export interface AlarmPoint {
  ts: number
  value: number
}

export interface WindowChangeAlarm {
  change: number
  direction: 'increase' | 'decrease'
  fromValue: number
  fromTs: number
  toTs: number
  toValue: number
}

export function getWindowChangeAlarm(
  points: AlarmPoint[],
  anchorTs: number,
  windowSeconds: number,
  range: number
): WindowChangeAlarm | undefined {
  if (windowSeconds <= 0 || range < 0) return undefined

  const startTs = anchorTs - windowSeconds * 1000
  const windowPoints = points
    .filter((point) => point.ts > startTs && point.ts <= anchorTs)
    .sort((left, right) => left.ts - right.ts)

  let alarm: WindowChangeAlarm | undefined

  for (let index = 1; index < windowPoints.length; index += 1) {
    const previousPoint = windowPoints[index - 1]
    const currentPoint = windowPoints[index]
    const delta = currentPoint.value - previousPoint.value
    const change = Math.abs(delta)

    if (change <= range) continue

    alarm = {
      change,
      direction: delta > 0 ? 'increase' : 'decrease',
      fromValue: previousPoint.value,
      fromTs: previousPoint.ts,
      toTs: currentPoint.ts,
      toValue: currentPoint.value
    }
  }

  return alarm
}