Implementing redis caching for receipts

Signed-off-by: Ethan Wellenreiter <ewellenreiter@gmail.com>

backend/internal/storage/cache/redis_receipts.go

@@ -0,0 +1,55 @@
+package cache
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+
+	"git.ewellenr.ca/receipt_indexer/backend/internal/storage"
+	"github.com/redis/go-redis/v9"
+)
+
+type ReceiptStore struct {
+	rdb *redis.Client
+}
+
+func (s *ReceiptStore) generateCacheKey(id int64) string {
+	return fmt.Sprintf("receipt-%d", id)
+}
+
+func (s *ReceiptStore) Get(ctx context.Context, id int64) (*storage.Receipt, error) {
+	cacheKey := s.generateCacheKey(id)
+
+	data, err := s.rdb.Get(ctx, cacheKey).Result()
+	if err == redis.Nil {
+		return nil, nil
+	} else if err != nil {
+		return nil, err
+	}
+
+	var receipt storage.Receipt
+	if data != "" {
+		err := json.Unmarshal([]byte(data), &receipt)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	return &receipt, nil
+}
+
+func (s *ReceiptStore) Set(ctx context.Context, receipt *storage.Receipt) error {
+	cacheKey := s.generateCacheKey(receipt.ID)
+
+	json, err := json.Marshal(receipt)
+	if err != nil {
+		return err
+	}
+
+	return s.rdb.Set(ctx, cacheKey, json, ReceiptExpTime).Err()
+}
+
+func (s *ReceiptStore) Delete(ctx context.Context, id int64) {
+	cacheKey := s.generateCacheKey(id)
+	s.rdb.Del(ctx, cacheKey)
+}