# kronos

Share events between services.

## Setup

Nix is required.

- Set up environment.

```bash
direnv allow
```

- Set up pre-commit hooks.

```bash
pre-commit install
```

- Install as editable package.

```bash
pip install -e .
```

## Run

Once installed, run:

```bash
kronos
```

TODO: add parameters.
TODO: add info on how to run as a Podman service.

## High level design

`kronos` is an application able to sync events from a single source of truth to multiple consumer services.
E.g., an event defined by Mobilizon is modified -> Discord, Meetup, any other, are updated.

It is deployed as a Docker container, running as a service.
Persistent storage is required for SQLite database.
Secrets management is used to handle credentials.
`systemd` timer is configured to trigger the app.
E.g., `kronos` is being run every three hours to perform events update.

Each app run performs the following:
- Request event data from source of truth service (e.g., Mobilizon).
- Compare event data between received and stored in the database.
  - Update if new data available (last change date is later than known).
  - Stop execution otherwise.
- Send updates event data to consumers.

```plain
┌───────────────────────────────────────────────────────────────────────────────────────────────┐
│                                                                                               │
│ CONTAINER                                                                                     │
│                                                                                               │
│              ┌───────────────┐               ┌────────┐                                       │
│              │               │               │        │                                       │
│              │ systemd timer │               │ volume │                                       │
│              │               │               │        │                                       │
│              └───────┬───────┘               └────┬───┘                                       │
│                      │                            │                                           │
│ ┌────────────────────┴────────────────────────────┼─────────────────────────────────────────┐ │
│ │                                                 │                                         │ │
│ │  APP                                            │                                         │ │
│ │            ┌───────────────┐               ┌────┴─────┐                ┌────────────────┐ │ │
│ │   trigger  │               │  event data   │          │  event data    │                │ │ │
│ │ ──────────►│ data provider ├──────────────►│ database ├───────────────►│ data consumers │ │ │
│ │            │               │               │          │                │                │ │ │
│ │            └───────────────┘               └──────────┘                └────────────────┘ │ │
│ │                                                                                           │ │
│ └───────────────────────────────────────────────────────────────────────────────────────────┘ │
│                                                                                               │
└───────────────────────────────────────────────────────────────────────────────────────────────┘
```