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+<?php
+/**
+ * A content object represents page content, e.g. the text to show on a page.
+ * Content objects have no knowledge about how they relate to wiki pages.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ * http://www.gnu.org/copyleft/gpl.html
+ *
+ * @since 1.21
+ *
+ * @file
+ * @ingroup Content
+ *
+ * @author Daniel Kinzler
+ */
+
+/**
+ * Base interface for content objects.
+ *
+ * @ingroup Content
+ */
+interface Content {
+
+	/**
+	 * @since 1.21
+	 *
+	 * @return string A string representing the content in a way useful for
+	 *   building a full text search index. If no useful representation exists,
+	 *   this method returns an empty string.
+	 *
+	 * @todo Test that this actually works
+	 * @todo Make sure this also works with LuceneSearch / WikiSearch
+	 */
+	public function getTextForSearchIndex();
+
+	/**
+	 * @since 1.21
+	 *
+	 * @return string|bool The wikitext to include when another page includes this
+	 * content, or false if the content is not includable in a wikitext page.
+	 *
+	 * @todo Allow native handling, bypassing wikitext representation, like
+	 *  for includable special pages.
+	 * @todo Allow transclusion into other content models than Wikitext!
+	 * @todo Used in WikiPage and MessageCache to get message text. Not so
+	 *  nice. What should we use instead?!
+	 */
+	public function getWikitextForTransclusion();
+
+	/**
+	 * Returns a textual representation of the content suitable for use in edit
+	 * summaries and log messages.
+	 *
+	 * @since 1.21
+	 *
+	 * @param int $maxLength Maximum length of the summary text.
+	 *
+	 * @return string The summary text.
+	 */
+	public function getTextForSummary( $maxLength = 250 );
+
+	/**
+	 * Returns native representation of the data. Interpretation depends on
+	 * the data model used, as given by getDataModel().
+	 *
+	 * @since 1.21
+	 *
+	 * @return mixed The native representation of the content. Could be a
+	 *    string, a nested array structure, an object, a binary blob...
+	 *    anything, really.
+	 *
+	 * @note Caller must be aware of content model!
+	 */
+	public function getNativeData();
+
+	/**
+	 * Returns the content's nominal size in "bogo-bytes".
+	 *
+	 * @return int
+	 */
+	public function getSize();
+
+	/**
+	 * Returns the ID of the content model used by this Content object.
+	 * Corresponds to the CONTENT_MODEL_XXX constants.
+	 *
+	 * @since 1.21
+	 *
+	 * @return string The model id
+	 */
+	public function getModel();
+
+	/**
+	 * Convenience method that returns the ContentHandler singleton for handling
+	 * the content model that this Content object uses.
+	 *
+	 * Shorthand for ContentHandler::getForContent( $this )
+	 *
+	 * @since 1.21
+	 *
+	 * @return ContentHandler
+	 */
+	public function getContentHandler();
+
+	/**
+	 * Convenience method that returns the default serialization format for the
+	 * content model that this Content object uses.
+	 *
+	 * Shorthand for $this->getContentHandler()->getDefaultFormat()
+	 *
+	 * @since 1.21
+	 *
+	 * @return string
+	 */
+	public function getDefaultFormat();
+
+	/**
+	 * Convenience method that returns the list of serialization formats
+	 * supported for the content model that this Content object uses.
+	 *
+	 * Shorthand for $this->getContentHandler()->getSupportedFormats()
+	 *
+	 * @since 1.21
+	 *
+	 * @return string[] List of supported serialization formats
+	 */
+	public function getSupportedFormats();
+
+	/**
+	 * Returns true if $format is a supported serialization format for this
+	 * Content object, false if it isn't.
+	 *
+	 * Note that this should always return true if $format is null, because null
+	 * stands for the default serialization.
+	 *
+	 * Shorthand for $this->getContentHandler()->isSupportedFormat( $format )
+	 *
+	 * @since 1.21
+	 *
+	 * @param string $format The serialization format to check.
+	 *
+	 * @return bool Whether the format is supported
+	 */
+	public function isSupportedFormat( $format );
+
+	/**
+	 * Convenience method for serializing this Content object.
+	 *
+	 * Shorthand for $this->getContentHandler()->serializeContent( $this, $format )
+	 *
+	 * @since 1.21
+	 *
+	 * @param string $format The desired serialization format, or null for the default format.
+	 *
+	 * @return string Serialized form of this Content object.
+	 */
+	public function serialize( $format = null );
+
+	/**
+	 * Returns true if this Content object represents empty content.
+	 *
+	 * @since 1.21
+	 *
+	 * @return bool Whether this Content object is empty
+	 */
+	public function isEmpty();
+
+	/**
+	 * Returns whether the content is valid. This is intended for local validity
+	 * checks, not considering global consistency.
+	 *
+	 * Content needs to be valid before it can be saved.
+	 *
+	 * This default implementation always returns true.
+	 *
+	 * @since 1.21
+	 *
+	 * @return bool
+	 */
+	public function isValid();
+
+	/**
+	 * Returns true if this Content objects is conceptually equivalent to the
+	 * given Content object.
+	 *
+	 * Contract:
+	 *
+	 * - Will return false if $that is null.
+	 * - Will return true if $that === $this.
+	 * - Will return false if $that->getModel() != $this->getModel().
+	 * - Will return false if $that->getNativeData() is not equal to $this->getNativeData(),
+	 *   where the meaning of "equal" depends on the actual data model.
+	 *
+	 * Implementations should be careful to make equals() transitive and reflexive:
+	 *
+	 * - $a->equals( $b ) <=> $b->equals( $a )
+	 * - $a->equals( $b ) &&  $b->equals( $c ) ==> $a->equals( $c )
+	 *
+	 * @since 1.21
+	 *
+	 * @param Content $that The Content object to compare to.
+	 *
+	 * @return bool True if this Content object is equal to $that, false otherwise.
+	 */
+	public function equals( Content $that = null );
+
+	/**
+	 * Return a copy of this Content object. The following must be true for the
+	 * object returned:
+	 *
+	 * if $copy = $original->copy()
+	 *
+	 * - get_class($original) === get_class($copy)
+	 * - $original->getModel() === $copy->getModel()
+	 * - $original->equals( $copy )
+	 *
+	 * If and only if the Content object is immutable, the copy() method can and
+	 * should return $this. That is, $copy === $original may be true, but only
+	 * for immutable content objects.
+	 *
+	 * @since 1.21
+	 *
+	 * @return Content A copy of this object
+	 */
+	public function copy();
+
+	/**
+	 * Returns true if this content is countable as a "real" wiki page, provided
+	 * that it's also in a countable location (e.g. a current revision in the
+	 * main namespace).
+	 *
+	 * @since 1.21
+	 *
+	 * @param bool|null $hasLinks If it is known whether this content contains
+	 *    links, provide this information here, to avoid redundant parsing to
+	 *    find out.
+	 *
+	 * @return bool
+	 */
+	public function isCountable( $hasLinks = null );
+
+	/**
+	 * Parse the Content object and generate a ParserOutput from the result.
+	 * $result->getText() can be used to obtain the generated HTML. If no HTML
+	 * is needed, $generateHtml can be set to false; in that case,
+	 * $result->getText() may return null.
+	 *
+	 * @note To control which options are used in the cache key for the
+	 *       generated parser output, implementations of this method
+	 *       may call ParserOutput::recordOption() on the output object.
+	 *
+	 * @param Title $title The page title to use as a context for rendering.
+	 * @param int $revId Optional revision ID being rendered.
+	 * @param ParserOptions $options Any parser options.
+	 * @param bool $generateHtml Whether to generate HTML (default: true). If false,
+	 *        the result of calling getText() on the ParserOutput object returned by
+	 *        this method is undefined.
+	 *
+	 * @since 1.21
+	 *
+	 * @return ParserOutput
+	 */
+	public function getParserOutput( Title $title, $revId = null,
+		ParserOptions $options = null, $generateHtml = true );
+
+	// TODO: make RenderOutput and RenderOptions base classes
+
+	/**
+	 * Returns a list of DataUpdate objects for recording information about this
+	 * Content in some secondary data store. If the optional second argument,
+	 * $old, is given, the updates may model only the changes that need to be
+	 * made to replace information about the old content with information about
+	 * the new content.
+	 *
+	 * This default implementation calls
+	 * $this->getParserOutput( $content, $title, null, null, false ),
+	 * and then calls getSecondaryDataUpdates( $title, $recursive ) on the
+	 * resulting ParserOutput object.
+	 *
+	 * Subclasses may implement this to determine the necessary updates more
+	 * efficiently, or make use of information about the old content.
+	 *
+	 * @note Implementations should call the SecondaryDataUpdates hook, like
+	 *   AbstractContent does.
+	 *
+	 * @param Title $title The context for determining the necessary updates
+	 * @param Content $old An optional Content object representing the
+	 *    previous content, i.e. the content being replaced by this Content
+	 *    object.
+	 * @param bool $recursive Whether to include recursive updates (default:
+	 *    false).
+	 * @param ParserOutput $parserOutput Optional ParserOutput object.
+	 *    Provide if you have one handy, to avoid re-parsing of the content.
+	 *
+	 * @return DataUpdate[] A list of DataUpdate objects for putting information
+	 *    about this content object somewhere.
+	 *
+	 * @since 1.21
+	 */
+	public function getSecondaryDataUpdates( Title $title, Content $old = null,
+		$recursive = true, ParserOutput $parserOutput = null );
+
+	/**
+	 * Construct the redirect destination from this content and return an
+	 * array of Titles, or null if this content doesn't represent a redirect.
+	 * The last element in the array is the final destination after all redirects
+	 * have been resolved (up to $wgMaxRedirects times).
+	 *
+	 * @since 1.21
+	 *
+	 * @return Title[]|null List of Titles, with the destination last.
+	 */
+	public function getRedirectChain();
+
+	/**
+	 * Construct the redirect destination from this content and return a Title,
+	 * or null if this content doesn't represent a redirect.
+	 * This will only return the immediate redirect target, useful for
+	 * the redirect table and other checks that don't need full recursion.
+	 *
+	 * @since 1.21
+	 *
+	 * @return Title|null The corresponding Title.
+	 */
+	public function getRedirectTarget();
+
+	/**
+	 * Construct the redirect destination from this content and return the
+	 * Title, or null if this content doesn't represent a redirect.
+	 *
+	 * This will recurse down $wgMaxRedirects times or until a non-redirect
+	 * target is hit in order to provide (hopefully) the Title of the final
+	 * destination instead of another redirect.
+	 *
+	 * There is usually no need to override the default behavior, subclasses that
+	 * want to implement redirects should override getRedirectTarget().
+	 *
+	 * @since 1.21
+	 *
+	 * @return Title|null
+	 */
+	public function getUltimateRedirectTarget();
+
+	/**
+	 * Returns whether this Content represents a redirect.
+	 * Shorthand for getRedirectTarget() !== null.
+	 *
+	 * @since 1.21
+	 *
+	 * @return bool
+	 */
+	public function isRedirect();
+
+	/**
+	 * If this Content object is a redirect, this method updates the redirect target.
+	 * Otherwise, it does nothing.
+	 *
+	 * @since 1.21
+	 *
+	 * @param Title $target The new redirect target
+	 *
+	 * @return Content A new Content object with the updated redirect (or $this
+	 *   if this Content object isn't a redirect)
+	 */
+	public function updateRedirect( Title $target );
+
+	/**
+	 * Returns the section with the given ID.
+	 *
+	 * @since 1.21
+	 *
+	 * @param string|int $sectionId Section identifier as a number or string
+	 * (e.g. 0, 1 or 'T-1'). The ID "0" retrieves the section before the first heading, "1" the
+	 * text between the first heading (included) and the second heading (excluded), etc.
+	 *
+	 * @return Content|bool|null The section, or false if no such section
+	 *    exist, or null if sections are not supported.
+	 */
+	public function getSection( $sectionId );
+
+	/**
+	 * Replaces a section of the content and returns a Content object with the
+	 * section replaced.
+	 *
+	 * @since 1.21
+	 *
+	 * @param string|int|null|bool $sectionId Section identifier as a number or string
+	 * (e.g. 0, 1 or 'T-1'), null/false or an empty string for the whole page
+	 * or 'new' for a new section.
+	 * @param Content $with New content of the section
+	 * @param string $sectionTitle New section's subject, only if $section is 'new'
+	 *
+	 * @return string|null Complete article text, or null if error
+	 */
+	public function replaceSection( $sectionId, Content $with, $sectionTitle = '' );
+
+	/**
+	 * Returns a Content object with pre-save transformations applied (or this
+	 * object if no transformations apply).
+	 *
+	 * @since 1.21
+	 *
+	 * @param Title $title
+	 * @param User $user
+	 * @param ParserOptions $parserOptions
+	 *
+	 * @return Content
+	 */
+	public function preSaveTransform( Title $title, User $user, ParserOptions $parserOptions );
+
+	/**
+	 * Returns a new WikitextContent object with the given section heading
+	 * prepended, if supported. The default implementation just returns this
+	 * Content object unmodified, ignoring the section header.
+	 *
+	 * @since 1.21
+	 *
+	 * @param string $header
+	 *
+	 * @return Content
+	 */
+	public function addSectionHeader( $header );
+
+	/**
+	 * Returns a Content object with preload transformations applied (or this
+	 * object if no transformations apply).
+	 *
+	 * @since 1.21
+	 *
+	 * @param Title $title
+	 * @param ParserOptions $parserOptions
+	 * @param array $params
+	 *
+	 * @return Content
+	 */
+	public function preloadTransform( Title $title, ParserOptions $parserOptions, $params = [] );
+
+	/**
+	 * Prepare Content for saving. Called before Content is saved by WikiPage::doEditContent() and in
+	 * similar places.
+	 *
+	 * This may be used to check the content's consistency with global state. This function should
+	 * NOT write any information to the database.
+	 *
+	 * Note that this method will usually be called inside the same transaction
+	 * bracket that will be used to save the new revision.
+	 *
+	 * Note that this method is called before any update to the page table is
+	 * performed. This means that $page may not yet know a page ID.
+	 *
+	 * @since 1.21
+	 *
+	 * @param WikiPage $page The page to be saved.
+	 * @param int $flags Bitfield for use with EDIT_XXX constants, see WikiPage::doEditContent()
+	 * @param int $parentRevId The ID of the current revision
+	 * @param User $user
+	 *
+	 * @return Status A status object indicating whether the content was
+	 *   successfully prepared for saving. If the returned status indicates
+	 *   an error, a rollback will be performed and the transaction aborted.
+	 *
+	 * @see WikiPage::doEditContent()
+	 */
+	public function prepareSave( WikiPage $page, $flags, $parentRevId, User $user );
+
+	/**
+	 * Returns a list of updates to perform when this content is deleted.
+	 * The necessary updates may be taken from the Content object, or depend on
+	 * the current state of the database.
+	 *
+	 * @since 1.21
+	 *
+	 * @param WikiPage $page The deleted page
+	 * @param ParserOutput|null $parserOutput Optional parser output object
+	 *    for efficient access to meta-information about the content object.
+	 *    Provide if you have one handy.
+	 *
+	 * @return DeferrableUpdate[] A list of DeferrableUpdate instances that will clean up the
+	 *    database after deletion.
+	 */
+	public function getDeletionUpdates( WikiPage $page,
+		ParserOutput $parserOutput = null );
+
+	/**
+	 * Returns true if this Content object matches the given magic word.
+	 *
+	 * @since 1.21
+	 *
+	 * @param MagicWord $word The magic word to match
+	 *
+	 * @return bool Whether this Content object matches the given magic word.
+	 */
+	public function matchMagicWord( MagicWord $word );
+
+	/**
+	 * Converts this content object into another content object with the given content model,
+	 * if that is possible.
+	 *
+	 * @param string $toModel The desired content model, use the CONTENT_MODEL_XXX flags.
+	 * @param string $lossy Optional flag, set to "lossy" to allow lossy conversion. If lossy
+	 * conversion is not allowed, full round-trip conversion is expected to work without losing
+	 * information.
+	 *
+	 * @return Content|bool A content object with the content model $toModel, or false if
+	 * that conversion is not supported.
+	 */
+	public function convert( $toModel, $lossy = '' );
+	// @todo ImagePage and CategoryPage interfere with per-content action handlers
+	// @todo nice&sane integration of GeSHi syntax highlighting
+	//   [11:59] <vvv> Hooks are ugly; make CodeHighlighter interface and a
+	//   config to set the class which handles syntax highlighting
+	//   [12:00] <vvv> And default it to a DummyHighlighter
+
+}