Architecture & Dependency Diagram

This page describes the project architecture and how the major layers depend on each other.

Dependency Diagram

┌──────────────────────────────────────────────────────────────────────────────┐
│ Application hosts                                                            │
│                                                                              │
│  CrestApps.Core.Mvc.Web   Aspire AppHost   Custom MVC / Razor / Blazor app   │
└───────────────────────────────┬──────────────────────────────────────────────┘
                                │
                                ▼
┌──────────────────────────────────────────────────────────────────────────────┐
│ Core foundation                                                              │
│                                                                              │
│  CrestApps.Core                 CrestApps.Core.Abstractions                  │
│  CrestApps.Core.Infrastructure  CrestApps.Core.Infrastructure.Abstractions   │
└───────────────────────────────┬──────────────────────────────────────────────┘
                                │
                                ▼
┌──────────────────────────────────────────────────────────────────────────────┐
│ AI runtime and feature packages                                              │
│                                                                              │
│  AI runtime   Chat   A2A   MCP   SignalR   Templates   Copilot   Markdown    │
│  Azure utilities                                                             │
└───────────────────────────────┬──────────────────────────────────────────────┘
                                │
                ┌───────────────┴────────────────┬─────────────────────────────┐
                ▼                                ▼                             ▼
┌──────────────────────────────┐  ┌──────────────────────────────┐  ┌──────────────────────────────┐
│ Provider integrations        │  │ Search and data sources      │  │ Storage implementations      │
│                              │  │                              │  │                              │
│ OpenAI / Azure OpenAI        │  │ Azure AI Search              │  │ Entity Framework Core        │
│ Ollama / Azure AI Inference  │  │ Elasticsearch                │  │ YesSql                       │
│ PDF / OpenXml / FTP / SFTP   │  │                              │  │                              │
└──────────────────────────────┘  └──────────────────────────────┘  └──────────────────────────────┘

Layer Descriptions

Project	Role
CrestApps.Core.Abstractions	Core interfaces: ICatalog<T>, INamedEntity, ExtensibleEntity, IODataValidator
CrestApps.Core.AI.Abstractions	AI interfaces: IAICompletionService, IAIProfileManager, IOrchestrator, models
CrestApps.Core	Default implementations of core abstractions, IServiceCollection extensions
CrestApps.Core.AI	AI orchestration, DefaultOrchestrator, tool execution, completion services
CrestApps.Core.AI.Chat	Chat session management, prompt storage, IAIChatSessionManager
CrestApps.Core.AI.Documents	Document ingestion, uploaded-file storage abstraction, document tools, and document RAG
CrestApps.Core.AI.OpenAI	OpenAI provider (ChatClient, streaming, tool calls)
CrestApps.Core.AI.OpenAI.Azure	Azure OpenAI provider with data source integration
CrestApps.Core.AI.Ollama	Ollama provider for locally hosted LLMs
CrestApps.Core.AI.AzureAIInference	Azure AI Inference / GitHub Models provider
CrestApps.Core.AI.Copilot	GitHub Copilot chat orchestration, OAuth flow, credential management
CrestApps.Core.Azure.AISearch	Azure AI Search provider primitives for client setup, index management, document management, and OData filters
CrestApps.Core.AI.Azure.AISearch	Azure AI Search integration for AI document index profiles, AI memory search, and AI data-source registrations
CrestApps.Core.Elasticsearch	Elasticsearch provider primitives for client setup, index management, document management, and query/filter translation
CrestApps.Core.AI.Elasticsearch	Elasticsearch integration for AI document index profiles, AI memory search, and AI data-source registrations
CrestApps.Core.AI.Mcp	Model Context Protocol (MCP) client and server
CrestApps.Core.AI.Mcp.Ftp	FTP/FTPS MCP resource type handler
CrestApps.Core.AI.Mcp.Sftp	SFTP MCP resource type handler
CrestApps.Core.Azure	Azure-specific utilities and integration helpers
CrestApps.Core.SignalR	SignalR hub abstractions for real-time AI chat
CrestApps.Core.Support	General utility classes
CrestApps.Core.Templates	Prompt template engine

Storage layer

Project	Role
CrestApps.Core.Data.EntityCore	Entity Framework Core-based catalog and store implementation
CrestApps.Core.Data.YesSql	YesSql-based document catalog implementation (SQLite, PostgreSQL, SQL Server)

Application layer

Project	Role
CrestApps.Core.Mvc.Web	Standalone ASP.NET Core MVC application with full admin UI
Blazor / Other	Blazor Server/WASM (CrestApps.Core.Blazor.Web), minimal APIs, etc.

Data Flow

User → UI (MVC/Blazor/OC) → SignalR Hub → Orchestrator → AI Provider → LLM
                                  ↓                              ↑
                          Session Manager ←──── Prompt Store ────┘
                                  ↓
                          YesSql / Custom Store

1. User sends a message via the UI (browser)
2. SignalR Hub receives the message and resolves the AI profile
3. Orchestrator builds the conversation context (system prompt, history, tools)
4. AI Provider (OpenAI, Azure, Ollama) streams the response
5. Prompt Store persists both user and assistant messages
6. SignalR Hub streams response chunks back to the client

Extensibility Points

Interface	Purpose	Default Implementation
IAICompletionService	AI provider abstraction	OpenAI, Azure OpenAI, Ollama
IOrchestrator	Controls AI request pipeline	DefaultOrchestrator
ICatalog<T>	CRUD for named entities	NamedSourceDocumentCatalog<T> (YesSql)
IAIProfileManager	Profile CRUD	DefaultAIProfileManager
IAIChatSessionManager	Session lifecycle	YesSql-based implementation
IAIChatSessionPromptStore	Prompt persistence	YesSql-based implementation
ICatalogEntryHandler<T>	Entity lifecycle hooks	Per-provider handlers