/*
The audit log: JSON Lines in `${HUB_DATA}/audit.log`, one entry per line, newest last on
disk and newest first from `list`. Rotated at 10 MB to audit.log.1 (one kept). If the
folder is not writable, one line goes to stderr and the log lives in memory (last 1000).

Entries carry fixed fields only. Callers never pass passwords, tokens or request bodies.
*/
import { appendFileSync, existsSync, mkdirSync, readFileSync, renameSync, rmSync, statSync } from 'node:fs'
import path from 'node:path'

export const MAX_BYTES = 10 * 1024 * 1024
const RING = 1000
const DETAIL_MAX = 300

export interface AuditEntry {
  ts: string
  user: string
  role?: string
  ip: string
  action: string
  server?: string
  target?: string
  outcome: 'ok' | 'failed' | 'refused'
  detail?: string
}

export type AuditInput = Omit<AuditEntry, 'ts'>

const cut = (value: string, max: number): string => value.slice(0, max)

export class Audit {
  #file: string
  #maxBytes: number
  #now: () => number
  #ring: AuditEntry[] = []
  #size = 0
  #memoryOnly = false
  #listener: ((entry: AuditEntry) => void) | null = null

  constructor(dir: string, options: { maxBytes?: number; now?: () => number } = {}) {
    this.#maxBytes = options.maxBytes ?? MAX_BYTES
    this.#now = options.now ?? Date.now
    this.#file = path.join(dir, 'audit.log')
    try {
      mkdirSync(dir, { recursive: true })
      this.#size = existsSync(this.#file) ? statSync(this.#file).size : 0
      appendFileSync(this.#file, '')
    } catch (e) {
      this.#fallBack(e)
    }
  }

  get inMemory(): boolean {
    return this.#memoryOnly
  }

  #fallBack(e: unknown): void {
    if (!this.#memoryOnly) {
      console.error(
        `hub: audit log is not writable (${e instanceof Error ? e.message : String(e)}); keeping the last ${RING} entries in memory.`,
      )
    }
    this.#memoryOnly = true
  }

  /** One function is told about every entry as it is written (the webhook uses it for failed writes). */
  onEntry(listener: (entry: AuditEntry) => void): void {
    this.#listener = listener
  }

  log(input: AuditInput): void {
    const entry: AuditEntry = {
      ts: new Date(this.#now()).toISOString(),
      user: cut(input.user, 64),
      ...(input.role === undefined ? {} : { role: input.role }),
      ip: cut(input.ip, 64),
      action: input.action,
      ...(input.server === undefined ? {} : { server: input.server }),
      ...(input.target === undefined ? {} : { target: cut(input.target, 200) }),
      outcome: input.outcome,
      ...(input.detail === undefined ? {} : { detail: cut(input.detail, DETAIL_MAX) }),
    }
    this.#ring.push(entry)
    try {
      this.#listener?.(entry)
    } catch {
      // A listener never stops the log.
    }
    if (this.#ring.length > RING) this.#ring.shift()
    if (this.#memoryOnly) return
    const line = JSON.stringify(entry) + '\n'
    try {
      if (this.#size + Buffer.byteLength(line) > this.#maxBytes) this.#rotate()
      appendFileSync(this.#file, line)
      this.#size += Buffer.byteLength(line)
    } catch (e) {
      this.#fallBack(e)
    }
  }

  #rotate(): void {
    rmSync(`${this.#file}.1`, { force: true })
    renameSync(this.#file, `${this.#file}.1`)
    this.#size = 0
  }

  #read(file: string): AuditEntry[] {
    if (!existsSync(file)) return []
    const out: AuditEntry[] = []
    for (const line of readFileSync(file, 'utf8').split('\n')) {
      if (line === '') continue
      try {
        out.push(JSON.parse(line) as AuditEntry)
      } catch {
        // A torn line is skipped.
      }
    }
    return out
  }

  /** Newest first. `before` is an ISO time or epoch milliseconds: only older entries are returned. */
  list(limit = 200, before?: string): AuditEntry[] {
    const max = Math.min(Math.max(Math.trunc(limit) || 200, 1), 1000)
    let cutoff = Infinity
    if (before !== undefined && before !== '') {
      const t = /^\d+$/.test(before) ? Number(before) : Date.parse(before)
      if (Number.isFinite(t)) cutoff = t
    }
    const all = this.#memoryOnly ? this.#ring : [...this.#read(`${this.#file}.1`), ...this.#read(this.#file)]
    const result: AuditEntry[] = []
    for (let i = all.length - 1; i >= 0 && result.length < max; i--) {
      if (Date.parse(all[i].ts) < cutoff) result.push(all[i])
    }
    return result
  }
}