# Live Inventory CDC Demo

Small POC website showing browser CRUD actions flowing through Postgres, Debezium Server, NATS JetStream, a Go SSE backend, and back into the browser.

The important demo behavior is that mutation endpoints only return `command accepted`. The visible inventory cards are refreshed when the matching CDC event arrives over `/events`.

## Development Run

Development uses `compose.yml` for Postgres, NATS JetStream, Debezium, and helper containers. The Go web app runs as a native host process.

Install the host tools:

```bash
sudo dnf install golang podman
```

Use Taskfile as the main interface:

```bash
task --list
```

Terminal 1, start containerized Postgres, NATS, and Debezium:

```bash
task infra
```

Terminal 2, run the Go backend/frontend:

```bash
task backend
```

Then open:

```text
http://localhost:8080
```

Postgres is published to the host on:

```text
localhost:5453
```

NATS is published to the host on:

```text
localhost:4222
```

Development Debezium uses the internal compose addresses `postgres:5432` and `nats:4222`.

The Go backend defaults to:

```text
DATABASE_URL=postgres://postgres:postgres@localhost:5453/postgres?sslmode=disable
NATS_URL=nats://localhost:4222
```

## Production Run

Production uses user-level Podman quadlets for containers and a user systemd service for the Go backend.

Install the production units:

```bash
task prod:install
```

Start everything:

```bash
task prod:start
```

Stop everything:

```bash
task prod:down
```

Follow production logs:

```bash
task prod:logs
```

Production Debezium uses the internal quadlet network addresses `cdc-postgres:5432` and `cdc-nats:4222`.

## Production User Units

Quadlet files are installed to:

```text
~/.config/containers/systemd/
```

The Go backend service is installed to:

```text
~/.config/systemd/user/cdc-inventory.service
```

The service files are:

| Unit | Purpose |
|---|---|
| `cdc-postgres.service` | Postgres with logical replication enabled |
| `cdc-nats.service` | NATS JetStream |
| `cdc-debezium.service` | Debezium Server |
| `cdc-inventory.service` | Native Go backend/frontend |
| `cdc-seed.service` | One-shot seed helper |
| `cdc-inspect.service` | One-shot NATS inspect helper |

## Useful Checks

Inspect stream subjects and recent events:

```bash
task inspect
```

For production:

```bash
task prod:inspect
```

Generate a fresh burst of create/update/delete events:

```bash
task seed
```

For production:

```bash
task prod:seed
```

Stop development infrastructure:

```bash
task down
```

## Endpoints

| Method | Path | Purpose |
|---|---|---|
| `GET` | `/` | Demo page |
| `GET` | `/health` | Health check |
| `GET` | `/api/inventory` | Current database snapshot |
| `POST` | `/api/inventory` | Create inventory item |
| `PATCH` | `/api/inventory/{id}/sell` | Decrement quantity by 1 |
| `PATCH` | `/api/inventory/{id}/restock` | Increment quantity |
| `PATCH` | `/api/inventory/{id}` | Rename, move, or set quantity |
| `DELETE` | `/api/inventory/{id}` | Delete item |
| `GET` | `/events` | Server-Sent Events from CDC stream |

## Pipeline

```text
Browser action
-> Go backend writes to Postgres
-> Debezium captures the DB change
-> Debezium publishes to NATS JetStream
-> Go backend consumes the event
-> Go backend streams it to browser with SSE
-> Browser updates inventory and audit trail
```