add wifi_stations check type

README.md

@@ -8,14 +8,17 @@
 
 ## Features
 
-- **Extensible Check System**: Modular check types (ping, with more planned) via a Registry/Factory pattern.
+- **Extensible Check System**: Modular check types via a Registry/Factory pattern. Each check type implements a common `Check` interface and declares its own metrics through a `Descriptor`.
+- **Built-in Check Types**:
+  - **ping**: ICMP echo requests for host availability and latency.
+  - **wifi_stations**: Scrapes a Prometheus metrics endpoint for connected WiFi client counts per radio interface.
+- **Multi-Metric Checks**: Checks can produce multiple metrics stored as separate data sources in a single RRD file. Multi-metric checks render as stacked area graphs.
 - **Host Status Aggregation**: Each host has an aggregate status (`up`, `down`, `degraded`, `unknown`) computed from all its checks. A check must be alive and have reported within the last 5 minutes to count as healthy.
-- **Ping Monitoring**: Sends ICMP Echo Requests to check host availability.
-- **Latency Logging**: Uses RRD to store latency data over time.
-- **Graphs Generation**: Generates historical latency graphs (15 minutes, 4 hours, 8 hours, etc.) for each host.
+- **RRD Storage**: Uses Round Robin Databases for time-series data, with configurable archives from 1-minute resolution (1 week) to 8-hour resolution (5 years).
+- **Graph Generation**: Generates historical graphs at multiple time scales (15 minutes through 5 years) for each check type on each host.
 - **Simple Web Interface**: Serves an HTML/JS front-end to display host status and dynamically loaded graphs. Available in table and flame graph formats.
 - **REST API**: Exposes JSON data of all hosts and their status at `GET /api`.
-- **Prometheus Support**: Exposes metrics in prometheus format at `GET /metrics`.
+- **Prometheus Support**: Exposes metrics in Prometheus format at `GET /metrics`.
 
 ## Requirements
 
@@ -102,6 +105,65 @@ Ensure the following are installed:
 - **Port** (`--port`): Port on which the API and front-end are served.
 - **Logging Level** (`--log-level`): Set the verbosity of logs (e.g., `debug`, `info`, `warn`, `error`, `fatal`, `panic`).
 
+### Host Configuration
+
+Hosts are defined in a JSON file. Each host can specify an address and a set of checks. Hosts without an explicit `checks` block default to a ping check.
+
+```json
+{
+	"router": {},
+	"google": {
+		"address": "8.8.8.8",
+		"checks": {
+			"ping": { "timeout": "5s" }
+		}
+	},
+	"ap1": {
+		"checks": {
+			"ping": {},
+			"wifi_stations": {
+				"radios": ["phy0-ap0", "phy1-ap0"]
+			}
+		}
+	},
+	"disabled-example": {
+		"checks": {
+			"ping": { "enabled": false }
+		}
+	}
+}
+```
+
+### Check Types
+
+#### ping
+
+Sends ICMP echo requests to check host availability and measure latency.
+
+| Option    | Type   | Default | Description                    |
+| --------- | ------ | ------- | ------------------------------ |
+| `timeout` | string | `"3s"`  | Ping timeout (Go duration)     |
+| `count`   | number | `1`     | Number of ping packets to send |
+| `enabled` | bool   | `true`  | Set to `false` to disable      |
+
+#### wifi_stations
+
+Scrapes a Prometheus metrics endpoint for `wifi_stations{ifname="..."}` gauge values, reporting connected client counts per radio interface. Each configured radio becomes a separate data source in the RRD, rendered as a stacked area graph.
+
+| Option    | Type     | Default                      | Description                                |
+| --------- | -------- | ---------------------------- | ------------------------------------------ |
+| `radios`  | []string | _(required)_                 | List of `ifname` label values to monitor   |
+| `url`     | string   | `http://{host}:9100/metrics` | Full URL override for the metrics endpoint |
+| `timeout` | string   | `"5s"`                       | HTTP scrape timeout (Go duration)          |
+| `enabled` | bool     | `true`                       | Set to `false` to disable                  |
+
+The target host expects a Prometheus node exporter (or compatible) exposing metrics like:
+
+```
+wifi_stations{ifname="phy0-ap0"} 3
+wifi_stations{ifname="phy1-ap0"} 7
+```
+
 ## Host Status
 
 Each host has an aggregate status derived from all its enabled checks:
@@ -136,6 +198,26 @@ Returns JSON with the status of all hosts:
 			}
 		}
 	},
+	"ap1": {
+		"status": "up",
+		"checks": {
+			"ping": {
+				"alive": true,
+				"metrics": {
+					"latency_us": 237
+				},
+				"lastupdate": 1700000000
+			},
+			"wifi_stations": {
+				"alive": true,
+				"metrics": {
+					"phy0-ap0": 3,
+					"phy1-ap0": 7
+				},
+				"lastupdate": 1700000000
+			}
+		}
+	},
 	"router": {
 		"status": "unknown",
 		"checks": {}
@@ -152,6 +234,8 @@ Exposes Prometheus-formatted metrics:
 ```
 check_alive{host="google", address="8.8.8.8", check="ping"} 1
 check_metric{host="google", address="8.8.8.8", check="ping", metric="latency_us"} 12345
+check_alive{host="ap1", address="", check="ping"} 1
+check_metric{host="ap1", address="", check="ping", metric="latency_us"} 237
 ```
 
 ## Data Directory Layout
@@ -165,20 +249,26 @@ data/
 │   │   └── ping.rrd
 │   ├── google/
 │   │   └── ping.rrd
+│   ├── ap1/
+│   │   ├── ping.rrd
+│   │   └── wifi_stations.rrd
 │   └── ...
 └── graphs/
     └── imgs/
         ├── router/
         │   ├── router_ping_15m.png
         │   ├── router_ping_1h.png
         │   └── ...
-        ├── google/
-        │   ├── google_ping_15m.png
+        ├── ap1/
+        │   ├── ap1_ping_15m.png
+        │   ├── ap1_ping_1h.png
+        │   ├── ap1_wifi_stations_15m.png
+        │   ├── ap1_wifi_stations_1h.png
         │   └── ...
         └── ...
 ```
 
-Each check type gets its own RRD file (e.g., `ping.rrd`), making it straightforward to add new check types in the future without filename collisions.
+Each check type gets its own RRD file (e.g., `ping.rrd`, `wifi_stations.rrd`). Multi-metric checks store all their data sources in a single RRD file.
 
 ## Makefile Targets
 

pkg/check/check.go

@@ -8,9 +8,11 @@
 // provides a uniform shape regardless of check type: success/failure,
 // a set of named metrics, and an optional error.
 //
-// Each check type provides a Descriptor that declares what metrics it
-// produces, allowing the system to generically wire up storage and
-// visualization without per-type knowledge.
+// Each check instance provides a Descriptor via Describe() that declares
+// what metrics it produces. This allows check instances with config-dependent
+// metrics (e.g. wifi_stations with a variable number of radios) to declare
+// their own metric shape, while checks with static metrics (e.g. ping) can
+// simply return a package-level constant.
 //
 // The Registry provides type discovery, allowing check types to be
 // registered by name and instantiated from configuration at runtime.
@@ -25,6 +27,11 @@ type Check interface {
 	// Type returns the registered name of this check type (e.g. "ping", "http").
 	Type() string
 
+	// Describe returns the Descriptor for this check instance, declaring
+	// what metrics it produces. The descriptor may vary between instances
+	// of the same check type depending on configuration.
+	Describe() Descriptor
+
 	// Run executes the check and returns a Result.
 	// The provided context can be used for cancellation and timeouts.
 	Run(ctx context.Context) Result

pkg/check/descriptor.go

@@ -21,11 +21,11 @@ type MetricDef struct {
 	Scale int
 }
 
-// Descriptor declares static metadata about a check type, including
-// what metrics it produces. This is registered alongside the Factory
-// so the system can generically wire up storage and graphs without
-// per-type knowledge.
+// Descriptor declares metadata about a check instance, including what
+// metrics it produces. Each check instance returns its own Descriptor
+// via Check.Describe(), allowing config-dependent metric shapes (e.g.
+// a wifi_stations check with a variable number of radios).
 type Descriptor struct {
-	// Metrics lists the metrics this check type produces.
+	// Metrics lists the metrics this check instance produces.
 	Metrics []MetricDef
 }

pkg/check/ping/ping.go

@@ -92,6 +92,12 @@ func (p *Ping) Type() string {
 	return TypeName
 }
 
+// Describe returns the Descriptor for this ping check instance.
+// Ping always produces the same metrics regardless of configuration.
+func (p *Ping) Describe() check.Descriptor {
+	return Desc
+}
+
 // Run executes the ping check and returns a Result.
 func (p *Ping) Run(ctx context.Context) check.Result {
 	now := time.Now()