import { CookieAttributes } from 'js-cookie'
import { allowedCookieDomain, getCookie, removeCookie, setCookie } from './cookies'
import { topDomain } from './top-domain'

let domain: string | undefined = undefined
try {
  domain = topDomain(new URL(window.location.href))
} catch (_) {
  domain = undefined
}

export type SessionOptions = {
  cookie_defaults?: CookieAttributes
}

export function hostName(domain: string | undefined) {
  domain = domain || ''
  try {
    const withProtocol = domain.startsWith('http') ? domain : `https://${domain}`
    const url = new URL(withProtocol)
    return url.hostname
  } catch (_) {
    return domain
  }
}

const MIN_TTL = 20 * 60 * 1000 // 20 minutes
const MAX_TTL = 4 * 60 * 60 * 1000 // 4 hours

const cookieDefaults: CookieAttributes = {
  expires: 1, // 1 day
  domain,
  path: '/',
  sameSite: 'lax'
}

function sessionId(): Session | undefined {
  const sesh = window.localStorage.getItem('ko_sid') || getCookie('ko_sid')

  if (sesh) {
    try {
      return JSON.parse(sesh)
    } catch (err) {
      console.warn('Failed to parse session', err)
    }
  }
}

export interface Session {
  id: string
  lastTouched: number
}

function setSession(session: Session, options?: SessionOptions) {
  const value = JSON.stringify(session)

  // do not set cookie if the domain is not at least the same top level domain
  if (allowedCookieDomain(domain, options?.cookie_defaults?.domain)) {
    setCookie('ko_sid', value, { ...cookieDefaults, ...options?.cookie_defaults })
  } else {
    removeCookie('ko_sid', cookieDefaults)
  }

  window.localStorage.setItem('ko_sid', value)
  return session
}

function start(options?: SessionOptions): Session {
  const now = new Date().getTime()

  const session: Session = {
    id: now.toString(),
    lastTouched: now
  }

  return setSession(session, options)
}

function maxLength(sessionId: string) {
  const now = new Date().getTime()
  const sessionStart = parseInt(sessionId, 10)
  return now - sessionStart > MAX_TTL
}

function valid(session: Session) {
  const now = new Date().getTime()
  const delta = now - session.lastTouched
  return delta < MIN_TTL
}

function touch(sesh: Session, options?: SessionOptions) {
  const session: Session = {
    id: sesh.id,
    lastTouched: new Date().getTime()
  }

  return setSession(session, options)
}

/**
 * Initialize a session if one doesn't exist, or return the existing session
 * if it hasn't expired or exceeded the TTL.
 * @returns the current session
 */
function fetch(options?: SessionOptions): Session {
  const existing = sessionId()
  if (existing && valid(existing) && !maxLength(existing.id)) {
    return touch(existing, options)
  }

  return start(options)
}

function init(options?: SessionOptions): Session {
  return fetch(options)
}

function reset(options?: SessionOptions): Session {
  return start(options)
}

function clear() {
  removeCookie('ko_sid', cookieDefaults)
  window.localStorage.removeItem('ko_sid')
}

export const session = { init, fetch, reset, sessionId, clear }