package pilorama

import (
	"container/heap"
)

type heapInfo struct {
	id       Node
	filename string
}

type filenameHeap []heapInfo

func (h filenameHeap) Len() int           { return len(h) }
func (h filenameHeap) Less(i, j int) bool { return h[i].filename < h[j].filename }
func (h filenameHeap) Swap(i, j int)      { h[i], h[j] = h[j], h[i] }
func (h *filenameHeap) Push(x any) {
	*h = append(*h, x.(heapInfo))
}

func (h *filenameHeap) Pop() any {
	old := *h
	n := len(old)
	x := old[n-1]
	*h = old[0 : n-1]
	return x
}

// fixedHeap maintains a fixed number of smallest elements started at some point.
type fixedHeap struct {
	start *string
	max   string
	count int
	h     *filenameHeap
}

func newHeap(start *string, count int) *fixedHeap {
	h := new(filenameHeap)
	heap.Init(h)

	return &fixedHeap{
		start: start,
		max:   "",
		count: count,
		h:     h,
	}
}

func (h *fixedHeap) push(id Node, filename string) bool {
	if h.start != nil && filename <= *h.start {
		return false
	}
	heap.Push(h.h, heapInfo{id: id, filename: filename})
	if h.h.Len() > h.count {
		heap.Remove(h.h, h.h.Len()-1)
	}
	return true
}

func (h *fixedHeap) pop() (heapInfo, bool) {
	if h.h.Len() != 0 {
		return heap.Pop(h.h).(heapInfo), true
	}
	return heapInfo{}, false
}