Switch to LatestMap-style node controls

This allows plugins to add controls to nodes that already have some
controls set by other plugin. Previously only the last plugin that
sets the controls in the node would have its controls visible. That
was because of NodeControls' Merge function that actually weren't
merging data from two inputs, but rather returning data that was newer
and discarding the older one.

examples/plugins/iowait/main.go

@@ -89,8 +89,8 @@ type topology struct {
 }
 
 type node struct {
-	Metrics  map[string]metric `json:"metrics"`
-	Controls nodeControls      `json:"controls"`
+	Metrics        map[string]metric       `json:"metrics"`
+	LatestControls map[string]controlEntry `json:"latestControls,omitempty"`
 }
 
 type metric struct {
@@ -104,9 +104,13 @@ type sample struct {
 	Value float64   `json:"value"`
 }
 
-type nodeControls struct {
-	Timestamp time.Time `json:"timestamp,omitempty"`
-	Controls  []string  `json:"controls,omitempty"`
+type controlEntry struct {
+	Timestamp time.Time   `json:"timestamp"`
+	Value     controlData `json:"value"`
+}
+
+type controlData struct {
+	Dead bool `json:"dead"`
 }
 
 type metricTemplate struct {
@@ -140,8 +144,8 @@ func (p *Plugin) makeReport() (*report, error) {
 		Host: topology{
 			Nodes: map[string]node{
 				p.getTopologyHost(): {
-					Metrics:  metrics,
-					Controls: p.nodeControls(),
+					Metrics:        metrics,
+					LatestControls: p.latestControls(),
 				},
 			},
 			MetricTemplates: p.metricTemplates(),
@@ -181,16 +185,20 @@ func (p *Plugin) metrics() (map[string]metric, error) {
 	return metrics, nil
 }
 
-// Get the topology controls and node's controls JSON snippet
-func (p *Plugin) nodeControls() nodeControls {
-	id, _, _ := p.controlDetails()
-	return nodeControls{
-		Timestamp: time.Now(),
-		Controls:  []string{id},
+func (p *Plugin) latestControls() map[string]controlEntry {
+	ts := time.Now()
+	ctrls := map[string]controlEntry{}
+	for _, details := range p.allControlDetails() {
+		ctrls[details.id] = controlEntry{
+			Timestamp: ts,
+			Value: controlData{
+				Dead: details.dead,
+			},
+		}
 	}
+	return ctrls
 }
 
-// Get the metrics and metric_templates JSON snippets
 func (p *Plugin) metricTemplates() map[string]metricTemplate {
 	id, name := p.metricIDAndName()
 	return map[string]metricTemplate{
@@ -203,17 +211,17 @@ func (p *Plugin) metricTemplates() map[string]metricTemplate {
 	}
 }
 
-// Get the topology controls and node's controls JSON snippet
 func (p *Plugin) controls() map[string]control {
-	id, human, icon := p.controlDetails()
-	return map[string]control{
-		id: {
-			ID:    id,
-			Human: human,
-			Icon:  icon,
+	ctrls := map[string]control{}
+	for _, details := range p.allControlDetails() {
+		ctrls[details.id] = control{
+			ID:    details.id,
+			Human: details.human,
+			Icon:  details.icon,
 			Rank:  1,
-		},
+		}
 	}
+	return ctrls
 }
 
 // Report is called by scope when a new report is needed. It is part of the
@@ -299,11 +307,37 @@ func (p *Plugin) metricValue() (float64, error) {
 	return idle()
 }
 
-func (p *Plugin) controlDetails() (string, string, string) {
-	if p.iowaitMode {
-		return "switchToIdle", "Switch to idle", "fa-beer"
+type controlDetails struct {
+	id    string
+	human string
+	icon  string
+	dead  bool
+}
+
+func (p *Plugin) allControlDetails() []controlDetails {
+	return []controlDetails{
+		{
+			id:    "switchToIdle",
+			human: "Switch to idle",
+			icon:  "fa-beer",
+			dead:  !p.iowaitMode,
+		},
+		{
+			id:    "switchToIOWait",
+			human: "Switch to IO wait",
+			icon:  "fa-hourglass",
+			dead:  p.iowaitMode,
+		},
 	}
-	return "switchToIOWait", "Switch to IO wait", "fa-hourglass"
+}
+
+func (p *Plugin) controlDetails() (string, string, string) {
+	for _, details := range p.allControlDetails() {
+		if !details.dead {
+			return details.id, details.human, details.icon
+		}
+	}
+	return "", "", ""
 }
 
 func iowait() (float64, error) {