export interface SerialQueueOptions {
  /** Minimum delay between task starts. 0 = unpaced. */
  minIntervalMs?: number
}

export class SerialQueue {
  private tail: Promise<unknown> = Promise.resolve()
  private lastStart = 0
  private minIntervalMs: number

  constructor(opts: SerialQueueOptions = {}) {
    this.minIntervalMs = opts.minIntervalMs ?? 0
  }

  run<T>(fn: () => Promise<T>): Promise<T> {
    const result = this.tail.then(async () => {
      if (this.minIntervalMs > 0) {
        const wait = this.lastStart + this.minIntervalMs - Date.now()
        if (wait > 0) await new Promise((r) => setTimeout(r, wait))
      }
      this.lastStart = Date.now()
      return fn()
    })
    this.tail = result.catch(() => {})
    return result
  }
}