refactor: Simplify TokenBuilder and ValueConverter

packages/parser/src/language/common/tokenBuilder.ts

@@ -0,0 +1,28 @@
+import type { GrammarAST, Stream, TokenBuilderOptions } from 'langium';
+import type { TokenType } from '../chevrotainWrapper.js';
+
+import { DefaultTokenBuilder } from 'langium';
+
+export abstract class MermaidTokenBuilder extends DefaultTokenBuilder {
+  private keywords: Set<string>;
+
+  public constructor(keywords: string[]) {
+    super();
+    this.keywords = new Set<string>(keywords);
+  }
+
+  protected override buildKeywordTokens(
+    rules: Stream<GrammarAST.AbstractRule>,
+    terminalTokens: TokenType[],
+    options?: TokenBuilderOptions
+  ): TokenType[] {
+    const tokenTypes: TokenType[] = super.buildKeywordTokens(rules, terminalTokens, options);
+    // to restrict users, they mustn't have any non-whitespace characters after the keyword.
+    tokenTypes.forEach((tokenType: TokenType): void => {
+      if (this.keywords.has(tokenType.name) && tokenType.PATTERN !== undefined) {
+        tokenType.PATTERN = new RegExp(tokenType.PATTERN.toString() + '(?!\\S)');
+      }
+    });
+    return tokenTypes;
+  }
+}