Implement GetNotePipe

This pipe transforms a note ID or alias to a Note object
by loading it from the database.
It also performs error handling

Signed-off-by: David Mehren <git@herrmehren.de>

src/notes/get-note.pipe.ts

@@ -0,0 +1,43 @@
+/*
+ * SPDX-FileCopyrightText: 2021 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+import {
+  ArgumentMetadata,
+  BadRequestException,
+  Injectable,
+  NotFoundException,
+  PipeTransform,
+} from '@nestjs/common';
+
+import { ForbiddenIdError, NotInDBError } from '../errors/errors';
+import { ConsoleLoggerService } from '../logger/console-logger.service';
+import { Note } from './note.entity';
+import { NotesService } from './notes.service';
+
+@Injectable()
+export class GetNotePipe implements PipeTransform<string, Promise<Note>> {
+  constructor(
+    private readonly logger: ConsoleLoggerService,
+    private noteService: NotesService,
+  ) {
+    this.logger.setContext(GetNotePipe.name);
+  }
+
+  async transform(noteIdOrAlias: string, _: ArgumentMetadata): Promise<Note> {
+    let note: Note;
+    try {
+      note = await this.noteService.getNoteByIdOrAlias(noteIdOrAlias);
+    } catch (e) {
+      if (e instanceof NotInDBError) {
+        throw new NotFoundException(e.message);
+      }
+      if (e instanceof ForbiddenIdError) {
+        throw new BadRequestException(e.message);
+      }
+      throw e;
+    }
+    return note;
+  }
+}