From 66eba874c3c8f4b4aa05fbd0ea46c27c22777c7f Mon Sep 17 00:00:00 2001
From: djkazic <kevincai96@gmail.com>
Date: Wed, 26 Jun 2024 12:02:53 -0400
Subject: [PATCH] collectors: add StateCollector

---
 collectors/prometheus.go      |  1 +
 collectors/state_collector.go | 98 +++++++++++++++++++++++++++++++++++
 2 files changed, 99 insertions(+)
 create mode 100644 collectors/state_collector.go

diff --git a/collectors/prometheus.go b/collectors/prometheus.go
index 3515098..5377c08 100644
--- a/collectors/prometheus.go
+++ b/collectors/prometheus.go
@@ -104,6 +104,7 @@ func NewPrometheusExporter(cfg *PrometheusConfig, lnd *lndclient.LndServices,
 		NewWalletCollector(lnd, errChan),
 		NewPeerCollector(lnd.Client, errChan),
 		NewInfoCollector(lnd.Client, errChan),
+		NewStateCollector(lnd, errChan),
 	}
 
 	if !monitoringCfg.DisableHtlc {
diff --git a/collectors/state_collector.go b/collectors/state_collector.go
new file mode 100644
index 0000000..46f5b2b
--- /dev/null
+++ b/collectors/state_collector.go
@@ -0,0 +1,98 @@
+package collectors
+
+import (
+	"context"
+	"fmt"
+	"sync"
+	"time"
+
+	"github.com/lightninglabs/lndclient"
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+type StateCollector struct {
+	lnd *lndclient.LndServices
+
+	// Use one gauge to track the starting time of LND.
+	timeToStartDesc *prometheus.Desc
+
+	// startTime records a best-effort timestamp of when LND was started.
+	startTime time.Time
+
+	// endTime records when LND makes a transition from RPC_ACTIVE to
+	// SERVER_ACTIVE.
+	endTime time.Time
+
+	// mutex is a lock for preventing concurrent writes to startTime or
+	// endTime.
+	mutex sync.RWMutex
+
+	// errChan is a channel that we send any errors that we encounter into.
+	// This channel should be buffered so that it does not block sends.
+	errChan chan<- error
+}
+
+// NewStateCollector returns a new instance of the StateCollector.
+func NewStateCollector(lnd *lndclient.LndServices,
+	errChan chan<- error) *StateCollector {
+
+	sc := &StateCollector{
+		lnd: lnd,
+		timeToStartDesc: prometheus.NewDesc(
+			"lnd_time_to_start_secs",
+			"time to start in seconds",
+			nil, nil,
+		),
+		errChan: errChan,
+	}
+
+	go sc.monitorStateChanges()
+	return sc
+}
+
+// monitorStateChanges checks the state every second to catch fast transitions.
+func (s *StateCollector) monitorStateChanges() {
+	for {
+		state, err := s.lnd.State.GetState(context.Background())
+		if err != nil {
+			s.errChan <- fmt.Errorf("StateCollector GetState failed with: %v", err)
+			continue
+		}
+
+		s.mutex.Lock()
+		if state.String() == "RPC_ACTIVE" {
+			s.startTime = time.Now()
+		} else if state.String() == "SERVER_ACTIVE" && !s.startTime.IsZero() {
+			s.endTime = time.Now()
+		}
+		s.mutex.Unlock()
+
+		time.Sleep(1 * time.Second)
+	}
+}
+
+// Describe sends the super-set of all possible descriptors of metrics
+// collected by this Collector to the provided channel and returns once the
+// last descriptor has been sent.
+//
+// NOTE: Part of the prometheus.Collector interface.
+func (s *StateCollector) Describe(ch chan<- *prometheus.Desc) {
+	ch <- s.timeToStartDesc
+}
+
+// Collect is called by the Prometheus registry when collecting metrics.
+//
+// NOTE: Part of the prometheus.Collector interface.
+func (s *StateCollector) Collect(ch chan<- prometheus.Metric) {
+	// Lock for read
+	s.mutex.RLock()
+	defer s.mutex.RUnlock()
+
+	// We have set both a startTime and endTime, calculate the difference and emit a metric.
+	if !s.startTime.IsZero() && !s.endTime.IsZero() {
+		timeToStartInSecs := s.endTime.Sub(s.startTime).Seconds()
+		ch <- prometheus.MustNewConstMetric(
+			s.timeToStartDesc, prometheus.GaugeValue, timeToStartInSecs,
+		)
+	}
+}