Feature/add pagination

package.json

@@ -33,6 +33,7 @@
     "dotenv": "^16.0.2",
     "express": "^4.18.1",
     "mongoose": "^6.6.1",
+    "querystring": "^0.2.1",
     "swagger-ui-express": "^4.5.0",
     "winston": "^3.8.2"
   },

src/app.ts

@@ -10,6 +10,8 @@ config();
 
 const serve = async () : Promise<void> => {
     const app: Application = express();
+    app.use(express.json());
+    app.set('json spaces', 2)
 
     try {
         await Database.connect();

src/v1/controllers/problems.ts

@@ -1,12 +1,12 @@
 import { Request, Response } from "express";
-import { ProblemData, ProblemService } from "../services";
+import { ResponseJson, ProblemService, Query } from "../services";
 
 export class ProblemController {
-  public static async getAllProblems(req: Request, res: Response) {
-    let problems  : ProblemData[] | Error;
+  public static async getAllProblems(req: Request<{}, {}, {}, Query>, res: Response) {
+    let responseJson  : ResponseJson;
 
     try {
-      problems = await ProblemService.getAllProblems();
+      responseJson = await ProblemService.getAllProblems(req);
     } catch (e) {
       res.status(500).json({
         message: "Unexpected error getting problems",
@@ -15,9 +15,6 @@ export class ProblemController {
       return e;
     }
 
-    res.status(200).json({
-      message: "Successfully fetched problems",
-      questions: problems
-    });
+    res.status(200).json(responseJson);
   }
 }

src/v1/services/index.ts

@@ -1,6 +1,7 @@
-import { ProblemService, ProblemData } from "./problems";
+import { ProblemService, ResponseJson, Query } from "./problems";
 
 export {
   ProblemService,
-  ProblemData
+  ResponseJson,
+  Query
 };

src/v1/services/problems.ts

@@ -1,25 +1,52 @@
 import { IProblem, Problems } from '../models/problems';
 import { logger } from '../../logger';
+import { Request } from 'express';
 
-export interface ProblemData {
+export interface ResponseJson {
+  message: string;
+  questions: ProblemData[];
+  paging: PagingData;
+}
+
+interface ProblemData {
   title: string;
   title_slug: string;
   id: Number;
   difficulty: Number;
   is_premium: boolean;
 };
 
+interface PagingData {
+  total: number;
+  page: number;
+  pages: number;
+}
+
+export interface Query {
+  limit: string;
+  offset: string;
+};
+
 export class ProblemService {
-  public static async getAllProblems() : Promise<ProblemData[] | Error> {
+  public static async getAllProblems(req : Request<{}, {}, {}, Query>) : Promise<ResponseJson> {
     let data : IProblem[];
+    let total : number;
+    const limit : number = parseInt(req.query.limit);
+    const offset : number = parseInt(req.query.offset);
 
     try {
-      data = await Problems.find({});
+      data = await Problems.find({})
+        .limit(limit)
+        .skip(offset);
+      total = await Problems.count();
     } catch(e : any) {
       logger.error("Exception caught retrieving leetcode problems from database: " + e);
-      return new Error("Error retrieving problems " + e);
+      throw new Error("Error retrieving problems " + e);
     }
 
+    const totalPages = Math.ceil(total / limit) || 1;
+    const currentPage = Math.ceil(total % offset) || 1;
+
     const parsedData : ProblemData[] = data.map(problem  => { 
       return {
         title: problem.title,
@@ -30,6 +57,18 @@ export class ProblemService {
       };
     });
 
-    return parsedData;
+    const paging : PagingData = {
+      total,
+      page: currentPage,
+      pages: totalPages
+    };
+
+    const responseJson : ResponseJson = {
+      message: "Successfully retrieved all leetcode problems",
+      questions: parsedData,
+      paging
+    }
+
+    return responseJson;
   }
 }