Novault-backend/internal/cache/exchange_rate_cache.go

package cache

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"strconv"
	"time"

	"github.com/redis/go-redis/v9"

	"accounting-app/internal/config"
)

// Redis key constants for exchange rate cache
const (
	RatesCacheKey = "exchange_rates:all"
	RateCacheKey  = "exchange_rates:rate:"
	SyncStatusKey = "exchange_rates:sync_status"
)

// SyncStatus represents the synchronization status of exchange rates
type SyncStatus struct {
	LastSyncTime   time.Time `json:"last_sync_time"`
	LastSyncStatus string    `json:"last_sync_status"` // success, failed
	NextSyncTime   time.Time `json:"next_sync_time"`
	RatesCount     int       `json:"rates_count"`
	ErrorMessage   string    `json:"error_message,omitempty"`
}

// ExchangeRateCache provides Redis caching for exchange rates
type ExchangeRateCache struct {
	client     *redis.Client
	keyPrefix  string
	expiration time.Duration
}

// NewExchangeRateCache creates a new ExchangeRateCache instance
func NewExchangeRateCache(redisClient *RedisClient, cfg *config.Config) *ExchangeRateCache {
	expiration := cfg.CacheExpiration
	if expiration == 0 {
		expiration = 10 * time.Minute // Default to 10 minutes
	}

	return &ExchangeRateCache{
		client:     redisClient.Client(),
		keyPrefix:  "",
		expiration: expiration,
	}
}

// GetAll retrieves all exchange rates from the cache
// Returns a map of currency code to rate (1 Currency = Rate CNY)
func (c *ExchangeRateCache) GetAll(ctx context.Context) (map[string]float64, error) {
	result, err := c.client.HGetAll(ctx, RatesCacheKey).Result()
	if err != nil {
		return nil, fmt.Errorf("failed to get all rates from cache: %w", err)
	}

	if len(result) == 0 {
		return nil, nil // Cache miss - no data
	}

	rates := make(map[string]float64, len(result))
	for currency, rateStr := range result {
		rate, err := strconv.ParseFloat(rateStr, 64)
		if err != nil {
			// Skip invalid rate values
			continue
		}
		rates[currency] = rate
	}

	return rates, nil
}

// Get retrieves a single currency's exchange rate from the cache
// Returns the rate (1 Currency = Rate CNY) or an error if not found
func (c *ExchangeRateCache) Get(ctx context.Context, currency string) (float64, error) {
	rateStr, err := c.client.HGet(ctx, RatesCacheKey, currency).Result()
	if err != nil {
		if errors.Is(err, redis.Nil) {
			return 0, fmt.Errorf("rate for currency %s not found in cache", currency)
		}
		return 0, fmt.Errorf("failed to get rate for %s from cache: %w", currency, err)
	}

	rate, err := strconv.ParseFloat(rateStr, 64)
	if err != nil {
		return 0, fmt.Errorf("invalid rate value for %s in cache: %w", currency, err)
	}

	return rate, nil
}

// SetAll stores all exchange rates in the cache with TTL
// rates is a map of currency code to rate (1 Currency = Rate CNY)
func (c *ExchangeRateCache) SetAll(ctx context.Context, rates map[string]float64) error {
	if len(rates) == 0 {
		return nil
	}

	// Convert rates to string map for Redis Hash
	rateStrings := make(map[string]interface{}, len(rates))
	for currency, rate := range rates {
		rateStrings[currency] = strconv.FormatFloat(rate, 'f', 6, 64)
	}

	// Use pipeline for atomic operation
	pipe := c.client.Pipeline()

	// Delete existing key to ensure clean state
	pipe.Del(ctx, RatesCacheKey)

	// Set all rates in hash
	pipe.HSet(ctx, RatesCacheKey, rateStrings)

	// Set TTL
	pipe.Expire(ctx, RatesCacheKey, c.expiration)

	_, err := pipe.Exec(ctx)
	if err != nil {
		return fmt.Errorf("failed to set rates in cache: %w", err)
	}

	return nil
}

// GetSyncStatus retrieves the synchronization status from the cache
func (c *ExchangeRateCache) GetSyncStatus(ctx context.Context) (*SyncStatus, error) {
	data, err := c.client.Get(ctx, SyncStatusKey).Bytes()
	if err != nil {
		if errors.Is(err, redis.Nil) {
			return nil, nil // No sync status stored yet
		}
		return nil, fmt.Errorf("failed to get sync status from cache: %w", err)
	}

	var status SyncStatus
	if err := json.Unmarshal(data, &status); err != nil {
		return nil, fmt.Errorf("failed to unmarshal sync status: %w", err)
	}

	return &status, nil
}

// SetSyncStatus stores the synchronization status in the cache
func (c *ExchangeRateCache) SetSyncStatus(ctx context.Context, status *SyncStatus) error {
	if status == nil {
		return errors.New("sync status cannot be nil")
	}

	data, err := json.Marshal(status)
	if err != nil {
		return fmt.Errorf("failed to marshal sync status: %w", err)
	}

	// Sync status doesn't expire - it's always relevant
	err = c.client.Set(ctx, SyncStatusKey, data, 0).Err()
	if err != nil {
		return fmt.Errorf("failed to set sync status in cache: %w", err)
	}

	return nil
}

// Exists checks if the rates cache exists and is not expired
func (c *ExchangeRateCache) Exists(ctx context.Context) (bool, error) {
	exists, err := c.client.Exists(ctx, RatesCacheKey).Result()
	if err != nil {
		return false, fmt.Errorf("failed to check cache existence: %w", err)
	}
	return exists > 0, nil
}

// Delete removes all exchange rate data from the cache
func (c *ExchangeRateCache) Delete(ctx context.Context) error {
	pipe := c.client.Pipeline()
	pipe.Del(ctx, RatesCacheKey)
	pipe.Del(ctx, SyncStatusKey)
	_, err := pipe.Exec(ctx)
	if err != nil {
		return fmt.Errorf("failed to delete cache: %w", err)
	}
	return nil
}

// GetExpiration returns the cache expiration duration
func (c *ExchangeRateCache) GetExpiration() time.Duration {
	return c.expiration
}