<?php

namespace MediaWiki\Extension\DiscussionTools;

use DOMDocument;
use DOMElement;
use DOMNode;
use stdClass;

class CommentModifier {

	private function __construct() {
	}

	/**
	 * Add an attribute to a list item to remove pre-whitespace in Parsoid
	 *
	 * @param DOMElement $listItem List item element
	 */
	private static function whitespaceParsoidHack( DOMElement $listItem ) : void {
		// HACK: Setting data-parsoid removes the whitespace after the list item,
		// which makes nested lists work.
		// This is undocumented behaviour and probably very fragile.
		$listItem->setAttribute( 'data-parsoid', '{}' );
	}

	private static $blockElementTypes = [
		'div', 'p',
		// Tables
		'table', 'tbody', 'thead', 'tfoot', 'caption', 'th', 'tr', 'td',
		// Lists
		'ul', 'ol', 'li', 'dl', 'dt', 'dd',
		// HTML5 heading content
		'h1', 'h2', 'h3', 'h4', 'h5', 'h6', 'hgroup',
		// HTML5 sectioning content
		'article', 'aside', 'body', 'nav', 'section', 'footer', 'header', 'figure',
		'figcaption', 'fieldset', 'details', 'blockquote',
		// Other
		'hr', 'button', 'canvas', 'center', 'col', 'colgroup', 'embed',
		'map', 'object', 'pre', 'progress', 'video'
	];

	/**
	 * @param DOMNode $node Node
	 * @return bool Node is a block element
	 */
	private static function isBlockElement( DOMNode $node ) : bool {
		return $node->nodeType === XML_ELEMENT_NODE &&
			in_array( strtolower( $node->tagName ), self::$blockElementTypes );
	}

	/**
	 * Given a comment and a reply link, add the reply link to its document's DOM tree, at the end of
	 * the comment.
	 *
	 * @param stdClass $comment Comment data returned by parser#groupThreads
	 * @param DOMElement $linkNode Reply link
	 */
	public static function addReplyLink( stdClass $comment, DOMElement $linkNode ) : void {
		$target = $comment->range->endContainer;

		// Skip to the end of the "paragraph". This only looks at tag names and can be fooled by CSS, but
		// avoiding that would be more difficult and slower.
		while ( $target->nextSibling && !self::isBlockElement( $target->nextSibling ) ) {
			$target = $target->nextSibling;
		}

		// Insert the link before trailing whitespace.
		// In the MediaWiki parser output, <ul>/<dl> nodes are preceded by a newline. Normally it isn't
		// visible on the page. But if we insert an inline element (the reply link) after it, it becomes
		// meaningful and gets rendered, which results in additional spacing before some reply links.
		// Split the text node, so that we can insert the link before the trailing whitespace.
		if ( $target->nodeType === XML_TEXT_NODE ) {
			preg_match( '/\s*$/', $target->nodeValue, $matches, PREG_OFFSET_CAPTURE );
			$byteOffset = $matches[0][1];
			$charOffset = mb_strlen(
				substr( $target->nodeValue, 0, $byteOffset )
			);
			$target->splitText( $charOffset );
		}

		$target->parentNode->insertBefore( $linkNode, $target->nextSibling );
	}

	/**
	 * Get a node (if any) that contains the given comment, and nothing else.
	 *
	 * @param stdClass $comment Comment data returned by parser#groupThreads
	 * @return DOMElement|null
	 */
	private static function getFullyCoveredWrapper( $comment ) {
		$ancestor = $comment->range->commonAncestorContainer;

		$isIgnored = function ( $node ) {
			// Ignore empty text nodes
			return $node->nodeType === XML_TEXT_NODE && CommentUtils::htmlTrim( $node->nodeValue ) === '';
		};

		$firstNonemptyChild = function ( $node ) use ( $isIgnored ) {
			$node = $node->firstChild;
			while ( $node && $isIgnored( $node ) ) {
				$node = $node->nextSibling;
			}
			return $node;
		};

		$lastNonemptyChild = function ( $node ) use ( $isIgnored ) {
			$node = $node->lastChild;
			while ( $node && $isIgnored( $node ) ) {
				$node = $node->previousSibling;
			}
			return $node;
		};

		$startMatches = false;
		$node = $ancestor;
		while ( $node ) {
			if ( $comment->range->startContainer === $node && $comment->range->startOffset === 0 ) {
				$startMatches = true;
				break;
			}
			$node = $firstNonemptyChild( $node );
		}

		$endMatches = false;
		$node = $ancestor;
		while ( $node ) {
			$length = ( $node->nodeType === XML_TEXT_NODE ) ?
				strlen( rtrim( $node->nodeValue, "\t\n\f\r " ) ) :
				// PHP bug: childNodes can be null for comment nodes
				// (it should always be a DOMNodeList, even if the node can't have children)
				( $node->childNodes ? $node->childNodes->length : 0 );
			if ( $comment->range->endContainer === $node && $comment->range->endOffset === $length ) {
				$endMatches = true;
				break;
			}
			$node = $lastNonemptyChild( $node );
		}

		if ( $startMatches && $endMatches ) {
			// If this is the only child, go up one more level
			while (
				$ancestor->parentNode &&
				$firstNonemptyChild( $ancestor->parentNode ) === $lastNonemptyChild( $ancestor->parentNode )
			) {
				$ancestor = $ancestor->parentNode;
			}
			return $ancestor;
		}
		return null;
	}

	/**
	 * Given a comment, add a list item to its document's DOM tree, inside of which a reply to said
	 * comment can be added.
	 *
	 * The DOM tree is suitably rearranged to ensure correct indentation level of the reply (wrapper
	 * nodes are added, and other nodes may be moved around).
	 *
	 * @param stdClass $comment Comment data returned by parser#groupThreads
	 * @return DOMElement
	 */
	public static function addListItem( stdClass $comment ) : DOMElement {
		$listTypeMap = [
			'li' => 'ul',
			'dd' => 'dl'
		];

		// 1. Start at given comment
		// 2. Skip past all comments with level greater than the given
		//    (or in other words, all replies, and replies to replies, and so on)
		// 3. Add comment with level of the given comment plus 1

		$curComment = $comment;
		while ( count( $curComment->replies ) ) {
			$curComment = end( $curComment->replies );
		}

		$desiredLevel = $comment->level + 1;
		$curLevel = $curComment->level;
		$target = $curComment->range->endContainer;

		// Skip to the end of the "paragraph". This only looks at tag names and can be fooled by CSS, but
		// avoiding that would be more difficult and slower.
		while ( $target->nextSibling && !self::isBlockElement( $target->nextSibling ) ) {
			$target = $target->nextSibling;
		}

		// target is a text node or an inline element at the end of a "paragraph"
		// (not necessarily paragraph node).
		// First, we need to find a block-level parent that we can mess with.
		// If we can't find a surrounding list item or paragraph (e.g. maybe we're inside a table cell
		// or something), take the parent node and hope for the best.
		$parent = CommentUtils::closestElement( $target, [ 'li', 'dd', 'p' ] ) ??
			$target->parentNode;
		while ( $target->parentNode !== $parent ) {
			$target = $target->parentNode;
		}
		// parent is a list item or paragraph (hopefully)
		// target is an inline node within it

		if ( $curLevel < $desiredLevel ) {
			// Insert more lists after the target to increase nesting.

			// If the comment is fully covered by some wrapper element, insert replies outside that wrapper.
			// This will often just be a paragraph node (<p>), but it can be a <div> or <table> that serves
			// as some kind of a fancy frame, which are often used for barnstars and announcements.
			if ( $curLevel === 1 && ( $wrapper = self::getFullyCoveredWrapper( $curComment ) ) ) {
				$target = $wrapper;
				$parent = $target->parentNode;
			}

			// If we can't insert a list directly inside this element, insert after it.
			// The wrapper check above handles most cases, but this special case is still needed for comments
			// consisting of multiple paragraphs with no fancy frames.
			// TODO Improve this check
			if ( strtolower( $parent->tagName ) === 'p' || strtolower( $parent->tagName ) === 'pre' ) {
				$parent = $parent->parentNode;
				$target = $target->parentNode;
			}

			// Decide on tag names for lists and items
			$itemType = strtolower( $parent->tagName );
			$itemType = isset( $listTypeMap[ $itemType ] ) ? $itemType : 'dd';
			$listType = $listTypeMap[ $itemType ];

			// Insert required number of wrappers
			while ( $curLevel < $desiredLevel ) {
				$list = $target->ownerDocument->createElement( $listType );
				// Setting modified would only be needed for removeAddedListItem,
				// which isn't needed on the server
				// $list->setAttribute( 'dt-modified', 'new' );
				$item = $target->ownerDocument->createElement( $itemType );
				// $item->setAttribute( 'dt-modified', 'new' );
				self::whitespaceParsoidHack( $item );

				$parent->insertBefore( $list, $target->nextSibling );
				$list->appendChild( $item );

				$target = $item;
				$parent = $list;
				$curLevel++;
			}
		} elseif ( $curLevel >= $desiredLevel ) {
			// Split the ancestor nodes after the target to decrease nesting.

			do {
				// If target is the last child of its parent, no need to split it
				if ( $target->nextSibling ) {
					// Create new identical node after the parent
					$newNode = $parent->cloneNode( false );
					// $parent->setAttribute( 'dt-modified', 'split' );
					$parent->parentNode->insertBefore( $newNode, $parent->nextSibling );

					// Move nodes following target to the new node
					while ( $target->nextSibling ) {
						$newNode->appendChild( $target->nextSibling );
					}
				}

				$target = $parent;
				$parent = $parent->parentNode;

				// Decrease nesting level if we escaped outside of a list
				if ( isset( $listTypeMap[ strtolower( $target->tagName ) ] ) ) {
					$curLevel--;
				}
			} while ( $curLevel >= $desiredLevel );

			// parent is now a list, target is a list item
			$item = $target->ownerDocument->createElement( $target->tagName );
			// $item->setAttribute( 'dt-modified', 'new' );
			self::whitespaceParsoidHack( $item );
			$parent->insertBefore( $item, $target->nextSibling );
		}

		return $item;
	}

	// removeAddedListItem is only needed in the client

	/**
	 * Unwrap a top level list, converting list item text to paragraphs
	 *
	 * Assumes that the list is the only child of it's parent.
	 *
	 * @param DOMElement $list List element (dl/ol/ul)
	 */
	public static function unwrapList( DOMElement $list ) : void {
		$doc = $list->ownerDocument;
		$container = $list->parentNode;

		$container->removeChild( $list );
		while ( $list->firstChild ) {
			if ( $list->firstChild->nodeType === XML_ELEMENT_NODE ) {
				// Move <dd> contents to <p>
				$p = $doc->createElement( 'p' );
				while ( $list->firstChild->firstChild ) {
					// If contents is a block element, place outside the paragraph
					// and start a new paragraph after
					if ( self::isBlockElement( $list->firstChild->firstChild ) ) {
						if ( $p->firstChild ) {
							$container->appendChild( $p );
						}
						$container->appendChild( $list->firstChild->firstChild );
						$p = $doc->createElement( 'p' );
					} else {
						$p->appendChild( $list->firstChild->firstChild );
					}
				}
				if ( $p->firstChild ) {
					$container->appendChild( $p );
				}
				$list->removeChild( $list->firstChild );
			} else {
				// Text node / comment node, probably empty
				$container->appendChild( $list->firstChild );
			}
		}
	}

	/**
	 * Add another list item after the given one.
	 *
	 * @param DOMElement $previousItem
	 * @return DOMElement
	 */
	public static function addSiblingListItem( DOMElement $previousItem ) : DOMElement {
		$listItem = $previousItem->ownerDocument->createElement( $previousItem->tagName->toLowerCase() );
		self::whitespaceParsoidHack( $listItem );
		$previousItem->parentNode->insertBefore( $listItem, $previousItem->nextSibling );
		return $listItem;
	}

	/**
	 * Create an element that will convert to the provided wikitext
	 *
	 * @param DOMDocument $doc Document
	 * @param string $wt Wikitext
	 * @return DOMElement Element
	 */
	public static function createWikitextNode( DOMDocument $doc, string $wt ) : DOMElement {
		$span = $doc->createElement( 'span' );

		$span->setAttribute( 'typeof', 'mw:Transclusion' );
		$span->setAttribute( 'data-mw', json_encode( [ 'parts' => [ $wt ] ] ) );

		return $span;
	}
}