Merge pull request #25212 from nextcloud/enh/preview-markdown

Enhance markdown file preview rendering

lib/private/Preview/MarkDown.php

@@ -24,6 +24,9 @@
 
 namespace OC\Preview;
 
+use OCP\Files\File;
+use OCP\IImage;
+
 class MarkDown extends TXT {
 	/**
 	 * {@inheritDoc}
@@ -31,4 +34,111 @@ class MarkDown extends TXT {
 	public function getMimeType(): string {
 		return '/text\/(x-)?markdown/';
 	}
+
+	public function getThumbnail(File $file, int $maxX, int $maxY): ?IImage {
+		$content = $file->fopen('r');
+
+		if ($content === false) {
+			return null;
+		}
+
+		$content = stream_get_contents($content,3000);
+
+		//don't create previews of empty text files
+		if (trim($content) === '') {
+			return null;
+		}
+
+		// Merge text paragraph lines that might belong together
+		$content = preg_replace('/^(\s*)\*\s/mU', '$1- ', $content);
+
+		$content = preg_replace('/((?!^(\s*-|#)).*)(\w|\\|\.)(\r\n|\n|\r)(\w|\*)/mU', '$1 $3', $content);
+
+		// Remove markdown symbols that we cannot easily represent in rendered text in the preview
+		$content = preg_replace('/\*\*(.*)\*\*/U', '$1', $content);
+		$content = preg_replace('/\*(.*)\*/U', '$1', $content);
+		$content = preg_replace('/\_\_(.*)\_\_/U', '$1', $content);
+		$content = preg_replace('/\_(.*)\_/U', '$1', $content);
+		$content = preg_replace('/\~\~(.*)\~\~/U', '$1', $content);
+
+		$content = preg_replace('/\!?\[((.|\n)*)\]\((.*)\)/mU', '$1 ($3)', $content);
+		$content = preg_replace('/\n\n+/', "\n", $content);
+
+		$content = preg_replace('/[\x{10000}-\x{10FFFF}]/u', '', $content);
+
+		$lines = preg_split("/\r\n|\n|\r/", $content);
+
+		// Define text size of text file preview
+		$fontSize = $maxX ? (int) ((1 / ($maxX >= 512 ? 60 : 40) * $maxX)) : 10;
+
+		$image = imagecreate($maxX, $maxY);
+		imagecolorallocate($image, 255, 255, 255);
+		$textColor = imagecolorallocate($image, 0, 0, 0);
+
+		$fontFile  = __DIR__ . '/../../../core/fonts/NotoSans-Regular.ttf';
+		$fontFileBold  = __DIR__ . '/../../../core/fonts/NotoSans-Bold.ttf';
+
+		$canUseTTF = function_exists('imagettftext');
+
+		$textOffset = (int)min($maxX * 0.05, $maxY * 0.05);
+		$nextLineStart = 0;
+		$y = $textOffset;
+		foreach ($lines as $line) {
+			$actualFontSize = $fontSize;
+			if (mb_strpos($line, '# ') === 0) {
+				$actualFontSize *= 2;
+			}
+			if (mb_strpos($line, '## ') === 0) {
+				$actualFontSize *= 1.8;
+			}
+			if (mb_strpos($line, '### ') === 0) {
+				$actualFontSize *= 1.6;
+			}
+			if (mb_strpos($line, '#### ') === 0) {
+				$actualFontSize *= 1.4;
+			}
+			if (mb_strpos($line, '##### ') === 0) {
+				$actualFontSize *= 1.2;
+			}
+			if (mb_strpos($line, '###### ') === 0) {
+				$actualFontSize *= 1.1;
+			}
+
+			// Add spacing before headlines
+			if ($actualFontSize !== $fontSize && $y !== $textOffset) {
+				$y += (int)($actualFontSize * 2);
+			}
+
+			$x = $textOffset;
+			$y += (int)($nextLineStart + $actualFontSize);
+
+			if ($canUseTTF === true) {
+				$wordWrap = (int)((1 / $actualFontSize * 1.3) * $maxX);
+
+				// Get rid of markdown symbols that we still needed for the font size
+				$line = preg_replace('/^#*\s/', '', $line);
+
+				$wrappedText = wordwrap($line, $wordWrap,"\n");
+				$linesWrapped = count(explode("\n", $wrappedText));
+				imagettftext($image, $actualFontSize, 0, $x, $y, $textColor, $actualFontSize === $fontSize ? $fontFile : $fontFileBold, $wrappedText);
+				$nextLineStart = (int)($linesWrapped * ceil($actualFontSize * 2));
+				if ($actualFontSize !== $fontSize && $y !== $textOffset) {
+					$nextLineStart -= $actualFontSize;
+				}
+			} else {
+				$y -= (int)$fontSize;
+				imagestring($image, 1, $x, $y, $line, $textColor);
+				$nextLineStart = $fontSize;
+			}
+
+			if ($y >= $maxY) {
+				break;
+			}
+		}
+
+		$imageObject = new \OC_Image();
+		$imageObject->setResource($image);
+
+		return $imageObject->valid() ? $imageObject : null;
+	}
 }