package com

import "math"

func NewCrossLog() *CrossLog {
	return &CrossLog{}
}

type CrossLog struct {
	PrevVal float64
	Sign    int // 最近一次交叉符号：1上穿，-1下穿
	XAt     int // 最近一次交叉序号
	Num     int // 当前序号
}

func (l *CrossLog) Update(sub float64) {
	l.Num += 1
	if sub == 0 {
		return
	}
	if math.IsNaN(l.PrevVal) || l.PrevVal == 0 {
		l.PrevVal = sub
	} else {
		if factor := l.PrevVal * sub; factor < 0 {
			l.PrevVal = sub
			l.XAt = l.Num
			if sub > 0 {
				l.Sign = 1
			} else {
				l.Sign = -1
			}
		}
	}
}

func (l *CrossLog) Get() int {
	return l.Sign * (l.Num - l.XAt + 1)
}