API: Added alert state validation before changing its state (#21375)

* added alert state validation before changing its state

* modified boolean condition

* converted most occurring string into const

* referred the const of alert models

pkg/api/alerting.go

@@ -354,9 +354,10 @@ func NotificationTest(c *models.ReqContext, dto dtos.NotificationTestCommand) Re
 //POST /api/alerts/:alertId/pause
 func PauseAlert(c *models.ReqContext, dto dtos.PauseAlertCommand) Response {
 	alertID := c.ParamsInt64("alertId")
+	result := make(map[string]interface{})
+	result["alertId"] = alertID
 
 	query := models.GetAlertByIdQuery{Id: alertID}
-
 	if err := bus.Dispatch(&query); err != nil {
 		return Error(500, "Get Alert failed", err)
 	}
@@ -370,6 +371,17 @@ func PauseAlert(c *models.ReqContext, dto dtos.PauseAlertCommand) Response {
 		return Error(403, "Access denied to this dashboard and alert", nil)
 	}
 
+	// Alert state validation
+	if query.Result.State != models.AlertStatePaused && !dto.Paused {
+		result["state"] = "un-paused"
+		result["message"] = "Alert is already un-paused"
+		return JSON(200, result)
+	} else if query.Result.State == models.AlertStatePaused && dto.Paused {
+		result["state"] = models.AlertStatePaused
+		result["message"] = "Alert is already paused"
+		return JSON(200, result)
+	}
+
 	cmd := models.PauseAlertCommand{
 		OrgId:    c.OrgId,
 		AlertIds: []int64{alertID},
@@ -387,12 +399,8 @@ func PauseAlert(c *models.ReqContext, dto dtos.PauseAlertCommand) Response {
 		pausedState = "paused"
 	}
 
-	result := map[string]interface{}{
-		"alertId": alertID,
-		"state":   response,
-		"message": "Alert " + pausedState,
-	}
-
+	result["state"] = response
+	result["message"] = "Alert " + pausedState
 	return JSON(200, result)
 }