import type { LivelinePoint } from '../types'

/**
 * Binary search to find interpolated value at a given time.
 * Returns null if time is outside data range.
 */
export function interpolateAtTime(
  points: LivelinePoint[],
  time: number,
): number | null {
  if (points.length === 0) return null
  if (time <= points[0].time) return points[0].value
  if (time >= points[points.length - 1].time) return points[points.length - 1].value

  // Binary search for the interval containing `time`
  let lo = 0
  let hi = points.length - 1
  while (hi - lo > 1) {
    const mid = (lo + hi) >> 1
    if (points[mid].time <= time) lo = mid
    else hi = mid
  }

  const p1 = points[lo]
  const p2 = points[hi]
  const dt = p2.time - p1.time
  if (dt === 0) return p1.value
  const t = (time - p1.time) / dt
  return p1.value + (p2.value - p1.value) * t
}