# CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

## Common Commands

### Development
```bash
# Install dependencies
mix deps.get

# Compile the project
mix compile

# Run in development (non-halt mode)
mix run --no-halt

# Run tests
mix test

# Run specific test
mix test test/systant_test.exs

# Enter development shell (via Nix)
nix develop

# Run both server and dashboard together (recommended)
just dev
# or directly: hivemind

# Run components individually
just server      # or: cd server && mix run --no-halt
just dashboard   # or: cd dashboard && mix phx.server

# Other just commands
just deps        # Install dependencies for both projects
just compile     # Compile both projects
just test        # Run tests for both projects
just clean       # Clean both projects
```

### Production
```bash
# Build production release
MIX_ENV=prod mix release

# Run production release
_build/prod/rel/systant/bin/systant start
```

## Architecture Overview

This is an Elixir OTP application that serves as a systemd daemon for MQTT-based system monitoring, designed for deployment across multiple NixOS hosts to integrate with Home Assistant.

### Core Components
- **Systant.Application** (`lib/systant/application.ex`): OTP application supervisor that starts the MQTT client
- **Systant.MqttClient** (`lib/systant/mqtt_client.ex`): GenServer handling MQTT connection, metrics publishing, and command subscriptions
- **Systant.MqttHandler** (`lib/systant/mqtt_handler.ex`): Custom Tortoise handler for processing command messages with security validation
- **Systant.CommandExecutor** (`lib/systant/command_executor.ex`): Secure command execution engine with whitelist validation and audit logging
- **Systant.SystemMetrics** (`lib/systant/system_metrics.ex`): Comprehensive Linux system metrics collection with configuration support
- **Systant.Config** (`lib/systant/config.ex`): TOML-based configuration loader with environment variable overrides
- **Dashboard.Application** (`dashboard/lib/dashboard/application.ex`): Phoenix LiveView dashboard application
- **Dashboard.MqttSubscriber** (`dashboard/lib/dashboard/mqtt_subscriber.ex`): Real-time MQTT subscriber that feeds data to the LiveView dashboard

### Key Libraries
- **Tortoise**: MQTT client library for pub/sub functionality
- **Jason**: JSON encoding/decoding for message payloads
- **Toml**: TOML configuration file parsing
- **Phoenix LiveView**: Real-time dashboard framework

### MQTT Behavior
- Publishes comprehensive system metrics (CPU, memory, disk, GPU, network, temperature, processes) to stats topic
- Subscribes to commands topic for incoming events that can trigger user-customizable actions
- Uses hostname-based randomized client ID to avoid conflicts across multiple hosts
- Configurable startup delay (default 5 seconds) before first metrics publish
- Real-time metrics collection with configurable intervals
- **Connection verification**: Tests MQTT connectivity on startup with timeout-based validation
- **Graceful shutdown**: Exits cleanly via `System.stop(1)` when MQTT broker unavailable (prevents crash dumps)

### Configuration System
Systant uses a TOML-based configuration system with environment variable overrides:

- **Config File**: `systant.toml` (current dir, `~/.config/systant/`, or `/etc/systant/`)
- **Module Control**: Enable/disable metric collection modules (cpu, memory, disk, gpu, network, temperature, processes, system)
- **Filtering Options**: Configurable filtering for disks, network interfaces, processes
- **Environment Overrides**: `MQTT_HOST`, `MQTT_PORT`, `SYSTANT_INTERVAL`, `SYSTANT_LOG_LEVEL`

#### Key Configuration Sections
- `[general]`: Collection intervals, enabled modules
- `[mqtt]`: Broker settings, client ID prefix, credentials
- `[commands]`: Command execution settings, security options
- `[[commands.available]]`: User-defined command definitions with security parameters
- `[disk]`: Mount filtering, filesystem exclusions
- `[gpu]`: NVIDIA/AMD GPU limits and settings
- `[network]`: Interface filtering, traffic thresholds
- `[processes]`: Top process limits, sorting options
- `[temperature]`: CPU/sensor temperature monitoring

### Default Configuration
- **MQTT Host**: `mqtt.home` (configurable via `MQTT_HOST`)
- **Stats Topic**: `systant/${hostname}/stats` (per-host topics)
- **Command Topic**: `systant/${hostname}/commands` (per-host topics) 
- **Response Topic**: `systant/${hostname}/responses` (command responses)
- **Publish Interval**: 30 seconds (configurable via `SYSTANT_INTERVAL`)
- **Command System**: Enabled by default with example commands (restart, info, df, ps, ping)

### NixOS Deployment
This project includes a complete Nix packaging and NixOS module:

- **Package**: `nix/package.nix` - Builds the Elixir release using beamPackages.mixRelease
- **Module**: `nix/nixos-module.nix` - Provides `services.systant` configuration options
- **Development**: Use `nix develop` for development shell with Elixir/Erlang

The NixOS module supports:
- Configurable MQTT connection settings
- Per-host topic naming using `${config.networking.hostName}`
- Environment variable configuration for runtime settings
- Systemd service with security hardening
- Auto-restart and logging to systemd journal

## Dashboard

The project includes a Phoenix LiveView dashboard (`dashboard/`) that provides real-time monitoring of all systant instances.

### Dashboard Features
- Real-time host status updates via MQTT subscription
- LiveView interface showing all connected hosts
- Automatic reconnection and error handling

### Dashboard MQTT Configuration
- Subscribes to `systant/+/stats` to receive updates from all hosts
- Uses hostname-based client ID: `systant-dashboard-${hostname}` to avoid conflicts
- Connects to `mqtt.home:1883` (same broker as systant instances)

### Important Implementation Notes
- **Tortoise Handler**: The `handle_message/3` callback must return `{:ok, state}`, not `[]`
- **Topic Parsing**: Topics may arrive as lists or strings, handle both formats
- **Client ID Conflicts**: Use unique client IDs to prevent connection instability

## Development Roadmap

### Phase 1: System Metrics Collection (Completed)
- ✅ **SystemMetrics Module**: `server/lib/systant/system_metrics.ex` - Comprehensive metrics collection  
- ✅ **CPU Metrics**: Load averages (1/5/15min) via `/proc/loadavg`
- ✅ **Memory Metrics**: System memory data via `/proc/meminfo` with usage percentages
- ✅ **Disk Metrics**: Disk usage and capacity via `df` command with configurable filtering
- ✅ **GPU Metrics**: NVIDIA (nvidia-smi) and AMD (rocm-smi) GPU monitoring with temperature, utilization, memory
- ✅ **Network Metrics**: Interface statistics via `/proc/net/dev` with traffic filtering  
- ✅ **Temperature Metrics**: CPU temperature and lm-sensors data via system files and `sensors` command
- ✅ **Process Metrics**: Top processes by CPU/memory via `ps` command with configurable limits
- ✅ **System Info**: Uptime via `/proc/uptime`, kernel version, OS info, Erlang runtime data
- ✅ **MQTT Integration**: Real metrics published with configurable intervals replacing simple messages
- ✅ **Configuration System**: Complete TOML-based configuration with environment overrides
- ✅ **Dashboard Integration**: Phoenix LiveView dashboard with real-time graphical metrics display

#### Implementation Details
- Uses Linux native system commands and `/proc` filesystem for accuracy over Erlang os_mon
- Configuration-driven metric collection with per-module enable/disable capabilities
- Advanced filtering: disk mounts/types, network interfaces, process thresholds
- Graceful error handling with fallbacks when commands/files unavailable
- JSON payload structure: `{timestamp, hostname, cpu, memory, disk, gpu, network, temperature, processes, system}`
- Dashboard displays metrics as progress bars and cards with color-coded status indicators
- TOML configuration with environment variable overrides for deployment flexibility

### Phase 2: Command System (Completed)
- ✅ **Command Execution**: `server/lib/systant/command_executor.ex` - Secure command processing with whitelist validation
- ✅ **MQTT Handler**: `server/lib/systant/mqtt_handler.ex` - Custom Tortoise handler for command message processing
- ✅ **User Configuration**: Commands fully configurable via `systant.toml` with security parameters
- ✅ **MQTT Integration**: Commands via `systant/{hostname}/commands`, responses via `systant/{hostname}/responses`
- ✅ **Security Features**: Whitelist-only execution, parameter validation, timeouts, comprehensive logging
- ✅ **Built-in Commands**: `list` command shows all available user-defined commands

#### Command System Features
- **User-Configurable Commands**: Define custom commands in `systant.toml` with triggers, allowed parameters, timeouts
- **Enterprise Security**: No arbitrary shell execution, strict parameter validation, execution timeouts
- **Simple Interface**: Send `{"command":"trigger","params":[...]}`, receive structured JSON responses
- **Request Tracking**: Auto-generated request IDs for command/response correlation
- **Comprehensive Logging**: Full audit trail of all command executions with timing and results

#### Example Command Usage
```bash
# Send commands via MQTT
mosquitto_pub -t "systant/hostname/commands" -m '{"command":"list"}'
mosquitto_pub -t "systant/hostname/commands" -m '{"command":"info"}'
mosquitto_pub -t "systant/hostname/commands" -m '{"command":"df","params":["/home"]}'
mosquitto_pub -t "systant/hostname/commands" -m '{"command":"restart","params":["nginx"]}'

# Listen for responses
mosquitto_sub -t "systant/+/responses"
```

### Phase 3: Home Assistant Integration (Completed)
- ✅ **MQTT Auto-Discovery**: `server/lib/systant/ha_discovery.ex` - Publishes HA discovery configurations for automatic device registration
- ✅ **Device Registration**: Creates unified "Systant {hostname}" device in Home Assistant with comprehensive sensor suite
- ✅ **Sensor Auto-Discovery**: CPU load averages, memory usage, system uptime, temperatures, GPU metrics, disk usage, network throughput
- ✅ **Configuration Integration**: TOML-based enable/disable with `homeassistant.discovery_enabled` setting
- ✅ **Value Templates**: Proper JSON path extraction for nested metrics data with error handling
- ✅ **Real-time Updates**: Seamless integration with existing MQTT stats publishing - no additional topics needed

#### Home Assistant Integration Features
- **Automatic Discovery**: No custom integration required - uses standard MQTT discovery protocol
- **Device Grouping**: All sensors grouped under single "Systant {hostname}" device for clean organization  
- **Comprehensive Metrics**: CPU, memory, disk, GPU (NVIDIA/AMD), network throughput, temperature, and system sensors
- **Configuration Control**: Enable/disable discovery via `systant.toml` configuration
- **Template Flexibility**: Advanced Jinja2 templates handle optional/missing data gracefully
- **Topic Structure**: Discovery on `homeassistant/#`, stats remain on `systant/{hostname}/stats`

#### Setup Instructions
1. **Configure MQTT Discovery**: Set `homeassistant.discovery_enabled = true` in `systant.toml`
2. **Start Systant**: Discovery messages published automatically on startup (1s after MQTT connection)
3. **Check Home Assistant**: Device and sensors appear automatically in MQTT integration
4. **Verify Metrics**: All sensors should show current values within 30 seconds

#### Available Sensors
- **CPU**: Load averages (1m, 5m, 15m), temperature
- **Memory**: Usage percentage, used/total in GB
- **Disk**: Root and home filesystem usage percentages  
- **GPU**: NVIDIA/AMD utilization, temperature, memory usage
- **Network**: RX/TX throughput in MB/s for primary interface (real-time bandwidth monitoring)
- **System**: Uptime in hours, kernel version, online status

### Future Plans
- Multi-host deployment for comprehensive system monitoring
- Advanced alerting and threshold monitoring
- Historical data retention and trending