// OVE — encrypted per-visitor music service logins (v6.6).
//
// A visitor can log in to their own music services (YouTube, SoundCloud,
// Spotify, Apple Music) by pasting that service's login cookie. Storage
// model — everything stays on the visitor's computer:
//
//   • the cookie text is encrypted with AES-GCM (Web Crypto) using a
//     256-bit key that is generated once, is marked NON-extractable and
//     lives in IndexedDB ("ove-secure") — so no script, not even this one,
//     can read the key material back out of the browser's key store;
//   • only the ciphertext (base64 iv + base64 data) is written to
//     localStorage ("ove.musicSessions.v1");
//   • the plaintext cookie exists in memory only: while saving, and for a
//     moment when a link the visitor plays is resolved (it is sent to this
//     site's own server as part of that resolve request — the server uses
//     it transiently for yt-dlp and never stores it).
//
// If the IndexedDB key is ever missing (cleared) while ciphertext remains,
// the sessions are unreadable and get dropped — logging in again is the
// only recovery, which is exactly what "remove credentials" means here.

'use client'

import { isServiceId, serviceForUrl, type ServiceId } from '@/lib/music-services'

const LS_KEY = 'ove.musicSessions.v1'
const DB_NAME = 'ove-secure'
const DB_VERSION = 1
const KEY_STORE = 'keys'
const KEY_ID = 'music-cookies'

export const MAX_COOKIE_LENGTH = 65_536

export interface SessionSummary {
  /** services with a readable (decryptable) saved login */
  loggedIn: Partial<Record<ServiceId, { savedAt: number }>>
  /** storage/persistence is unavailable in this browser context */
  unavailable?: string
}

export interface CookieAuth {
  service: ServiceId
  cookies: string
}

interface StoredSession {
  iv: string
  ct: string
  savedAt: number
}

interface SessionsFile {
  v: 1
  sessions: Partial<Record<ServiceId, StoredSession>>
}

// ---- availability -----------------------------------------------------------

function cryptoAvailable(): boolean {
  return (
    typeof window !== 'undefined' &&
    typeof window.crypto?.subtle?.encrypt === 'function' &&
    typeof indexedDB !== 'undefined'
  )
}

// ---- IndexedDB key store (non-extractable AES-GCM key) ----------------------

function openDb(): Promise<IDBDatabase> {
  return new Promise((resolve, reject) => {
    const req = indexedDB.open(DB_NAME, DB_VERSION)
    req.onupgradeneeded = () => {
      if (!req.result.objectStoreNames.contains(KEY_STORE)) {
        req.result.createObjectStore(KEY_STORE, { keyPath: 'id' })
      }
    }
    req.onsuccess = () => resolve(req.result)
    req.onerror = () => reject(req.error ?? new Error('IndexedDB unavailable'))
    req.onblocked = () => reject(new Error('IndexedDB blocked by another tab'))
  })
}

async function getOrCreateKey(): Promise<CryptoKey> {
  const db = await openDb()
  try {
    const read = (): Promise<{ key?: unknown } | undefined> =>
      new Promise((resolve, reject) => {
        const tx = db.transaction(KEY_STORE, 'readonly')
        const req = tx.objectStore(KEY_STORE).get(KEY_ID)
        req.onsuccess = () => resolve(req.result)
        req.onerror = () => reject(req.error)
      })
    const found = await read()
    if (found && found.key instanceof CryptoKey) return found.key
    const key = await crypto.subtle.generateKey(
      { name: 'AES-GCM', length: 256 },
      false, // non-extractable — the raw key never leaves the browser key store
      ['encrypt', 'decrypt'],
    )
    await new Promise<void>((resolve, reject) => {
      const tx = db.transaction(KEY_STORE, 'readwrite')
      tx.objectStore(KEY_STORE).put({ id: KEY_ID, key })
      tx.oncomplete = () => resolve()
      tx.onabort = () => reject(tx.error ?? new Error('Key store write failed'))
      tx.onerror = () => reject(tx.error)
    })
    return key
  } finally {
    db.close()
  }
}

// ---- localStorage session file ----------------------------------------------

function readFile(): SessionsFile {
  try {
    const raw = localStorage.getItem(LS_KEY)
    if (!raw) return { v: 1, sessions: {} }
    const parsed = JSON.parse(raw) as SessionsFile
    if (parsed === null || typeof parsed !== 'object' || parsed.v !== 1) {
      return { v: 1, sessions: {} }
    }
    const sessions: SessionsFile['sessions'] = {}
    for (const [id, s] of Object.entries(parsed.sessions ?? {})) {
      if (
        isServiceId(id) &&
        s !== null &&
        typeof s === 'object' &&
        typeof s.iv === 'string' &&
        typeof s.ct === 'string' &&
        typeof s.savedAt === 'number'
      ) {
        sessions[id] = s
      }
    }
    return { v: 1, sessions }
  } catch {
    return { v: 1, sessions: {} }
  }
}

function writeFile(file: SessionsFile): void {
  localStorage.setItem(LS_KEY, JSON.stringify(file))
}

// ---- encrypt / decrypt -------------------------------------------------------

function toB64(buf: ArrayBuffer): string {
  const bytes = new Uint8Array(buf)
  let s = ''
  for (let i = 0; i < bytes.length; i++) s += String.fromCharCode(bytes[i])
  return btoa(s)
}

function fromB64(s: string): Uint8Array<ArrayBuffer> {
  const bin = atob(s)
  const bytes = new Uint8Array(bin.length)
  for (let i = 0; i < bin.length; i++) bytes[i] = bin.charCodeAt(i)
  return bytes
}

async function encryptText(key: CryptoKey, text: string): Promise<StoredSession> {
  const iv = crypto.getRandomValues(new Uint8Array(12))
  const ct = await crypto.subtle.encrypt(
    { name: 'AES-GCM', iv },
    key,
    new TextEncoder().encode(text),
  )
  return { iv: toB64(iv.buffer), ct: toB64(ct), savedAt: Date.now() }
}

async function decryptText(key: CryptoKey, session: StoredSession): Promise<string | null> {
  try {
    const plain = await crypto.subtle.decrypt(
      { name: 'AES-GCM', iv: fromB64(session.iv) },
      key,
      fromB64(session.ct),
    )
    return new TextDecoder().decode(plain)
  } catch {
    return null // wrong key or tampered ciphertext
  }
}

// ---- public API --------------------------------------------------------------

/** Save (or replace) the login cookie for one service. */
export async function saveMusicSession(
  service: ServiceId,
  cookieText: string,
): Promise<{ ok: true } | { ok: false; error: string }> {
  const text = cookieText.trim()
  if (text.length < 8) {
    return { ok: false, error: 'That looks too short to be a cookie — paste the whole Cookie header value or a cookies.txt export.' }
  }
  if (text.length > MAX_COOKIE_LENGTH) {
    return { ok: false, error: 'That cookie data is too large (over 64KB).' }
  }
  if (!cryptoAvailable()) {
    return { ok: false, error: 'This browser context is not secure (needs https) — logins cannot be stored here.' }
  }
  try {
    const key = await getOrCreateKey()
    const file = readFile()
    file.sessions[service] = await encryptText(key, text)
    writeFile(file)
    return { ok: true }
  } catch {
    return { ok: false, error: 'Could not store the login in this browser (storage or crypto unavailable).' }
  }
}

/** Which services have a readable saved login. */
export async function listMusicSessions(): Promise<SessionSummary> {
  if (!cryptoAvailable()) {
    return { loggedIn: {}, unavailable: 'secure-context' }
  }
  try {
    const key = await getOrCreateKey()
    const file = readFile()
    const loggedIn: SessionSummary['loggedIn'] = {}
    let dropped = false
    for (const [id, session] of Object.entries(file.sessions)) {
      if (!isServiceId(id)) continue
      const plain = await decryptText(key, session)
      if (plain === null || plain.trim().length === 0) {
        delete file.sessions[id]
        dropped = true
      } else {
        loggedIn[id] = { savedAt: session.savedAt }
      }
    }
    if (dropped) writeFile(file)
    return { loggedIn }
  } catch {
    return { loggedIn: {}, unavailable: 'storage-error' }
  }
}

/** Remove every saved login (the "Log out of all" button). */
export async function clearAllMusicSessions(): Promise<void> {
  try {
    localStorage.removeItem(LS_KEY)
  } catch {
    /* nothing to remove */
  }
}

/** Remove the saved login for one service only (per-service "Log out"). */
export async function removeMusicSession(service: ServiceId): Promise<void> {
  try {
    const file = readFile()
    if (file.sessions[service]) {
      delete file.sessions[service]
      writeFile(file)
    }
  } catch {
    /* nothing to remove */
  }
}

/**
 * Look up the saved login matching a link the visitor is about to play.
 * Returns the decrypted cookie text + service id, or null when the link's
 * service has no login (or the link belongs to no known service).
 */
export async function getCookieForUrl(url: string): Promise<CookieAuth | null> {
  const service = serviceForUrl(url)
  if (service === null) return null
  if (!cryptoAvailable()) return null
  try {
    const key = await getOrCreateKey()
    const session = readFile().sessions[service]
    if (!session) return null
    const plain = await decryptText(key, session)
    if (plain === null || plain.trim().length === 0) return null
    return { service, cookies: plain }
  } catch {
    return null
  }
}