()
    if fetched is None:
        return False
    buy, sell = fetched
    with Session(engine) as session:
        rate = ExchangeRate(date=datetime.utcnow(), buy_rate=buy, sell_rate=sell)
        session.add(rate)
        session.commit()
        session.refresh(rate)
        _remember(rate)
    return True


def _refresh_other_rate(code: str) -> bool:
    """Force-fetch {code}/CRC and update in-memory cache. Returns True on success."""
    if code in _COINGECKO_IDS:
        rate = _fetch_crypto_crc(code)
    else:
        rate = _fetch_fiat_crc_mid(code)
    if rate is None:
        return False
    _xcrc_cache[code] = (rate, datetime.utcnow())
    _last_known_xcrc[code] = rate
    return True


def refresh_all_rates() -> dict[str, bool]:
    """Force-refresh every supported currency.

    Each currency is refreshed independently — one failure does not affect others.
    On success the DB (for USD) and in-memory caches are updated. On failure the
    previous value is retained via `_last_known_*` / stale-DB fallback, so callers
    always see the most recent working rate.
    """
    from app.models.models import Currency

    results: dict[str, bool] = {}

    try:
        results["USD"] = _refresh_usd_rate()
    except Exception:
        logger.exception("USD rate refresh failed")
        results["USD"] = False

    for currency in Currency:
        code = currency.value
        if code in ("CRC", "USD"):
            continue
        try:
            results[code] = _refresh_other_rate(code)
        except Exception:
            logger.exception("%s rate refresh failed", code)
            results[code] = False

    return results


async def refresh_rates_periodically(
    interval_seconds: int = REFRESH_INTERVAL_SECONDS,
) -> None:
    """Background loop that refreshes all currency rates every `interval_seconds`.

    Never raises — failures are logged and the last-known rates are retained.
    Runs one refresh immediately on startup, then sleeps on the fixed interval.
    """
    while True:
        try:
            report = await asyncio.to_thread(refresh_all_rates)
            ok = sorted(k for k, v in report.items() if v)
            failed = sorted(k for k, v in report.items() if not v)
            logger.info(
                "Exchange rate refresh complete: ok=%s failed=%s", ok, failed
            )
        except Exception:
            logger.exception("Exchange rate refresh loop crashed")
        await asyncio.sleep(interval_seconds)


def get_rate_history(session: Session, days: int = 30) -> list[ExchangeRate]:
    """Get historical exchange rates."""
    cutoff = datetime.utcnow() - timedelta(days=days)
    return list(
        session.exec(
            select(ExchangeRate)
            .where(ExchangeRate.date > cutoff)
            .order_by(col(ExchangeRate.date).desc())
        ).all()
    )