stock-tax-analyzer/backend/main.go

package main

import (
	"encoding/json"
	"fmt"
	"io"
	"log"
	"net/http"
	"strings"
	"time"
)

type StockPriceRequest struct {
	Tickers []string `json:"tickers"`
}

type StockPrice struct {
	Ticker  string  `json:"ticker"`
	USD     float64 `json:"usd"`
	EUR     float64 `json:"eur"`
	Success bool    `json:"success"`
	Error   string  `json:"error,omitempty"`
}

type StockPricesResponse struct {
	Prices       map[string]StockPrice `json:"prices"`
	ExchangeRate float64               `json:"exchangeRate"`
}

type YahooChartResponse struct {
	Chart struct {
		Result []struct {
			Meta struct {
				RegularMarketPrice float64 `json:"regularMarketPrice"`
			} `json:"meta"`
		} `json:"result"`
		Error *struct {
			Description string `json:"description"`
		} `json:"error"`
	} `json:"chart"`
}

type ExchangeRateResponse struct {
	Rates map[string]float64 `json:"rates"`
}

func fetchExchangeRate() (float64, error) {
	client := &http.Client{Timeout: 10 * time.Second}
	resp, err := client.Get("https://api.exchangerate-api.com/v4/latest/USD")
	if err != nil {
		return 0.92, fmt.Errorf("failed to fetch exchange rate: %w", err)
	}
	defer resp.Body.Close()

	var rateData ExchangeRateResponse
	if err := json.NewDecoder(resp.Body).Decode(&rateData); err != nil {
		return 0.92, fmt.Errorf("failed to decode exchange rate: %w", err)
	}

	if eurRate, ok := rateData.Rates["EUR"]; ok {
		return eurRate, nil
	}

	return 0.92, fmt.Errorf("EUR rate not found")
}

func fetchStockPrice(ticker string) (float64, error) {
	client := &http.Client{Timeout: 10 * time.Second}

	// Try different ticker formats for European stocks
	tickersToTry := []string{ticker}

	// If ticker doesn't have exchange suffix, try adding common ones
	if !strings.Contains(ticker, ".") {
		tickersToTry = append(tickersToTry,
			ticker+".L",  // London Stock Exchange
			ticker+".AS", // Amsterdam
			ticker+".PA", // Paris
			ticker+".DE", // XETRA (Germany)
			ticker+".MI", // Milan
		)
	}

	var lastErr error
	for _, tryTicker := range tickersToTry {
		// Try Yahoo Finance API
		url := fmt.Sprintf("https://query1.finance.yahoo.com/v8/finance/chart/%s?interval=1d&range=1d", tryTicker)
		req, err := http.NewRequest("GET", url, nil)
		if err != nil {
			lastErr = err
			continue
		}

		req.Header.Set("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36")

		resp, err := client.Do(req)
		if err != nil {
			lastErr = fmt.Errorf("failed to fetch from Yahoo: %w", err)
			continue
		}
		defer resp.Body.Close()

		body, err := io.ReadAll(resp.Body)
		if err != nil {
			lastErr = fmt.Errorf("failed to read response: %w", err)
			continue
		}

		var chartData YahooChartResponse
		if err := json.Unmarshal(body, &chartData); err != nil {
			lastErr = fmt.Errorf("failed to decode Yahoo response: %w", err)
			continue
		}

		if chartData.Chart.Error != nil {
			lastErr = fmt.Errorf("Yahoo API error: %s", chartData.Chart.Error.Description)
			continue
		}

		if len(chartData.Chart.Result) > 0 {
			price := chartData.Chart.Result[0].Meta.RegularMarketPrice
			if price > 0 {
				log.Printf("Successfully fetched price for %s (tried as %s): $%.2f", ticker, tryTicker, price)
				return price, nil
			}
		}
	}

	if lastErr != nil {
		return 0, fmt.Errorf("price not found after trying all formats: %w", lastErr)
	}
	return 0, fmt.Errorf("price not found in response")
}

func stockPricesHandler(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodPost {
		http.Error(w, "Method not allowed", http.StatusMethodNotAllowed)
		return
	}

	var req StockPriceRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		http.Error(w, "Invalid request body", http.StatusBadRequest)
		return
	}

	// Fetch exchange rate
	exchangeRate, err := fetchExchangeRate()
	if err != nil {
		log.Printf("Warning: Using fallback exchange rate: %v", err)
		exchangeRate = 0.92 // Fallback
	}

	prices := make(map[string]StockPrice)

	// Fetch prices for each ticker
	for _, ticker := range req.Tickers {
		ticker = strings.TrimSpace(ticker)
		if ticker == "" {
			continue
		}

		usdPrice, err := fetchStockPrice(ticker)
		if err != nil {
			log.Printf("Error fetching price for %s: %v", ticker, err)
			prices[ticker] = StockPrice{
				Ticker:  ticker,
				Success: false,
				Error:   err.Error(),
			}
		} else {
			prices[ticker] = StockPrice{
				Ticker:  ticker,
				USD:     usdPrice,
				EUR:     usdPrice * exchangeRate,
				Success: true,
			}
		}

		// Small delay to avoid rate limiting
		time.Sleep(100 * time.Millisecond)
	}

	response := StockPricesResponse{
		Prices:       prices,
		ExchangeRate: exchangeRate,
	}

	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(response)
}

func main() {
	// API endpoint
	http.HandleFunc("/api/stock-prices", stockPricesHandler)

	// Serve static files from /app/static directory
	fs := http.FileServer(http.Dir("/app/static"))
	http.Handle("/", fs)

	port := ":8080"
	log.Printf("Server starting on port %s", port)
	if err := http.ListenAndServe(port, nil); err != nil {
		log.Fatal(err)
	}
}