package service

import (
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"log"
	"math"
	"net/http"
	"time"

	"accounting-app/internal/models"
	"accounting-app/internal/repository"
)

// YunAPIClient handles fetching exchange rates from yunapi.cn
type YunAPIClient struct {
	apiURL           string
	apiKey           string
	httpClient       *http.Client
	exchangeRateRepo *repository.ExchangeRateRepository
	maxRetries       int
}

// YunAPIResponse represents the response from yunapi.cn
// The API returns rates relative to CNY (e.g., USD: 6.9756 means 1 USD = 6.9756 CNY)
type YunAPIResponse map[string]float64

// Common errors
var (
	ErrAPIRequestFailed = errors.New("API request failed")
	ErrInvalidResponse  = errors.New("invalid API response")
)

// NewYunAPIClient creates a new YunAPIClient instance
func NewYunAPIClient(apiURL string, exchangeRateRepo *repository.ExchangeRateRepository) *YunAPIClient {
	return &YunAPIClient{
		apiURL: apiURL,
		httpClient: &http.Client{
			Timeout: 30 * time.Second,
		},
		exchangeRateRepo: exchangeRateRepo,
		maxRetries:       3,
	}
}

// NewYunAPIClientWithConfig creates a new YunAPIClient with full configuration
func NewYunAPIClientWithConfig(apiURL, apiKey string, maxRetries int, exchangeRateRepo *repository.ExchangeRateRepository) *YunAPIClient {
	client := NewYunAPIClient(apiURL, exchangeRateRepo)
	client.apiKey = apiKey
	if maxRetries > 0 {
		client.maxRetries = maxRetries
	}
	return client
}

// FetchAndSaveRates fetches exchange rates from yunapi.cn and saves them to the database
func (c *YunAPIClient) FetchAndSaveRates() error {
	log.Println("[YunAPI] Fetching exchange rates...")

	// Fetch rates with retry
	rates, err := c.fetchRatesWithRetry()
	if err != nil {
		return err
	}

	// Save rates to database
	return c.saveRates(rates)
}

// ForceRefresh forces an immediate refresh of exchange rates
// Returns the number of rates saved and any error
func (c *YunAPIClient) ForceRefresh() (int, error) {
	log.Println("[YunAPI] Force refreshing exchange rates...")

	rates, err := c.fetchRatesWithRetry()
	if err != nil {
		return 0, err
	}

	savedCount, err := c.saveRatesWithCount(rates)
	if err != nil {
		return 0, err
	}

	log.Printf("[YunAPI] Force refresh completed: saved %d exchange rates", savedCount)
	return savedCount, nil
}

// FetchRates fetches exchange rates from the API with retry logic
// Returns a map of currency code to rate (1 Currency = Rate CNY)
// This method does not save to database - use FetchAndSaveRates for that
func (c *YunAPIClient) FetchRates() (YunAPIResponse, error) {
	return c.fetchRatesWithRetry()
}

// fetchRatesWithRetry fetches rates from the API with exponential backoff retry
func (c *YunAPIClient) fetchRatesWithRetry() (YunAPIResponse, error) {
	var lastErr error

	for attempt := 0; attempt < c.maxRetries; attempt++ {
		if attempt > 0 {
			// Exponential backoff: 1s, 2s, 4s, ...
			backoff := time.Duration(math.Pow(2, float64(attempt-1))) * time.Second
			log.Printf("[YunAPI] Retry attempt %d/%d after %v", attempt+1, c.maxRetries, backoff)
			time.Sleep(backoff)
		}

		rates, err := c.fetchRates()
		if err == nil {
			return rates, nil
		}

		lastErr = err
		log.Printf("[YunAPI] Attempt %d failed: %v", attempt+1, err)
	}

	return nil, fmt.Errorf("failed after %d retries: %w", c.maxRetries, lastErr)
}

// fetchRates makes a single API request to fetch exchange rates
func (c *YunAPIClient) fetchRates() (YunAPIResponse, error) {
	// Build request URL
	url := c.apiURL
	if c.apiKey != "" {
		url = fmt.Sprintf("%s?key=%s", c.apiURL, c.apiKey)
	}

	// Make HTTP GET request
	resp, err := c.httpClient.Get(url)
	if err != nil {
		return nil, fmt.Errorf("%w: %v", ErrAPIRequestFailed, err)
	}
	defer resp.Body.Close()

	// Check status code
	if resp.StatusCode != http.StatusOK {
		body, _ := io.ReadAll(resp.Body)
		return nil, fmt.Errorf("%w: status %d, body: %s", ErrAPIRequestFailed, resp.StatusCode, string(body))
	}

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

	// Parse JSON response
	var rates YunAPIResponse
	if err := json.Unmarshal(body, &rates); err != nil {
		return nil, fmt.Errorf("%w: %v", ErrInvalidResponse, err)
	}

	if len(rates) == 0 {
		return nil, fmt.Errorf("%w: empty response", ErrInvalidResponse)
	}

	log.Printf("[YunAPI] Successfully fetched %d currency rates", len(rates))
	return rates, nil
}

// saveRates saves exchange rates to the database
func (c *YunAPIClient) saveRates(rates YunAPIResponse) error {
	now := time.Now()
	var exchangeRates []models.ExchangeRate

	// The API returns rates as: 1 [Currency] = X CNY
	// We store them as: FromCurrency -> ToCurrency with Rate
	for currencyCode, rateToCNY := range rates {
		// Map API currency codes to our supported currencies
		currency := mapToCurrency(currencyCode)
		if currency == "" {
			continue // Skip unsupported currencies
		}

		// Skip CNY itself
		if currency == models.CurrencyCNY {
			continue
		}

		// Create exchange rate: Currency -> CNY
		// e.g., USD -> CNY = 6.9756 (meaning 1 USD = 6.9756 CNY)
		exchangeRate := models.ExchangeRate{
			FromCurrency:  currency,
			ToCurrency:    models.CurrencyCNY,
			Rate:          rateToCNY,
			EffectiveDate: now,
		}

		exchangeRates = append(exchangeRates, exchangeRate)
	}

	if len(exchangeRates) == 0 {
		return nil
	}

	// Use synchronized batch insert
	if err := c.exchangeRateRepo.BatchUpsertOptimized(exchangeRates); err != nil {
		return fmt.Errorf("failed to batch save exchange rates: %w", err)
	}

	log.Printf("[YunAPI] Successfully batch saved %d exchange rates", len(exchangeRates))
	return nil
}

// saveRatesWithCount saves exchange rates and returns the count of saved rates
func (c *YunAPIClient) saveRatesWithCount(rates YunAPIResponse) (int, error) {
	now := time.Now()
	var exchangeRates []models.ExchangeRate

	for currencyCode, rateToCNY := range rates {
		currency := mapToCurrency(currencyCode)
		if currency == "" {
			continue
		}

		if currency == models.CurrencyCNY {
			continue
		}

		exchangeRate := models.ExchangeRate{
			FromCurrency:  currency,
			ToCurrency:    models.CurrencyCNY,
			Rate:          rateToCNY,
			EffectiveDate: now,
		}

		exchangeRates = append(exchangeRates, exchangeRate)
	}

	if len(exchangeRates) == 0 {
		return 0, nil
	}

	// Use synchronized batch insert
	if err := c.exchangeRateRepo.BatchUpsertOptimized(exchangeRates); err != nil {
		return 0, fmt.Errorf("failed to batch save exchange rates: %w", err)
	}

	return len(exchangeRates), nil
}

// GetAPIURL returns the configured API URL
func (c *YunAPIClient) GetAPIURL() string {
	return c.apiURL
}

// mapToCurrency maps API currency codes to our supported Currency type
// Supports all 37 currencies from YunAPI
func mapToCurrency(code string) models.Currency {
	switch code {
	// Major currencies
	case "CNY":
		return models.CurrencyCNY
	case "USD":
		return models.CurrencyUSD
	case "EUR":
		return models.CurrencyEUR
	case "JPY":
		return models.CurrencyJPY
	case "GBP":
		return models.CurrencyGBP
	case "HKD":
		return models.CurrencyHKD

	// Asia Pacific
	case "AUD":
		return models.CurrencyAUD
	case "NZD":
		return models.CurrencyNZD
	case "SGD":
		return models.CurrencySGD
	case "KRW":
		return models.CurrencyKRW
	case "THB":
		return models.CurrencyTHB
	case "TWD":
		return models.CurrencyTWD
	case "MOP":
		return models.CurrencyMOP
	case "PHP":
		return models.CurrencyPHP
	case "IDR":
		return models.CurrencyIDR
	case "INR":
		return models.CurrencyINR
	case "VND":
		return models.CurrencyVND
	case "MNT":
		return models.CurrencyMNT
	case "KHR":
		return models.CurrencyKHR
	case "NPR":
		return models.CurrencyNPR
	case "PKR":
		return models.CurrencyPKR
	case "BND":
		return models.CurrencyBND

	// Europe
	case "CHF":
		return models.CurrencyCHF
	case "SEK":
		return models.CurrencySEK
	case "NOK":
		return models.CurrencyNOK
	case "DKK":
		return models.CurrencyDKK
	case "CZK":
		return models.CurrencyCZK
	case "HUF":
		return models.CurrencyHUF
	case "RUB":
		return models.CurrencyRUB
	case "TRY":
		return models.CurrencyTRY

	// Americas
	case "CAD":
		return models.CurrencyCAD
	case "MXN":
		return models.CurrencyMXN
	case "BRL":
		return models.CurrencyBRL

	// Middle East & Africa
	case "AED":
		return models.CurrencyAED
	case "SAR":
		return models.CurrencySAR
	case "QAR":
		return models.CurrencyQAR
	case "KWD":
		return models.CurrencyKWD
	case "ILS":
		return models.CurrencyILS
	case "ZAR":
		return models.CurrencyZAR

	default:
		return "" // Unsupported currency
	}
}