🚀 CodeClash

Scalable Online Judge & Competitive Programming Platform

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📖 Overview

CodeClash is a scalable online judge and competitive programming platform built to support coding contests, algorithmic problem solving, and secure code evaluation.

The platform provides contest management, Docker-based isolated execution, background processing, real-time updates, observability, and distributed caching for high-load scenarios.

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🔭 System Architecture

🧠 Key Engineering Decisions

• Clean Architecture + CQRS — enforces a one-way dependency flow (API → Application → Domain), keeping business logic independent of EF Core, Redis, or Docker.
• Dual DbContext for Identity — separating ApplicationIdentityDbContext from ApplicationDbContext avoids coupling domain entities to ASP.NET Identity's schema, while IdentityId provides the link.
• Redis caching for contest data — live standings and problem sets are cached during active contests, computed via EF LINQ aggregation and Redis sorted sets, with pagination to reduce database load under concurrent traffic.
• Hangfire for background jobs — used for post-contest processing (e.g., rank-up calculations) that shouldn't block request/response cycles.
• SignalR for real-time features — dedicated hubs isolate real-time concerns from REST endpoints.
• Docker-isolated judging — code execution runs in sandboxed containers to prevent untrusted submissions from affecting the host.

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✨ Features

• 🏆 Contests — creation, scheduling, registration, participant management, live standings.
• 📝 Problems — CRUD operations, Problem difficulty levels, topics/categorization, test cases, image/description support.
• 🕵️ Plagiarism Detection — Detects highly similar accepted submissions using code normalization → N-Grams → FNV-1a hashing → Winnowing fingerprinting → Jaccard similarity, helping identify potential copied solutions while reducing comparison cost.
• ⚡ Online Judge — Docker-isolated execution, real-time judging, execution time & memory tracking, Multi-language support ready.
• 🔐 Authentication & Authorization — JWT + refresh tokens, ASP.NET Identity, role-based authorization, email confirmation
• 📡 Real-time — SignalR hubs (e.g., contest editor, video chat).
• 🔍 Search — Elasticsearch-powered filtering and searching.
• 📊 Observability — OpenTelemetry tracing, structured logging via Serilog + Seq.
• 🧩 Architecture & Design — - Clean Architecture, CQRS Pattern, MediatR, Repository Pattern, Unit of Work.

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🛠 Tech Stack

Category	Technologies
Backend	ASP.NET Core 9, C#
Architecture	Clean Architecture, CQRS, MediatR, Repository + Unit of Work
Database	PostgreSQL, EF Core
Caching	Redis (StackExchange.Redis)
Real-time	SignalR
Background Jobs	Hangfire
Auth	JWT, ASP.NET Identity, Refresh Tokens, Email Confirmation
Containerization	Docker
Observability	OpenTelemetry, Serilog, Seq
Search	ElasticSearch
Testing	xUnit, Moq
Docs	Swagger / OpenAPI

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📂 Project Structure

src/
├── CodeClash.API/             # Controllers, middleware, Swagger config, SignalR hub registration
├── CodeClash.Application/     # CQRS commands/queries, MediatR handlers, validators, DTOs
├── CodeClash.Domain/          # Entities, enums, domain rules — framework-agnostic
├── CodeClash.Infrastructure/  # EF Core configs, Redis, Docker judge runner, Identity, Hangfire jobs

tests/
├── CodeClash.UnitTests/        # Handler and domain logic tests
└── CodeClash.IntegrationTests/ # API and persistence integration tests

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🗄 Domain Model

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🚀 Installation Guide

Prerequisites

• .NET 9 SDK
• PostgreSQL
• Redis
• Docker

🐳 Run with Docker (recommended)

git clone https://github.com/SeifMohmmed/CodeClash.git
cd CodeClash
docker-compose up --build

▶️ Run Locally

dotnet build
dotnet run --project src/CodeClash.API

Included Docker services: ASP.NET Core API, PostgreSQL, Redis, Seq, ElasticSearch.

📑 API docs available at https://localhost:5001/swagger/index.html once running.

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📡 API Endpoints

--- ## ⚙️ Environment Setup

Configure appsettings.Development.json:

{
  "ConnectionStrings": {
    "Database": "",
    "Redis": ""
  },
  "Jwt": {
    "Key": "",
    "Issuer": "",
    "Audience": ""
  }
}

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🧪 Testing

dotnet test

Stack: xUnit + Moq, covering handler logic (unit) and API/persistence flows (integration).

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