Add solution for Challenge 13 (#721)

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

Author: Johrespi

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

@@ -0,0 +1,219 @@
+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) {
+	// TODO: Open a SQLite database connection
+	// TODO: Create the products table if it doesn't exist
+	// The table should have columns: id, name, price, quantity, category
+
+	db, err := sql.Open("sqlite3", dbPath)
+	if err != nil {
+		return nil, err
+	}
+
+	createTableQuery := ` CREATE TABLE IF NOT EXISTS products (
+  		id INTEGER PRIMARY KEY AUTOINCREMENT,
+        name TEXT NOT NULL,
+        price REAL NOT NULL,
+        quantity INTEGER NOT NULL,
+        category TEXT NOT NULL
+    );`
+
+	_, err = db.Exec(createTableQuery)
+	if err != nil {
+		return nil, err
+	}
+
+	return db, nil
+}
+
+// CreateProduct adds a new product to the database
+func (ps *ProductStore) CreateProduct(product *Product) error {
+	// TODO: Insert the product into the database
+	// TODO: Update the product.ID with the database-generated ID
+	stmt := `INSERT INTO products (name, price, quantity, category) VALUES(?, ?, ?, ?)`
+
+	dbResult, err := ps.db.Exec(stmt, product.Name, product.Price, product.Quantity, product.Category)
+	if err != nil {
+		return err
+	}
+
+	id, err := dbResult.LastInsertId()
+	if err != nil {
+		return err
+	}
+	product.ID = id
+
+	return nil
+}
+
+// GetProduct retrieves a product by ID
+func (ps *ProductStore) GetProduct(id int64) (*Product, error) {
+	// TODO: Query the database for a product with the given ID
+	// TODO: Return a Product struct populated with the data or an error if not found
+
+	stmt := `SELECT id, name, price, quantity, category FROM products WHERE id = ?`
+	row := ps.db.QueryRow(stmt, id)
+
+	var product Product
+	err := row.Scan(&product.ID, &product.Name, &product.Price, &product.Quantity, &product.Category)
+	if err != nil {
+		if err == sql.ErrNoRows {
+			return nil, errors.New("product not found")
+		}
+		return nil, err
+	}
+
+	return &product, nil
+
+}
+
+// UpdateProduct updates an existing product
+func (ps *ProductStore) UpdateProduct(product *Product) error {
+	// TODO: Update the product in the database
+	// TODO: Return an error if the product doesn't exist
+
+	p, err := ps.GetProduct(product.ID)
+	if err != nil {
+		return err
+	}
+
+	p.ID = product.ID
+	p.Name = product.Name
+	p.Price = product.Price
+	p.Quantity = product.Quantity
+	p.Category = product.Category
+
+	stmt := `UPDATE products SET name = ?, price = ?, quantity = ?, category = ? WHERE id = ?`
+
+	_, err = ps.db.Exec(stmt, p.Name, p.Price, p.Quantity, p.Category, p.ID)
+	if err != nil {
+		return err
+	}
+
+	return nil
+
+}
+
+// DeleteProduct removes a product by ID
+func (ps *ProductStore) DeleteProduct(id int64) error {
+	// TODO: Delete the product from the database
+	// TODO: Return an error if the product doesn't exist
+
+	stmt := `DELETE FROM products WHERE id = ?`
+
+	result, err := ps.db.Exec(stmt, id)
+	if err != nil {
+		return err
+	}
+
+	rowsAffected, err := result.RowsAffected()
+	if err != nil {
+		return err
+	}
+	if rowsAffected == 0 {
+		return errors.New("product not found")
+	}
+
+	return nil
+
+}
+
+// ListProducts returns all products with optional filtering by category
+func (ps *ProductStore) ListProducts(category string) ([]*Product, error) {
+	// TODO: Query the database for products
+	// TODO: If category is not empty, filter by category
+	// TODO: Return a slice of Product pointers
+	stmt := `SELECT id, name, price, quantity, category FROM products
+		WHERE (? = '' OR category = ?)`
+
+	var products []*Product
+
+	rows, err := ps.db.Query(stmt, category, category)
+	if err != nil {
+		return nil, err
+	}
+
+	defer rows.Close()
+
+	for rows.Next() {
+		var product Product
+		err := rows.Scan(&product.ID, &product.Name, &product.Price, &product.Quantity, &product.Category)
+		if err != nil {
+			return nil, err
+		}
+		products = append(products, &product)
+	}
+
+	return products, nil
+
+}
+
+// BatchUpdateInventory updates the quantity of multiple products in a single transaction
+func (ps *ProductStore) BatchUpdateInventory(updates map[int64]int) error {
+	// TODO: Start a transaction
+	// TODO: For each product ID in the updates map, update its quantity
+	// TODO: If any update fails, roll back the transaction
+	// TODO: Otherwise, commit the transaction
+
+	tx, err := ps.db.Begin()
+	if err != nil {
+		return err
+	}
+
+	defer func() {
+		if err != nil {
+			tx.Rollback()
+		}
+	}()
+
+	stmt := `UPDATE products SET quantity = ? WHERE id = ?`
+
+	for productID, newQuantity := range updates {
+		result, err := tx.Exec(stmt, newQuantity, productID)
+		if err != nil {
+			return err
+		}
+
+		rowsAffected, err := result.RowsAffected()
+		if err != nil {
+			return err
+		}
+		if rowsAffected == 0 {
+			return fmt.Errorf("product with ID %d not found", productID)
+		}
+
+	}
+	return tx.Commit()
+}
+
+func main() {
+	// Optional: you can write code here to test your implementation
+}