Implemented the book exercise

Co-authored-by: Copilot <copilot@github.com>

web/06/eigene_loesungen/Aufgabe_02/book.go

@@ -0,0 +1,137 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+)
+
+type Book struct {
+	Title  string `json:"title"`
+	Author string `json:"author"`
+	Read   bool   `json:"read"`
+	ID     int    `json:"id"`
+}
+
+func addBook(title string, author string) error {
+
+	fmt.Println("add...")
+
+	books, err := readJson()
+
+	if err != nil {
+		return err
+	}
+
+	var newID int
+	if len(books) == 0 {
+		newID = 1
+	} else {
+		last := books[len(books)-1]
+		newID = last.ID + 1
+	}
+
+	newBook := Book{Title: title, Author: author, Read: false, ID: newID}
+
+	books = append(books, newBook)
+
+	erro := writeJson(books)
+
+	if erro != nil {
+		return erro
+	}
+
+	return nil
+
+}
+
+func listBooks() error {
+
+	fmt.Println("list...")
+
+	books, err := readJson()
+
+	if err != nil {
+		return err
+	}
+
+	fmt.Println("Hier ist Ihre aktuelle Buchübersicht:\n")
+
+	for _, book := range books {
+		fmt.Println("Titel:", book.Title)
+		fmt.Println("Author:", book.Author)
+		fmt.Println("Gelesen:", book.Read)
+		fmt.Println("ID:", book.ID)
+		fmt.Println("============================================")
+	}
+
+	return nil
+}
+
+func markBook(id int) error {
+
+	books, err := readJson()
+
+	if err != nil {
+		return err
+	}
+
+	for i := 0; i < len(books); i++ {
+		if books[i].ID == id {
+			books[i].Read = true
+
+			erro := writeJson(books)
+
+			if erro != nil {
+				return erro
+			}
+
+			return nil
+		}
+	}
+
+	return fmt.Errorf("ID %d nicht gefunden!", id)
+}
+
+func readJson() ([]Book, error) {
+
+	fmt.Println("read json...")
+
+	data, err := os.ReadFile("books.json")
+
+	if err != nil {
+		return nil, err
+	}
+
+	var books []Book
+	err = json.Unmarshal(data, &books)
+	if err != nil {
+		fmt.Println(err)
+		return nil, err
+	}
+
+	return books, nil
+
+}
+
+func writeJson(books []Book) error {
+	data, err := json.MarshalIndent(books, "", "	")
+	if err != nil {
+		return err
+	}
+
+	return os.WriteFile("books.json", data, 0644)
+}
+
+func ensureFileExists() error {
+	_, err := os.Stat("books.json")
+
+	if os.IsNotExist(err) {
+		// Initialer Inhalt: leeres JSON-Array
+		initialData := []byte("[]")
+
+		return os.WriteFile("books.json", initialData, 0644)
+	}
+
+	return err
+}

web/06/eigene_loesungen/Aufgabe_02/main.go

@@ -0,0 +1,55 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"strconv"
+)
+
+func main() {
+
+	if len(os.Args) == 1 {
+		fmt.Println("Kein Befehl angegeben!")
+		return
+	}
+
+	if err := ensureFileExists(); err != nil {
+		fmt.Println("Fehler beim prüfen der Datei:", err)
+		return
+	}
+
+	switch args := os.Args; args[1] {
+	case "add", "Add":
+		if len(args) < 4 {
+			fmt.Println("Nutzung: add <title> <author>")
+			return
+		}
+		if err := addBook(args[2], args[3]); err != nil {
+			fmt.Println("Fehler beim Hinzufügen:", err)
+		}
+
+	case "list", "List":
+		if err := listBooks(); err != nil {
+			fmt.Println("Fehler beim Auflisten:", err)
+		}
+
+	case "read", "Read":
+		if len(args) < 3 {
+			fmt.Println("Nutzung: read <id>")
+			return
+		}
+		convId, err := strconv.Atoi(args[2])
+		if err != nil || convId <= 0 {
+			fmt.Println("ID ist keine positive Ganzzahl!")
+			return
+		}
+
+		if err := markBook(convId); err != nil {
+			fmt.Println("Fehler beim Markieren:", err)
+		}
+
+	default:
+		fmt.Println("Unknown command!")
+		fmt.Println("Nutzung: add|list|read")
+	}
+}