Load lexer by mimetype

TODO.md

@@ -8,8 +8,8 @@
 * ✅ Implement lexer loader that respects aliases
 * ✅ Implement lexer loader by file extension
 * ✅ Add --line-numbers to terminal formatter
-* Implement lexer loader by mime type
+* ✅ Implement lexer loader by mime type
 * ✅ Implement Delegating lexers
 * ✅ Add RstLexer
 * Add Mako template lexer
-* Implement heuristic lexer detection
+* ✅ Implement heuristic lexer detection

src/lexer.cr

@@ -9,13 +9,21 @@ module Tartrazine
 
   # Get the lexer object for a language name
   # FIXME: support mimetypes
-  def self.lexer(name : String? = nil, filename : String? = nil) : BaseLexer
+  def self.lexer(name : String? = nil, filename : String? = nil, mimetype : String? = nil) : BaseLexer
     return lexer_by_name(name) if name && name != "autodetect"
     return lexer_by_filename(filename) if filename
+    return lexer_by_mimetype(mimetype) if mimetype
 
     Lexer.from_xml(LexerFiles.get("/#{LEXERS_BY_NAME["plaintext"]}.xml").gets_to_end)
   end
 
+  private def self.lexer_by_mimetype(mimetype : String) : BaseLexer
+    lexer_file_name = LEXERS_BY_MIMETYPE.fetch(mimetype, nil)
+    raise Exception.new("Unknown mimetype: #{mimetype}") if lexer_file_name.nil?
+
+    Lexer.from_xml(LexerFiles.get("/#{lexer_file_name}.xml").gets_to_end)
+  end
+
   private def self.lexer_by_name(name : String) : BaseLexer
     lexer_file_name = LEXERS_BY_NAME.fetch(name.downcase, nil)
     return create_delegating_lexer(name) if lexer_file_name.nil? && name.includes? "+"