primo commit

administrator/components/com_contenthistory/contenthistory.xml

@@ -0,0 +1,33 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<extension type="component" method="upgrade">
+	<name>com_contenthistory</name>
+	<author>Joomla! Project</author>
+	<creationDate>2013-05</creationDate>
+	<copyright>(C) 2013 Open Source Matters, Inc.</copyright>
+	<license>GNU General Public License version 2 or later; see LICENSE.txt</license>
+	<authorEmail>admin@joomla.org</authorEmail>
+	<authorUrl>www.joomla.org</authorUrl>
+	<version>4.0.0</version>
+	<description>COM_CONTENTHISTORY_XML_DESCRIPTION</description>
+	<namespace path="src">Joomla\Component\Contenthistory</namespace>
+	<files folder="site">
+			<folder>src</folder>
+	</files>
+	<media destination="com_contenthistory" folder="media">
+		<folder>js</folder>
+	</media>
+	<administration>
+		<files folder="admin">
+			<filename>contenthistory.xml</filename>
+			<folder>helpers</folder>
+			<folder>services</folder>
+			<folder>src</folder>
+			<folder>tmpl</folder>
+		</files>
+		<languages folder="admin">
+			<language tag="en-GB">language/en-GB/com_contenthistory.ini</language>
+			<language tag="en-GB">language/en-GB/com_contenthistory.sys.ini</language>
+		</languages>
+	</administration>
+</extension>
+

administrator/components/com_contenthistory/helpers/contenthistory.php

@@ -0,0 +1,27 @@
+<?php
+
+/**
+ * @package     Joomla.Administrator
+ * @subpackage  com_contenthistory
+ *
+ * @copyright   (C) 2013 Open Source Matters, Inc. <https://www.joomla.org>
+ * @license     GNU General Public License version 2 or later; see LICENSE.txt
+ *
+ * @phpcs:disable PSR1.Classes.ClassDeclaration.MissingNamespace
+ */
+
+// phpcs:disable PSR1.Files.SideEffects
+\defined('_JEXEC') or die;
+// phpcs:enable PSR1.Files.SideEffects
+
+/**
+ * Categories helper.
+ *
+ * @since       3.2
+ *
+ * @deprecated  4.3 will be removed in 6.0
+ *              Use \Joomla\Component\Contenthistory\Administrator\Helper\ContenthistoryHelper instead
+ */
+class ContenthistoryHelper extends \Joomla\Component\Contenthistory\Administrator\Helper\ContenthistoryHelper
+{
+}

administrator/components/com_contenthistory/services/provider.php

@@ -0,0 +1,53 @@
+<?php
+
+/**
+ * @package     Joomla.Administrator
+ * @subpackage  com_contenthistory
+ *
+ * @copyright   (C) 2018 Open Source Matters, Inc. <https://www.joomla.org>
+ * @license     GNU General Public License version 2 or later; see LICENSE.txt
+ */
+
+\defined('_JEXEC') or die;
+
+use Joomla\CMS\Dispatcher\ComponentDispatcherFactoryInterface;
+use Joomla\CMS\Extension\ComponentInterface;
+use Joomla\CMS\Extension\MVCComponent;
+use Joomla\CMS\Extension\Service\Provider\ComponentDispatcherFactory;
+use Joomla\CMS\Extension\Service\Provider\MVCFactory;
+use Joomla\CMS\MVC\Factory\MVCFactoryInterface;
+use Joomla\DI\Container;
+use Joomla\DI\ServiceProviderInterface;
+
+/**
+ * The content history service provider.
+ *
+ * @since  4.0.0
+ */
+return new class () implements ServiceProviderInterface {
+    /**
+     * Registers the service provider with a DI container.
+     *
+     * @param   Container  $container  The DI container.
+     *
+     * @return  void
+     *
+     * @since   4.0.0
+     */
+    public function register(Container $container)
+    {
+        $container->registerServiceProvider(new MVCFactory('\\Joomla\\Component\\Contenthistory'));
+        $container->registerServiceProvider(new ComponentDispatcherFactory('\\Joomla\\Component\\Contenthistory'));
+
+        $container->set(
+            ComponentInterface::class,
+            function (Container $container) {
+                $component = new MVCComponent($container->get(ComponentDispatcherFactoryInterface::class));
+
+                $component->setMVCFactory($container->get(MVCFactoryInterface::class));
+
+                return $component;
+            }
+        );
+    }
+};

administrator/components/com_contenthistory/src/Controller/DisplayController.php

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+<?php
+
+/**
+ * @package     Joomla.Administrator
+ * @subpackage  com_contenthistory
+ *
+ * @copyright   (C) 2013 Open Source Matters, Inc. <https://www.joomla.org>
+ * @license     GNU General Public License version 2 or later; see LICENSE.txt
+ */
+
+namespace Joomla\Component\Contenthistory\Administrator\Controller;
+
+use Joomla\CMS\MVC\Controller\BaseController;
+
+// phpcs:disable PSR1.Files.SideEffects
+\defined('_JEXEC') or die;
+// phpcs:enable PSR1.Files.SideEffects
+
+/**
+ * Contenthistory Controller
+ *
+ * @since  3.2
+ */
+class DisplayController extends BaseController
+{
+}

administrator/components/com_contenthistory/src/Controller/HistoryController.php

@@ -0,0 +1,96 @@
+<?php
+
+/**
+ * @package     Joomla.Administrator
+ * @subpackage  com_contenthistory
+ *
+ * @copyright   (C) 2013 Open Source Matters, Inc. <https://www.joomla.org>
+ * @license     GNU General Public License version 2 or later; see LICENSE.txt
+ */
+
+namespace Joomla\Component\Contenthistory\Administrator\Controller;
+
+use Joomla\CMS\Language\Text;
+use Joomla\CMS\MVC\Controller\AdminController;
+use Joomla\CMS\Router\Route;
+use Joomla\CMS\Session\Session;
+
+// phpcs:disable PSR1.Files.SideEffects
+\defined('_JEXEC') or die;
+// phpcs:enable PSR1.Files.SideEffects
+
+/**
+ * Contenthistory list controller class.
+ *
+ * @since  3.2
+ */
+class HistoryController extends AdminController
+{
+    /**
+     * Proxy for getModel.
+     *
+     * @param   string  $name    The name of the model
+     * @param   string  $prefix  The prefix for the model
+     * @param   array   $config  An additional array of parameters
+     *
+     * @return  \Joomla\CMS\MVC\Model\BaseDatabaseModel  The model
+     *
+     * @since   3.2
+     */
+    public function getModel($name = 'History', $prefix = 'Administrator', $config = ['ignore_request' => true])
+    {
+        return parent::getModel($name, $prefix, $config);
+    }
+
+    /**
+     * Toggles the keep forever value for one or more history rows. If it was Yes, changes to No. If No, changes to Yes.
+     *
+     * @return  void
+     *
+     * @since   3.2
+     */
+    public function keep()
+    {
+        $this->checkToken();
+
+        // Get items to toggle keep forever from the request.
+        $cid = (array) $this->input->get('cid', [], 'int');
+
+        // Remove zero values resulting from input filter
+        $cid = array_filter($cid);
+
+        if (empty($cid)) {
+            $this->app->enqueueMessage(Text::_('COM_CONTENTHISTORY_NO_ITEM_SELECTED'), 'warning');
+        } else {
+            // Get the model.
+            $model = $this->getModel();
+
+            // Toggle keep forever status of the selected items.
+            if ($model->keep($cid)) {
+                $this->setMessage(Text::plural('COM_CONTENTHISTORY_N_ITEMS_KEEP_TOGGLE', \count($cid)));
+            } else {
+                $this->setMessage($model->getError(), 'error');
+            }
+        }
+
+        $this->setRedirect(
+            Route::_(
+                'index.php?option=com_contenthistory&view=history&layout=modal&tmpl=component&item_id='
+                . $this->input->getCmd('item_id') . '&' . Session::getFormToken() . '=1',
+                false
+            )
+        );
+    }
+
+    /**
+     * Gets the URL arguments to append to a list redirect.
+     *
+     * @return  string  The arguments to append to the redirect URL.
+     *
+     * @since   4.0.0
+     */
+    protected function getRedirectToListAppend()
+    {
+        return '&layout=modal&tmpl=component&item_id=' . $this->input->get('item_id') . '&' . Session::getFormToken() . '=1';
+    }
+}

administrator/components/com_contenthistory/src/Controller/PreviewController.php

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+<?php
+
+/**
+ * @package     Joomla.Administrator
+ * @subpackage  com_contenthistory
+ *
+ * @copyright   (C) 2013 Open Source Matters, Inc. <https://www.joomla.org>
+ * @license     GNU General Public License version 2 or later; see LICENSE.txt
+ */
+
+namespace Joomla\Component\Contenthistory\Administrator\Controller;
+
+use Joomla\CMS\MVC\Controller\BaseController;
+
+// phpcs:disable PSR1.Files.SideEffects
+\defined('_JEXEC') or die;
+// phpcs:enable PSR1.Files.SideEffects
+
+/**
+ * Contenthistory list controller class.
+ *
+ * @since  3.2
+ */
+class PreviewController extends BaseController
+{
+    /**
+     * Proxy for getModel.
+     *
+     * @param   string  $name    The name of the model
+     * @param   string  $prefix  The prefix for the model
+     * @param   array   $config  An additional array of parameters
+     *
+     * @return  \Joomla\CMS\MVC\Model\BaseDatabaseModel  The model
+     *
+     * @since   3.2
+     */
+    public function getModel($name = 'Preview', $prefix = 'Administrator', $config = ['ignore_request' => true])
+    {
+        return parent::getModel($name, $prefix, $config);
+    }
+}

administrator/components/com_contenthistory/src/Dispatcher/Dispatcher.php

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+<?php
+
+/**
+ * @package     Joomla.Administrator
+ * @subpackage  com_contenthistory
+ *
+ * @copyright   (C) 2017 Open Source Matters, Inc. <https://www.joomla.org>
+ * @license     GNU General Public License version 2 or later; see LICENSE.txt
+ */
+
+namespace Joomla\Component\Contenthistory\Administrator\Dispatcher;
+
+use Joomla\CMS\Access\Exception\NotAllowed;
+use Joomla\CMS\Dispatcher\ComponentDispatcher;
+
+// phpcs:disable PSR1.Files.SideEffects
+\defined('_JEXEC') or die;
+// phpcs:enable PSR1.Files.SideEffects
+
+/**
+ * ComponentDispatcher class for com_associations
+ *
+ * @since  4.0.0
+ */
+class Dispatcher extends ComponentDispatcher
+{
+    /**
+     * Method to check component access permission
+     *
+     * @since   4.0.0
+     *
+     * @return  void
+     *
+     * @throws  \Exception|NotAllowed
+     */
+    protected function checkAccess()
+    {
+        // Check the user has permission to access this component if in the backend
+        if ($this->app->getIdentity()->guest) {
+            throw new NotAllowed($this->app->getLanguage()->_('JERROR_ALERTNOAUTHOR'), 403);
+        }
+    }
+}

administrator/components/com_contenthistory/src/Helper/ContenthistoryHelper.php

@@ -0,0 +1,363 @@
+<?php
+
+/**
+ * @package     Joomla.Administrator
+ * @subpackage  com_contenthistory
+ *
+ * @copyright   (C) 2017 Open Source Matters, Inc. <https://www.joomla.org>
+ * @license     GNU General Public License version 2 or later; see LICENSE.txt
+ */
+
+namespace Joomla\Component\Contenthistory\Administrator\Helper;
+
+use Joomla\CMS\Factory;
+use Joomla\CMS\Filesystem\File;
+use Joomla\CMS\Language\Text;
+use Joomla\CMS\Table\ContentHistory;
+use Joomla\CMS\Table\ContentType;
+use Joomla\CMS\Table\Table;
+use Joomla\Database\ParameterType;
+use Joomla\Filesystem\Folder;
+use Joomla\Filesystem\Path;
+
+// phpcs:disable PSR1.Files.SideEffects
+\defined('_JEXEC') or die;
+// phpcs:enable PSR1.Files.SideEffects
+
+/**
+ * Categories helper.
+ *
+ * @since  3.2
+ */
+class ContenthistoryHelper
+{
+    /**
+     * Method to put all field names, including nested ones, in a single array for easy lookup.
+     *
+     * @param   \stdClass  $object  Standard class object that may contain one level of nested objects.
+     *
+     * @return  array  Associative array of all field names, including ones in a nested object.
+     *
+     * @since   3.2
+     */
+    public static function createObjectArray($object)
+    {
+        $result = [];
+
+        if ($object === null) {
+            return $result;
+        }
+
+        foreach ($object as $name => $value) {
+            $result[$name] = $value;
+
+            if (\is_object($value)) {
+                foreach ($value as $subName => $subValue) {
+                    $result[$subName] = $subValue;
+                }
+            }
+        }
+
+        return $result;
+    }
+
+    /**
+     * Method to decode JSON-encoded fields in a standard object. Used to unpack JSON strings in the content history data column.
+     *
+     * @param   string  $jsonString  JSON String to convert to an object.
+     *
+     * @return  \stdClass  Object with any JSON-encoded fields unpacked.
+     *
+     * @since   3.2
+     */
+    public static function decodeFields($jsonString)
+    {
+        $object = json_decode($jsonString);
+
+        if (\is_object($object)) {
+            foreach ($object as $name => $value) {
+                if (!\is_null($value) && $subObject = json_decode($value)) {
+                    $object->$name = $subObject;
+                }
+            }
+        }
+
+        return $object;
+    }
+
+    /**
+     * Method to get field labels for the fields in the JSON-encoded object.
+     * First we see if we can find translatable labels for the fields in the object.
+     * We translate any we can find and return an array in the format object->name => label.
+     *
+     * @param   \stdClass    $object      Standard class object in the format name->value.
+     * @param   ContentType  $typesTable  Table object with content history options.
+     *
+     * @return  \stdClass  Contains two associative arrays.
+     *                    $formValues->labels in the format name => label (for example, 'id' => 'Article ID').
+     *                    $formValues->values in the format name => value (for example, 'state' => 'Published'.
+     *                    This translates the text from the selected option in the form.
+     *
+     * @since   3.2
+     */
+    public static function getFormValues($object, ContentType $typesTable)
+    {
+        $labels              = [];
+        $values              = [];
+        $expandedObjectArray = static::createObjectArray($object);
+        static::loadLanguageFiles($typesTable->type_alias);
+
+        if ($formFile = static::getFormFile($typesTable)) {
+            if ($xml = simplexml_load_file($formFile)) {
+                // Now we need to get all of the labels from the form
+                $fieldArray = $xml->xpath('//field');
+                $fieldArray = array_merge($fieldArray, $xml->xpath('//fields'));
+
+                foreach ($fieldArray as $field) {
+                    if ($label = (string) $field->attributes()->label) {
+                        $labels[(string) $field->attributes()->name] = Text::_($label);
+                    }
+                }
+
+                // Get values for any list type fields
+                $listFieldArray = $xml->xpath('//field[@type="list" or @type="radio"]');
+
+                foreach ($listFieldArray as $field) {
+                    $name = (string) $field->attributes()->name;
+
+                    if (isset($expandedObjectArray[$name])) {
+                        $optionFieldArray = $field->xpath('option[@value="' . $expandedObjectArray[$name] . '"]');
+
+                        $valueText = null;
+
+                        if (\is_array($optionFieldArray) && \count($optionFieldArray)) {
+                            $valueText = trim((string) $optionFieldArray[0]);
+                        }
+
+                        $values[(string) $field->attributes()->name] = Text::_($valueText);
+                    }
+                }
+            }
+        }
+
+        $result         = new \stdClass();
+        $result->labels = $labels;
+        $result->values = $values;
+
+        return $result;
+    }
+
+    /**
+     * Method to get the XML form file for this component. Used to get translated field names for history preview.
+     *
+     * @param   ContentType  $typesTable  Table object with content history options.
+     *
+     * @return  mixed  \JModel object if successful, false if no model found.
+     *
+     * @since   3.2
+     */
+    public static function getFormFile(ContentType $typesTable)
+    {
+        // First, see if we have a file name in the $typesTable
+        $options = json_decode($typesTable->content_history_options);
+
+        if (\is_object($options) && isset($options->formFile) && is_file(JPATH_ROOT . '/' . $options->formFile)) {
+            $result = JPATH_ROOT . '/' . $options->formFile;
+        } else {
+            $aliasArray = explode('.', $typesTable->type_alias);
+            $component  = ($aliasArray[1] == 'category') ? 'com_categories' : $aliasArray[0];
+            $path       = Folder::makeSafe(JPATH_ADMINISTRATOR . '/components/' . $component . '/models/forms/');
+            array_shift($aliasArray);
+            $file   = File::makeSafe(implode('.', $aliasArray) . '.xml');
+            $result = is_file($path . $file) ? $path . $file : false;
+        }
+
+        return $result;
+    }
+
+    /**
+     * Method to query the database using values from lookup objects.
+     *
+     * @param   \stdClass  $lookup  The std object with the values needed to do the query.
+     * @param   mixed      $value   The value used to find the matching title or name. Typically the id.
+     *
+     * @return  mixed  Value from database (for example, name or title) on success, false on failure.
+     *
+     * @since   3.2
+     */
+    public static function getLookupValue($lookup, $value)
+    {
+        $result = false;
+
+        if (isset($lookup->sourceColumn) && isset($lookup->targetTable) && isset($lookup->targetColumn) && isset($lookup->displayColumn)) {
+            $db    = Factory::getDbo();
+            $value = (int) $value;
+            $query = $db->getQuery(true);
+            $query->select($db->quoteName($lookup->displayColumn))
+                ->from($db->quoteName($lookup->targetTable))
+                ->where($db->quoteName($lookup->targetColumn) . ' = :value')
+                ->bind(':value', $value, ParameterType::INTEGER);
+            $db->setQuery($query);
+
+            try {
+                $result = $db->loadResult();
+            } catch (\Exception $e) {
+                // Ignore any errors and just return false
+                return false;
+            }
+        }
+
+        return $result;
+    }
+
+    /**
+     * Method to remove fields from the object based on values entered in the #__content_types table.
+     *
+     * @param   \stdClass    $object     Object to be passed to view layout file.
+     * @param   ContentType  $typeTable  Table object with content history options.
+     *
+     * @return  \stdClass  object with hidden fields removed.
+     *
+     * @since   3.2
+     */
+    public static function hideFields($object, ContentType $typeTable)
+    {
+        if ($options = json_decode($typeTable->content_history_options)) {
+            if (isset($options->hideFields) && \is_array($options->hideFields)) {
+                foreach ($options->hideFields as $field) {
+                    unset($object->$field);
+                }
+            }
+        }
+
+        return $object;
+    }
+
+    /**
+     * Method to load the language files for the component whose history is being viewed.
+     *
+     * @param   string  $typeAlias  The type alias, for example 'com_content.article'.
+     *
+     * @return  void
+     *
+     * @since   3.2
+     */
+    public static function loadLanguageFiles($typeAlias)
+    {
+        $aliasArray = explode('.', $typeAlias);
+
+        if (\is_array($aliasArray) && \count($aliasArray) == 2) {
+            $component = ($aliasArray[1] == 'category') ? 'com_categories' : $aliasArray[0];
+            $lang      = Factory::getLanguage();
+
+            /**
+             * Loading language file from the administrator/language directory then
+             * loading language file from the administrator/components/extension/language directory
+             */
+            $lang->load($component, JPATH_ADMINISTRATOR)
+            || $lang->load($component, Path::clean(JPATH_ADMINISTRATOR . '/components/' . $component));
+
+            // Force loading of backend global language file
+            $lang->load('joomla', Path::clean(JPATH_ADMINISTRATOR));
+        }
+    }
+
+    /**
+     * Method to create object to pass to the layout. Format is as follows:
+     * field is std object with name, value.
+     *
+     * Value can be a std object with name, value pairs.
+     *
+     * @param   \stdClass  $object      The std object from the JSON string. Can be nested 1 level deep.
+     * @param   \stdClass  $formValues  Standard class of label and value in an associative array.
+     *
+     * @return  \stdClass  Object with translated labels where available
+     *
+     * @since   3.2
+     */
+    public static function mergeLabels($object, $formValues)
+    {
+        $result = new \stdClass();
+
+        if ($object === null) {
+            return $result;
+        }
+
+        $labelsArray = $formValues->labels;
+        $valuesArray = $formValues->values;
+
+        foreach ($object as $name => $value) {
+            $result->$name        = new \stdClass();
+            $result->$name->name  = $name;
+            $result->$name->value = $valuesArray[$name] ?? $value;
+            $result->$name->label = $labelsArray[$name] ?? $name;
+
+            if (\is_object($value)) {
+                $subObject = new \stdClass();
+
+                foreach ($value as $subName => $subValue) {
+                    $subObject->$subName        = new \stdClass();
+                    $subObject->$subName->name  = $subName;
+                    $subObject->$subName->value = $valuesArray[$subName] ?? $subValue;
+                    $subObject->$subName->label = $labelsArray[$subName] ?? $subName;
+                    $result->$name->value       = $subObject;
+                }
+            }
+        }
+
+        return $result;
+    }
+
+    /**
+     * Method to prepare the object for the preview and compare views.
+     *
+     * @param   ContentHistory  $table  Table object loaded with data.
+     *
+     * @return  \stdClass  Object ready for the views.
+     *
+     * @since   3.2
+     */
+    public static function prepareData(ContentHistory $table)
+    {
+        $object     = static::decodeFields($table->version_data);
+        $typesTable = Table::getInstance('ContentType', 'Joomla\\CMS\\Table\\');
+        $typeAlias  = explode('.', $table->item_id);
+        array_pop($typeAlias);
+        $typesTable->load(['type_alias' => implode('.', $typeAlias)]);
+        $formValues = static::getFormValues($object, $typesTable);
+        $object     = static::mergeLabels($object, $formValues);
+        $object     = static::hideFields($object, $typesTable);
+        $object     = static::processLookupFields($object, $typesTable);
+
+        return $object;
+    }
+
+    /**
+     * Method to process any lookup values found in the content_history_options column for this table.
+     * This allows category title and user name to be displayed instead of the id column.
+     *
+     * @param   \stdClass    $object      The std object from the JSON string. Can be nested 1 level deep.
+     * @param   ContentType  $typesTable  Table object loaded with data.
+     *
+     * @return  \stdClass  Object with lookup values inserted.
+     *
+     * @since   3.2
+     */
+    public static function processLookupFields($object, ContentType $typesTable)
+    {
+        if ($options = json_decode($typesTable->content_history_options)) {
+            if (isset($options->displayLookup) && \is_array($options->displayLookup)) {
+                foreach ($options->displayLookup as $lookup) {
+                    $sourceColumn = $lookup->sourceColumn ?? false;
+                    $sourceValue  = $object->$sourceColumn->value ?? false;
+
+                    if ($sourceColumn && $sourceValue && ($lookupValue = static::getLookupValue($lookup, $sourceValue))) {
+                        $object->$sourceColumn->value = $lookupValue;
+                    }
+                }
+            }
+        }
+
+        return $object;
+    }
+}

administrator/components/com_contenthistory/src/Model/CompareModel.php

@@ -0,0 +1,185 @@
+<?php
+
+/**
+ * @package     Joomla.Administrator
+ * @subpackage  com_contenthistory
+ *
+ * @copyright   (C) 2013 Open Source Matters, Inc. <https://www.joomla.org>
+ * @license     GNU General Public License version 2 or later; see LICENSE.txt
+ */
+
+namespace Joomla\Component\Contenthistory\Administrator\Model;
+
+use Joomla\CMS\Access\Exception\NotAllowed;
+use Joomla\CMS\Factory;
+use Joomla\CMS\HTML\HTMLHelper;
+use Joomla\CMS\Language\Text;
+use Joomla\CMS\MVC\Model\ListModel;
+use Joomla\CMS\Table\ContentHistory;
+use Joomla\CMS\Table\ContentType;
+use Joomla\CMS\Table\Table;
+use Joomla\Component\Contenthistory\Administrator\Helper\ContenthistoryHelper;
+
+// phpcs:disable PSR1.Files.SideEffects
+\defined('_JEXEC') or die;
+// phpcs:enable PSR1.Files.SideEffects
+
+/**
+ * Methods supporting a list of contenthistory records.
+ *
+ * @since  3.2
+ */
+class CompareModel extends ListModel
+{
+    /**
+     * Method to get a version history row.
+     *
+     * @return  array|boolean    On success, array of populated tables. False on failure.
+     *
+     * @since   3.2
+     *
+     * @throws  NotAllowed   Thrown if not authorised to edit an item
+     */
+    public function getItems()
+    {
+        $input = Factory::getApplication()->getInput();
+
+        /** @var ContentHistory $table1 */
+        $table1 = $this->getTable('ContentHistory');
+
+        /** @var ContentHistory $table2 */
+        $table2 = $this->getTable('ContentHistory');
+
+        $id1 = $input->getInt('id1');
+        $id2 = $input->getInt('id2');
+
+        if (!$id1 || \is_array($id1) || !$id2 || \is_array($id2)) {
+            $this->setError(Text::_('COM_CONTENTHISTORY_ERROR_INVALID_ID'));
+
+            return false;
+        }
+
+        $result = [];
+
+        if (!$table1->load($id1) || !$table2->load($id2)) {
+            $this->setError(Text::_('COM_CONTENTHISTORY_ERROR_VERSION_NOT_FOUND'));
+
+            // Assume a failure to load the content means broken data, abort mission
+            return false;
+        }
+
+        // Get the first history record's content type record so we can check ACL
+        /** @var ContentType $contentTypeTable */
+        $contentTypeTable = $this->getTable('ContentType');
+        $typeAlias        = explode('.', $table1->item_id);
+        array_pop($typeAlias);
+        $typeAlias        = implode('.', $typeAlias);
+
+        if (!$contentTypeTable->load(['type_alias' => $typeAlias])) {
+            $this->setError(Text::_('COM_CONTENTHISTORY_ERROR_FAILED_LOADING_CONTENT_TYPE'));
+
+            // Assume a failure to load the content type means broken data, abort mission
+            return false;
+        }
+
+        $user = $this->getCurrentUser();
+
+        // Access check
+        if (!$user->authorise('core.edit', $table1->item_id) && !$this->canEdit($table1)) {
+            throw new NotAllowed(Text::_('JERROR_ALERTNOAUTHOR'), 403);
+        }
+
+        $nullDate = $this->getDatabase()->getNullDate();
+
+        foreach ([$table1, $table2] as $table) {
+            $object               = new \stdClass();
+            $object->data         = ContenthistoryHelper::prepareData($table);
+            $object->version_note = $table->version_note;
+
+            // Let's use custom calendars when present
+            $object->save_date = HTMLHelper::_('date', $table->save_date, Text::_('DATE_FORMAT_LC6'));
+
+            $dateProperties = [
+                'modified_time',
+                'created_time',
+                'modified',
+                'created',
+                'checked_out_time',
+                'publish_up',
+                'publish_down',
+            ];
+
+            foreach ($dateProperties as $dateProperty) {
+                if (
+                    property_exists($object->data, $dateProperty)
+                    && $object->data->$dateProperty->value !== null
+                    && $object->data->$dateProperty->value !== $nullDate
+                ) {
+                    $object->data->$dateProperty->value = HTMLHelper::_(
+                        'date',
+                        $object->data->$dateProperty->value,
+                        Text::_('DATE_FORMAT_LC6')
+                    );
+                }
+            }
+
+            $result[] = $object;
+        }
+
+        return $result;
+    }
+
+    /**
+     * Method to get a table object, load it if necessary.
+     *
+     * @param   string  $type    The table name. Optional.
+     * @param   string  $prefix  The class prefix. Optional.
+     * @param   array   $config  Configuration array for model. Optional.
+     *
+     * @return  Table   A Table object
+     *
+     * @since   3.2
+     */
+    public function getTable($type = 'Contenthistory', $prefix = 'Joomla\\CMS\\Table\\', $config = [])
+    {
+        return Table::getInstance($type, $prefix, $config);
+    }
+
+    /**
+     * Method to test whether a record is editable
+     *
+     * @param   ContentHistory  $record  A Table object.
+     *
+     * @return  boolean  True if allowed to edit the record. Defaults to the permission set in the component.
+     *
+     * @since   3.6
+     */
+    protected function canEdit($record)
+    {
+        $result = false;
+
+        if (!empty($record->item_id)) {
+            /**
+             * Make sure user has edit privileges for this content item. Note that we use edit permissions
+             * for the content item, not delete permissions for the content history row.
+             */
+            $user   = $this->getCurrentUser();
+            $result = $user->authorise('core.edit', $record->item_id);
+
+            // Finally try session (this catches edit.own case too)
+            if (!$result) {
+                /** @var ContentType $contentTypeTable */
+                $contentTypeTable = $this->getTable('ContentType');
+
+                $typeAlias        = explode('.', $record->item_id);
+                $id               = array_pop($typeAlias);
+                $typeAlias        = implode('.', $typeAlias);
+                $contentTypeTable->load(['type_alias' => $typeAlias]);
+                $typeEditables = (array) Factory::getApplication()->getUserState(str_replace('.', '.edit.', $contentTypeTable->type_alias) . '.id');
+                $result        = \in_array((int) $id, $typeEditables);
+            }
+        }
+
+        return $result;
+    }
+}

administrator/components/com_contenthistory/src/Model/HistoryModel.php

@@ -0,0 +1,395 @@
+<?php
+
+/**
+ * @package     Joomla.Administrator
+ * @subpackage  com_contenthistory
+ *
+ * @copyright   (C) 2013 Open Source Matters, Inc. <https://www.joomla.org>
+ * @license     GNU General Public License version 2 or later; see LICENSE.txt
+ */
+
+namespace Joomla\Component\Contenthistory\Administrator\Model;
+
+use Joomla\CMS\Access\Exception\NotAllowed;
+use Joomla\CMS\Component\ComponentHelper;
+use Joomla\CMS\Factory;
+use Joomla\CMS\Helper\CMSHelper;
+use Joomla\CMS\Language\Text;
+use Joomla\CMS\Log\Log;
+use Joomla\CMS\MVC\Factory\MVCFactoryInterface;
+use Joomla\CMS\MVC\Model\ListModel;
+use Joomla\CMS\Table\ContentHistory;
+use Joomla\CMS\Table\ContentType;
+use Joomla\CMS\Table\Table;
+use Joomla\Database\ParameterType;
+use Joomla\Database\QueryInterface;
+
+// phpcs:disable PSR1.Files.SideEffects
+\defined('_JEXEC') or die;
+// phpcs:enable PSR1.Files.SideEffects
+
+/**
+ * Methods supporting a list of contenthistory records.
+ *
+ * @since  3.2
+ */
+class HistoryModel extends ListModel
+{
+    /**
+     * Constructor.
+     *
+     * @param   array                 $config   An optional associative array of configuration settings.
+     * @param   ?MVCFactoryInterface  $factory  The factory.
+     *
+     * @see     \Joomla\CMS\MVC\Model\BaseDatabaseModel
+     * @since   3.2
+     */
+    public function __construct($config = [], ?MVCFactoryInterface $factory = null)
+    {
+        if (empty($config['filter_fields'])) {
+            $config['filter_fields'] = [
+                'version_id',
+                'h.version_id',
+                'version_note',
+                'h.version_note',
+                'save_date',
+                'h.save_date',
+                'editor_user_id',
+                'h.editor_user_id',
+            ];
+        }
+
+        parent::__construct($config, $factory);
+    }
+
+    /**
+     * Method to test whether a record is editable
+     *
+     * @param   ContentHistory  $record  A Table object.
+     *
+     * @return  boolean  True if allowed to edit the record. Defaults to the permission set in the component.
+     *
+     * @since   3.2
+     */
+    protected function canEdit($record)
+    {
+        if (empty($record->item_id)) {
+            return false;
+        }
+
+        /**
+         * Make sure user has edit privileges for this content item. Note that we use edit permissions
+         * for the content item, not delete permissions for the content history row.
+         */
+        $user   = $this->getCurrentUser();
+
+        if ($user->authorise('core.edit', $record->item_id)) {
+            return true;
+        }
+
+        // Finally try session (this catches edit.own case too)
+        /** @var ContentType $contentTypeTable */
+        $contentTypeTable = $this->getTable('ContentType');
+
+        $typeAlias        = explode('.', $record->item_id);
+        $id               = array_pop($typeAlias);
+        $typeAlias        = implode('.', $typeAlias);
+        $contentTypeTable->load(['type_alias' => $typeAlias]);
+        $typeEditables = (array) Factory::getApplication()->getUserState(str_replace('.', '.edit.', $contentTypeTable->type_alias) . '.id');
+        $result        = \in_array((int) $id, $typeEditables);
+
+        return $result;
+    }
+
+    /**
+     * Method to test whether a history record can be deleted. Note that we check whether we have edit permissions
+     * for the content item row.
+     *
+     * @param   ContentHistory  $record  A Table object.
+     *
+     * @return  boolean  True if allowed to delete the record. Defaults to the permission set in the component.
+     *
+     * @since   3.6
+     */
+    protected function canDelete($record)
+    {
+        return $this->canEdit($record);
+    }
+
+    /**
+     * Method to delete one or more records from content history table.
+     *
+     * @param   array  $pks  An array of record primary keys.
+     *
+     * @return  boolean  True if successful, false if an error occurs.
+     *
+     * @since   3.2
+     */
+    public function delete(&$pks)
+    {
+        $pks   = (array) $pks;
+        $table = $this->getTable();
+
+        // Iterate the items to delete each one.
+        foreach ($pks as $i => $pk) {
+            if ($table->load($pk)) {
+                if ((int) $table->keep_forever === 1) {
+                    unset($pks[$i]);
+                    continue;
+                }
+
+                if ($this->canEdit($table)) {
+                    if (!$table->delete($pk)) {
+                        $this->setError($table->getError());
+
+                        return false;
+                    }
+                } else {
+                    // Prune items that you can't change.
+                    unset($pks[$i]);
+                    $error = $this->getError();
+
+                    if ($error) {
+                        try {
+                            Log::add($error, Log::WARNING, 'jerror');
+                        } catch (\RuntimeException $exception) {
+                            Factory::getApplication()->enqueueMessage($error, 'warning');
+                        }
+
+                        return false;
+                    }
+
+                    try {
+                        Log::add(Text::_('JLIB_APPLICATION_ERROR_DELETE_NOT_PERMITTED'), Log::WARNING, 'jerror');
+                    } catch (\RuntimeException $exception) {
+                        Factory::getApplication()->enqueueMessage(Text::_('JLIB_APPLICATION_ERROR_DELETE_NOT_PERMITTED'), 'warning');
+                    }
+
+                    return false;
+                }
+            } else {
+                $this->setError($table->getError());
+
+                return false;
+            }
+        }
+
+        // Clear the component's cache
+        $this->cleanCache();
+
+        return true;
+    }
+
+    /**
+     * Method to get an array of data items.
+     *
+     * @return  mixed  An array of data items on success, false on failure.
+     *
+     * @since   3.4.5
+     *
+     * @throws  NotAllowed   Thrown if not authorised to edit an item
+     */
+    public function getItems()
+    {
+        $items = parent::getItems();
+        $user  = $this->getCurrentUser();
+
+        if ($items === false) {
+            return false;
+        }
+
+        // This should be an array with at least one element
+        if (!\is_array($items) || !isset($items[0])) {
+            return $items;
+        }
+
+        // Access check
+        if (!$user->authorise('core.edit', $items[0]->item_id) && !$this->canEdit($items[0])) {
+            throw new NotAllowed(Text::_('JERROR_ALERTNOAUTHOR'), 403);
+        }
+
+        return $items;
+    }
+
+    /**
+     * Method to get a table object, load it if necessary.
+     *
+     * @param   string  $type    The table name. Optional.
+     * @param   string  $prefix  The class prefix. Optional.
+     * @param   array   $config  Configuration array for model. Optional.
+     *
+     * @return  Table   A Table object
+     *
+     * @since   3.2
+     */
+    public function getTable($type = 'ContentHistory', $prefix = 'Joomla\\CMS\\Table\\', $config = [])
+    {
+        return Table::getInstance($type, $prefix, $config);
+    }
+    /**
+     * Method to toggle on and off the keep forever value for one or more records from content history table.
+     *
+     * @param   array  $pks  An array of record primary keys.
+     *
+     * @return  boolean  True if successful, false if an error occurs.
+     *
+     * @since   3.2
+     */
+    public function keep(&$pks)
+    {
+        $pks   = (array) $pks;
+        $table = $this->getTable();
+
+        // Iterate the items to delete each one.
+        foreach ($pks as $i => $pk) {
+            if ($table->load($pk)) {
+                if ($this->canEdit($table)) {
+                    $table->keep_forever = $table->keep_forever ? 0 : 1;
+
+                    if (!$table->store()) {
+                        $this->setError($table->getError());
+
+                        return false;
+                    }
+                } else {
+                    // Prune items that you can't change.
+                    unset($pks[$i]);
+                    $error = $this->getError();
+
+                    if ($error) {
+                        try {
+                            Log::add($error, Log::WARNING, 'jerror');
+                        } catch (\RuntimeException $exception) {
+                            Factory::getApplication()->enqueueMessage($error, 'warning');
+                        }
+
+                        return false;
+                    }
+
+                    try {
+                        Log::add(Text::_('COM_CONTENTHISTORY_ERROR_KEEP_NOT_PERMITTED'), Log::WARNING, 'jerror');
+                    } catch (\RuntimeException $exception) {
+                        Factory::getApplication()->enqueueMessage(Text::_('COM_CONTENTHISTORY_ERROR_KEEP_NOT_PERMITTED'), 'warning');
+                    }
+
+                    return false;
+                }
+            } else {
+                $this->setError($table->getError());
+
+                return false;
+            }
+        }
+
+        // Clear the component's cache
+        $this->cleanCache();
+
+        return true;
+    }
+
+    /**
+     * Method to auto-populate the model state.
+     *
+     * Note. Calling getState in this method will result in recursion.
+     *
+     * @param   string  $ordering   An optional ordering field.
+     * @param   string  $direction  An optional direction (asc|desc).
+     *
+     * @return  void
+     *
+     * @since   3.2
+     */
+    protected function populateState($ordering = 'h.save_date', $direction = 'DESC')
+    {
+        $input  = Factory::getApplication()->getInput();
+        $itemId = $input->get('item_id', '', 'string');
+
+        $this->setState('item_id', $itemId);
+        $this->setState('sha1_hash', $this->getSha1Hash());
+
+        // Load the parameters.
+        $params = ComponentHelper::getParams('com_contenthistory');
+        $this->setState('params', $params);
+
+        // List state information.
+        parent::populateState($ordering, $direction);
+    }
+
+    /**
+     * Build an SQL query to load the list data.
+     *
+     * @return  QueryInterface
+     *
+     * @since   3.2
+     */
+    protected function getListQuery()
+    {
+        // Create a new query object.
+        $db     = $this->getDatabase();
+        $query  = $db->getQuery(true);
+        $itemId = $this->getState('item_id');
+
+        // Select the required fields from the table.
+        $query->select(
+            $this->getState(
+                'list.select',
+                [
+                    $db->quoteName('h.version_id'),
+                    $db->quoteName('h.item_id'),
+                    $db->quoteName('h.version_note'),
+                    $db->quoteName('h.save_date'),
+                    $db->quoteName('h.editor_user_id'),
+                    $db->quoteName('h.character_count'),
+                    $db->quoteName('h.sha1_hash'),
+                    $db->quoteName('h.version_data'),
+                    $db->quoteName('h.keep_forever'),
+                ]
+            )
+        )
+            ->from($db->quoteName('#__history', 'h'))
+            ->where($db->quoteName('h.item_id') . ' = :itemid')
+            ->bind(':itemid', $itemId, ParameterType::STRING)
+
+        // Join over the users for the editor
+            ->select($db->quoteName('uc.name', 'editor'))
+            ->join(
+                'LEFT',
+                $db->quoteName('#__users', 'uc'),
+                $db->quoteName('uc.id') . ' = ' . $db->quoteName('h.editor_user_id')
+            );
+
+        // Add the list ordering clause.
+        $orderCol  = $this->state->get('list.ordering');
+        $orderDirn = $this->state->get('list.direction');
+        $query->order($db->quoteName($orderCol) . $orderDirn);
+
+        return $query;
+    }
+
+    /**
+     * Get the sha1 hash value for the current item being edited.
+     *
+     * @return  string  sha1 hash of row data
+     *
+     * @since   3.2
+     */
+    protected function getSha1Hash()
+    {
+        $result    = false;
+        $item_id   = Factory::getApplication()->getInput()->getCmd('item_id', '');
+        $typeAlias = explode('.', $item_id);
+        Table::addIncludePath(JPATH_ADMINISTRATOR . '/components/' . $typeAlias[0] . '/tables');
+        $typeTable = $this->getTable('ContentType');
+        $typeTable->load(['type_alias' => $typeAlias[0] . '.' . $typeAlias[1]]);
+        $contentTable = $typeTable->getContentTable();
+
+        if ($contentTable && $contentTable->load($typeAlias[2])) {
+            $helper = new CMSHelper();
+
+            $dataObject = $helper->getDataObject($contentTable);
+            $result     = $this->getTable('ContentHistory')->getSha1(json_encode($dataObject), $typeTable);
+        }
+
+        return $result;
+    }
+}

administrator/components/com_contenthistory/src/Model/PreviewModel.php

@@ -0,0 +1,150 @@
+<?php
+
+/**
+ * @package     Joomla.Administrator
+ * @subpackage  com_contenthistory
+ *
+ * @copyright   (C) 2013 Open Source Matters, Inc. <https://www.joomla.org>
+ * @license     GNU General Public License version 2 or later; see LICENSE.txt
+ */
+
+namespace Joomla\Component\Contenthistory\Administrator\Model;
+
+use Joomla\CMS\Access\Exception\NotAllowed;
+use Joomla\CMS\Factory;
+use Joomla\CMS\HTML\HTMLHelper;
+use Joomla\CMS\Language\Text;
+use Joomla\CMS\MVC\Model\ItemModel;
+use Joomla\CMS\Table\ContentHistory;
+use Joomla\CMS\Table\ContentType;
+use Joomla\CMS\Table\Table;
+use Joomla\Component\Contenthistory\Administrator\Helper\ContenthistoryHelper;
+
+// phpcs:disable PSR1.Files.SideEffects
+\defined('_JEXEC') or die;
+// phpcs:enable PSR1.Files.SideEffects
+
+/**
+ * Methods supporting a list of contenthistory records.
+ *
+ * @since  3.2
+ */
+class PreviewModel extends ItemModel
+{
+    /**
+     * Method to get a version history row.
+     *
+     * @param   integer  $pk  The id of the item
+     *
+     * @return  \stdClass|boolean    On success, standard object with row data. False on failure.
+     *
+     * @since   3.2
+     *
+     * @throws  NotAllowed   Thrown if not authorised to edit an item
+     */
+    public function getItem($pk = null)
+    {
+        /** @var ContentHistory $table */
+        $table     = $this->getTable('ContentHistory');
+        $versionId = Factory::getApplication()->getInput()->getInt('version_id');
+
+        if (!$versionId || \is_array($versionId) || !$table->load($versionId)) {
+            return false;
+        }
+
+        $user = $this->getCurrentUser();
+
+        // Access check
+        if (!$user->authorise('core.edit', $table->item_id) && !$this->canEdit($table)) {
+            throw new NotAllowed(Text::_('JERROR_ALERTNOAUTHOR'), 403);
+        }
+
+        $result               = new \stdClass();
+        $result->version_note = $table->version_note;
+        $result->data         = ContenthistoryHelper::prepareData($table);
+
+        // Let's use custom calendars when present
+        $result->save_date = HTMLHelper::_('date', $table->save_date, Text::_('DATE_FORMAT_LC6'));
+
+        $dateProperties = [
+            'modified_time',
+            'created_time',
+            'modified',
+            'created',
+            'checked_out_time',
+            'publish_up',
+            'publish_down',
+        ];
+
+        $nullDate = $this->getDatabase()->getNullDate();
+
+        foreach ($dateProperties as $dateProperty) {
+            if (
+                property_exists($result->data, $dateProperty)
+                && $result->data->$dateProperty->value !== null
+                && $result->data->$dateProperty->value !== $nullDate
+            ) {
+                $result->data->$dateProperty->value = HTMLHelper::_(
+                    'date',
+                    $result->data->$dateProperty->value,
+                    Text::_('DATE_FORMAT_LC6')
+                );
+            }
+        }
+
+        return $result;
+    }
+
+    /**
+     * Method to get a table object, load it if necessary.
+     *
+     * @param   string  $type    The table name. Optional.
+     * @param   string  $prefix  The class prefix. Optional.
+     * @param   array   $config  Configuration array for model. Optional.
+     *
+     * @return  Table   A Table object
+     *
+     * @since   3.2
+     */
+    public function getTable($type = 'ContentHistory', $prefix = 'Joomla\\CMS\\Table\\', $config = [])
+    {
+        return Table::getInstance($type, $prefix, $config);
+    }
+
+    /**
+     * Method to test whether a record is editable
+     *
+     * @param   ContentHistory  $record  A Table object.
+     *
+     * @return  boolean  True if allowed to edit the record. Defaults to the permission set in the component.
+     *
+     * @since   3.6
+     */
+    protected function canEdit($record)
+    {
+        $result = false;
+
+        if (!empty($record->item_id)) {
+            /**
+             * Make sure user has edit privileges for this content item. Note that we use edit permissions
+             * for the content item, not delete permissions for the content history row.
+             */
+            $user   = $this->getCurrentUser();
+            $result = $user->authorise('core.edit', $record->item_id);
+
+            // Finally try session (this catches edit.own case too)
+            if (!$result) {
+                /** @var ContentType $contentTypeTable */
+                $contentTypeTable = $this->getTable('ContentType');
+
+                $typeAlias        = explode('.', $record->item_id);
+                $id               = array_pop($typeAlias);
+                $typeAlias        = implode('.', $typeAlias);
+                $typeEditables    = (array) Factory::getApplication()->getUserState(str_replace('.', '.edit.', $contentTypeTable->type_alias) . '.id');
+                $result           = \in_array((int) $id, $typeEditables);
+            }
+        }
+
+        return $result;
+    }
+}

administrator/components/com_contenthistory/src/View/Compare/HtmlView.php

@@ -0,0 +1,62 @@
+<?php
+
+/**
+ * @package     Joomla.Administrator
+ * @subpackage  com_contenthistory
+ *
+ * @copyright   (C) 2013 Open Source Matters, Inc. <https://www.joomla.org>
+ * @license     GNU General Public License version 2 or later; see LICENSE.txt
+ */
+
+namespace Joomla\Component\Contenthistory\Administrator\View\Compare;
+
+use Joomla\CMS\MVC\View\GenericDataException;
+use Joomla\CMS\MVC\View\HtmlView as BaseHtmlView;
+
+// phpcs:disable PSR1.Files.SideEffects
+\defined('_JEXEC') or die;
+// phpcs:enable PSR1.Files.SideEffects
+
+/**
+ * View class for a list of contenthistory.
+ *
+ * @since  3.2
+ */
+class HtmlView extends BaseHtmlView
+{
+    /**
+     * An array of items
+     *
+     * @var  array
+     */
+    protected $items;
+
+    /**
+     * The model state
+     *
+     * @var  \Joomla\Registry\Registry
+     */
+    protected $state;
+
+    /**
+     * Method to display the view.
+     *
+     * @param   string  $tpl  A template file to load. [optional]
+     *
+     * @return  void
+     *
+     * @since   3.2
+     */
+    public function display($tpl = null)
+    {
+        $this->state = $this->get('State');
+        $this->items = $this->get('Items');
+
+        // Check for errors.
+        if (\count($errors = $this->get('Errors'))) {
+            throw new GenericDataException(implode("\n", $errors), 500);
+        }
+
+        parent::display($tpl);
+    }
+}

administrator/components/com_contenthistory/src/View/History/HtmlView.php

@@ -0,0 +1,148 @@
+<?php
+
+/**
+ * @package     Joomla.Administrator
+ * @subpackage  com_contenthistory
+ *
+ * @copyright   (C) 2013 Open Source Matters, Inc. <https://www.joomla.org>
+ * @license     GNU General Public License version 2 or later; see LICENSE.txt
+ */
+
+namespace Joomla\Component\Contenthistory\Administrator\View\History;
+
+use Joomla\CMS\Factory;
+use Joomla\CMS\Filter\InputFilter;
+use Joomla\CMS\MVC\View\GenericDataException;
+use Joomla\CMS\MVC\View\HtmlView as BaseHtmlView;
+use Joomla\CMS\Pagination\Pagination;
+use Joomla\CMS\Router\Route;
+use Joomla\CMS\Session\Session;
+use Joomla\CMS\Toolbar\Toolbar;
+use Joomla\CMS\Toolbar\ToolbarFactoryInterface;
+
+// phpcs:disable PSR1.Files.SideEffects
+\defined('_JEXEC') or die;
+// phpcs:enable PSR1.Files.SideEffects
+
+/**
+ * View class for a list of contenthistory.
+ *
+ * @since  3.2
+ */
+class HtmlView extends BaseHtmlView
+{
+    /**
+     * An array of items
+     *
+     * @var  array
+     */
+    protected $items;
+
+    /**
+     * The model state
+     *
+     * @var  Pagination
+     */
+    protected $pagination;
+
+    /**
+     * The model state
+     *
+     * @var  \Joomla\Registry\Registry
+     */
+    protected $state;
+
+    /**
+     * The toolbar for the history modal. Note this is rendered inside the modal rather than using the regular module
+     *
+     * @var  Toolbar
+     */
+    protected $toolbar;
+
+    /**
+     * Method to display the view.
+     *
+     * @param   string  $tpl  A template file to load. [optional]
+     *
+     * @return  void
+     *
+     * @since   3.2
+     */
+    public function display($tpl = null)
+    {
+        $this->state      = $this->get('State');
+        $this->items      = $this->get('Items');
+        $this->pagination = $this->get('Pagination');
+
+        // Check for errors.
+        if (\count($errors = $this->get('Errors'))) {
+            throw new GenericDataException(implode("\n", $errors), 500);
+        }
+
+        $this->toolbar = $this->addToolbar();
+
+        parent::display($tpl);
+    }
+
+    /**
+     * Add the page toolbar.
+     *
+     * @return  Toolbar
+     *
+     * @since  4.0.0
+     */
+    protected function addToolbar(): Toolbar
+    {
+        /** @var Toolbar $toolbar */
+        $toolbar = Factory::getContainer()->get(ToolbarFactoryInterface::class)->createToolbar('toolbar');
+
+        // Cache a session token for reuse throughout.
+        $token = Session::getFormToken();
+
+        // Clean up input to ensure a clean url.
+        $filter     = InputFilter::getInstance();
+        $aliasArray = explode('.', $this->state->item_id);
+
+        if ($aliasArray[1] === 'category') {
+            $option = 'com_categories';
+            $append = '&amp;extension=' . $filter->clean($aliasArray[0], 'cmd');
+        } else {
+            $option = $aliasArray[0];
+            $append = '';
+        }
+
+        $task       = $filter->clean($aliasArray[1], 'cmd') . '.loadhistory';
+
+        // Build the final urls.
+        $loadUrl    = Route::_('index.php?option=' . $filter->clean($option, 'cmd') . $append . '&amp;task=' . $task . '&amp;' . $token . '=1');
+        $previewUrl = Route::_('index.php?option=com_contenthistory&view=preview&layout=preview&tmpl=component&' . $token . '=1');
+        $compareUrl = Route::_('index.php?option=com_contenthistory&view=compare&layout=compare&tmpl=component&' . $token . '=1');
+
+        $toolbar->basicButton('load', 'COM_CONTENTHISTORY_BUTTON_LOAD')
+            ->attributes(['data-url' => $loadUrl])
+            ->icon('icon-upload')
+            ->buttonClass('btn btn-success')
+            ->listCheck(true);
+
+        $toolbar->basicButton('preview', 'COM_CONTENTHISTORY_BUTTON_PREVIEW')
+            ->attributes(['data-url' => $previewUrl])
+            ->icon('icon-search')
+            ->listCheck(true);
+
+        $toolbar->basicButton('compare', 'COM_CONTENTHISTORY_BUTTON_COMPARE')
+            ->attributes(['data-url' => $compareUrl])
+            ->icon('icon-search-plus')
+            ->listCheck(true);
+
+        $toolbar->basicButton('keep', 'COM_CONTENTHISTORY_BUTTON_KEEP', 'history.keep')
+            ->icon('icon-lock')
+            ->listCheck(true);
+
+        $toolbar->basicButton('delete', 'COM_CONTENTHISTORY_BUTTON_DELETE', 'history.delete')
+            ->buttonClass('btn btn-danger')
+            ->icon('icon-times')
+            ->listCheck(true);
+
+        return $toolbar;
+    }
+}

administrator/components/com_contenthistory/src/View/Preview/HtmlView.php

@@ -0,0 +1,69 @@
+<?php
+
+/**
+ * @package     Joomla.Administrator
+ * @subpackage  com_contenthistory
+ *
+ * @copyright   (C) 2013 Open Source Matters, Inc. <https://www.joomla.org>
+ * @license     GNU General Public License version 2 or later; see LICENSE.txt
+ */
+
+namespace Joomla\Component\Contenthistory\Administrator\View\Preview;
+
+use Joomla\CMS\Language\Text;
+use Joomla\CMS\MVC\View\GenericDataException;
+use Joomla\CMS\MVC\View\HtmlView as BaseHtmlView;
+
+// phpcs:disable PSR1.Files.SideEffects
+\defined('_JEXEC') or die;
+// phpcs:enable PSR1.Files.SideEffects
+
+/**
+ * View class for a list of contenthistory.
+ *
+ * @since  1.5
+ */
+class HtmlView extends BaseHtmlView
+{
+    /**
+     * An array of items
+     *
+     * @var  \stdClass|false
+     */
+    protected $item;
+
+    /**
+     * The model state
+     *
+     * @var  \Joomla\Registry\Registry
+     */
+    protected $state;
+
+    /**
+     * Method to display the view.
+     *
+     * @param   string  $tpl  A template file to load. [optional]
+     *
+     * @return  void
+     *
+     * @since   3.2
+     */
+    public function display($tpl = null)
+    {
+        $this->state = $this->get('State');
+        $this->item  = $this->get('Item');
+
+        if (false === $this->item) {
+            $this->getLanguage()->load('com_content', JPATH_SITE, null, true);
+
+            throw new \Exception(Text::_('COM_CONTENT_ERROR_ARTICLE_NOT_FOUND'), 404);
+        }
+
+        // Check for errors.
+        if (\count($errors = $this->get('Errors'))) {
+            throw new GenericDataException(implode("\n", $errors), 500);
+        }
+
+        parent::display($tpl);
+    }
+}

administrator/components/com_contenthistory/tmpl/compare/compare.php

@@ -0,0 +1,82 @@
+<?php
+
+/**
+ * @package     Joomla.Administrator
+ * @subpackage  com_contenthistory
+ *
+ * @copyright   (C) 2013 Open Source Matters, Inc. <https://www.joomla.org>
+ * @license     GNU General Public License version 2 or later; see LICENSE.txt
+ */
+
+defined('_JEXEC') or die;
+
+use Joomla\CMS\Language\Text;
+use Joomla\CMS\Session\Session;
+
+/** @var \Joomla\Component\Contenthistory\Administrator\View\Compare\HtmlView $this */
+
+Session::checkToken('get') or die(Text::_('JINVALID_TOKEN'));
+
+$version2 = $this->items[0];
+$version1 = $this->items[1];
+$object1  = $version1->data;
+$object2  = $version2->data;
+
+/** @var Joomla\CMS\WebAsset\WebAssetManager $wa */
+$wa = $this->getDocument()->getWebAssetManager();
+$wa->useScript('com_contenthistory.admin-compare-compare');
+
+?>
+<div role="main">
+    <h1 class="mb-3"><?php echo Text::_('COM_CONTENTHISTORY_COMPARE_TITLE'); ?></h1>
+
+    <table id="diff" class="table">
+        <caption class="visually-hidden">
+            <?php echo Text::_('COM_CONTENTHISTORY_COMPARE_CAPTION'); ?>
+        </caption>
+        <thead>
+            <tr>
+                <th scope="col" class="w-25"><?php echo Text::_('COM_CONTENTHISTORY_PREVIEW_FIELD'); ?></th>
+                <th scope="col"><?php echo Text::_('COM_CONTENTHISTORY_COMPARE_OLD'); ?></th>
+                <th scope="col"><?php echo Text::_('COM_CONTENTHISTORY_COMPARE_NEW'); ?></th>
+                <th scope="col"><?php echo Text::_('COM_CONTENTHISTORY_COMPARE_DIFF'); ?></th>
+            </tr>
+        </thead>
+        <tbody>
+        <?php foreach ($object1 as $name => $value) : ?>
+            <?php if (isset($value->value) && isset($object2->$name->value) && $value->value != $object2->$name->value) : ?>
+                <?php if (is_object($value->value)) : ?>
+                    <tr>
+                        <td colspan="4">
+                            <strong><?php echo $value->label; ?></strong>
+                        </td>
+                    </tr>
+                    <?php foreach ($value->value as $subName => $subValue) : ?>
+                        <?php $newSubValue = $object2->$name->value->$subName->value ?? ''; ?>
+                        <?php if ($subValue->value || $newSubValue) : ?>
+                            <?php if ($subValue->value != $newSubValue) : ?>
+                                <tr>
+                                    <th scope="row"><em>&nbsp;&nbsp;<?php echo $subValue->label; ?></em></th>
+                                    <td class="original"><?php echo htmlspecialchars($subValue->value, ENT_COMPAT, 'UTF-8'); ?></td>
+                                    <td class="changed" ><?php echo htmlspecialchars($newSubValue, ENT_COMPAT, 'UTF-8'); ?></td>
+                                    <td class="diff">&nbsp;</td>
+                                </tr>
+                            <?php endif; ?>
+                        <?php endif; ?>
+                    <?php endforeach; ?>
+                <?php else : ?>
+                    <tr>
+                        <th scope="row">
+                            <?php echo $value->label; ?>
+                        </th>
+                        <td class="original"><?php echo htmlspecialchars($value->value); ?></td>
+                        <?php $object2->$name->value = is_object($object2->$name->value) ? json_encode($object2->$name->value) : $object2->$name->value; ?>
+                        <td class="changed"><?php echo htmlspecialchars($object2->$name->value, ENT_COMPAT, 'UTF-8'); ?></td>
+                        <td class="diff">&nbsp;</td>
+                    </tr>
+                <?php endif; ?>
+            <?php endif; ?>
+        <?php endforeach; ?>
+        </tbody>
+    </table>
+</div>

administrator/components/com_contenthistory/tmpl/history/modal.php

@@ -0,0 +1,124 @@
+<?php
+
+/**
+ * @package     Joomla.Administrator
+ * @subpackage  com_contenthistory
+ *
+ * @copyright   (C) 2013 Open Source Matters, Inc. <https://www.joomla.org>
+ * @license     GNU General Public License version 2 or later; see LICENSE.txt
+ */
+
+defined('_JEXEC') or die;
+
+use Joomla\CMS\HTML\HTMLHelper;
+use Joomla\CMS\Language\Text;
+use Joomla\CMS\Router\Route;
+use Joomla\CMS\Session\Session;
+
+/** @var \Joomla\Component\Contenthistory\Administrator\View\History\HtmlView $this */
+
+Session::checkToken('get') or die(Text::_('JINVALID_TOKEN'));
+
+$hash           = $this->state->get('sha1_hash');
+$formUrl        = 'index.php?option=com_contenthistory&view=history&layout=modal&tmpl=component&item_id=' . $this->state->get('item_id') . '&' . Session::getFormToken() . '=1';
+
+Text::script('COM_CONTENTHISTORY_BUTTON_SELECT_ONE_VERSION', true);
+Text::script('COM_CONTENTHISTORY_BUTTON_SELECT_TWO_VERSIONS', true);
+Text::script('JLIB_HTML_PLEASE_MAKE_A_SELECTION_FROM_THE_LIST');
+
+$inlineJS = <<<JS
+document.querySelectorAll('.js-link-open-window').forEach((link) => link.addEventListener('click', (e) => {
+  e.preventDefault();
+  window.open(link.dataset.url, 'win2', 'width=800,height=600,resizable=yes,scrollbars=yes')
+}));
+JS;
+
+/** @var Joomla\CMS\WebAsset\WebAssetManager $wa */
+$wa = $this->getDocument()->getWebAssetManager();
+$wa->useScript('multiselect')
+    ->useScript('com_contenthistory.admin-history-modal')
+    ->useScript('list-view')
+    ->addInlineScript($inlineJS, [], ['type' => 'module']);
+?>
+<div class="container-popup">
+    <div id="subhead" class="subhead noshadow mb-3">
+        <?php echo $this->toolbar->render(); ?>
+    </div>
+    <form action="<?php echo Route::_($formUrl); ?>" method="post" name="adminForm" id="adminForm">
+        <table class="table table-sm">
+            <caption class="visually-hidden">
+                <?php echo Text::_('COM_CONTENTHISTORY_VERSION_CAPTION'); ?>
+            </caption>
+            <thead>
+                <tr>
+                    <td class="w-1 text-center">
+                        <input class="form-check-input" type="checkbox" name="checkall-toggle" value="" title="<?php echo Text::_('JGLOBAL_CHECK_ALL'); ?>" onclick="Joomla.checkAll(this)">
+                    </td>
+                    <th scope="col" class="w-15">
+                        <?php echo Text::_('JDATE'); ?>
+                    </th>
+                    <th scope="col" class="w-15 d-none d-md-table-cell">
+                        <?php echo Text::_('COM_CONTENTHISTORY_VERSION_NOTE'); ?>
+                    </th>
+                    <th scope="col" class="w-10">
+                        <?php echo Text::_('COM_CONTENTHISTORY_KEEP_VERSION'); ?>
+                    </th>
+                    <th scope="col" class="w-15 d-none d-md-table-cell">
+                        <?php echo Text::_('JAUTHOR'); ?>
+                    </th>
+                    <th scope="col" class="w-10 text-end">
+                        <?php echo Text::_('COM_CONTENTHISTORY_CHARACTER_COUNT'); ?>
+                    </th>
+                </tr>
+            </thead>
+            <tbody>
+                <?php $i = 0; ?>
+                <?php foreach ($this->items as $item) : ?>
+                    <tr class="row<?php echo $i % 2; ?>">
+                        <td class="text-center">
+                            <?php echo HTMLHelper::_('grid.id', $i, $item->version_id, false, 'cid', 'cb', $item->save_date); ?>
+                        </td>
+                        <th scope="row">
+                            <a href="#" class="js-link-open-window save-date" data-url="<?php echo Route::_('index.php?option=com_contenthistory&view=preview&layout=preview&tmpl=component&' . Session::getFormToken() . '=1&version_id=' . $item->version_id); ?>">
+                                <?php echo HTMLHelper::_('date', $item->save_date, Text::_('DATE_FORMAT_LC6')); ?>
+                            </a>
+                            <?php if ($item->sha1_hash == $hash) : ?>
+                                <span class="icon-star" aria-hidden="true"></span><span class="visually-hidden"><?php echo Text::_('JCURRENT'); ?></span>
+                            <?php endif; ?>
+                        </th>
+                        <td class="d-none d-md-table-cell">
+                            <?php echo htmlspecialchars($item->version_note); ?>
+                        </td>
+                        <td>
+                            <?php if ($item->keep_forever) : ?>
+                                <button type="button" class="js-grid-item-action btn btn-secondary btn-sm" data-item-id="cb<?php echo $i; ?>" data-item-task="history.keep">
+                                    <?php echo Text::_('JYES'); ?>
+                                    &nbsp;<span class="icon-lock" aria-hidden="true"></span>
+                                </button>
+                            <?php else : ?>
+                                <button type="button" class="js-grid-item-action btn btn-secondary btn-sm" data-item-id="cb<?php echo $i; ?>" data-item-task="history.keep">
+                                    <?php echo Text::_('JNO'); ?>
+                                </button>
+                            <?php endif; ?>
+                        </td>
+                        <td class="d-none d-md-table-cell">
+                            <?php echo empty($item->editor) ? $item->editor_user_id : htmlspecialchars($item->editor); ?>
+                        </td>
+                        <td class="text-end">
+                            <?php echo number_format((int) $item->character_count, 0, Text::_('DECIMALS_SEPARATOR'), Text::_('THOUSANDS_SEPARATOR')); ?>
+                        </td>
+                    </tr>
+                    <?php $i++; ?>
+                <?php endforeach; ?>
+            </tbody>
+        </table>
+
+        <?php /* load the pagination. */ ?>
+        <?php echo $this->pagination->getListFooter(); ?>
+
+        <input type="hidden" name="task" value="">
+        <input type="hidden" name="boxchecked" value="0">
+        <?php echo HTMLHelper::_('form.token'); ?>
+
+    </form>
+</div>

administrator/components/com_contenthistory/tmpl/preview/preview.php

@@ -0,0 +1,67 @@
+<?php
+
+/**
+ * @package     Joomla.Administrator
+ * @subpackage  com_contenthistory
+ *
+ * @copyright   (C) 2013 Open Source Matters, Inc. <https://www.joomla.org>
+ * @license     GNU General Public License version 2 or later; see LICENSE.txt
+ */
+
+defined('_JEXEC') or die;
+
+use Joomla\CMS\Language\Text;
+use Joomla\CMS\Session\Session;
+
+/** @var \Joomla\Component\Contenthistory\Administrator\View\Preview\HtmlView $this */
+
+Session::checkToken('get') or die(Text::_('JINVALID_TOKEN'));
+
+?>
+<div role="main">
+    <h1>
+        <?php echo Text::sprintf('COM_CONTENTHISTORY_PREVIEW_SUBTITLE_DATE', $this->item->save_date); ?>
+    </h1>
+    <?php if ($this->item->version_note) : ?>
+        <h2>
+            <?php echo Text::sprintf('COM_CONTENTHISTORY_PREVIEW_SUBTITLE', $this->item->version_note); ?>
+        </h2>
+    <?php endif; ?>
+
+    <table class="table">
+        <caption class="visually-hidden">
+            <?php echo Text::_('COM_CONTENTHISTORY_PREVIEW_CAPTION'); ?>
+        </caption>
+        <thead>
+            <tr>
+                <th class="w-25" scope="col"><?php echo Text::_('COM_CONTENTHISTORY_PREVIEW_FIELD'); ?></th>
+                <th scope="col"><?php echo Text::_('COM_CONTENTHISTORY_PREVIEW_VALUE'); ?></th>
+            </tr>
+        </thead>
+        <tbody>
+        <?php foreach ($this->item->data as $name => $value) : ?>
+            <?php if (is_object($value->value)) : ?>
+                <tr>
+                    <td colspan="2">
+                        <?php echo $value->label; ?>
+                    </td>
+                </tr>
+                <?php foreach ($value->value as $subName => $subValue) : ?>
+                    <?php if ($subValue && isset($subValue->value)) : ?>
+                        <?php $subValue->value = (\is_object($subValue->value) || \is_array($subValue->value)) ? \json_encode($subValue->value, \JSON_UNESCAPED_UNICODE) : $subValue->value; ?>
+                        <tr>
+                            <th scope="row"><em>&nbsp;&nbsp;<?php echo $subValue->label; ?></em></th>
+                            <td><?php echo $subValue->value; ?></td>
+                        </tr>
+                    <?php endif; ?>
+                <?php endforeach; ?>
+            <?php else : ?>
+                <tr>
+                    <th scope="row"><?php echo $value->label; ?></th>
+                    <td><?php echo $value->value; ?></td>
+                </tr>
+            <?php endif; ?>
+        <?php endforeach; ?>
+        </tbody>
+    </table>
+</div>