CREATE TABLE IF NOT EXISTS invoices (
    id INT AUTO_INCREMENT PRIMARY KEY,
    customer_id INT,
    invoice_date DATE NOT NULL,
    type ENUM('sale', 'purchase') NOT NULL,
    total_amount DECIMAL(15, 2) DEFAULT 0.00,
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    FOREIGN KEY (customer_id) REFERENCES customers(id) ON DELETE SET NULL
);

CREATE TABLE IF NOT EXISTS invoice_items (
    id INT AUTO_INCREMENT PRIMARY KEY,
    invoice_id INT NOT NULL,
    item_id INT NOT NULL,
    quantity DECIMAL(15, 2) NOT NULL,
    unit_price DECIMAL(15, 2) NOT NULL,
    total_price DECIMAL(15, 2) NOT NULL,
    FOREIGN KEY (invoice_id) REFERENCES invoices(id) ON DELETE CASCADE,
    FOREIGN KEY (item_id) REFERENCES stock_items(id) ON DELETE CASCADE
);