# Architecture

This page shows how the go-web-monitor packages layer together in one diagram, then lists each layer's responsibility and the principles shared across layers.

## System Overview

```mermaid
graph TB
    Main[cmd/tui<br/>main] -->|util.Read / util.Save| Store[(.webMonitor.json)]
    Main -->|service.New| Monitor[service.Monitor]
    Main -->|service.NewUI| UI[service.UI]
    UI -->|Ticker every minute / refresh| Monitor
    UI -->|command methods| Monitor
    Monitor -->|Check: HEAD → GET| Site[Target site]
    Monitor -->|util.CheckExpire| TLS[Target site :443]
    Monitor -->|sendEmail / TestEmail| SMTP[service.SMTP]
    SMTP --> Mail[Mail server]
    Monitor -->|Save| Store
```

## Layers

| Layer | Package / File | Responsibility |
|-------|----------------|----------------|
| Entry | `cmd/tui/main.go` | Creates or reads `.webMonitor.json`, wires `Monitor` and `UI`, then runs |
| Interface | `internal/service/ui.go` | tview interface, one-minute schedule, command parsing, table and panel rendering |
| Monitor core | `internal/service/monitor.go` | Watch list and status table, HTTP probing, failure counting, alert triggering, SMTP config management |
| Mailer | `internal/service/smtp.go` | Picks plain / implicit TLS / STARTTLS by port and sends HTML email |
| Utilities | `internal/util/` | JSON config file IO and SSL certificate days remaining |
| Data model | `internal/model/model.go` | `Website`, `Config`, `MonitorData` |

## Cross-Cutting Principles

| Principle | Implementation |
|-----------|----------------|
| One persistence file | All state and settings live in `.webMonitor.json` in the current directory; no database or external service |
| State lives in Monitor | `UI` holds no data and reads or writes only through `Monitor` getters and command methods |
| Shared state guarded by `sync.RWMutex` | `list`, `status`, `config`, and `isShow` share one lock (coverage is incomplete; see [Known Limitations](/known-limitations)) |
| Standard-library networking | HTTP, TLS, and SMTP use only the standard library; the only third-party packages are `tview` and `tcell` |

## Further Reading

- Full module-level diagrams (module internals, sequence, state machines): [doc/architecture.md](https://github.com/pardnchiu/go-web-monitor/blob/main/doc/architecture.md)
- The flow of one check round: [Monitoring Cycle](/monitoring-cycle)