package product

import (
	"context"
	"encoding/json"
	"fmt"
	"net/http"
)

// OpenFoodFacts is the client for the Open Food Facts public API.
type OpenFoodFacts struct {
	httpClient *http.Client
}

// NewOpenFoodFacts creates a new OpenFoodFacts client with the default HTTP client.
func NewOpenFoodFacts() *OpenFoodFacts {
	return &OpenFoodFacts{httpClient: &http.Client{}}
}

// offProduct is the JSON shape returned by the Open Food Facts v2 API.
type offProduct struct {
	ProductName string      `json:"product_name"`
	Brands      string      `json:"brands"`
	Nutriments  offNutriments `json:"nutriments"`
}

type offNutriments struct {
	EnergyKcal100g *float64 `json:"energy-kcal_100g"`
	Proteins100g   *float64 `json:"proteins_100g"`
	Fat100g        *float64 `json:"fat_100g"`
	Carbohydrates100g *float64 `json:"carbohydrates_100g"`
	Fiber100g      *float64 `json:"fiber_100g"`
}

type offResponse struct {
	Status  int        `json:"status"`
	Product offProduct `json:"product"`
}

// Fetch retrieves a product from Open Food Facts by barcode.
// Returns an error if the product is not found or the API call fails.
func (client *OpenFoodFacts) Fetch(requestContext context.Context, barcode string) (*Product, error) {
	url := fmt.Sprintf("https://world.openfoodfacts.org/api/v2/product/%s.json", barcode)
	httpRequest, requestError := http.NewRequestWithContext(requestContext, http.MethodGet, url, nil)
	if requestError != nil {
		return nil, fmt.Errorf("build open food facts request: %w", requestError)
	}
	httpRequest.Header.Set("User-Agent", "FoodAI/1.0")

	httpResponse, fetchError := client.httpClient.Do(httpRequest)
	if fetchError != nil {
		return nil, fmt.Errorf("open food facts request: %w", fetchError)
	}
	defer httpResponse.Body.Close()

	if httpResponse.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("open food facts returned status %d for barcode %s", httpResponse.StatusCode, barcode)
	}

	var offResp offResponse
	if decodeError := json.NewDecoder(httpResponse.Body).Decode(&offResp); decodeError != nil {
		return nil, fmt.Errorf("decode open food facts response: %w", decodeError)
	}
	if offResp.Status == 0 {
		return nil, fmt.Errorf("product %s not found in open food facts", barcode)
	}

	canonicalName := offResp.Product.ProductName
	if canonicalName == "" {
		canonicalName = barcode // Fall back to barcode as canonical name
	}

	barcodeValue := barcode
	catalogProduct := &Product{
		CanonicalName:   canonicalName,
		Barcode:         &barcodeValue,
		CaloriesPer100g: offResp.Product.Nutriments.EnergyKcal100g,
		ProteinPer100g:  offResp.Product.Nutriments.Proteins100g,
		FatPer100g:      offResp.Product.Nutriments.Fat100g,
		CarbsPer100g:    offResp.Product.Nutriments.Carbohydrates100g,
		FiberPer100g:    offResp.Product.Nutriments.Fiber100g,
	}
	return catalogProduct, nil
}