refactor(backend): switch to DDD

backend/internal/infrastructure/persistence/postgres/db.go

@@ -0,0 +1,50 @@
+package postgres
+
+import (
+	"context"
+	"fmt"
+	"time"
+
+	"github.com/jackc/pgx/v5"
+	"github.com/jackc/pgx/v5/pgxpool"
+
+	"tanabata/internal/domain"
+)
+
+// Initialize PostgreSQL database driver
+func New(dbURL string) (*pgxpool.Pool, error) {
+	poolConfig, err := pgxpool.ParseConfig(dbURL)
+	if err != nil {
+		return nil, fmt.Errorf("error while parsing connection string: %w", err)
+	}
+
+	poolConfig.MaxConns = 100
+	poolConfig.MinConns = 0
+	poolConfig.MaxConnLifetime = time.Hour
+	poolConfig.HealthCheckPeriod = 30 * time.Second
+
+	db, err := pgxpool.NewWithConfig(context.Background(), poolConfig)
+	if err != nil {
+		return nil, fmt.Errorf("error while initializing DB connections pool: %w", err)
+	}
+	return db, nil
+}
+
+// Transaction wrapper
+func transaction(ctx context.Context, db *pgxpool.Pool, handler func(context.Context, pgx.Tx) *domain.DomainError) (domainErr *domain.DomainError) {
+	tx, err := db.Begin(ctx)
+	if err != nil {
+		domainErr = domain.NewUnexpectedError(err)
+		return
+	}
+	domainErr = handler(ctx, tx)
+	if domainErr != nil {
+		tx.Rollback(ctx)
+		return
+	}
+	err = tx.Commit(ctx)
+	if err != nil {
+		domainErr = domain.NewUnexpectedError(err)
+	}
+	return
+}