solid-csharp

Before writing any new code it requires a DRY check -- grep the codebase and Core/Services/Core/Contracts for existing logic to reuse before creating something new. See principles.md for the 5 SOLID principles and patterns.md for directory layout, testing, and record usage.

SOLID C# - Modular Architecture

Agent Workflow (MANDATORY)

Before ANY implementation, spawn 3 agents in parallel, one Agent call each with a name:

1. fuse-ai-pilot:explore-codebase - Analyze existing architecture
2. fuse-ai-pilot:research-expert - Verify .NET docs via Context7
3. fuse-ai-pilot:sniper - Post-implementation validation

---

DRY - Reuse Before Creating (MANDATORY)

Before writing ANY new code:

1. Grep the codebase for similar interfaces, services, or logic
2. Check shared locations: Core/Services/, Core/Contracts/
3. If similar code exists -> extend/reuse instead of duplicate
4. If code will be used by 2+ features -> create it in Core/

---

Architecture (Modules MANDATORY)

Layer	Location	Max Lines
Controllers	Modules/[Feature]/Controllers/	50
Services	Modules/[Feature]/Services/	100
Repositories	Modules/[Feature]/Repositories/	100
Contracts	Modules/[Feature]/Contracts/	30
Models	Modules/[Feature]/Models/	50
Shared	Core/{Services,Contracts,Models}/	-

NEVER use flat structure - always Modules/[Feature]/

---

Critical Rules (MANDATORY)

Rule	Value
File limit	100 lines (split at 90)
Controllers	< 50 lines, delegate to services
Interfaces	Contracts/ directory ONLY
XML docs	Every public member documented
DI	Use Microsoft.Extensions.DependencyInjection
Small interfaces	1-3 members max
Records	Prefer record for DTOs and value objects

---

Reference Guide

Topic	Reference	When to consult
SOLID Principles	principles.md	Quick reference for all 5 principles
Patterns & Structure	patterns.md	Directory layout, testing, records

---

Forbidden

Anti-Pattern	Fix
Files > 100 lines	Split at 90
Interfaces in impl files	Move to Contracts/ directory
Fat interfaces (4+ members)	Split into focused interfaces
Flat project structure	Use Modules/[Feature]/
new for dependencies	Use constructor injection + DI
Service Locator pattern	Use constructor injection