Add mathfraktur rendering for chrome

Chrome and similar browsers do not support the
mathvariant attribute that can be used to change
math fonts conveniently. Like for mathcal there is
a table that can be used to translate from latin
to mathfraktur chars.

Bug: T378433
Change-Id: Id8c3e121ed104ba3f08329b4151a7e3bec699754

src/WikiTexVC/MMLmappings/BaseParsing.php

@@ -788,12 +788,19 @@ class BaseParsing {
 		$state = [];
 
 		// Unicode fixes for the operators
-		if ( $mathvariant == Variants::DOUBLESTRUCK ) {
+		switch ( $mathvariant ) {
+			case Variants::DOUBLESTRUCK:
 				$state = [ "double-struck-literals" => true ];
-		} elseif ( $mathvariant == Variants::CALLIGRAPHIC ) {
+				break;
+			case Variants::CALLIGRAPHIC:
 				$state = [ "calligraphic" => true ];
-		} elseif ( $mathvariant == Variants::BOLDCALLIGRAPHIC ) {
+				break;
+			case Variants::BOLDCALLIGRAPHIC:
 				$state = [ "bold-calligraphic" => true ];
+				break;
+			case Variants::FRAKTUR:
+				$state = [ "fraktur" => true ];
+				break;
 		}
 
 		if ( $node instanceof Fun1nb ) {

src/WikiTexVC/MMLmappings/Util/MMLParsingUtil.php

@@ -149,6 +149,36 @@ class MMLParsingUtil {
 		return self::matchAlphanumeric( $inputString, $map );
 	}
 
+	public static function mapToFrakturUnicode( $inputString ): string {
+		$res = '';
+		$specialCases = [ 'C' => 'ℭ',
+			'H' => 'ℌ',
+			'I' => 'ℑ',
+			'R' => 'ℜ',
+			'Z' => 'ℤ' ];
+		foreach ( mb_str_split( $inputString ) as $chr ) {
+			// see https://www.w3.org/TR/mathml-core/#fraktur-mappings
+			if ( isset( $specialCases[$chr] ) ) {
+				$res .= $specialCases[$chr];
+				continue;
+			}
+			if ( $chr >= 'A' && $chr <= 'Z' ) {
+				$code = self::addToChr( $chr, '1D4C3' );
+				$res .= '&#x' . $code . ';';
+			} elseif ( $chr >= 'a' && $chr <= 'z' ) {
+				$code = self::addToChr( $chr, '1D4BD' );
+				$res .= '&#x' . $code . ';';
+			} else {
+				$res .= $chr;
+			}
+		}
+		return $res;
+	}
+
+	private static function addToChr( $chr, $base ): string {
+		return strtoupper( dechex( mb_ord( $chr ) + hexdec( $base ) ) );
+	}
+
 	public static function matchAlphanumeric( $inputString, $map ) {
 		// Replace each character in the input string with its caligraphic Unicode equivalent
 		return preg_replace_callback( '/[A-Za-z0-9]/u', static function ( $matches ) use ( $map ) {

src/WikiTexVC/Nodes/Literal.php

@@ -34,7 +34,7 @@ class Literal extends TexNode {
 
 	public function changeUnicodeFontInput( $input, $state ) {
 		/**
-		 * In some font modifications, it is required to explicitly use unicode
+		 * In some font modifications, it is required to explicitly use Unicode
 		 * characters instead of (only) attributes in MathML to indicate the font.
 		 * This is mostly because of Chrome behaviour. I.e. see: https://phabricator.wikimedia.org/T352196
 		 */
@@ -42,6 +42,8 @@ class Literal extends TexNode {
 			return MMLParsingUtil::mapToDoubleStruckUnicode( $input );
 		} elseif ( isset( $state["calligraphic"] ) ) {
 			return MMLParsingUtil::mapToCaligraphicUnicode( $input );
+		} elseif ( isset( $state["fraktur"] ) ) {
+			return MMLParsingUtil::mapToFrakturUnicode( $input );
 		}
 		return $input;
 	}

tests/phpunit/unit/WikiTexVC/MMLRenderTest.php

@@ -15,6 +15,16 @@ use MediaWikiUnitTestCase;
  * @covers \MediaWiki\Extension\Math\WikiTexVC\TexVC
  */
 class MMLRenderTest extends MediaWikiUnitTestCase {
+
+	public function testMathFRakUnicode() {
+		$input = "\\mathfrak{O},  \\mathfrak{K}, \\mathfrak{t}, \\mathfrak{C}";
+		$mathMLtexVC = $this->generateMML( $input );
+		$this->assertStringContainsString( '𝔒', $mathMLtexVC );
+		$this->assertStringContainsString( '𝔎', $mathMLtexVC );
+		$this->assertStringContainsString( '𝔱', $mathMLtexVC );
+		$this->assertStringContainsString( 'ℭ', $mathMLtexVC );
+	}
+
 	public function testMathCalUnicode() {
 		$input = "\\mathcal{O},  \\mathcal{K}, \\mathcal{t}, \\mathcal{c}";
 		$mathMLtexVC = $this->generateMML( $input );

tests/phpunit/unit/WikiTexVC/MMLmappings/MMLParsingUtilTest.php

@@ -29,4 +29,23 @@ class MMLParsingUtilTest extends MediaWikiUnitTestCase {
 		$this->assertNull( $result );
 	}
 
+	public function testUnicode_afr() {
+		$result = MMLParsingUtil::mapToFrakturUnicode( 'a' );
+		$this->assertEquals( '𝔞', $result );
+	}
+
+	public function testUnicode_bfr() {
+		$result = MMLParsingUtil::mapToFrakturUnicode( 'B' );
+		$this->assertEquals( '𝔅', $result );
+	}
+
+	public function testUnicode_Cfr() {
+		$result = MMLParsingUtil::mapToFrakturUnicode( 'C' );
+		$this->assertEquals( 'ℭ', $result );
+	}
+
+	public function testUnicodeUtf8Input() {
+		$result = MMLParsingUtil::mapToFrakturUnicode( '𝔄' );
+		$this->assertEquals( '𝔄', $result );
+	}
 }