<?php

function _autop_newline_preservation_helper( $matches ) {
	return str_replace( "\n", "<WPPreserveNewline />", $matches[0] );
}

function get_html_split_regex() {
	static $regex;

	if ( ! isset( $regex ) ) {
		$comments =
			  '!'           // Start of comment, after the <.
			. '(?:'         // Unroll the loop: Consume everything until --> is found.
			.     '-(?!->)' // Dash not followed by end of comment.
			.     '[^\-]*+' // Consume non-dashes.
			. ')*+'         // Loop possessively.
			. '(?:-->)?';   // End of comment. If not found, match all input.

		$cdata =
			  '!\[CDATA\['  // Start of comment, after the <.
			. '[^\]]*+'     // Consume non-].
			. '(?:'         // Unroll the loop: Consume everything until ]]> is found.
			.     '](?!]>)' // One ] not followed by end of comment.
			.     '[^\]]*+' // Consume non-].
			. ')*+'         // Loop possessively.
			. '(?:]]>)?';   // End of comment. If not found, match all input.

		$escaped =
			  '(?='           // Is the element escaped?
			.    '!--'
			. '|'
			.    '!\[CDATA\['
			. ')'
			. '(?(?=!-)'      // If yes, which type?
			.     $comments
			. '|'
			.     $cdata
			. ')';

		$regex =
			  '/('              // Capture the entire match.
			.     '<'           // Find start of element.
			.     '(?'          // Conditional expression follows.
			.         $escaped  // Find end of escaped element.
			.     '|'           // ... else ...
			.         '[^>]*>?' // Find end of normal element.
			.     ')'
			. ')/';
	}

	return $regex;
}

function wp_html_split( $input ) {
	return preg_split( get_html_split_regex(), $input, -1, PREG_SPLIT_DELIM_CAPTURE );
}

function wp_replace_in_html_tags( $haystack, $replace_pairs ) {
	// Find all elements.
	$textarr = wp_html_split( $haystack );
	$changed = false;

	// Optimize when searching for one item.
	if ( 1 === count( $replace_pairs ) ) {
		// Extract $needle and $replace.
		foreach ( $replace_pairs as $needle => $replace );

		// Loop through delimiters (elements) only.
		for ( $i = 1, $c = count( $textarr ); $i < $c; $i += 2 ) {
			if ( false !== strpos( $textarr[$i], $needle ) ) {
				$textarr[$i] = str_replace( $needle, $replace, $textarr[$i] );
				$changed = true;
			}
		}
	} else {
		// Extract all $needles.
		$needles = array_keys( $replace_pairs );

		// Loop through delimiters (elements) only.
		for ( $i = 1, $c = count( $textarr ); $i < $c; $i += 2 ) {
			foreach ( $needles as $needle ) {
				if ( false !== strpos( $textarr[$i], $needle ) ) {
					$textarr[$i] = strtr( $textarr[$i], $replace_pairs );
					$changed = true;
					// After one strtr() break out of the foreach loop and look at next element.
					break;
				}
			}
		}
	}

	if ( $changed ) {
		$haystack = implode( $textarr );
	}

	return $haystack;
}

function wpautop( $pee, $br = true ) {
	$pre_tags = array();

	if ( trim($pee) === '' )
		return '';

	// Just to make things a little easier, pad the end.
	$pee = $pee . "\n";

	/*
	 * Pre tags shouldn't be touched by autop.
	 * Replace pre tags with placeholders and bring them back after autop.
	 */
	if ( strpos($pee, '<pre') !== false ) {
		$pee_parts = explode( '</pre>', $pee );
		$last_pee = array_pop($pee_parts);
		$pee = '';
		$i = 0;

		foreach ( $pee_parts as $pee_part ) {
			$start = strpos($pee_part, '<pre');

			// Malformed html?
			if ( $start === false ) {
				$pee .= $pee_part;
				continue;
			}

			$name = "<pre wp-pre-tag-$i></pre>";
			$pre_tags[$name] = substr( $pee_part, $start ) . '</pre>';

			$pee .= substr( $pee_part, 0, $start ) . $name;
			$i++;
		}

		$pee .= $last_pee;
	}
	// Change multiple <br>s into two line breaks, which will turn into paragraphs.
	$pee = preg_replace('|<br\s*/?>\s*<br\s*/?>|', "\n\n", $pee);

	$allblocks = '(?:table|thead|tfoot|caption|col|colgroup|tbody|tr|td|th|div|dl|dd|dt|ul|ol|li|pre|form|map|area|blockquote|address|math|style|p|h[1-6]|hr|fieldset|legend|section|article|aside|hgroup|header|footer|nav|figure|figcaption|details|menu|summary)';

	// Add a double line break above block-level opening tags.
	$pee = preg_replace('!(<' . $allblocks . '[\s/>])!', "\n\n$1", $pee);

	// Add a double line break below block-level closing tags.
	$pee = preg_replace('!(</' . $allblocks . '>)!', "$1\n\n", $pee);

	// Standardize newline characters to "\n".
	$pee = str_replace(array("\r\n", "\r"), "\n", $pee);

	// Find newlines in all elements and add placeholders.
	$pee = wp_replace_in_html_tags( $pee, array( "\n" => " <!-- wpnl --> " ) );

	// Collapse line breaks before and after <option> elements so they don't get autop'd.
	if ( strpos( $pee, '<option' ) !== false ) {
		$pee = preg_replace( '|\s*<option|', '<option', $pee );
		$pee = preg_replace( '|</option>\s*|', '</option>', $pee );
	}

	/*
	 * Collapse line breaks inside <object> elements, before <param> and <embed> elements
	 * so they don't get autop'd.
	 */
	if ( strpos( $pee, '</object>' ) !== false ) {
		$pee = preg_replace( '|(<object[^>]*>)\s*|', '$1', $pee );
		$pee = preg_replace( '|\s*</object>|', '</object>', $pee );
		$pee = preg_replace( '%\s*(</?(?:param|embed)[^>]*>)\s*%', '$1', $pee );
	}

	/*
	 * Collapse line breaks inside <audio> and <video> elements,
	 * before and after <source> and <track> elements.
	 */
	if ( strpos( $pee, '<source' ) !== false || strpos( $pee, '<track' ) !== false ) {
		$pee = preg_replace( '%([<\[](?:audio|video)[^>\]]*[>\]])\s*%', '$1', $pee );
		$pee = preg_replace( '%\s*([<\[]/(?:audio|video)[>\]])%', '$1', $pee );
		$pee = preg_replace( '%\s*(<(?:source|track)[^>]*>)\s*%', '$1', $pee );
	}

	// Remove more than two contiguous line breaks.
	$pee = preg_replace("/\n\n+/", "\n\n", $pee);

	// Split up the contents into an array of strings, separated by double line breaks.
	$pees = preg_split('/\n\s*\n/', $pee, -1, PREG_SPLIT_NO_EMPTY);

	// Reset $pee prior to rebuilding.
	$pee = '';

	// Rebuild the content as a string, wrapping every bit with a <p>.
	foreach ( $pees as $tinkle ) {
		$pee .= '<p>' . trim($tinkle, "\n") . "</p>\n";
	}

	// Under certain strange conditions it could create a P of entirely whitespace.
	$pee = preg_replace('|<p>\s*</p>|', '', $pee);

	// Add a closing <p> inside <div>, <address>, or <form> tag if missing.
	$pee = preg_replace('!<p>([^<]+)</(div|address|form)>!', "<p>$1</p></$2>", $pee);

	// If an opening or closing block element tag is wrapped in a <p>, unwrap it.
	$pee = preg_replace('!<p>\s*(</?' . $allblocks . '[^>]*>)\s*</p>!', "$1", $pee);

	// In some cases <li> may get wrapped in <p>, fix them.
	$pee = preg_replace("|<p>(<li.+?)</p>|", "$1", $pee);

	// If a <blockquote> is wrapped with a <p>, move it inside the <blockquote>.
	$pee = preg_replace('|<p><blockquote([^>]*)>|i', "<blockquote$1><p>", $pee);
	$pee = str_replace('</blockquote></p>', '</p></blockquote>', $pee);

	// If an opening or closing block element tag is preceded by an opening <p> tag, remove it.
	$pee = preg_replace('!<p>\s*(</?' . $allblocks . '[^>]*>)!', "$1", $pee);

	// If an opening or closing block element tag is followed by a closing <p> tag, remove it.
	$pee = preg_replace('!(</?' . $allblocks . '[^>]*>)\s*</p>!', "$1", $pee);

	// Optionally insert line breaks.
	if ( $br ) {
		// Replace newlines that shouldn't be touched with a placeholder.
		$pee = preg_replace_callback('/<(script|style).*?<\/\\1>/s', '_autop_newline_preservation_helper', $pee);

		// Normalize <br>
		$pee = str_replace( array( '<br>', '<br/>' ), '<br />', $pee );

		// Replace any new line characters that aren't preceded by a <br /> with a <br />.
		$pee = preg_replace('|(?<!<br />)\s*\n|', "<br />\n", $pee);

		// Replace newline placeholders with newlines.
		$pee = str_replace('<WPPreserveNewline />', "\n", $pee);
	}

	// If a <br /> tag is after an opening or closing block tag, remove it.
	$pee = preg_replace('!(</?' . $allblocks . '[^>]*>)\s*<br />!', "$1", $pee);

	// If a <br /> tag is before a subset of opening or closing block tags, remove it.
	$pee = preg_replace('!<br />(\s*</?(?:p|li|div|dl|dd|dt|th|pre|td|ul|ol)[^>]*>)!', '$1', $pee);
	$pee = preg_replace( "|\n</p>$|", '</p>', $pee );

	// Replace placeholder <pre> tags with their original content.
	if ( !empty($pre_tags) )
		$pee = str_replace(array_keys($pre_tags), array_values($pre_tags), $pee);

	// Restore newlines in all elements.
	if ( false !== strpos( $pee, '<!-- wpnl -->' ) ) {
		$pee = str_replace( array( ' <!-- wpnl --> ', '<!-- wpnl -->' ), "\n", $pee );
	}

	return $pee;
}