diff values

src/smq/snmp/snmp.go

@@ -5,6 +5,8 @@ import (
 	"log"
 	"time"
   "encoding/json"
+  "strconv"
+  "math"
 
 	"smq/config"
 	"smq/mqtt"
@@ -16,6 +18,7 @@ type variable_t struct {
   Label string `json:"label"`
   Variable string `json:"variable"`
   Value string `json:"value"`
+  DiffValue string `json:"diffValue"`
 }
 
 type message_t struct {
@@ -24,6 +27,45 @@ type message_t struct {
   Variables map[string]variable_t `json:"variables"`
 }
 
+type lastValue_t struct {
+  Timestamp time.Time
+  Value string
+}
+
+var lastValues map[string]lastValue_t = make(map[string]lastValue_t)
+
+func calculateDifference(key string, newValue string) (string, error) {
+  currentTime := time.Now()
+  lvv, ok := lastValues[key]
+  if ok {
+    log.Printf("lvv for %s exists: %s", key, lvv.Value)
+    oldValueI, err1 := strconv.Atoi(lvv.Value)
+    if err1 != nil {
+      return "", fmt.Errorf("failed to convert lastValue: %s, %v", lvv.Value, err1)
+    }
+    newValueI, err2 := strconv.Atoi(newValue)
+    if err2 != nil {
+      return "", fmt.Errorf("failed to convert newValue: %s, %v", newValue, err2)
+    }
+    diffValueI := newValueI - oldValueI
+    diffTime := int(math.Round(currentTime.Sub(lvv.Timestamp).Seconds()))
+    diffValuePerSecond := diffValueI / diffTime
+    log.Printf("Diff: %d, Duration: %d, Diff per second: %d", diffValueI, diffTime, diffValuePerSecond)
+    lastValues[key] = lastValue_t {
+      Timestamp: currentTime,
+      Value: newValue,
+    }
+    return strconv.Itoa(diffValuePerSecond), nil
+  } else {
+    log.Printf("create lvv for %s", key)
+    lastValues[key] = lastValue_t {
+      Timestamp: currentTime,
+      Value: newValue,
+    }
+    return "0", nil
+  }
+  return "0", nil
+}
 
 func Start() {
 	for {
@@ -72,11 +114,24 @@ func Start() {
                 convertedValue = fmt.Sprintf("%d", gosnmp.ToBigInt(variable.Value))
               }
 
+              diffValue := "0"
+              if oidTopic.Diff == "true" {
+                log.Println("Calculate difference to last value")
+                key := endpoint.Endpoint + ":" + oidTopic.OID
+                diff, err := calculateDifference(key, convertedValue)
+                if err != nil {
+                  log.Printf("Error when building difference: %v", err)
+                } else {
+                  diffValue = diff 
+                }
+              }
+
               log.Printf("%s = %s", oidTopic.OID, convertedValue)
               v := variable_t {
                 Label: oidTopic.Label,
                 Variable: oidTopic.OID,
                 Value: convertedValue,
+                DiffValue: diffValue,
               }
               message.Variables[oidTopic.Label] = v