/*
What the hub keeps per app under `${HUB_DATA}/apps/<app>/`:

  baseline.json   the desired config, as TEXT (some configs are not JSON)
  overrides.json  the fields that stay local to each server, and their values
  history/        the config a server had before the hub changed it (50 files kept)

Every write is a temp file and a rename, mode 0600: these files hold configs.
*/
import { createHash } from 'node:crypto'
import { existsSync, mkdirSync, readFileSync, readdirSync, renameSync, rmSync, statSync, writeFileSync } from 'node:fs'
import path from 'node:path'

export const KEEP_HISTORY = 50

/* A folder name for an app: letters, digits and . _ - only, with a short hash when anything had to change. */
export function safeName(name: string): string {
  const cleaned = name.replace(/[^A-Za-z0-9._-]/g, '_').replace(/\.{2,}/g, '_').replace(/^\.+/, '_').slice(0, 80)
  if (cleaned === name && cleaned !== '') return cleaned
  return `${cleaned === '' ? '_' : cleaned}-${createHash('sha256').update(name).digest('hex').slice(0, 6)}`
}

export const appDir = (dataDir: string, app: string): string => path.join(dataDir, 'apps', safeName(app))

export function writeAtomic(file: string, text: string): void {
  mkdirSync(path.dirname(file), { recursive: true })
  const temp = `${file}.${process.pid}.tmp`
  try {
    writeFileSync(temp, text, { mode: 0o600 })
    renameSync(temp, file)
  } catch (e) {
    rmSync(temp, { force: true })
    throw e
  }
}

export interface Baseline {
  app: string
  text: string
  importedFrom?: string
  updatedAt: string
  updatedBy: string
}

export interface Overrides {
  /** Dot paths (`a.b.0.c`) of the fields that are not synchronised. */
  paths: string[]
  /** server -> path -> value */
  values: Record<string, Record<string, unknown>>
}

export const EMPTY_OVERRIDES: Overrides = { paths: [], values: {} }

function readJson(file: string): unknown {
  if (!existsSync(file)) return null
  try {
    return JSON.parse(readFileSync(file, 'utf8'))
  } catch {
    return null
  }
}

export function readBaseline(dataDir: string, app: string): Baseline | null {
  const data = readJson(path.join(appDir(dataDir, app), 'baseline.json')) as Partial<Baseline> | null
  if (data === null || typeof data.text !== 'string') return null
  return {
    app,
    text: data.text,
    ...(typeof data.importedFrom === 'string' ? { importedFrom: data.importedFrom } : {}),
    updatedAt: String(data.updatedAt ?? ''),
    updatedBy: String(data.updatedBy ?? ''),
  }
}

export function writeBaseline(dataDir: string, baseline: Baseline): void {
  writeAtomic(path.join(appDir(dataDir, baseline.app), 'baseline.json'), JSON.stringify(baseline, null, 2) + '\n')
}

export function readOverrides(dataDir: string, app: string): Overrides {
  const data = readJson(path.join(appDir(dataDir, app), 'overrides.json')) as Partial<Overrides> | null
  if (data === null || !Array.isArray(data.paths)) return { paths: [], values: {} }
  const values = data.values !== null && typeof data.values === 'object' ? data.values : {}
  return { paths: data.paths.filter((p): p is string => typeof p === 'string'), values }
}

export function writeOverrides(dataDir: string, app: string, overrides: Overrides): void {
  writeAtomic(path.join(appDir(dataDir, app), 'overrides.json'), JSON.stringify(overrides, null, 2) + '\n')
}

export type HistoryKind = 'before-uninstall' | 'before-apply' | 'before-set' | 'before-save'

export interface HistoryEntry {
  /** The file name; the only handle `readHistory` accepts. */
  id: string
  at: string
  /** A server id, or `baseline` for an earlier text of the baseline. */
  server: string
  kind: string
  size: number
  hash: string
}

const HISTORY_FILE = /^(\d{4}-\d{2}-\d{2})T(\d{2})-(\d{2})-(\d{2}\.\d{3}Z)__(.+)__(before-[a-z-]+)\.txt$/

const historyDir = (dataDir: string, app: string): string => path.join(appDir(dataDir, app), 'history')

/* Newest first. Never the text. */
export function listHistory(dataDir: string, app: string): HistoryEntry[] {
  const dir = historyDir(dataDir, app)
  if (!existsSync(dir)) return []
  const entries: HistoryEntry[] = []
  for (const name of readdirSync(dir)) {
    const m = HISTORY_FILE.exec(name)
    if (m === null) continue
    try {
      const text = readFileSync(path.join(dir, name), 'utf8')
      entries.push({
        id: name,
        at: `${m[1]}T${m[2]}:${m[3]}:${m[4]}`,
        server: m[5],
        kind: m[6],
        size: Buffer.byteLength(text),
        hash: createHash('sha256').update(text).digest('hex').slice(0, 16),
      })
    } catch {
      // A file that vanished while listing is skipped.
    }
  }
  return entries.sort((a, b) => (a.id < b.id ? 1 : a.id > b.id ? -1 : 0))
}

/* The text of one entry. `id` has to be a name the listing returns, so nothing outside the folder can be read. */
export function readHistory(dataDir: string, app: string, id: string): string | null {
  const known = listHistory(dataDir, app).find((e) => e.id === id)
  return known === undefined ? null : readFileSync(path.join(historyDir(dataDir, app), known.id), 'utf8')
}

/* The apps that have a baseline, by the name stored in the file. */
export function listBaselineApps(dataDir: string): string[] {
  const root = path.join(dataDir, 'apps')
  if (!existsSync(root)) return []
  const apps: string[] = []
  for (const dir of readdirSync(root)) {
    try {
      if (!statSync(path.join(root, dir)).isDirectory()) continue
      const data = readJson(path.join(root, dir, 'baseline.json')) as Partial<Baseline> | null
      if (data !== null && typeof data.app === 'string' && typeof data.text === 'string') apps.push(data.app)
    } catch {
      // Not an app folder.
    }
  }
  return apps.sort((a, b) => a.localeCompare(b))
}

/*
Saves a server's config as it was before the hub changed it. The name starts with the time, so
sorting the names sorts the files by age; the oldest beyond KEEP_HISTORY are deleted.
*/
export function writeHistory(
  dataDir: string,
  app: string,
  server: string,
  text: string,
  kind: HistoryKind,
  now: number,
): string {
  const dir = path.join(appDir(dataDir, app), 'history')
  const stamp = new Date(now).toISOString().replace(/:/g, '-')
  const file = path.join(dir, `${stamp}__${safeName(server)}__${kind}.txt`)
  writeAtomic(file, text)
  const files = readdirSync(dir).filter((f) => f.endsWith('.txt')).sort()
  for (const old of files.slice(0, Math.max(0, files.length - KEEP_HISTORY))) rmSync(path.join(dir, old), { force: true })
  return file
}