(core) move home server into core

Summary: This moves enough server material into core to run a home server.  The data engine is not yet incorporated (though in manual testing it works when ported).

Test Plan: existing tests pass

Reviewers: dsagal

Reviewed By: dsagal

Differential Revision: https://phab.getgrist.com/D2552

app/server/lib/FileParserElement.ts

@@ -0,0 +1,49 @@
+import {PluginInstance} from 'app/common/PluginInstance';
+import {ParseFileAPI} from 'app/plugin/FileParserAPI';
+import {checkers} from 'app/plugin/TypeCheckers';
+
+import {FileParser} from 'app/plugin/PluginManifest';
+
+import * as path from 'path';
+
+/**
+ * Encapsulates together a file parse contribution with its plugin instance and callable stubs for
+ * `parseFile` implementation provided by the plugin.
+ *
+ * Implements as well a `getMatching` static method to get all file parsers matching a filename from
+ * the list of plugin instances.
+ *
+ */
+export class FileParserElement {
+
+  /**
+   * Get all file parser that matches fileName from the list of plugins instances.
+   */
+  public static getMatching(pluginInstances: PluginInstance[], fileName: string): FileParserElement[] {
+    const fileParserElements: FileParserElement[] = [];
+    for (const plugin of pluginInstances) {
+      const fileParsers = plugin.definition.manifest.contributions.fileParsers;
+      if (fileParsers) {
+        for (const fileParser of fileParsers) {
+          if (matchFileParser(fileParser, fileName)) {
+            fileParserElements.push(new FileParserElement(plugin, fileParser));
+          }
+        }
+      }
+    }
+    return fileParserElements;
+  }
+
+  public parseFileStub: ParseFileAPI;
+
+  private constructor(public plugin: PluginInstance, public fileParser: FileParser) {
+    this.parseFileStub = plugin.getStub<ParseFileAPI>(fileParser.parseFile, checkers.ParseFileAPI);
+  }
+
+}
+
+function matchFileParser(fileParser: FileParser, fileName: string): boolean {
+  const ext = path.extname(fileName).slice(1),
+    fileExtensions = fileParser.fileExtensions;
+  return fileExtensions && fileExtensions.includes(ext);
+}