export class CronScheduler {
  private timers: Map<string, ReturnType<typeof setInterval>> = new Map()

  parse(cron: string): { next: () => number } {
    const parts = cron.trim().split(/\s+/)
    if (parts.length !== 5) throw new Error(`Invalid cron: ${cron}`)

    const [min, hour, day, month, weekday] = parts
    const mins = this.parseField(min, 0, 59)
    const hours = this.parseField(hour, 0, 23)
    const days = this.parseField(day, 1, 31)
    const months = this.parseField(month, 1, 12)
    const weekdays = this.parseField(weekday, 0, 6)

    return {
      next: () => {
        const now = new Date()
        const candidates: number[] = []
        for (let m = 0; m < 60; m++) {
          for (let h = 0; h < 24; h++) {
            for (let d = 1; d <= 31; d++) {
              for (let mo = 1; mo <= 12; mo++) {
                if (mins.has(m) && hours.has(h) && days.has(d) && months.has(mo)) {
                  const candidate = new Date(now.getFullYear(), mo - 1, d, h, m, 0, 0)
                  if (candidate > now && weekdays.has(candidate.getDay())) {
                    candidates.push(candidate.getTime())
                  }
                }
              }
            }
          }
        }
        candidates.sort((a, b) => a - b)
        return candidates[0] || (now.getTime() + 60000)
      }
    }
  }

  private parseField(field: string, min: number, max: number): Set<number> {
    const result = new Set<number>()
    if (field === "*") {
      for (let i = min; i <= max; i++) result.add(i)
      return result
    }
    for (const part of field.split(",")) {
      if (part.includes("/")) {
        const [range, step] = part.split("/")
        const s = parseInt(step)
        const [rMin, rMax] = range === "*" ? [min, max] : range.split("-").map(Number)
        for (let i = rMin!; i <= (rMax ?? rMin!); i += s) {
          if (i >= min && i <= max) result.add(i)
        }
      } else if (part.includes("-")) {
        const [lo, hi] = part.split("-").map(Number)
        for (let i = lo!; i <= hi!; i++) {
          if (i >= min && i <= max) result.add(i)
        }
      } else {
        const v = parseInt(part)
        if (v >= min && v <= max) result.add(v)
      }
    }
    return result
  }

  start(name: string, intervalMs: number, fn: () => void): void {
    this.stop(name)
    const t = setInterval(fn, intervalMs)
    this.timers.set(name, t)
  }

  stop(name: string): void {
    const t = this.timers.get(name)
    if (t) {
      clearInterval(t)
      this.timers.delete(name)
    }
  }

  stopAll(): void {
    for (const t of this.timers.values()) clearInterval(t)
    this.timers.clear()
  }
}