refactor: turn Python generator into a service (#692)

### Summary of Changes

Turn the Python generator into a service. The CLI now calls this service
instead of containing the entire implementation.

This has several advantages:
* It facilitates testing, since no files have to be created on disk
anymore.
* It also makes it easier to integrate the Python generator into VS
Code, since it no longer has to go through the CLI.
* It reduces dependencies between CLI, language, and VS Code, which
might help when restructuring the repo using NPM workspaces.

Co-authored-by: WinPlay02 <[email protected]>

package.json

@@ -106,7 +106,8 @@
         "langium": "^2.0.2",
         "true-myth": "^7.1.0",
         "vscode-languageclient": "^9.0.1",
-        "vscode-languageserver": "^9.0.1"
+        "vscode-languageserver": "^9.0.1",
+        "vscode-languageserver-textdocument": "^1.0.11"
     },
     "devDependencies": {
         "@lars-reimann/eslint-config": "^5.1.4",

src/cli/cli-util.ts

@@ -1,16 +1,9 @@
 import chalk from 'chalk';
 import path from 'path';
 import fs from 'fs';
-import { AstNode, LangiumDocument, LangiumServices, URI } from 'langium';
+import { LangiumDocument, LangiumServices, URI } from 'langium';
 
 /* c8 ignore start */
-export const extractAstNode = async function <T extends AstNode>(
-    fileName: string,
-    services: LangiumServices,
-): Promise<T> {
-    return (await extractDocument(fileName, services)).parseResult?.value as T;
-};
-
 export const extractDocument = async function (fileName: string, services: LangiumServices): Promise<LangiumDocument> {
     const extensions = services.LanguageMetaData.fileExtensions;
     if (!extensions.includes(path.extname(fileName))) {
@@ -45,19 +38,6 @@ export const extractDocument = async function (fileName: string, services: Langi
         process.exit(1);
     }
 
-    return document;
+    return document as LangiumDocument;
 };
 /* c8 ignore stop */
-
-interface FilePathData {
-    destination: string;
-    name: string;
-}
-
-export const extractDestinationAndName = function (filePath: string, destination: string | undefined): FilePathData {
-    const baseFilePath = path.basename(filePath, path.extname(filePath)).replace(/[.-]/gu, '');
-    return {
-        destination: destination ?? path.join(path.dirname(baseFilePath), 'generated'),
-        name: path.basename(baseFilePath),
-    };
-};