/*
The hub's own accounts: roles, password hashes and the users file.

`${HUB_DATA}/users.json` holds `{ users: [{ name, role, hash, disabled? }] }`, where hash is
`scrypt$N$r$p$saltB64$keyB64`. The pure functions below are what the CLI (users-cli.ts)
and the tests call; `Users` is what the running hub asks.
*/
import { randomBytes, scrypt, scryptSync, timingSafeEqual } from 'node:crypto'
import { existsSync, mkdirSync, readFileSync, renameSync, statSync, writeFileSync, chmodSync, rmSync } from 'node:fs'
import path from 'node:path'
import type { Bootstrap } from './config.ts'

export type Role = 'viewer' | 'operator' | 'apps-admin' | 'admin'
export type Capability = 'read' | 'apps.write' | 'operate' | 'audit.read' | 'admin'

export const ROLES: readonly Role[] = ['viewer', 'operator', 'apps-admin', 'admin']

/* A simple rank. operator and apps-admin are siblings: use `can` to ask about a capability. */
const RANK: Record<Role, number> = { viewer: 1, operator: 2, 'apps-admin': 2, admin: 3 }

const CAPABILITIES: Record<Role, readonly Capability[]> = {
  viewer: ['read'],
  operator: ['read', 'operate'],
  'apps-admin': ['read', 'apps.write'],
  admin: ['read', 'apps.write', 'operate', 'audit.read', 'admin'],
}

export const isRole = (value: unknown): value is Role => typeof value === 'string' && (ROLES as readonly string[]).includes(value)

export const rank = (role: Role): number => RANK[role]

/** True when `role` ranks at least as high as `min`. */
export const requires = (role: Role, min: Role): boolean => RANK[role] >= RANK[min]

export const can = (role: Role, capability: Capability): boolean => CAPABILITIES[role].includes(capability)

export interface UserRecord {
  name: string
  role: Role
  hash: string
  disabled?: boolean
}

/* ---- Passwords ---- */

const N = 16384
const R = 8
const P = 1
const KEYLEN = 64

export function hashPassword(password: string): string {
  const salt = randomBytes(16)
  const key = scryptSync(password, salt, KEYLEN, { N, r: R, p: P })
  return `scrypt$${N}$${R}$${P}$${salt.toString('base64')}$${key.toString('base64')}`
}

interface Parsed {
  n: number
  r: number
  p: number
  salt: Buffer
  key: Buffer
}

function parseHash(stored: string): Parsed | null {
  const parts = stored.split('$')
  if (parts.length !== 6 || parts[0] !== 'scrypt') return null
  const [n, r, p] = [Number(parts[1]), Number(parts[2]), Number(parts[3])]
  if (![n, r, p].every((v) => Number.isInteger(v) && v > 0) || n > 1 << 20 || r > 32 || p > 16) return null
  const salt = Buffer.from(parts[4], 'base64')
  const key = Buffer.from(parts[5], 'base64')
  return salt.length === 0 || key.length === 0 ? null : { n, r, p, salt, key }
}

export const isHash = (stored: string): boolean => parseHash(stored) !== null

function derive(password: string, h: Parsed): Promise<Buffer> {
  return new Promise((resolve, reject) => {
    scrypt(password, h.salt, h.key.length, { N: h.n, r: h.r, p: h.p, maxmem: 256 * h.n * h.r }, (err, key) =>
      err ? reject(err) : resolve(key),
    )
  })
}

/** Checks a password against a stored hash; false for a malformed hash. Does not block the loop. */
export async function verifyPassword(password: string, stored: string): Promise<boolean> {
  const h = parseHash(stored)
  if (h === null) return false
  try {
    return timingSafeEqual(await derive(password, h), h.key)
  } catch {
    return false
  }
}

/* ---- The file: parse and pure edits ---- */

const NAME = /^[A-Za-z0-9._@-]{1,64}$/

export function validateName(name: string): void {
  if (!NAME.test(name)) throw new Error('A user name is 1 to 64 letters, digits, . _ @ -.')
}

const same = (a: string, b: string): boolean => a.toLowerCase() === b.toLowerCase()

export function parseUsersFile(text: string): UserRecord[] {
  let data: unknown
  try {
    data = JSON.parse(text)
  } catch {
    throw new Error('users.json is not valid JSON.')
  }
  const list = (data as { users?: unknown } | null)?.users
  if (!Array.isArray(list)) throw new Error('users.json must be {"users": [...]}.')
  const users: UserRecord[] = []
  for (const item of list as Record<string, unknown>[]) {
    const name = item?.name
    if (typeof name !== 'string' || !NAME.test(name)) throw new Error(`users.json: invalid user name ${JSON.stringify(name)}.`)
    if (!isRole(item.role)) throw new Error(`users.json: user "${name}" has an unknown role.`)
    if (typeof item.hash !== 'string' || !isHash(item.hash)) throw new Error(`users.json: user "${name}" has no valid hash.`)
    if (users.some((u) => same(u.name, name))) throw new Error(`users.json lists "${name}" twice.`)
    const record: UserRecord = { name, role: item.role, hash: item.hash }
    if (item.disabled === true) record.disabled = true
    users.push(record)
  }
  return users
}

export const serializeUsers = (users: UserRecord[]): string => JSON.stringify({ users }, null, 2) + '\n'

export const findUser = (users: UserRecord[], name: string): UserRecord | undefined => users.find((u) => same(u.name, name))

function must(users: UserRecord[], name: string): UserRecord {
  const found = findUser(users, name)
  if (found === undefined) throw new Error(`No user "${name}".`)
  return found
}

export function checkPassword(password: string): void {
  if (password.length < 8) throw new Error('The password must be at least 8 characters.')
}

function checkRole(role: string): Role {
  if (!isRole(role)) throw new Error(`The role must be one of: ${ROLES.join(', ')}.`)
  return role
}

/* Each edit returns a new list; the caller writes it. */

export function addUser(users: UserRecord[], name: string, role: string, password: string): UserRecord[] {
  validateName(name)
  const checked = checkRole(role)
  checkPassword(password)
  if (findUser(users, name) !== undefined) throw new Error(`User "${name}" already exists.`)
  return [...users, { name, role: checked, hash: hashPassword(password) }]
}

export function setPassword(users: UserRecord[], name: string, password: string): UserRecord[] {
  checkPassword(password)
  const target = must(users, name)
  return users.map((u) => (u === target ? { ...u, hash: hashPassword(password) } : u))
}

export function setRole(users: UserRecord[], name: string, role: string): UserRecord[] {
  const checked = checkRole(role)
  const target = must(users, name)
  return users.map((u) => (u === target ? { ...u, role: checked } : u))
}

export function setDisabled(users: UserRecord[], name: string, disabled: boolean): UserRecord[] {
  const target = must(users, name)
  return users.map((u) => {
    if (u !== target) return u
    const { disabled: _old, ...rest } = u
    return disabled ? { ...rest, disabled: true } : rest
  })
}

/** One line per user, never the hash. */
export const describeUsers = (users: UserRecord[]): string[] =>
  users.map((u) => `${u.name}\t${u.role}${u.disabled === true ? '\tdisabled' : ''}`)

/* ---- The file: disk ---- */

export const usersPath = (dir: string): string => path.join(dir, 'users.json')

/** The users, or null when the file does not exist. Throws when it exists but is invalid. */
export function readUsersFile(dir: string): UserRecord[] | null {
  const file = usersPath(dir)
  if (!existsSync(file)) return null
  return parseUsersFile(readFileSync(file, 'utf8'))
}

/** Writes a temp file and renames it over users.json; mode 0600 where the platform honours it. */
export function writeUsersFile(dir: string, users: UserRecord[]): void {
  mkdirSync(dir, { recursive: true })
  const file = usersPath(dir)
  const temp = `${file}.${process.pid}.tmp`
  try {
    writeFileSync(temp, serializeUsers(users), { mode: 0o600 })
    try {
      chmodSync(temp, 0o600)
    } catch {
      // Not every platform has modes.
    }
    renameSync(temp, file)
  } catch (e) {
    rmSync(temp, { force: true })
    throw e
  }
}

/* ---- The running hub's view ---- */

/* Compared when the role, hash or disabled flag changes, so a session can tell its user was edited. */
export const signature = (u: UserRecord): string => `${u.role}|${u.hash}|${u.disabled === true ? 'x' : ''}`

export class Users {
  #dir: string
  #users: UserRecord[]
  #fromFile: boolean
  #mtime = 0
  #warned = false
  /** A one-line notice for the start-up log, or null. */
  readonly notice: string | null
  /* Checked when a name is unknown, so an unknown name costs the same as a wrong password. */
  #dummy = hashPassword(randomBytes(8).toString('hex'))

  private constructor(dir: string, users: UserRecord[], fromFile: boolean, notice: string | null) {
    this.#dir = dir
    this.#users = users
    this.#fromFile = fromFile
    this.notice = notice
    if (fromFile) this.#mtime = this.#stat()
  }

  /*
  users.json when it exists (HUB_USER and HUB_PASSWORD are then ignored); else the one admin
  from the environment; else an error. The file is never written here.
  */
  static load(dir: string, bootstrap: Bootstrap | null): Users {
    const fromFile = readUsersFile(dir)
    if (fromFile !== null) {
      const notice =
        bootstrap === null ? null : `${usersPath(dir)} exists: HUB_USER and HUB_PASSWORD are ignored.`
      return new Users(dir, fromFile, true, notice)
    }
    if (bootstrap === null) {
      throw new Error(
        `No users: ${usersPath(dir)} does not exist and HUB_USER / HUB_PASSWORD are not set. ` +
          'Create a user with: node --experimental-strip-types hub/users-cli.ts add <name> admin',
      )
    }
    validateName(bootstrap.user)
    const record: UserRecord = { name: bootstrap.user, role: 'admin', hash: hashPassword(bootstrap.password) }
    return new Users(dir, [record], false, `No ${usersPath(dir)}: the single admin from HUB_USER / HUB_PASSWORD is in use.`)
  }

  #stat(): number {
    try {
      return statSync(usersPath(this.#dir)).mtimeMs
    } catch {
      return 0
    }
  }

  /* Cheap enough to run on every request: one stat. A broken file keeps the last good list. */
  refresh(): void {
    if (!this.#fromFile) return
    const mtime = this.#stat()
    if (mtime === this.#mtime) return
    this.#mtime = mtime
    try {
      const next = readUsersFile(this.#dir)
      this.#users = next ?? []
      this.#warned = false
    } catch (e) {
      if (!this.#warned) console.error(`hub: ${e instanceof Error ? e.message : String(e)} Keeping the previous users.`)
      this.#warned = true
    }
  }

  find(name: string): UserRecord | undefined {
    this.refresh()
    return findUser(this.#users, name)
  }

  /** The enabled user when the password is right, else null. Costs the same either way. */
  async authenticate(name: string, password: string): Promise<UserRecord | null> {
    const user = this.find(name.trim())
    const good = await verifyPassword(password, user?.hash ?? this.#dummy)
    return user !== undefined && good && user.disabled !== true ? user : null
  }

  /** True when the user was found and is disabled (for the audit log only). */
  isDisabled(name: string): boolean {
    return this.find(name.trim())?.disabled === true
  }
}