⚡ LeetRevise

Master algorithmic patterns through intelligent, adaptive spaced repetition.

About • Core Features • How It Works • Tech Stack • Getting Started • Configuration • API & Cron • Contributing • License

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About the Project

Software engineers frequently solve hundreds of LeetCode problems only to forget foundational patterns—such as dynamic programming state transitions, monotonic stack invariants, or topological sorting templates—weeks later.

LeetRevise bridges the retention gap by replacing passive re-solving with an adaptive, 6-stage spaced repetition schedule. The platform automatically synchronizes your accepted LeetCode submissions, calculates mathematically optimal milestone review dates, prioritizes high-impact scheduled revisions, and delivers a curated daily digest straight to your inbox so your problem-solving intuition remains sharp.

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Core Features

• Automated LeetCode Sync with Import Throttling: Connect your public LeetCode handle to fetch accepted submissions via GraphQL. Syncs are capped at the 6 most recent new problems per sync to avoid overwhelming the revision queue after long breaks, complemented by manual URL/slug fallbacks for custom problem tracking.
• Adaptive 6-Stage Spaced Repetition (SRS): Dynamic interval expansion ($1\text{d} \to 3\text{d} \to 7\text{d} \to 14\text{d} \to 30\text{d} \to 90\text{d}$) that dynamically advances, maintains, or resets stages based on self-reported recall performance.
• Multi-Tier Priority Classification: Intelligent 6-tier classification algorithm prioritizes active scheduled revisions due today over older unreviewed imports, ensuring urgent recall cycles are never buried under long-overdue backlog items.
• Curated Daily Email Digests with Backlog Surfacing: Automated transactional email reminders via Brevo (Sendinblue). Reminders send up to 3 prioritized active scheduled revisions and dynamically surface up to 2 older backlog problems in a dedicated "📦 From Your Backlog" section with relative time stamps (e.g., "Solved 18 days ago · Never reviewed"), preventing historical problems from being permanently ignored.
• Interactive Consistency & Performance Analytics:
  • Weekly Solve Consistency: 6-week bar graph featuring clear, unambiguous date-range tooltips (e.g., "Oct 25 – Oct 31, 2026") on hover.
  • Difficulty Breakdown: Visual percentage meters tracking Easy, Medium, and Hard problem distributions.
  • Streaks & Retention: Real-time streak tracking (current vs. personal best) with completion-rate metrics.
  • Weak Spot Identification: Analytics highlighting top forgotten topics to direct study efforts.
• Community Leaderboard: Real-time peer leaderboard comparing active revision streaks and total problem volume.
• Cloud Reliability & Cold-Start Safeguards: Integrated /api/ping keep-alive endpoint for cloud hosts (e.g., Render free tier) and /api/health diagnostics with database latency profiling.

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How It Works

1. Spaced Repetition Schedule

When a problem is synced, its initial review is scheduled for 1 day after the solved date. Subsequent review dates scale dynamically based on the review outcome:

Review Stage	Interval	Approximate Milestone
Stage 0	1 day	Initial Recall
Stage 1	3 days	Early Retention
Stage 2	7 days	1-Week Checkpoint
Stage 3	14 days	2-Week Consolidation
Stage 4	30 days	1-Month Mastery
Stage 5	90 days	Long-Term Retention

2. Review Outcome Grading

User Response	Stage Impact	Next Interval
Easy	Advances to next stage ($\text{+1}$)	Interval increases to the new stage's target
Effort	Retains current stage	Re-tested at the same stage interval
Forgot	Resets to Stage 0	Reset to 1-day interval for immediate recall
Skipped	Retains current stage	Postponed by 1 day without stage penalty

3. Priority Queue & Email Selection Engine

Problems are categorized into six priority tiers to balance active repetition against backlog recovery:

flowchart TD
    A["Active Due Problems (nextReviewAt <= now)"] --> B["Classify Problem Priority"]
    B --> C["Rank 1-4: Active Scheduled Revisions"]
    B --> D["Rank 5: Long-Overdue Backlog (>7d unreviewed)"]
    
    C --> E["Select up to 3 Active Problems"]
    D --> F["Select up to 2 Backlog Problems"]
    
    E --> G["Main Email Section: Due Today"]
    F --> H["Amber Section: From Your Backlog"]
    
    G & H --> I["Send Curated Daily Digest"]

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• Ranks 1 & 2 (Due Today): Scheduled stage transitions and initial reviews scheduled for today.
• Ranks 3 & 4 (Overdue Active): Stage 1+ scheduled revisions or recently solved problems that missed their target date.
• Rank 5 (Long-Overdue Backlog): Stage 0 problems solved $>7$ days ago with zero review history.
• Rank 6 (Upcoming): Future review dates (deferred until due).

The daily email selects up to 3 active scheduled problems plus up to 2 backlog problems, providing a manageable daily target without ignoring older problems.

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Tech Stack

Domain	Technologies
Frontend	React 19, TypeScript, Vite, Tailwind CSS, TanStack React Query, Recharts, Lucide Icons
Backend	Node.js, Express.js, TypeScript, Zod, Cookie-Parser, CORS
Database & ORM	PostgreSQL (Neon Serverless Postgres / Supabase), Prisma ORM
Email Delivery	Brevo (Sendinblue) Transactional REST API
Task Scheduler	cron-job.org HTTP Trigger / External Webhooks
Authentication	JWT (JSON Web Tokens), HTTP-Only Secure Cookies, Bcrypt.js
Deployment	Vercel (Frontend Client), Render (Backend API Service)

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Getting Started

Prerequisites

Ensure you have the following installed:

• Node.js: v18.0.0 or higher (Download Node.js)
• npm: v9.0.0 or higher (packaged with Node.js)
• Git: (Download Git)
• PostgreSQL Database: A local instance or hosted provider such as Neon or Supabase

Installation

1. Clone the repository:

   git clone https://github.com/VinitKumarGupta/LeetRevise.git
   cd LeetRevise

2. Install all dependencies across client, server, and root:

   npm run install:all

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Configuration

1. Create the server environment file:

   Create a .env file in the server directory (refer to server/.env.example):

   # PostgreSQL Connection (supports pooled and direct connection URLs)
   DATABASE_URL="postgresql://user:password@host/dbname?sslmode=require"
   DIRECT_DATABASE_URL="postgresql://user:password@host/dbname?sslmode=require"
   
   # Server Settings
   PORT=5000
   NODE_ENV="development"
   JWT_SECRET="your-secure-jwt-secret-key-min-32-chars"
   
   # Frontend Client URL (for CORS and email redirect links)
   APP_URL="http://localhost:5173"
   
   # Brevo (Sendinblue) Transactional Email (Optional for local testing)
   BREVO_API_KEY="xkeysib-your-brevo-api-key"
   EMAIL_FROM_ADDRESS="noreply.leetrevise@gmail.com"
   EMAIL_FROM_NAME="LeetRevise"
   
   # Secret token to protect the automated cron endpoint
   CRON_SECRET="your-secure-cron-trigger-token"

2. Generate Prisma Client and push schema:

   cd server
   npx prisma generate
   npx prisma db push
   cd ..

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Running the Application

Development Mode

Run both the Vite frontend and Express backend concurrently:

npm run dev

• Frontend Client: http://localhost:5173
• Backend API: http://localhost:5000

Production Build

npm run build
npm start

Running Tests

Execute the Jest test suite in the backend:

cd server
npm test

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API Endpoints & Cron

Core Endpoints

Method	Endpoint	Auth	Description
GET	/api/health	No	Server health status, database connectivity, and latency metrics
GET	/api/ping	No	Lightweight keep-alive ping for server cold-start prevention
POST	/api/auth/register	No	User account registration
POST	/api/auth/login	No	User authentication and HTTP-only cookie issuance
POST	/api/sync	Yes	Sync up to 6 latest accepted submissions from connected LeetCode
POST	/api/sync/manual	Yes	Manually add a problem by URL or title slug
GET	/api/problems	Yes	List user problems with search, difficulty, and stage filters
POST	/api/problems/:id/review	Yes	Submit review grade (easy, effort, forgot, skipped)
GET	/api/analytics	Yes	Fetch dashboard consistency stats, streaks, and difficulty ratios
GET	/api/leaderboard	Opt	Community streak and solve count rankings

Automated Email Reminders via Cron

The application exposes a dedicated endpoint to trigger daily reminder emails:

• Endpoint: ALL /api/notifications/send-due-reminders
• Authentication: Protected by CRON_SECRET. Supports:
  • Header: Authorization: Bearer <CRON_SECRET>
  • Header: x-cron-secret: <CRON_SECRET>
  • Query Parameter: ?secret=<CRON_SECRET>
• Immediate Test Trigger: POST /api/notifications/test-email (Authenticated user sends test digest to their registered email)
• Daily Cron Integration: Configure a free daily cron on cron-job.org pointing to:

  GET https://your-server.onrender.com/api/notifications/send-due-reminders?secret=your-secure-cron-trigger-token

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Contributing

Contributions, issues, and feature suggestions are welcome!

1. Fork the Repository (https://github.com/VinitKumarGupta/LeetRevise/fork)
2. Create your Feature Branch (git checkout -b feature/AmazingFeature)
3. Commit your Changes (git commit -m 'feat: Add AmazingFeature')
4. Push to the Branch (git push origin feature/AmazingFeature)
5. Open a Pull Request

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License

Distributed under the MIT License. See LICENSE for full details.