# Monitoring Cycle

This page explains when go-web-monitor checks sites, how it runs checks concurrently, and how each round's results reach the config file and the screen.

## Triggers

| Trigger | Source | Behavior |
|---------|--------|----------|
| Startup | `UI.start()` (`internal/service/ui.go:96`) | Runs one `Monitor.Update()` round as soon as the interface starts |
| Every minute | `time.NewTicker(1 * time.Minute)` | Runs `Update()` at a fixed interval; the interval is not configurable |
| `refresh` command | `handleCommand` | Runs one `Update()` round in a background goroutine right away |
| `add <url>` command | `Monitor.Add()` | Checks only the newly added site |

Exiting (`quit` or <kbd>Ctrl+C</kbd>) closes the quit channel, which stops the schedule loop.

## Flow of One Round

```mermaid
sequenceDiagram
    participant U as UI
    participant M as Monitor
    participant W as Target site
    participant F as .webMonitor.json
    U->>M: Update()
    par One goroutine per site
        M->>W: Check(url)
        W-->>M: model.Website
        M->>M: Update failure count, alert if needed
    end
    M->>F: Save()
    U->>U: QueueUpdateDraw(updateUI)
```

1. `Update()` (`internal/service/monitor.go:159`) starts one goroutine per URL in the watch list and waits for all of them with a `sync.WaitGroup`.
2. Each goroutine calls `Check()` to get the status code, duration, and SSL days remaining (see [HTTP Probing](/probing) and [SSL Expiry](/ssl-expiry)).
3. The result updates the site's failure count, and the 5th consecutive offline check sends an alert (see [Alert Rules](/alerting)).
4. When every goroutine finishes, `Save()` overwrites `.webMonitor.json` with the full status and SMTP config.
5. The interface redraws the table and System panel through `QueueUpdateDraw`.

## Duration Bound

A round takes as long as its slowest site. The worst case for one site is HEAD and GET each hitting the 10-second timeout, plus the SSL certificate connection; sites run in parallel, so these times do not add up across sites.

## When the Config File Is Written

| When | Content written |
|------|-----------------|
| End of each `Update()` round | Every site's status plus the SMTP config |
| After a successful `add` / `del` | Same |
| After any `smtp <key> <value>` command | Same |

Writes overwrite the whole file (`util.Save`), so manual edits made while the program runs are lost.