"""
USDA FoodData Central API client.
Uses DEMO_KEY by default (30 req/hr, no registration needed).
Falls back gracefully when rate-limited.
"""

import os
import requests
from typing import Optional
from src.cache import get_cached, set_cached


USDA_BASE_URL = "https://api.nal.usda.gov/fdc/v1"
USDA_API_KEY = os.environ.get("USDA_API_KEY", "DEMO_KEY")

KEY_NUTRIENTS = {
    1008: "Calories (kcal)", 1003: "Protein (g)", 1004: "Total Fat (g)",
    1005: "Carbohydrates (g)", 1079: "Fiber (g)", 2000: "Sugars (g)",
    1093: "Sodium (mg)", 1087: "Calcium (mg)", 1089: "Iron (mg)",
    1092: "Potassium (mg)", 1106: "Vitamin A (mcg)", 1162: "Vitamin C (mg)",
    1114: "Vitamin D (mcg)", 1090: "Magnesium (mg)", 1095: "Zinc (mg)",
    1253: "Cholesterol (mg)", 1258: "Saturated Fat (g)",
}


def search_food(query: str, max_results: int = 1) -> Optional[dict]:
    """Search USDA for a food item. Returns None on any failure."""
    cache_key = f"usda:{query}"
    cached = get_cached("nutrition_cache", cache_key)
    if cached is not None:
        return cached

    try:
        resp = requests.get(
            f"{USDA_BASE_URL}/foods/search",
            params={
                "api_key": USDA_API_KEY, "query": query,
                "pageSize": max_results, "dataType": "Foundation,SR Legacy",
            },
            timeout=10,
        )
        if resp.status_code == 429:
            print(f"USDA rate limit hit for '{query}'")
            return None
        resp.raise_for_status()
        data = resp.json()

        results = []
        for food in data.get("foods", []):
            nutrients = {}
            for n in food.get("foodNutrients", []):
                nid = n.get("nutrientId")
                if nid in KEY_NUTRIENTS:
                    nutrients[KEY_NUTRIENTS[nid]] = round(n.get("value", 0), 2)
            results.append({
                "description": food.get("description", ""),
                "nutrients": nutrients,
            })

        result = {"query": query, "foods": results}
        set_cached("nutrition_cache", cache_key, result, ttl_days=30)
        return result

    except Exception as e:
        print(f"USDA error for '{query}': {e}")
        return None


def lookup_ingredients(ingredient_list: list[str]) -> dict:
    """
    Look up nutritional data for ingredients.
    Returns dict mapping ingredient -> nutrition data (or None if lookup failed).
    """
    results = {}
    api_failures = 0
    for ingredient in ingredient_list:
        data = search_food(ingredient.strip())
        if data and data.get("foods"):
            best = data["foods"][0]
            results[ingredient] = {
                "matched_food": best["description"],
                "nutrients": best["nutrients"],
                "source": "USDA FoodData Central",
            }
        else:
            api_failures += 1
            results[ingredient] = None  # signal fallback needed

    return results, api_failures