-- Create customers table if it doesn't exist
CREATE TABLE IF NOT EXISTS customers (
    id INT AUTO_INCREMENT PRIMARY KEY,
    name VARCHAR(255) NOT NULL,
    phone VARCHAR(20) UNIQUE,
    email VARCHAR(255),
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

-- Add customer_id to orders table
SET @dbname = DATABASE();
SET @tablename = "orders";
SET @columnname = "customer_id";
SET @preparedStatement = (SELECT IF(
  (
    SELECT COUNT(*) FROM INFORMATION_SCHEMA.COLUMNS
    WHERE
      (table_name = @tablename)
      AND (table_schema = @dbname)
      AND (column_name = @columnname)
  ) > 0,
  "SELECT 1",
  "ALTER TABLE orders ADD COLUMN customer_id INT DEFAULT NULL AFTER order_type;"
));
PREPARE alterIfNotExists FROM @preparedStatement;
EXECUTE alterIfNotExists;
DEALLOCATE PREPARE alterIfNotExists;

-- Add foreign key if it doesn't exist
SET @constraintname = "fk_orders_customer";
SET @preparedStatement = (SELECT IF(
  (
    SELECT COUNT(*) FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS
    WHERE
      (table_name = @tablename)
      AND (table_schema = @dbname)
      AND (constraint_name = @constraintname)
  ) > 0,
  "SELECT 1",
  "ALTER TABLE orders ADD CONSTRAINT fk_orders_customer FOREIGN KEY (customer_id) REFERENCES customers(id) ON DELETE SET NULL;"
));
PREPARE addConstraint FROM @preparedStatement;
EXECUTE addConstraint;
DEALLOCATE PREPARE addConstraint;