import { createHash, createHmac, timingSafeEqual } from 'node:crypto'

export const SESSION_COOKIE = 'boundless_session'

interface SessionPayload {
  /** 签发时间（毫秒） */
  iat: number
  /** 过期时间（毫秒） */
  exp: number
}

/**
 * 会话令牌：`base64url(payload).签名`。
 * 签名密钥由服务端密钥和登录口令共同派生，所以修改口令后所有设备都会退出登录。
 */
export class SessionManager {
  private readonly key: Buffer
  private readonly passwordHash: Buffer
  readonly maxAgeMs: number

  constructor(secret: string, password: string, sessionDays: number) {
    this.key = createHmac('sha256', secret).update(`session:${password}`).digest()
    this.passwordHash = sha256(password)
    this.maxAgeMs = sessionDays * 24 * 60 * 60 * 1000
  }

  checkPassword(candidate: unknown) {
    if (typeof candidate !== 'string' || candidate.length > 1024) return false
    return timingSafeEqual(sha256(candidate), this.passwordHash)
  }

  issue(now = Date.now()) {
    const payload: SessionPayload = { iat: now, exp: now + this.maxAgeMs }
    const body = Buffer.from(JSON.stringify(payload)).toString('base64url')
    return `${body}.${this.sign(body)}`
  }

  verify(token: string | undefined | null, now = Date.now()): SessionPayload | null {
    if (!token) return null
    const [body, signature, extra] = token.split('.')
    if (!body || !signature || extra !== undefined) return null

    const expected = Buffer.from(this.sign(body))
    const actual = Buffer.from(signature)
    if (expected.length !== actual.length || !timingSafeEqual(expected, actual)) return null

    try {
      const payload = JSON.parse(Buffer.from(body, 'base64url').toString('utf8')) as SessionPayload
      if (typeof payload.exp !== 'number' || payload.exp <= now) return null
      return payload
    } catch {
      return null
    }
  }

  /** 已用过一半有效期的令牌需要续期，常用设备就不会突然被登出。 */
  shouldRenew(payload: SessionPayload, now = Date.now()) {
    return payload.exp - now < this.maxAgeMs / 2
  }

  private sign(body: string) {
    return createHmac('sha256', this.key).update(body).digest('base64url')
  }
}

function sha256(value: string) {
  return createHash('sha256').update(value).digest()
}

export function readCookie(header: string | null | undefined, name: string) {
  if (!header) return undefined
  for (const part of header.split(';')) {
    const index = part.indexOf('=')
    if (index === -1) continue
    if (part.slice(0, index).trim() === name) {
      try {
        return decodeURIComponent(part.slice(index + 1).trim())
      } catch {
        return undefined
      }
    }
  }
  return undefined
}

/**
 * 登录失败限流：同一来源 15 分钟内最多失败 10 次。
 * 只有一个人使用，内存记录就够了。
 */
export class LoginLimiter {
  private readonly failures = new Map<string, number[]>()
  private readonly maxFailures: number
  private readonly windowMs: number

  constructor(maxFailures = 10, windowMs = 15 * 60 * 1000) {
    this.maxFailures = maxFailures
    this.windowMs = windowMs
  }

  isBlocked(key: string, now = Date.now()) {
    return this.recent(key, now).length >= this.maxFailures
  }

  fail(key: string, now = Date.now()) {
    const list = this.recent(key, now)
    list.push(now)
    this.failures.set(key, list)
  }

  reset(key: string) {
    this.failures.delete(key)
  }

  private recent(key: string, now: number) {
    const list = (this.failures.get(key) ?? []).filter((time) => now - time < this.windowMs)
    if (list.length === 0) this.failures.delete(key)
    else this.failures.set(key, list)
    return list
  }
}

/**
 * 校验请求来源与当前站点一致，阻止其他网站借用登录状态发起请求或建立 WebSocket。
 * 没有 Origin 头（例如服务端脚本、curl）时放行，因为它们本来就带不上浏览器 Cookie。
 * 反向代理可能改写 Host，所以同时接受 X-Forwarded-Host。
 */
export function isSameOrigin(
  origin: string | null | undefined,
  hosts: Array<string | null | undefined>,
) {
  if (!origin) return true
  let originHost: string
  try {
    originHost = new URL(origin).host.toLowerCase()
  } catch {
    return false
  }
  return hosts.some((host) =>
    host
      ?.split(',')
      .map((item) => item.trim().toLowerCase())
      .includes(originHost),
  )
}