source: sqlite-database-integration/trunk/admin-page.php

<?php
/**
 * Functions for the admin page of the plugin.
 *
 * @since 1.0.0
 * @package wp-sqlite-integration
 */

/**
 * Add an admin menu page.
 *
 * @since 1.0.0
 */
function sqlite_add_admin_menu() {
        add_options_page(
                __( 'SQLite integration', 'sqlite-database-integration' ),
                __( 'SQLite integration', 'sqlite-database-integration' ),
                'manage_options',
                'sqlite-integration',
                'sqlite_integration_admin_screen'
        );
}
add_action( 'admin_menu', 'sqlite_add_admin_menu' );

/**
 * The admin page contents.
 */
function sqlite_integration_admin_screen() {
        $db_dropin_path = WP_CONTENT_DIR . '/db.php';

        /*
         * When an existing "db.php" drop-in is detected, let's check if it's a known
         * plugin that we can continue supporting even when we override the drop-in.
         */
        $override_db_dropin = false;
        if ( file_exists( $db_dropin_path ) && ! defined( 'SQLITE_DB_DROPIN_VERSION' ) ) {
                // Check for the Query Monitor plugin.
                // When "QM_DB" exists, it must have been loaded via the "db.php" file.
                if ( class_exists( 'QM_DB', false ) ) {
                        $override_db_dropin = true;
                }
        }

        ?>
        <div class="wrap">
                <h1><?php esc_html_e( 'SQLite integration.', 'sqlite-database-integration' ); ?></h1>
        </div>
        <!-- Set the wrapper width to 50em, to improve readability. -->
        <div style="max-width:50em;">
                <?php if ( defined( 'SQLITE_DB_DROPIN_VERSION' ) ) : ?>
                        <div class="notice notice-success">
                                <p><?php esc_html_e( 'SQLite is enabled.', 'sqlite-database-integration' ); ?></p>
                        </div>
                        <p>
                                <?php
                                        printf(
                                                /* translators: 1: Admin URL to deactivate the module, 2: db.php drop-in path, */
                                                __( 'The SQLite drop-in is enabled. To disable it and get back to your previous, MySQL database, you can <a href="%1$s">deactivate the plugin</a>. Alternatively, you can manually delete the %2$s file from your server.', 'sqlite-database-integration' ),
                                                esc_url( admin_url( 'plugins.php' ) ),
                                                '<code>' . esc_html( basename( WP_CONTENT_DIR ) ) . '/db.php</code>'
                                        );
                                ?>
                        </p>
                <?php elseif ( ! extension_loaded( 'pdo_sqlite' ) ) : ?>
                        <div class="notice notice-error">
                                <p><?php esc_html_e( 'We detected that the PDO SQLite driver is missing from your server (the pdo_sqlite extension is not loaded). Please make sure that SQLite is enabled in your PHP installation before proceeding.', 'sqlite-database-integration' ); ?></p>
                        </div>
                <?php elseif ( file_exists( $db_dropin_path ) && ! defined( 'SQLITE_DB_DROPIN_VERSION' ) && ! $override_db_dropin ) : ?>
                        <?php if ( defined( 'PERFLAB_SQLITE_DB_DROPIN_VERSION' ) ) : ?>
                                <div class="notice notice-warning">
                                        <p>
                                                <?php
                                                printf(
                                                        /* translators: %s: db.php drop-in path */
                                                        esc_html__( 'An older %s file was detected. Please click the button below to update the file.', 'sqlite-database-integration' ),
                                                        '<code>' . esc_html( basename( WP_CONTENT_DIR ) ) . '/db.php</code>'
                                                );
                                                ?>
                                        </p>
                                </div>
                                <a class="button button-primary" href="<?php echo esc_url( wp_nonce_url( admin_url( 'admin.php?page=sqlite-integration&confirm-install&upgrade-from-pl' ), 'sqlite-install' ) ); ?>">
                                        <?php
                                        printf(
                                                /* translators: %s: db.php drop-in path */
                                                esc_html__( 'Update %s file', 'sqlite-database-integration' ),
                                                '<code>' . esc_html( basename( WP_CONTENT_DIR ) ) . '/db.php</code>'
                                        );
                                        ?>
                                </a>
                        <?php else : ?>
                                <div class="notice notice-error">
                                        <p>
                                                <?php
                                                printf(
                                                        /* translators: %s: db.php drop-in path */
                                                        esc_html__( 'The SQLite plugin cannot be activated because a different %s drop-in already exists.', 'sqlite-database-integration' ),
                                                        '<code>' . esc_html( basename( WP_CONTENT_DIR ) ) . '/db.php</code>'
                                                );
                                                ?>
                                        </p>
                                </div>
                        <?php endif; ?>
                <?php elseif ( ! is_writable( WP_CONTENT_DIR ) ) : ?>
                        <div class="notice notice-error">
                                <p>
                                        <?php
                                        printf(
                                                /* translators: %s: db.php drop-in path */
                                                esc_html__( 'The SQLite plugin cannot be activated because the %s directory is not writable.', 'sqlite-database-integration' ),
                                                '<code>' . esc_html( basename( WP_CONTENT_DIR ) ) . '</code>'
                                        );
                                        ?>
                                </p>
                        </div>
                <?php else : ?>
                        <div class="notice notice-success">
                                <p><?php esc_html_e( 'All checks completed successfully, your site can use an SQLite database. You can proceed with the installation.', 'sqlite-database-integration' ); ?></p>
                        </div>
                        <h2><?php esc_html_e( 'Important note', 'sqlite-database-integration' ); ?></h2>
                        <p><?php esc_html_e( 'This plugin will switch to a separate database and install WordPress in it. You will need to reconfigure your site, and start with a fresh site. Disabling the plugin you will get back to your previous MySQL database, with all your previous data intact.', 'sqlite-database-integration' ); ?></p>

                        <?php if ( $override_db_dropin ) : ?>
                                <p>
                                        <strong>NOTE:</strong>
                                        <?php
                                        printf(
                                                /* translators: %s: db.php drop-in path */
                                                esc_html__( 'We’ve detected an existing database drop-in file at %s, created by the Query Monitor plugin.', 'sqlite-database-integration' ),
                                                '<code>' . esc_html( basename( WP_CONTENT_DIR ) ) . '/db.php</code>'
                                        );
                                        ?>
                                        <?php esc_html_e( 'To enable SQLite support, this file will need to be replaced.', 'sqlite-database-integration' ); ?>
                                        <?php esc_html_e( 'The Query Monitor plugin will continue to function correctly after the change. You can safely proceed with the installation.', 'sqlite-database-integration' ); ?>
                                </p>
                        <?php endif; ?>

                        <p><?php esc_html_e( 'By clicking the button below, you will be redirected to the WordPress installation screen to setup your new database', 'sqlite-database-integration' ); ?></p>

                        <a class="button button-primary" href="<?php echo esc_url( wp_nonce_url( admin_url( 'admin.php?page=sqlite-integration&confirm-install' ), 'sqlite-install' ) ); ?>"><?php esc_html_e( 'Install SQLite database', 'sqlite-database-integration' ); ?></a>
                <?php endif; ?>
        </div>
        <?php
}

/**
 * Adds a link to the admin bar.
 *
 * @since n.e.x.t
 *
 * @global wpdb $wpdb WordPress database abstraction object.
 *
 * @param WP_Admin_Bar $admin_bar The admin bar object.
 */
function sqlite_plugin_adminbar_item( $admin_bar ) {
        global $wpdb;

        if ( defined( 'SQLITE_DB_DROPIN_VERSION' ) && defined( 'DB_ENGINE' ) && 'sqlite' === DB_ENGINE ) {
                $suffix = defined( 'WP_SQLITE_AST_DRIVER' ) && WP_SQLITE_AST_DRIVER ? ' (AST)' : '';
                $title  = '<span style="color:#46B450;">' . __( 'Database: SQLite', 'sqlite-database-integration' ) . $suffix . '</span>';
        } elseif ( stripos( $wpdb->db_server_info(), 'maria' ) !== false ) {
                $title = '<span style="color:#DC3232;">' . __( 'Database: MariaDB', 'sqlite-database-integration' ) . '</span>';
        } else {
                $title = '<span style="color:#DC3232;">' . __( 'Database: MySQL', 'sqlite-database-integration' ) . '</span>';
        }

        $args = array(
                'id'     => 'sqlite-db-integration',
                'parent' => 'top-secondary',
                'title'  => $title,
                'href'   => esc_url( admin_url( 'options-general.php?page=sqlite-integration' ) ),
                'meta'   => false,
        );
        $admin_bar->add_node( $args );
}
add_action( 'admin_bar_menu', 'sqlite_plugin_adminbar_item', 999 );