refactor(backend): switch to DDD

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

@@ -0,0 +1,82 @@
+package postgres
+
+import (
+	"errors"
+	"fmt"
+	"net/http"
+	"strconv"
+	"strings"
+
+	"github.com/jackc/pgx/v5"
+	"github.com/jackc/pgx/v5/pgconn"
+)
+
+// Handle database error
+func handleDBError(errIn error) (statusCode int, err error) {
+	if errIn == nil {
+		statusCode = http.StatusOK
+		return
+	}
+	if errors.Is(errIn, pgx.ErrNoRows) {
+		err = fmt.Errorf("not found")
+		statusCode = http.StatusNotFound
+		return
+	}
+	var pgErr *pgconn.PgError
+	if errors.As(errIn, &pgErr) {
+		switch pgErr.Code {
+		case "22P02", "22007": // Invalid data format
+			err = fmt.Errorf("%s", pgErr.Message)
+			statusCode = http.StatusBadRequest
+			return
+		case "23505": // Unique constraint violation
+			err = fmt.Errorf("already exists")
+			statusCode = http.StatusConflict
+			return
+		}
+	}
+	return http.StatusInternalServerError, errIn
+}
+
+// Convert "filter" URL param to SQL "WHERE" condition
+func filterToSQL(filter string) (sql string, err error) {
+	// filterTokens := strings.Split(string(filter), ";")
+	sql = "(true)"
+	return
+}
+
+// Convert "sort" URL param to SQL "ORDER BY"
+func sortToSQL(sort string) (sql string, err error) {
+	if sort == "" {
+		return
+	}
+	sortOptions := strings.Split(sort, ",")
+	sql = " ORDER BY "
+	for i, sortOption := range sortOptions {
+		sortOrder := sortOption[:1]
+		sortColumn := sortOption[1:]
+		// parse sorting order marker
+		switch sortOrder {
+		case "+":
+			sortOrder = "ASC"
+		case "-":
+			sortOrder = "DESC"
+		default:
+			err = fmt.Errorf("invalid sorting order mark: %q", sortOrder)
+			return
+		}
+		// validate sorting column
+		var n int
+		n, err = strconv.Atoi(sortColumn)
+		if err != nil || n < 0 {
+			err = fmt.Errorf("invalid sorting column: %q", sortColumn)
+			return
+		}
+		// add sorting option to query
+		if i > 0 {
+			sql += ","
+		}
+		sql += fmt.Sprintf("%s %s NULLS LAST", sortColumn, sortOrder)
+	}
+	return
+}