priority_queue.go

// This code was largely copy-pasted from the container/heap examples:
// https://play.golang.org/p/nqe-zZ4o58R
package main

import (
	"container/heap"
	"time"
)

// implements heap.Interface and holds Items.
type PriorityQueue []*Item

func NewPriorityQueue() *PriorityQueue {
	x := new(PriorityQueue)
	heap.Init(x)
	return x
}

func (pq PriorityQueue) Len() int { return len(pq) }

func (pq PriorityQueue) Less(i, j int) bool {
	return pq[i].Expiry.Before(pq[j].Expiry)
}

func (pq PriorityQueue) Swap(i, j int) {
	pq[i], pq[j] = pq[j], pq[i]
	pq[i].index = i
	pq[j].index = j
}

func (pq *PriorityQueue) Push(x interface{}) {
	n := len(*pq)
	item := x.(*Item)
	item.index = n
	*pq = append(*pq, item)
}

func (pq *PriorityQueue) Pop() interface{} {
	old := *pq
	n := len(old)
	item := old[n-1]
	item.index = -1 // for safety
	*pq = old[0 : n-1]
	return item
}

// Return the time of the oldest entry in the priority queue
func (pq *PriorityQueue) Oldest() time.Time {
	return (*pq)[len(*pq)-1].Expiry
}