package tries

import (
	"math/big"
)

type Item interface {
	Priority() *big.Int
}

type MinHeap[I Item] struct {
	items []I
}

func NewMinHeap[I Item]() *MinHeap[I] {
	return &MinHeap[I]{items: make([]I, 0)}
}

func (h *MinHeap[I]) Push(item I) {
	h.items = append(h.items, item)
	h.upheap(len(h.items) - 1)
}

func (h *MinHeap[I]) Pop() (I, bool) {
	if len(h.items) == 0 {
		var zero I
		return zero, false
	}
	min := h.items[0]
	lastIdx := len(h.items) - 1
	h.items[0] = h.items[lastIdx]
	h.items = h.items[:lastIdx]
	if len(h.items) > 0 {
		h.downheap(0)
	}
	return min, true
}

func (h *MinHeap[I]) Peek() (I, bool) {
	if len(h.items) == 0 {
		var zero I
		return zero, false
	}
	return h.items[0], true
}

func (h *MinHeap[I]) Size() int {
	return len(h.items)
}

func (h *MinHeap[I]) upheap(i int) {
	for i > 0 {
		parent := (i - 1) / 2
		if h.items[i].Priority().Cmp(h.items[parent].Priority()) >= 0 {
			break
		}
		h.items[i], h.items[parent] = h.items[parent], h.items[i]
		i = parent
	}
}

func (h *MinHeap[I]) downheap(i int) {
	for {
		left := 2*i + 1
		right := 2*i + 2
		smallest := i

		if left < len(h.items) &&
			h.items[left].Priority().Cmp(h.items[smallest].Priority()) < 0 {
			smallest = left
		}
		if right < len(h.items) &&
			h.items[right].Priority().Cmp(h.items[smallest].Priority()) < 0 {
			smallest = right
		}

		if smallest == i {
			break
		}

		h.items[i], h.items[smallest] = h.items[smallest], h.items[i]
		i = smallest
	}
}