siteviewcounter/countersql/database.go

package countersql

import (
	"database/sql"
	"fmt"
)

// Configuration holds the DSN connection string and a resource Semaphore to limit the number of active connections
// Note: This is a copied design pattern I've used for other projects which had much more data inside a Configuration struct.
// Examples include semaphores and persistent connection pools, which I've stripped out for this project.
type Configuration struct {
	DSN string
}

// Connection represents a single connection to the database, however there may be many instances / connections
// Note: This is a copied design pattern I've used for other projects which had much more data inside a Connection struct.
type Connection struct {
	DB *sql.DB
}

// HasIPVisited returns true only if the IP address is present in the database
func (conn Connection) HasIPVisited(ipAddress string) (bool, error) {
	rows, err := conn.DB.Query(`SELECT id FROM visit WHERE ip_address = ? LIMIT 1;`, ipAddress)
	if err != nil {
		return false, fmt.Errorf("SELECT query failed: %v", err)
	}
	defer rows.Close()

	if !rows.Next() {
		return false, nil
	}

	return true, nil
}

// GetUniqueVisits counts the number of entires in the visits table, representing one unique source IP address per row
func (conn Connection) GetUniqueVisits() (int, error) {
	rows, err := conn.DB.Query(`SELECT COUNT(*) FROM visit`)
	if err != nil {
		return 0, fmt.Errorf("SELECT query failed: %v", err)
	}
	defer rows.Close()

	if !rows.Next() {
		return 0, nil
	}

	var uniqueVists int
	if err := rows.Scan(&uniqueVists); err != nil {
		return 0, fmt.Errorf("failed to scan database row: %v", err)
	}

	return uniqueVists, nil
}

// IncrementVisitor accepts an IP address and updates the row matching that IP address
// It does not check if the row matching the IP address supplied exists or not
func (conn Connection) IncrementVisitor(ipAddress string) error {
	_, err := conn.DB.Exec(`UPDATE visit SET visits = visits + 1, last_visited = NOW() WHERE ip_address = ?`, ipAddress)
	if err != nil {
		return fmt.Errorf("UPDATE query failed: %v", err)
	}

	return nil
}

// AddVisitor accepts an IP address and inserts a new row into the database as this represents a new unique visitor
func (conn Connection) AddVisitor(ipAddress string) error {
	_, err := conn.DB.Exec(`INSERT INTO visit (ip_address, visits, last_visited) VALUES (?, '0', NOW())`, ipAddress)
	if err != nil {
		return fmt.Errorf("INSERT query failed: %v", err)
	}

	return nil
}

// Connect will open a TCP connection to the database with the given DSN configuration
func (conf Configuration) Connect() (*Connection, error) {
	conn := &Connection{}
	var err error

	conn.DB, err = sql.Open("mysql", conf.DSN)
	if err != nil {
		return nil, fmt.Errorf("failed to open db: %v", err)
	}

	return conn, nil
}

// InitializeDatabase will check if tables exist in the database, and if not then create them.
func (conn Connection) InitializeDatabase() error {
	rows, err := conn.DB.Query(`SHOW TABLES`)
	if err != nil {
		return fmt.Errorf("SHOW TABLES query failed: %v", err)
	}
	defer rows.Close()

	if rows.Next() { // Table already exists, leave with no error
		return nil
	}

	// Table does not exist, create it
	_, err = conn.DB.Exec(`CREATE TABLE visit (
		id int(11) NOT NULL AUTO_INCREMENT,
		ip_address varchar(15) NOT NULL,
		visits int(11) NOT NULL,
		last_visited datetime NOT NULL,
		PRIMARY KEY (id)
	  ) ENGINE=InnoDB DEFAULT CHARSET=latin1;`)

	if err != nil {
		return fmt.Errorf("failed to create table: %v", err)
	}

	return nil
}