From cb0e32e83427a48a2d789da5ec3fb7ef97ae0713 Mon Sep 17 00:00:00 2001
From: Stefan Kalscheuer <stefan@stklcode.de>
Date: Wed, 3 Oct 2018 18:52:03 +0200
Subject: [PATCH] Implemented check if index on VARCHAR(255) is possible with
 InnoDB (fix #105)

---
 inc/class-statify-table.php | 68 ++++++++++++++++++++++++++++++++++---
 1 file changed, 64 insertions(+), 4 deletions(-)

diff --git a/inc/class-statify-table.php b/inc/class-statify-table.php
index 3bbbdc8..a44bc48 100644
--- a/inc/class-statify-table.php
+++ b/inc/class-statify-table.php
@@ -47,7 +47,6 @@ public static function init() {
 	 * @version 1.2.4
 	 */
 	public static function create() {
-
 		global $wpdb;
 
 		// If existent.
@@ -66,10 +65,11 @@ public static function create() {
 			  `referrer` varchar(255) NOT NULL default '',
 			  `target` varchar(255) NOT NULL default '',
 			  PRIMARY KEY  (`id`),
+			  KEY `created` (`created`)" .
+			( self::can_create_index() ? ',
 			  KEY `referrer` (`referrer`),
-			  KEY `target` (`target`),
-			  KEY `created` (`created`)
-			);"
+			  KEY `target` (`target`)' : '' ) . '
+			);'
 		);
 	}
 
@@ -87,4 +87,64 @@ public static function drop() {
 		// Remove.
 		$wpdb->query( "DROP TABLE IF EXISTS `$wpdb->statify`" );
 	}
+
+	/**
+	 * Check if indices on VARCHAR(255) columns can be created.
+	 *
+	 * @since 1.7.0
+	 *
+	 * @return boolean
+	 */
+	private static function can_create_index() {
+		global $wpdb;
+
+		// Check the storage engine. Only InnoDB is affected.
+		$row = $wpdb->get_row( "SHOW VARIABLES LIKE 'storage_engine'" );
+		if ( ! empty( $row ) && 'innodb' === strtolower( (string) $row->Value ) ) { // phpcs:ignore WordPress.NamingConventions.ValidVariableName.NotSnakeCaseMemberVar
+			// Check for default character set. Problem only occurs on utf8mb4 (4 Byte per character).
+			$default_charset = $wpdb->get_row( "SHOW VARIABLES LIKE 'character_set_database'" );
+			if ( ! empty( $default_charset ) && 'innodb' === strtolower( (string) $row->Value ) ) { // phpcs:ignore WordPress.NamingConventions.ValidVariableName.NotSnakeCaseMemberVar
+				// Check for presence of the "large_prefix" extension.
+				$row = $wpdb->get_row( "SHOW VARIABLES LIKE 'innodb_large_prefix'" );
+				if ( ! empty( $row ) && in_array( strtolower( (string) $row->Value ), array( '1', 'on' ) ) ) {  // phpcs:ignore WordPress.NamingConventions.ValidVariableName.NotSnakeCaseMemberVar
+					// "large_prefix" extension active, so we can abort here.
+					return true;
+				}
+
+				/*
+				 * If not enabled, we can check for DB version, because the row/storage format has
+				 *  changed in MySQL 5.7.7 and MariaDB 10.2, so the problem does not occur any more.
+				 */
+				$row = $wpdb->get_row( "SHOW VARIABLES LIKE 'version'" );
+				if ( empty( $row ) ) {
+					// Should not happen, but if we cannot determine the version, abort hiere.
+					return false;
+				}
+				$version_split = explode( '-', $row->Value, 2 );    // phpcs:ignore WordPress.NamingConventions.ValidVariableName.NotSnakeCaseMemberVar
+				$version       = $version_split[0];
+				if ( false !== strpos( strtolower( $row->Value ), 'mariadb' ) ) {   // phpcs:ignore WordPress.NamingConventions.ValidVariableName.NotSnakeCaseMemberVar
+					if ( version_compare( $version, '10.2', '>=' ) ) {
+						return true;
+					}
+				} elseif ( version_compare( $version, '5.7.7', '>=' ) ) {
+					return true;
+				}
+
+				// On older versions it will NOT work, if file format is Barracuda.
+				$row = $wpdb->get_row( "SHOW VARIABLES LIKE 'innodb_file_format'" );
+				if ( 'barracuda' !== strtolower( $row->Value ) ) {  // phpcs:ignore WordPress.NamingConventions.ValidVariableName.NotSnakeCaseMemberVar
+					return false;
+				}
+
+				// Also "innodb_file_per_table" is required then.
+				$row = $wpdb->get_row( "SHOW VARIABLES LIKE 'innodb_file_per_table'" );
+				if ( ! in_array( strtolower( $row->Value ), array( '1', 'on' ) ) ) {    // phpcs:ignore WordPress.NamingConventions.ValidVariableName.NotSnakeCaseMemberVar
+					return false;
+				}
+			}
+		}
+
+		// No reason found against creating indices, so return TRUE here.
+		return true;
+	}
 }