Change structure of code to a frontend and backend one

cmd/backend/db.go

@@ -0,0 +1,167 @@
+package backend
+
+import (
+	"bufio"
+	"database/sql"
+	"fmt"
+	"log"
+	"math"
+	"math/rand/v2"
+	"os"
+	"strings"
+	"syscall"
+	"time"
+
+	"github.com/go-sql-driver/mysql"
+	"golang.org/x/term"
+)
+
+var TxMaxRetries = 5
+
+type (
+	DB struct{ *sql.DB }
+	Tx struct{ *sql.Tx }
+
+	Attribute struct {
+		Value   any
+		Table   string
+		AttName string
+		ID      int64
+	}
+)
+
+func getUsername() (string, error) {
+	user := os.Getenv("DB_USER")
+	if user == "" {
+		var err error
+		fmt.Printf("DB Benutzer: ")
+		user, err = bufio.NewReader(os.Stdin).ReadString('\n')
+		if err != nil {
+			return "", fmt.Errorf("error reading username: %v", err)
+		}
+	}
+	return strings.TrimSpace(user), nil
+}
+
+func getPassword() (string, error) {
+	pass := os.Getenv("DB_PASS")
+	if pass == "" {
+		fmt.Printf("DB Passwort: ")
+		bytePass, err := term.ReadPassword(int(syscall.Stdin))
+		if err != nil {
+			return "", fmt.Errorf("error reading password: %v", err)
+		}
+		fmt.Println()
+		pass = strings.TrimSpace(string(bytePass))
+	}
+	return pass, nil
+}
+
+func getCredentials() (string, string, error) {
+	user, err := getUsername()
+	if err != nil {
+		return "", "", fmt.Errorf("error getting username: %v", err)
+	}
+
+	pass, err := getPassword()
+	if err != nil {
+		return "", "", fmt.Errorf("error getting password: %v", err)
+	}
+
+	return user, pass, nil
+}
+
+func wait(iteration int) {
+	waitTime := time.Duration(math.Pow(2, float64(iteration))) * 100 * time.Millisecond
+	jitter := time.Duration(rand.IntN(int(waitTime)/2)) * time.Millisecond
+	time.Sleep(waitTime + jitter)
+}
+
+func OpenDB(dbName string) (*DB, error) {
+	var err error
+	db := DB{DB: new(sql.DB)}
+
+	cfg := mysql.NewConfig()
+	cfg.DBName = dbName
+	cfg.User, cfg.Passwd, err = getCredentials()
+	if err != nil {
+		return nil, fmt.Errorf("error reading user credentials for DB: %v", err)
+	}
+
+	db.DB, err = sql.Open("mysql", cfg.FormatDSN())
+	if err != nil {
+		return nil, fmt.Errorf("error opening DB: %v", err)
+	}
+	if err = db.Ping(); err != nil {
+		return nil, fmt.Errorf("error pinging DB: %v", err)
+	}
+
+	return &db, nil
+}
+
+func (db *DB) UpdateAttributes(a ...*Attribute) error {
+	for i := 0; i < TxMaxRetries; i++ {
+		err := func() error {
+			tx, err := db.Begin()
+			if err != nil {
+				return fmt.Errorf("error starting transaction: %v", err)
+			}
+
+			for _, attribute := range a {
+				query := fmt.Sprintf(`
+                    UPDATE %s
+                    SET %s = ?
+                    WHERE id = ?
+                    `, attribute.Table, attribute.AttName)
+				if _, err := tx.Exec(query, attribute.Value, attribute.ID); err != nil {
+					if rollbackErr := tx.Rollback(); rollbackErr != nil {
+						log.Fatalf("transaction error: %v, rollback error: %v", err, rollbackErr)
+					}
+					return fmt.Errorf("error updating %v in DB: %v", attribute.AttName, err)
+				}
+			}
+
+			if err = tx.Commit(); err != nil {
+				return fmt.Errorf("error committing transaction: %v", err)
+			}
+			return nil
+		}()
+		if err == nil {
+			return nil
+		}
+
+		log.Println(err)
+		wait(i)
+	}
+	return fmt.Errorf("error: %v unsuccessful retries for DB operation, aborting", TxMaxRetries)
+}
+
+func (db *DB) CountEntries(table string) (int64, error) {
+	var count int64
+
+	query := fmt.Sprintf("SELECT COUNT(*) FROM %s", table)
+	row := db.QueryRow(query)
+	if err := row.Scan(&count); err != nil {
+		return 0, fmt.Errorf("error counting rows in user DB: %v", err)
+	}
+
+	return count, nil
+}
+
+func (tx *Tx) UpdateAttributes(a ...*Attribute) error {
+	for _, attribute := range a {
+		query := fmt.Sprintf(`
+            UPDATE %s
+            SET %s = ?
+            WHERE id = ?
+            `, attribute.Table, attribute.AttName)
+		if _, err := tx.Exec(query, attribute.Value, attribute.ID); err != nil {
+			if rollbackErr := tx.Rollback(); rollbackErr != nil {
+				log.Fatalf("transaction error: %v, rollback error: %v", err, rollbackErr)
+			}
+			return fmt.Errorf("error updating %v in DB: %v", attribute.AttName, err)
+		}
+	}
+
+	return nil
+}