Better tracking of channels count metric (#1369)

Track all channel states (cardinality shouldn't be too high).
Prevent duplicate transactions that messed up the gauge.

eclair-core/src/main/scala/fr/acinq/eclair/channel/Channel.scala

@@ -113,8 +113,6 @@ class Channel(val nodeParams: NodeParams, val wallet: EclairWallet, remoteNodeId
   // we pass these to helpers classes so that they have the logging context
   implicit def implicitLog: akka.event.DiagnosticLoggingAdapter = diagLog
 
-  Metrics.ChannelsCount.withoutTags().increment()
-
   // we assume that the peer is the channel's parent
   private val peer = context.parent
   // the last active connection we are aware of; note that the peer manages connections and asynchronously notifies
@@ -1384,7 +1382,6 @@ class Channel(val nodeParams: NodeParams, val wallet: EclairWallet, remoteNodeId
         case _ =>
       }
       log.info("shutting down")
-      Metrics.ChannelsCount.withoutTags().decrement()
       stop(FSM.Normal)
 
     case Event(MakeFundingTxResponse(fundingTx, _, _), _) =>
@@ -1691,7 +1688,6 @@ class Channel(val nodeParams: NodeParams, val wallet: EclairWallet, remoteNodeId
         // channel is closed, scheduling this actor for self destruction
         context.system.scheduler.scheduleOnce(10 seconds, self, 'shutdown)
       }
-
       if (nextState == OFFLINE) {
         // we can cancel the timer, we are not expecting anything when disconnected
         cancelTimer(RevocationTimeout.toString)
@@ -1739,13 +1735,9 @@ class Channel(val nodeParams: NodeParams, val wallet: EclairWallet, remoteNodeId
   }
 
   onTransition {
-    case _ -> OFFLINE => Metrics.ChannelsCount.withTag(Tags.State, Tags.States.Offline).increment()
-    case OFFLINE -> _ => Metrics.ChannelsCount.withTag(Tags.State, Tags.States.Offline).decrement()
-  }
-
-  onTransition {
-    case _ -> CLOSING => Metrics.ChannelsCount.withTag(Tags.State, Tags.States.Closing).increment()
-    case CLOSING -> _ => Metrics.ChannelsCount.withTag(Tags.State, Tags.States.Closing).decrement()
+    case state -> nextState if state != nextState =>
+      if (state != WAIT_FOR_INIT_INTERNAL) Metrics.ChannelsCount.withTag(Tags.State, state.toString).decrement()
+      if (nextState != WAIT_FOR_INIT_INTERNAL) Metrics.ChannelsCount.withTag(Tags.State, nextState.toString).increment()
   }
 
   /*

eclair-core/src/main/scala/fr/acinq/eclair/channel/Monitoring.scala

@@ -38,11 +38,6 @@ object Monitoring {
       val Closed = "closed"
     }
 
-    object States {
-      val Offline = "offline"
-      val Closing = "closing"
-    }
-
     object Origins {
       val Local = "local"
       val Remote = "remote"