refactor(snmp_zabbix): migrate scheduler to Min-Heap with consistent …

inputs/snmp_zabbix/priority_queue.go

@@ -0,0 +1,52 @@
+package snmp_zabbix
+
+import (
+	"time"
+)
+
+// ScheduledTask represents a group of items to be collected from a single agent at a specific interval.
+// It serves as the element in the Priority Queue.
+type ScheduledTask struct {
+	Agent    string
+	Interval time.Duration
+	NextRun  time.Time // Priority Key
+
+	// Payload: Items belonging to this (Agent, Interval) group
+	Items []MonitorItem
+
+	// Heap Index implementation (managed by heap.Interface)
+	index int
+}
+
+// ItemHeap implements heap.Interface for []*ScheduledTask
+type ItemHeap []*ScheduledTask
+
+func (pq ItemHeap) Len() int { return len(pq) }
+
+func (pq ItemHeap) Less(i, j int) bool {
+	// Min-Heap: The item with the earliest NextRun comes first.
+	return pq[i].NextRun.Before(pq[j].NextRun)
+}
+
+func (pq ItemHeap) Swap(i, j int) {
+	pq[i], pq[j] = pq[j], pq[i]
+	pq[i].index = i
+	pq[j].index = j
+}
+
+func (pq *ItemHeap) Push(x interface{}) {
+	n := len(*pq)
+	item := x.(*ScheduledTask)
+	item.index = n
+	*pq = append(*pq, item)
+}
+
+func (pq *ItemHeap) Pop() interface{} {
+	old := *pq
+	n := len(old)
+	item := old[n-1]
+	old[n-1] = nil  // avoid memory leak
+	item.index = -1 // for safety
+	*pq = old[0 : n-1]
+	return item
+}