Novault-backend/internal/service/exchange_rate_service_v2.go

package service

import (
	"context"
	"errors"
	"fmt"
	"log"
	"time"

	"accounting-app/internal/cache"
	"accounting-app/pkg/utils"
)

// Error definitions for exchange rate service v2
var (
	ErrCurrencyNotSupported    = errors.New("currency not supported")
	ErrRateNotFound            = errors.New("exchange rate not found")
	ErrAPIUnavailable          = errors.New("external API unavailable")
	ErrInvalidConversionAmount = errors.New("invalid conversion amount")
	ErrSyncFailed              = errors.New("sync failed")
)

// ExchangeRateDTO represents exchange rate data transfer object
type ExchangeRateDTO struct {
	Currency     string    `json:"currency"`
	CurrencyName string    `json:"currency_name"`
	Symbol       string    `json:"symbol"`
	Rate         float64   `json:"rate"`
	UpdatedAt    time.Time `json:"updated_at"`
}

// ConversionResultDTO represents currency conversion result
type ConversionResultDTO struct {
	OriginalAmount  float64   `json:"original_amount"`
	FromCurrency    string    `json:"from_currency"`
	ToCurrency      string    `json:"to_currency"`
	ConvertedAmount float64   `json:"converted_amount"`
	RateUsed        float64   `json:"rate_used"`
	ConvertedAt     time.Time `json:"converted_at"`
}

// SyncResultDTO represents sync operation result
type SyncResultDTO struct {
	Message      string    `json:"message"`
	RatesUpdated int       `json:"rates_updated"`
	SyncTime     time.Time `json:"sync_time"`
}

// CurrencyMetadata contains display information for a currency
type CurrencyMetadata struct {
	Name   string
	Symbol string
}

// currencyMetadataMap maps currency codes to their metadata
// Extended to support all currencies from YunAPI
var currencyMetadataMap = map[string]CurrencyMetadata{
	"CNY": {Name: "人民币", Symbol: "¥"},
	"USD": {Name: "美元", Symbol: "$"},
	"EUR": {Name: "欧元", Symbol: "€"},
	"JPY": {Name: "日元", Symbol: "¥"},
	"GBP": {Name: "英镑", Symbol: "£"},
	"HKD": {Name: "港币", Symbol: "HK$"},
	"AUD": {Name: "澳元", Symbol: "A$"},
	"CAD": {Name: "加元", Symbol: "C$"},
	"CHF": {Name: "瑞士法郎", Symbol: "CHF"},
	"SGD": {Name: "新加坡元", Symbol: "S$"},
	"THB": {Name: "泰铢", Symbol: "฿"},
	"KRW": {Name: "韩元", Symbol: "₩"},
	"AED": {Name: "阿联酋迪拉姆", Symbol: "د.إ"},
	"BND": {Name: "文莱元", Symbol: "B$"},
	"BRL": {Name: "巴西雷亚尔", Symbol: "R$"},
	"CZK": {Name: "捷克克朗", Symbol: "Kč"},
	"DKK": {Name: "丹麦克朗", Symbol: "kr"},
	"HUF": {Name: "匈牙利福林", Symbol: "Ft"},
	"IDR": {Name: "印尼盾", Symbol: "Rp"},
	"ILS": {Name: "以色列新谢克尔", Symbol: "₪"},
	"INR": {Name: "印度卢比", Symbol: "₹"},
	"KHR": {Name: "柬埔寨瑞尔", Symbol: "៛"},
	"KWD": {Name: "科威特第纳尔", Symbol: "د.ك"},
	"MNT": {Name: "蒙古图格里克", Symbol: "₮"},
	"MOP": {Name: "澳门元", Symbol: "MOP$"},
	"MXN": {Name: "墨西哥比索", Symbol: "Mex$"},
	"NOK": {Name: "挪威克朗", Symbol: "kr"},
	"NPR": {Name: "尼泊尔卢比", Symbol: "₨"},
	"NZD": {Name: "新西兰元", Symbol: "NZ$"},
	"PHP": {Name: "菲律宾比索", Symbol: "₱"},
	"PKR": {Name: "巴基斯坦卢比", Symbol: "₨"},
	"QAR": {Name: "卡塔尔里亚尔", Symbol: "﷼"},
	"RUB": {Name: "俄罗斯卢布", Symbol: "₽"},
	"SAR": {Name: "沙特里亚尔", Symbol: "﷼"},
	"SEK": {Name: "瑞典克朗", Symbol: "kr"},
	"TRY": {Name: "土耳其里拉", Symbol: "₺"},
	"TWD": {Name: "新台币", Symbol: "NT$"},
	"VND": {Name: "越南盾", Symbol: "₫"},
	"ZAR": {Name: "南非兰特", Symbol: "R"},
}

// GetCurrencyMetadata returns metadata for a currency code
func GetCurrencyMetadata(currency string) CurrencyMetadata {
	if meta, ok := currencyMetadataMap[currency]; ok {
		return meta
	}
	// Return default metadata for unknown currencies
	return CurrencyMetadata{Name: currency, Symbol: currency}
}

// IsCurrencySupported checks if a currency is supported
func IsCurrencySupported(currency string) bool {
	_, ok := currencyMetadataMap[currency]
	return ok
}

// ExchangeRateServiceV2 provides exchange rate business logic with Redis caching
type ExchangeRateServiceV2 struct {
	cache  *cache.ExchangeRateCache
	client *YunAPIClient
}

// NewExchangeRateServiceV2 creates a new ExchangeRateServiceV2 instance
func NewExchangeRateServiceV2(cache *cache.ExchangeRateCache, client *YunAPIClient) *ExchangeRateServiceV2 {
	return &ExchangeRateServiceV2{
		cache:  cache,
		client: client,
	}
}

// GetAllRates retrieves all exchange rates with cache-first strategy
// Returns rates for all currencies relative to CNY
func (s *ExchangeRateServiceV2) GetAllRates(ctx context.Context) ([]ExchangeRateDTO, error) {
	// Try to get from cache first
	rates, err := s.cache.GetAll(ctx)
	if err != nil {
		log.Printf("[ExchangeRateServiceV2] Cache error: %v, falling back to API", err)
	}

	// If cache hit, convert to DTOs
	if rates != nil && len(rates) > 0 {
		log.Printf("[ExchangeRateServiceV2] Cache hit: found %d rates", len(rates))
		return s.ratesToDTOs(rates), nil
	}

	// Cache miss - fetch from API
	log.Println("[ExchangeRateServiceV2] Cache miss, fetching from API")
	rates, err = s.fetchAndCacheRates(ctx)
	if err != nil {
		return nil, fmt.Errorf("failed to get rates: %w", err)
	}

	return s.ratesToDTOs(rates), nil
}

// GetRatesBatch retrieves multiple currencies' exchange rates in one call
// More efficient than calling GetRate multiple times
func (s *ExchangeRateServiceV2) GetRatesBatch(ctx context.Context, currencies []string) ([]ExchangeRateDTO, error) {
	if len(currencies) == 0 {
		return []ExchangeRateDTO{}, nil
	}

	// Validate all currencies first
	for _, currency := range currencies {
		if !IsCurrencySupported(currency) {
			return nil, fmt.Errorf("%w: %s", ErrCurrencyNotSupported, currency)
		}
	}

	// Try to get all from cache
	allRates, err := s.cache.GetAll(ctx)
	if err != nil || allRates == nil {
		// Cache miss - fetch from API
		allRates, err = s.fetchAndCacheRates(ctx)
		if err != nil {
			return nil, fmt.Errorf("failed to get rates: %w", err)
		}
	}

	// Filter requested currencies
	result := make([]ExchangeRateDTO, 0, len(currencies))
	for _, currency := range currencies {
		if currency == "CNY" {
			result = append(result, ExchangeRateDTO{
				Currency:     "CNY",
				CurrencyName: "人民币",
				Symbol:       "¥",
				Rate:         1.0,
				UpdatedAt:    time.Now(),
			})
			continue
		}

		if rate, ok := allRates[currency]; ok {
			meta := GetCurrencyMetadata(currency)
			result = append(result, ExchangeRateDTO{
				Currency:     currency,
				CurrencyName: meta.Name,
				Symbol:       meta.Symbol,
				Rate:         rate,
				UpdatedAt:    time.Now(),
			})
		} else {
			return nil, fmt.Errorf("%w: %s", ErrRateNotFound, currency)
		}
	}

	return result, nil
}

// GetRate retrieves a single currency's exchange rate with cache-first strategy
// Returns the rate for the specified currency relative to CNY
func (s *ExchangeRateServiceV2) GetRate(ctx context.Context, currency string) (*ExchangeRateDTO, error) {
	// Validate currency
	if !IsCurrencySupported(currency) {
		return nil, fmt.Errorf("%w: %s", ErrCurrencyNotSupported, currency)
	}

	// CNY to CNY is always 1
	if currency == "CNY" {
		return &ExchangeRateDTO{
			Currency:     "CNY",
			CurrencyName: "人民币",
			Symbol:       "¥",
			Rate:         1.0,
			UpdatedAt:    time.Now(),
		}, nil
	}

	// Try to get from cache first
	rate, err := s.cache.Get(ctx, currency)
	if err == nil {
		log.Printf("[ExchangeRateServiceV2] Cache hit for %s: %f", currency, rate)
		meta := GetCurrencyMetadata(currency)
		return &ExchangeRateDTO{
			Currency:     currency,
			CurrencyName: meta.Name,
			Symbol:       meta.Symbol,
			Rate:         rate,
			UpdatedAt:    time.Now(),
		}, nil
	}

	// Cache miss - try to fetch all rates from API and cache them
	log.Printf("[ExchangeRateServiceV2] Cache miss for %s, fetching from API", currency)
	rates, err := s.fetchAndCacheRates(ctx)
	if err != nil {
		// API failed - this is a critical error
		return nil, fmt.Errorf("failed to get rate for %s: %w", currency, err)
	}

	// Check if the requested currency exists in the fetched rates
	if rate, ok := rates[currency]; ok {
		meta := GetCurrencyMetadata(currency)
		return &ExchangeRateDTO{
			Currency:     currency,
			CurrencyName: meta.Name,
			Symbol:       meta.Symbol,
			Rate:         rate,
			UpdatedAt:    time.Now(),
		}, nil
	}

	return nil, fmt.Errorf("%w: %s", ErrRateNotFound, currency)
}

// GetRateWithFallback retrieves a rate with multiple fallback strategies
// This provides better reliability when cache or API fails
func (s *ExchangeRateServiceV2) GetRateWithFallback(ctx context.Context, currency string) (*ExchangeRateDTO, error) {
	// Validate currency
	if !IsCurrencySupported(currency) {
		return nil, fmt.Errorf("%w: %s", ErrCurrencyNotSupported, currency)
	}

	// CNY to CNY is always 1
	if currency == "CNY" {
		return &ExchangeRateDTO{
			Currency:     "CNY",
			CurrencyName: "人民币",
			Symbol:       "¥",
			Rate:         1.0,
			UpdatedAt:    time.Now(),
		}, nil
	}

	// Strategy 1: Try cache
	rate, err := s.cache.Get(ctx, currency)
	if err == nil {
		log.Printf("[ExchangeRateServiceV2] Cache hit for %s", currency)
		meta := GetCurrencyMetadata(currency)
		return &ExchangeRateDTO{
			Currency:     currency,
			CurrencyName: meta.Name,
			Symbol:       meta.Symbol,
			Rate:         rate,
			UpdatedAt:    time.Now(),
		}, nil
	}

	// Strategy 2: Try API
	log.Printf("[ExchangeRateServiceV2] Cache miss for %s, trying API", currency)
	rates, err := s.client.FetchRates()
	if err == nil {
		// Cache the fetched rates
		if cacheErr := s.cache.SetAll(ctx, rates); cacheErr != nil {
			log.Printf("[ExchangeRateServiceV2] Warning: failed to cache rates: %v", cacheErr)
		}

		if rate, ok := rates[currency]; ok {
			meta := GetCurrencyMetadata(currency)
			return &ExchangeRateDTO{
				Currency:     currency,
				CurrencyName: meta.Name,
				Symbol:       meta.Symbol,
				Rate:         rate,
				UpdatedAt:    time.Now(),
			}, nil
		}
	}

	// All strategies failed
	return nil, fmt.Errorf("%w: all fallback strategies failed for %s", ErrRateNotFound, currency)
}

// GetSyncStatus retrieves the current synchronization status
func (s *ExchangeRateServiceV2) GetSyncStatus(ctx context.Context) (*cache.SyncStatus, error) {
	status, err := s.cache.GetSyncStatus(ctx)
	if err != nil {
		return nil, fmt.Errorf("failed to get sync status: %w", err)
	}

	// Return default status if none exists
	if status == nil {
		return &cache.SyncStatus{
			LastSyncTime:   time.Time{},
			LastSyncStatus: "unknown",
			NextSyncTime:   time.Time{},
			RatesCount:     0,
		}, nil
	}

	return status, nil
}

// fetchAndCacheRates fetches rates from API and caches them
func (s *ExchangeRateServiceV2) fetchAndCacheRates(ctx context.Context) (map[string]float64, error) {
	// Fetch from API using the existing client's retry logic
	rates, err := s.client.FetchRates()
	if err != nil {
		return nil, fmt.Errorf("%w: %v", ErrAPIUnavailable, err)
	}

	// Cache the rates
	if err := s.cache.SetAll(ctx, rates); err != nil {
		log.Printf("[ExchangeRateServiceV2] Warning: failed to cache rates: %v", err)
		// Don't fail the request if caching fails
	}

	// Update sync status
	syncStatus := &cache.SyncStatus{
		LastSyncTime:   time.Now(),
		LastSyncStatus: "success",
		NextSyncTime:   time.Now().Add(s.cache.GetExpiration()),
		RatesCount:     len(rates),
	}
	if err := s.cache.SetSyncStatus(ctx, syncStatus); err != nil {
		log.Printf("[ExchangeRateServiceV2] Warning: failed to update sync status: %v", err)
	}

	return rates, nil
}

// ratesToDTOs converts a map of rates to a slice of ExchangeRateDTO
func (s *ExchangeRateServiceV2) ratesToDTOs(rates map[string]float64) []ExchangeRateDTO {
	dtos := make([]ExchangeRateDTO, 0, len(rates))

	for currency, rate := range rates {
		meta := GetCurrencyMetadata(currency)
		dtos = append(dtos, ExchangeRateDTO{
			Currency:     currency,
			CurrencyName: meta.Name,
			Symbol:       meta.Symbol,
			Rate:         rate,
			UpdatedAt:    time.Now(), // We don't store individual timestamps in cache
		})
	}

	return dtos
}

// ConvertCurrency converts an amount from one currency to another
// Uses CNY as the intermediate currency for conversions
// Returns the conversion result with two decimal places precision
func (s *ExchangeRateServiceV2) ConvertCurrency(ctx context.Context, amount float64, from, to string) (*ConversionResultDTO, error) {
	// Validate amount
	if amount < 0 {
		return nil, fmt.Errorf("%w: amount cannot be negative", ErrInvalidConversionAmount)
	}

	// Validate currencies
	if !IsCurrencySupported(from) {
		return nil, fmt.Errorf("%w: %s", ErrCurrencyNotSupported, from)
	}
	if !IsCurrencySupported(to) {
		return nil, fmt.Errorf("%w: %s", ErrCurrencyNotSupported, to)
	}

	// Handle same currency conversion (Requirement 6.3)
	if from == to {
		return &ConversionResultDTO{
			OriginalAmount:  amount,
			FromCurrency:    from,
			ToCurrency:      to,
			ConvertedAmount: utils.RoundToTwoDecimals(amount),
			RateUsed:        1.0,
			ConvertedAt:     time.Now(),
		}, nil
	}

	// Get rates for conversion - try cache first, fallback to API
	var fromRate, toRate float64
	var err error

	// Get all rates at once for better performance
	allRates, err := s.cache.GetAll(ctx)
	if err != nil || allRates == nil || len(allRates) == 0 {
		// Cache miss - fetch from API
		log.Println("[ExchangeRateServiceV2] Cache miss in conversion, fetching from API")
		allRates, err = s.fetchAndCacheRates(ctx)
		if err != nil {
			return nil, fmt.Errorf("failed to fetch rates for conversion: %w", err)
		}
	}

	// Get from rate
	if from == "CNY" {
		fromRate = 1.0
	} else {
		rate, ok := allRates[from]
		if !ok {
			return nil, fmt.Errorf("%w: %s", ErrRateNotFound, from)
		}
		fromRate = rate
	}

	// Get to rate
	if to == "CNY" {
		toRate = 1.0
	} else {
		rate, ok := allRates[to]
		if !ok {
			return nil, fmt.Errorf("%w: %s", ErrRateNotFound, to)
		}
		toRate = rate
	}

	// Calculate conversion using CNY as intermediate currency (Requirement 6.4)
	// Rate represents: 1 Currency = Rate CNY
	// Conversion formula:
	// - from CNY: result = amount / to_rate (CNY to target currency)
	// - to CNY: result = amount * from_rate (source currency to CNY)
	// - otherwise: result = amount * from_rate / to_rate (via CNY)
	var convertedAmount float64
	var rateUsed float64

	if from == "CNY" {
		// Converting from CNY to target currency
		// amount CNY / to_rate = result in target currency
		convertedAmount = amount / toRate
		rateUsed = 1.0 / toRate
	} else if to == "CNY" {
		// Converting from source currency to CNY
		// amount * from_rate = result in CNY
		convertedAmount = amount * fromRate
		rateUsed = fromRate
	} else {
		// Converting between two non-CNY currencies via CNY
		// amount * from_rate / to_rate = result
		convertedAmount = amount * fromRate / toRate
		rateUsed = fromRate / toRate
	}

	// Round to two decimal places (Requirement 6.5)
	convertedAmount = utils.RoundToTwoDecimals(convertedAmount)
	rateUsed = utils.RoundToTwoDecimals(rateUsed)

	return &ConversionResultDTO{
		OriginalAmount:  amount,
		FromCurrency:    from,
		ToCurrency:      to,
		ConvertedAmount: convertedAmount,
		RateUsed:        rateUsed,
		ConvertedAt:     time.Now(),
	}, nil
}

// GetCache returns the cache instance (for use by scheduler)
func (s *ExchangeRateServiceV2) GetCache() *cache.ExchangeRateCache {
	return s.cache
}

// GetClient returns the API client instance (for use by scheduler)
func (s *ExchangeRateServiceV2) GetClient() *YunAPIClient {
	return s.client
}