const matchTimeRegex = /^\s*(\d+)?(\.\d+)?\s*(ms|s|m|h|d)/

const unitMultiplier = (unit?: string) => {
  if (!unit) return 1
  if (unit === 'ms') return 1
  if (unit === 's') return 1000
  if (unit === 'm') return 1000 * 60
  if (unit === 'h') return 1000 * 60 * 60
  if (unit === 'd') return 1000 * 60 * 60 * 24
  throw new Error(`Invalid unit: ${unit}`)
}
const digitsMs = (digits: string | null, multiplier: number) => {
  if (!digits) return 0
  const value = parseInt(digits.slice(1))
  const divideBy = multiplier / Math.pow(10, digits.length - 1)
  return Math.round(value * divideBy)
}
/**
 * Converts a human-readable time string to milliseconds.
 * Supports units: `ms`, `s`, `m`, `h`, `d`. If a number is passed, it is returned as-is.
 *
 * @param time - A time string (e.g. `"500ms"`, `"1.5s"`, `"2h"`) or a numeric millisecond value
 * @returns The time in milliseconds, or `undefined` if `time` is falsy
 * @throws Error if the string format is invalid
 *
 * @example
 * ```ts
 * inMs("2s")   // 2000
 * inMs("1.5h") // 5400000
 * inMs(500)    // 500
 * ```
 */
export const inMs = (time?: string | number) => {
  if (typeof time === 'number') return time
  if (!time) return undefined
  const matches = time.match(matchTimeRegex)
  if (!matches) throw new Error(`Invalid time format: ${time}`)
  const [_, leftHandSide, digits, unit] = matches
  const multiplier = unitMultiplier(unit)
  const firstValue = parseInt(leftHandSide || '0') * multiplier
  const secondValue = digitsMs(digits, multiplier)

  return firstValue + secondValue
}