package database

import (
	"fmt"
	"log"
)

// Driver defines a structure for backend drivers to use when they registered themselves as a backend which implements
// the DB interface.
type Driver struct {
	// DbType is the identifier used to uniquely identify a specific database driver. There can be only one driver with
	// the same name.
	DbType string
	// Create is the function that will be invoked with all user-specified arguments to create the database. This
	// function must return ErrDbExists if the database already exists.
	Create func(args ...interface{}) (DB, error)
	// Open is the function that will be invoked with all user-specified arguments to open the database. This function
	// must return ErrDbDoesNotExist if the database has not already been created.
	Open func(args ...interface{}) (DB, error)
	// UseLogger uses a specified Logger to output package logging info.
	UseLogger func(logger log.Logger)
}

// driverList holds all of the registered database backends.
var drivers = make(map[string]*Driver)

// Create initializes and opens a database for the specified type. The arguments are specific to the database type
// driver. See the documentation for the database driver for further details. ErrDbUnknownType will be returned if the
// the database type is not registered.
func Create(dbType string, args ...interface{}) (DB, error) {
	drv, exists := drivers[dbType]
	if !exists {
		str := fmt.Sprintf("driver %q is not registered", dbType)
		return nil, makeError(ErrDbUnknownType, str, nil)
	}
	return drv.Create(args...)
}

// Open opens an existing database for the specified type. The arguments are specific to the database type driver. See
// the documentation for the database driver for further details. ErrDbUnknownType will be returned if the the database
// type is not registered.
func Open(dbType string, args ...interface{}) (DB, error) {
	drv, exists := drivers[dbType]
	if !exists {
		str := fmt.Sprintf("driver %q is not registered", dbType)
		return nil, makeError(ErrDbUnknownType, str, nil)
	}
	return drv.Open(args...)
}

// RegisterDriver adds a backend database driver to available interfaces. ErrDbTypeRegistered will be returned if the
// database type for the driver has already been registered.
func RegisterDriver(driver Driver) (e error) {
	if _, exists := drivers[driver.DbType]; exists {
		str := fmt.Sprintf("driver %q is already registered",
			driver.DbType,
		)
		return makeError(ErrDbTypeRegistered, str, nil)
	}
	drivers[driver.DbType] = &driver
	return nil
}

// SupportedDrivers returns a slice of strings that represent the database drivers that have been registered and are
// therefore supported.
func SupportedDrivers() []string {
	supportedDBs := make([]string, 0, len(drivers))
	for _, drv := range drivers {
		supportedDBs = append(supportedDBs, drv.DbType)
	}
	return supportedDBs
}