Add solution for Challenge 13 by Kosench (#835)

* Add solution for Challenge 13

* fix

---------

Co-authored-by: go-interview-practice-bot[bot] <230190823+go-interview-practice-bot[bot]@users.noreply.github.com>

Author: Kosench

challenge-13/submissions/Kosench/solution-template.go

@@ -0,0 +1,241 @@
+package main
+
+import (
+	"database/sql"
+	"errors"
+	"fmt"
+
+	_ "github.com/mattn/go-sqlite3"
+)
+
+// Product represents a product in the inventory system
+type Product struct {
+	ID       int64
+	Name     string
+	Price    float64
+	Quantity int
+	Category string
+}
+
+// ProductStore manages product operations
+type ProductStore struct {
+	db *sql.DB
+}
+
+// NewProductStore creates a new ProductStore with the given database connection
+func NewProductStore(db *sql.DB) *ProductStore {
+	return &ProductStore{db: db}
+}
+
+// InitDB sets up a new SQLite database and creates the products table
+func InitDB(dbPath string) (*sql.DB, error) {
+	db, err := sql.Open("sqlite3", dbPath)
+	if err != nil {
+		return nil, fmt.Errorf("failed to open database: %w", err)
+	}
+
+	if err := db.Ping(); err != nil {
+		db.Close()
+		return nil, fmt.Errorf("failed to ping database: %w", err)
+	}
+
+	query := `
+	CREATE TABLE IF NOT EXISTS products (
+	    id INTEGER PRIMARY KEY,
+	    name TEXT,
+	    price REAL NOT NULL CHECK(price >= 0),
+	    quantity INTEGER NOT NULL DEFAULT 0 CHECK(quantity >= 0),
+	    category TEXT
+	)`
+
+	_, err = db.Exec(query)
+	if err != nil {
+		db.Close()
+		return nil, fmt.Errorf("failed to create table: %w", err)
+	}
+
+	// The table should have columns: id, name, price, quantity, category
+	return db, nil
+}
+
+// CreateProduct adds a new product to the database
+func (ps *ProductStore) CreateProduct(product *Product) error {
+	query := `
+	INSERT INTO products (name, price, quantity, category)
+	VALUES (?, ?, ?, ?)
+	`
+
+	result, err := ps.db.Exec(query, product.Name, product.Price, product.Quantity, product.Category)
+	if err != nil {
+		return fmt.Errorf("failed to create product: %w", err)
+	}
+
+	id, err := result.LastInsertId()
+	if err != nil {
+		return fmt.Errorf("failed to get last insert id: %w", err)
+	}
+
+	product.ID = id
+
+	return nil
+}
+
+// GetProduct retrieves a product by ID
+func (ps *ProductStore) GetProduct(id int64) (*Product, error) {
+	query := `
+	SELECT id, name, price, quantity, category
+	FROM products
+	WHERE id = ?
+	`
+
+	row := ps.db.QueryRow(query, id)
+
+	p := &Product{}
+	err := row.Scan(&p.ID, &p.Name, &p.Price, &p.Quantity, &p.Category)
+	if err != nil {
+		if errors.Is(err, sql.ErrNoRows) {
+			return nil, fmt.Errorf("product with ID %d not found", id)
+		}
+		return nil, err
+	}
+
+	return p, nil
+}
+
+// UpdateProduct updates an existing product
+func (ps *ProductStore) UpdateProduct(product *Product) error {
+	query := `
+    UPDATE products
+    SET name = ?, price = ?, quantity = ?, category = ?
+    WHERE id = ?
+    `
+
+	result, err := ps.db.Exec(query,
+		product.Name,
+		product.Price,
+		product.Quantity,
+		product.Category,
+		product.ID,
+	)
+	if err != nil {
+		return fmt.Errorf("failed to update product: %w", err)
+	}
+
+	rowsAffected, err := result.RowsAffected()
+	if err != nil {
+		return fmt.Errorf("failed to get rows affected: %w", err)
+	}
+
+	if rowsAffected == 0 {
+		return fmt.Errorf("product with ID %d not found", product.ID)
+	}
+
+	return nil
+}
+
+// DeleteProduct removes a product by ID
+func (ps *ProductStore) DeleteProduct(id int64) error {
+	query := `DELETE FROM products WHERE id = ?`
+
+	result, err := ps.db.Exec(query, id)
+	if err != nil {
+		return fmt.Errorf("failed to delete product: %w", err)
+	}
+
+	rowsAffected, err := result.RowsAffected()
+	if err != nil {
+		return fmt.Errorf("failed to get rows affected: %w", err)
+	}
+
+	if rowsAffected == 0 {
+		return fmt.Errorf("product with ID %d not found", id)
+	}
+
+	return nil
+}
+
+// ListProducts returns all products with optional filtering by category
+func (ps *ProductStore) ListProducts(category string) ([]*Product, error) {
+	var query string
+	var rows *sql.Rows
+	var err error
+
+	if category == "" {
+		query = `
+		SELECT id, name, price, quantity, category
+		FROM products
+		`
+		rows, err = ps.db.Query(query)
+	} else {
+		query = `
+		SELECT id, name, price, quantity, category
+		FROM products
+		WHERE category = ?
+		`
+		rows, err = ps.db.Query(query, category)
+	}
+
+	if err != nil {
+		return nil, fmt.Errorf("failed to query products: %w", err)
+	}
+	defer rows.Close()
+
+	var products []*Product
+	for rows.Next() {
+		p := &Product{}
+		err := rows.Scan(&p.ID, &p.Name, &p.Price, &p.Quantity, &p.Category)
+		if err != nil {
+			return nil, fmt.Errorf("failed to scan product: %w", err)
+		}
+		products = append(products, p)
+	}
+
+	if err = rows.Err(); err != nil {
+		return nil, fmt.Errorf("error iterating products: %w", err)
+	}
+	return products, nil
+}
+
+// BatchUpdateInventory updates the quantity of multiple products in a single transaction
+func (ps *ProductStore) BatchUpdateInventory(updates map[int64]int) error {
+	tx, err := ps.db.Begin()
+	if err != nil {
+		return fmt.Errorf("failed to begin transaction: %w", err)
+	}
+
+	stmt, err := tx.Prepare("UPDATE products SET quantity = ? WHERE id = ?")
+	if err != nil {
+		tx.Rollback()
+		return fmt.Errorf("failed to prepare statement: %w", err)
+	}
+	defer stmt.Close()
+
+	for id, quantity := range updates {
+		result, err := stmt.Exec(quantity, id)
+		if err != nil {
+			tx.Rollback()
+			return fmt.Errorf("failed to update product %d: %w", id, err)
+		}
+
+		rowsAffected, err := result.RowsAffected()
+		if err != nil {
+			tx.Rollback()
+			return fmt.Errorf("failed to get rows affected: %w", err)
+		}
+
+		if rowsAffected == 0 {
+			tx.Rollback()
+			return fmt.Errorf("product with ID %d not found", id)
+		}
+	}
+
+	if err := tx.Commit(); err != nil {
+		return fmt.Errorf("failed to commit transaction: %w", err)
+	}
+
+	return nil
+}
+
+func main() {
+	// Optional: you can write code here to test your implementation
+}