WealthySmart/backend/app/services/exchange_rate.py

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

import httpx
from sqlmodel import Session, col, select

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

# 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)


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 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()
    )