import os
from typing import List

import httpx
from fastapi import APIRouter, HTTPException, Query, status

router = APIRouter(prefix="/exchange-rates", tags=["exchange-rates"]) 


@router.get("", status_code=status.HTTP_200_OK)
async def get_exchange_rates(symbols: str = Query("EUR,USD,NOK", description="Comma-separated currency codes to fetch vs CZK")):
    """
    Fetch exchange rates from UniRate API on the backend and return CZK-per-target rates.
    - Always requests CZK in addition to requested symbols to compute conversion from USD-base.
    - Returns a list of {currencyCode, rate} where rate is CZK per 1 unit of the target currency.
    """
    api_key = os.getenv("UNIRATE_API_KEY")
    if not api_key:
        raise HTTPException(status_code=500, detail="Server is not configured with UNIRATE_API_KEY")

    # Ensure CZK is included for conversion
    requested = [s.strip().upper() for s in symbols.split(",") if s.strip()]
    if "CZK" not in requested:
        requested.append("CZK")
    query_symbols = ",".join(sorted(set(requested)))

    url = f"https://unirateapi.com/api/rates?api_key={api_key}&symbols={query_symbols}"

    try:
        async with httpx.AsyncClient(timeout=httpx.Timeout(15.0)) as client:
            resp = await client.get(url)
            if resp.status_code != httpx.codes.OK:
                raise HTTPException(status_code=502, detail=f"Upstream UniRate error: HTTP {resp.status_code}")
            data = resp.json()
    except httpx.HTTPError as e:
        raise HTTPException(status_code=502, detail=f"Failed to contact UniRate: {str(e)}")

    # Validate response structure
    rates = data.get("rates") if isinstance(data, dict) else None
    base = data.get("base") if isinstance(data, dict) else None
    if not rates or base != "USD" or "CZK" not in rates:
        # Prefer upstream message when available
        detail = data.get("message") if isinstance(data, dict) else None
        if not detail and isinstance(data, dict):
            err = data.get("error")
            if isinstance(err, dict):
                detail = err.get("info")
        raise HTTPException(status_code=502, detail=detail or "Invalid response from UniRate API")

    czk_per_usd = rates["CZK"]

    # Build result excluding CZK itself
    result = []
    for code in requested:
        if code == "CZK":
            continue
        target_per_usd = rates.get(code)
        if target_per_usd in (None, 0):
            # Skip unavailable or invalid
            continue
        czk_per_target = czk_per_usd / target_per_usd
        result.append({"currencyCode": code, "rate": czk_per_target})

    return result