package core

import (
	"container/heap"
	"fmt"
)

type Timeline interface {
	IsEmpty() bool
	Insert(e IEvent) error
	OutFirst() (IEvent, error)
}

//Timeline是目前集群当前反映未来的事件时间线
//该时间线为因为新任务的提交，和机器更新，以及调度算法的改变而变化
type timeLine struct {
	eventQueue eventHeap
}

//初始化一个Timeline,根据三种类型的事件
func InitTimeline(i []IEvent) Timeline {
	var t timeLine
	t.eventQueue = make(eventHeap, 0)
	t.eventQueue = append(t.eventQueue, i...)
	heap.Init(&t.eventQueue)

	return &t
}

//从几条sortedList当中有着最先节点的list,然后将最先节点出列
//该最先节点就是下一个该执行的事件
func (t *timeLine) OutFirst() (IEvent, error) {
	if t.IsEmpty() {
		return nil, fmt.Errorf("there is no event in the queue")
	}
	return heap.Pop(&(t.eventQueue)).(IEvent), nil
}
func (t *timeLine) IsEmpty() bool {
	return len(t.eventQueue) == 0
}

// 向时间线加入新的事件
func (t *timeLine) Insert(e IEvent) error {
	heap.Push(&(t.eventQueue), e)
	return nil
}

//----------------private----------------------------------------------

// use the container/heap to realize the event_queue,the top of the heap is the first event will happen next
type eventHeap []IEvent

func (h eventHeap) Len() int           { return len(h) }
func (h eventHeap) Less(i, j int) bool { return h[i].HappenTime() < h[j].HappenTime() }
func (h eventHeap) Swap(i, j int)      { h[i], h[j] = h[j], h[i] }
func (h *eventHeap) Push(x interface{}) {
	// Push and Pop use pointer receivers because they modify the slice's length,
	// not just its contents.
	*h = append(*h, x.(IEvent))
}
func (h *eventHeap) Pop() interface{} {
	old := *h
	n := len(old)
	x := old[n-1]
	*h = old[0 : n-1]
	return x
}