# Concepts

This chapter describes the core concepts around the implementation and the IRC specification. Some material may be restated from the source but it is gathered here for reference purposes.

## IRC

For the core IRC concepts see: [IRC concepts](https://modern.ircdocs.horse/#irc-concepts)

## Implementation

### Client

This is something that sends bytes to our server according to the IRC protocol (something that communicates with the server but is not a server). This is also something outside of this implementation and this is modelled as something from which we receive and send bytes to.

### Server

This is our implementation which communicates with the client and other servers in the same network. According to IRC specification network consists of servers and even though there is server to server protocols available in practise one network consists of same server implementations and they can use any protocol they wish to communicate state changes between them. We will utilize this in our implementation.

### User

This entity models a real user (either human or bot) which uses the client to communicate with our server.

### Channel

Channels represent the logical conversation groups in an IRC network. These are synced between servers in the network. This entity ties users to channels in which they can exchange messages.

### Capability

When the client connects to the server they first have an exchange of information which tells the client what capabilities the server provides. This allows the client to establish reasonable communication with the server. In the implementation different capabilities are implemented in a modular manner which are queried during runtime to provide the capability information to the client.

# Architecture

In general principle we follow modular monolith approach where we have a single executable for the application but that application is composed of modules which are independent and focus on specific features (capabilities) and the runtime then ties these together. In addition there are modules which handles the low-level work of communication.

## Components

### Server

This is the main high-level component that drives our server instance.

#### Capability

There are multiple capability components that each implement a specific functionality to the server.

### Pool

This is the component which tracks the running service instance in the network it is attached to. Network can consist of single server instance. State changes in this instance are then propagated to other servers in pool.

#### Server Communicator

This sub-component of the pool manages the communication between server instances.

### State Manager

This component maintains the state information (users, channels, etc.) for the current instance. It is linked to the pool component and the pool observes the changes in the state manager and propagates them forward and vice versa. That is pool may receive state update from a different server instance and pool then signals these changes to this instance's state manager.

### Protocol Stack

This component maintains the reference information for different communication and message components about specific IRC code constants and other similar information in the IRC protocol.

### Communicator

This component is responsible for sending and receiving bytes between client and server. It ensures the correct formatting of messages and their validation. This component is also linked to the state manager.