Add comment model

frontend/models/comment.ts

@@ -0,0 +1,64 @@
+export class CommentItemList {
+  constructor(public commentItems: CommentItem[]) {}
+
+  static valueOf(items: CommentItem[]): CommentItemList {
+    return new CommentItemList(items)
+  }
+
+  add(item: CommentItem) {
+    this.commentItems.push(item)
+  }
+
+  update(item: CommentItem) {
+    const index = this.commentItems.findIndex(comment => comment.id === item.id)
+    this.commentItems.splice(index, 1, item)
+  }
+
+  delete(item: CommentItem) {
+    this.commentItems = this.commentItems.filter(comment => comment.id !== item.id)
+  }
+
+  count(): Number {
+    return this.commentItems.length
+  }
+
+  toArray(): Object[] {
+    return this.commentItems.map(item => item.toObject())
+  }
+}
+
+export class CommentItem {
+  constructor(
+    public id: number,
+    public user: number,
+    public username: string,
+    public document: number,
+    public documentText: string,
+    public text: string,
+    public createdAt: string
+  ) {}
+
+  static valueOf(
+    { id, user, username, document, document_text, text, created_at }:
+    { id: number, user: number, username: string, document: number,
+      document_text: string, text: string, created_at: string }
+  ): CommentItem {
+    return new CommentItem(id, user, username, document, document_text, text, created_at)
+  }
+
+  by(userId: number) {
+    return this.user === userId
+  }
+
+  toObject(): Object {
+    return {
+      id: this.id,
+      user: this.user,
+      username: this.username,
+      document: this.document,
+      document_text: this.documentText,
+      text: this.text,
+      created_at: this.createdAt
+    }
+  }
+}