fix(repository): Move backend code into subdirectory

Signed-off-by: Tilman Vatteroth <git@tilmanvatteroth.de>

backend/src/revisions/revision.entity.ts

@@ -0,0 +1,86 @@
+/*
+ * SPDX-FileCopyrightText: 2021 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+import {
+  Column,
+  CreateDateColumn,
+  Entity,
+  JoinTable,
+  ManyToMany,
+  ManyToOne,
+  PrimaryGeneratedColumn,
+} from 'typeorm';
+
+import { Note } from '../notes/note.entity';
+import { Edit } from './edit.entity';
+
+/**
+ * The state of a note at a particular point in time,
+ * with the content at that time and the diff to the previous revision.
+ *
+ */
+@Entity()
+export class Revision {
+  @PrimaryGeneratedColumn()
+  id: number;
+
+  /**
+   * The patch from the previous revision to this one.
+   */
+  @Column({
+    type: 'text',
+  })
+  patch: string;
+
+  /**
+   * The note content at this revision.
+   */
+  @Column({
+    type: 'text',
+  })
+  content: string;
+
+  /**
+   * The length of the note content.
+   */
+  @Column()
+  length: number;
+
+  /**
+   * Date at which the revision was created.
+   */
+  @CreateDateColumn()
+  createdAt: Date;
+
+  /**
+   * Note this revision belongs to.
+   */
+  @ManyToOne((_) => Note, (note) => note.revisions, { onDelete: 'CASCADE' })
+  note: Promise<Note>;
+
+  /**
+   * All edit objects which are used in the revision.
+   */
+  @ManyToMany((_) => Edit, (edit) => edit.revisions)
+  @JoinTable()
+  edits: Promise<Edit[]>;
+
+  // eslint-disable-next-line @typescript-eslint/no-empty-function
+  private constructor() {}
+
+  static create(
+    content: string,
+    patch: string,
+    note: Note,
+  ): Omit<Revision, 'id' | 'createdAt'> {
+    const newRevision = new Revision();
+    newRevision.patch = patch;
+    newRevision.content = content;
+    newRevision.length = content.length;
+    newRevision.note = Promise.resolve(note);
+    newRevision.edits = Promise.resolve([]);
+    return newRevision;
+  }
+}