package main

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

// ExchangeRateCache holds currency rates with automatic refresh
var (
	exchangeRates      = make(map[string]float64)
	lastUpdated        time.Time
	exchangeCacheMutex sync.RWMutex
	cacheExpiration    = 1 * time.Hour
	allCurrencies      []string
)

// CurrencyAPIResponse structure for exchange rate API
type CurrencyAPIResponse struct {
	Rates map[string]float64 `json:"rates"`
}

// UpdateExchangeRates fetches and caches currency rates
func UpdateExchangeRates() error {
	exchangeCacheMutex.Lock()
	defer exchangeCacheMutex.Unlock()

	// Use a reliable free API with good rate limits
	resp, err := http.Get("https://open.er-api.com/v6/latest/USD")
	if err != nil {
		return err
	}
	defer resp.Body.Close()

	body, err := io.ReadAll(resp.Body)
	if err != nil {
		return err
	}

	var apiResponse struct {
		Result string             `json:"result"`
		Rates  map[string]float64 `json:"rates"`
	}
	if err := json.Unmarshal(body, &apiResponse); err != nil {
		return err
	}

	if apiResponse.Result != "success" {
		return fmt.Errorf("API error: %s", apiResponse.Result)
	}

	// Cache the rates
	exchangeRates = apiResponse.Rates
	lastUpdated = time.Now()

	// Update list of all currencies
	allCurrencies = make([]string, 0, len(exchangeRates))
	for currency := range exchangeRates {
		allCurrencies = append(allCurrencies, currency)
	}

	log.Printf("Updated currency rates: %d currencies cached", len(allCurrencies))
	return nil
}

// PrecacheAllCurrencyPairs pre-caches conversion rates for all currency pairs
func PrecacheAllCurrencyPairs() {
	exchangeCacheMutex.RLock()
	defer exchangeCacheMutex.RUnlock()

	if len(exchangeRates) == 0 {
		log.Println("Skipping precache - no rates available")
		return
	}

	log.Printf("Starting precache of all currency pairs (%d currencies)", len(allCurrencies))

	// We'll pre-cache the most common pairs directly
	commonCurrencies := []string{"USD", "EUR", "GBP", "JPY", "CAD", "AUD", "CHF", "CNY", "INR"}

	for _, from := range commonCurrencies {
		for _, to := range allCurrencies {
			if from == to {
				continue
			}
			GetExchangeRate(from, to)
		}
	}
	log.Println("Common currency pairs precached")
}

// GetExchangeRate gets the current exchange rate with caching
func GetExchangeRate(from, to string) (float64, bool) {
	// Auto-update cache if expired
	if time.Since(lastUpdated) > cacheExpiration {
		UpdateExchangeRates() // Ignore errors, use stale data if needed
	}

	exchangeCacheMutex.RLock()
	defer exchangeCacheMutex.RUnlock()

	// Handle same currency
	if from == to {
		return 1, true
	}

	// Convert via USD if direct rate not available
	fromRate, fromExists := exchangeRates[from]
	toRate, toExists := exchangeRates[to]

	if !fromExists || !toExists {
		return 0, false
	}

	// Calculate cross rate: (1 USD / fromRate) * toRate
	return toRate / fromRate, true
}

// ParseCurrencyConversion detects and processes currency conversion queries
func ParseCurrencyConversion(query string) (float64, string, string, bool) {
	// Match patterns like: "100 USD to EUR", "50 eur in gbp", "¥1000 to USD"
	re := regexp.MustCompile(`(?i)([\d,]+(?:\.\d+)?)\s*([$€£¥₩₹₽A-Za-z]{1,6})\s+(?:to|in|➞|→)\s+([$€£¥₩₹₽A-Za-z]{1,6})`)
	matches := re.FindStringSubmatch(query)
	if len(matches) < 4 {
		return 0, "", "", false
	}

	// Clean and parse amount
	amountStr := strings.ReplaceAll(matches[1], ",", "")
	amount, err := strconv.ParseFloat(amountStr, 64)
	if err != nil {
		return 0, "", "", false
	}

	// Normalize currency symbols
	currencyMap := map[string]string{
		"$": "USD", "€": "EUR", "£": "GBP", "¥": "JPY", "₩": "KRW", "₹": "INR", "₽": "RUB",
		"usd": "USD", "eur": "EUR", "gbp": "GBP", "jpy": "JPY", "krw": "KRW", "inr": "INR", "rub": "RUB",
		"dollar": "USD", "euro": "EUR", "pound": "GBP", "yen": "JPY", "won": "KRW", "rupee": "INR", "ruble": "RUB",
	}

	fromCurr := strings.ToUpper(matches[2])
	if mapped, ok := currencyMap[fromCurr]; ok {
		fromCurr = mapped
	} else if len(fromCurr) > 3 {
		// Try to match longer names
		for k, v := range currencyMap {
			if strings.EqualFold(k, fromCurr) {
				fromCurr = v
				break
			}
		}
	}

	toCurr := strings.ToUpper(matches[3])
	if mapped, ok := currencyMap[toCurr]; ok {
		toCurr = mapped
	} else if len(toCurr) > 3 {
		// Try to match longer names
		for k, v := range currencyMap {
			if strings.EqualFold(k, toCurr) {
				toCurr = v
				break
			}
		}
	}

	return amount, fromCurr, toCurr, true
}

// ConvertCurrency handles the actual conversion
func ConvertCurrency(amount float64, from, to string) (float64, bool) {
	if from == to {
		return amount, true
	}

	rate, ok := GetExchangeRate(from, to)
	if !ok {
		// Try to find similar currencies
		from = strings.ToUpper(from)
		to = strings.ToUpper(to)

		// Check if we have the currency in our list
		exchangeCacheMutex.RLock()
		defer exchangeCacheMutex.RUnlock()

		_, fromExists := exchangeRates[from]
		_, toExists := exchangeRates[to]

		if !fromExists || !toExists {
			return 0, false
		}

		// Shouldn't happen due to the check above, but just in case
		return 0, false
	}

	return amount * rate, true
}