import { statfs } from 'node:fs/promises'
import logger from '@adonisjs/core/services/logger'

/** How often free space is measured. */
const CHECK_MS = 60_000
/** Resumed only this much above the floor: not paused and resumed at every flush. */
const MARGIN_GB = 1

/**
 * Free space on the filesystem holding `path`, against a floor: low below it, again fine MARGIN_GB above it. In a
 * container `/` is an overlay on the host's Docker root, which on homelab is the NVMe the catalog and the WAL are on.
 * The prober filled it ~0.8–1.1 GB an hour at ~200 articles/s, and nothing stopped it at the 10 GB floor (LOG.md
 * 2026-10-18 (77)). Off when the floor is 0.
 */
export class DiskSpace {
  private checkedAt = 0
  private low = false

  constructor(
    private what: string,
    private path: string,
    private floorGb: number,
    private free: (path: string) => Promise<number> = async (p) => {
      const s = await statfs(p)
      return s.bavail * s.bsize
    },
    private checkMs = CHECK_MS
  ) {}

  async short(): Promise<boolean> {
    if (!this.floorGb) return false
    if (Date.now() - this.checkedAt < this.checkMs) return this.low
    this.checkedAt = Date.now()
    const gb = (await this.free(this.path)) / 1e9
    const was = this.low
    this.low = gb < this.floorGb + (was ? MARGIN_GB : 0)
    if (this.low !== was) logger.info(`${gb.toFixed(1)} GB free (floor ${this.floorGb} GB): ${this.what} ${this.low ? 'paused' : 'resumed'}.`)
    return this.low
  }
}