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controllers/application/account/e2eeController.js

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+const mongoose = require('mongoose')
+const UserModel = require('../../../models/UserModel')
+const DeviceLinkSessionModel = require('../../../models/DeviceLinkSessionModel')
+
+const DEVICE_LINK_TTL_MS = 5 * 60 * 1000
+
+function findOwnSession (linkId, userId) {
+  if (!mongoose.Types.ObjectId.isValid(linkId)) return null
+  return DeviceLinkSessionModel.findOne({ _id: linkId, user: userId })
+}
+
+const putMyPublicKey = async (req, res, next) => {
+  try {
+    const userId = String(req.user._id)
+    const { publicKey } = req.body
+
+    if (!publicKey || typeof publicKey !== 'string' || publicKey.length < 32 || publicKey.length > 4096) {
+      return res.status(422).json({ error: 'publicKey is required' })
+    }
+
+    const trimmed = String(publicKey).trim()
+    const existing = await UserModel.findById(userId).select('e2ee_public_key').lean()
+
+    // کلید عمومی همیشه یکسان می‌مونه مگر کاربر واقعاً هویتِ E2EE‌ش رو عوض کنه (دستگاه
+    // جدید بدون لینک‌کردن، پاک‌شدن دیتای اپ و...). اگه از قبل یه کلید ثبت‌شده و مقدار
+    // تازه باهاش فرق داره، یعنی یا کلاینت واقعاً هویتش رو عوض کرده یا یه باگ کلاینتی
+    // (مثلاً race توی ساختن کلید) داره جایگزینش می‌کنه — فقط لاگ می‌کنیم تا قابل‌ردیابی
+    // باشه، بدون این‌که خودِ درخواست رو رد کنیم (چون سرور نمی‌تونه تشخیص بده کدوم درسته)
+    if (existing?.e2ee_public_key && existing.e2ee_public_key !== trimmed) {
+      console.warn(`[e2ee] public key rotated for user ${userId} (${existing.e2ee_public_key.length} -> ${trimmed.length} chars)`)
+    }
+
+    if (existing?.e2ee_public_key !== trimmed) {
+      await UserModel.findByIdAndUpdate(userId, { e2ee_public_key: trimmed })
+    }
+
+    res.json({ ok: true })
+  } catch (error) {
+    next(error)
+  }
+}
+
+const getPublicKeyByUserId = async (req, res, next) => {
+  try {
+    const { userId } = req.params
+    if (!userId) {
+      return res.status(400).json({ error: 'userId is required' })
+    }
+
+    const user = await UserModel.findById(userId).select('e2ee_public_key').lean()
+    if (!user) {
+      return res.status(404).json({ error: 'User not found' })
+    }
+
+    res.json({
+      userId: String(user._id),
+      publicKey: user.e2ee_public_key || null
+    })
+  } catch (error) {
+    next(error)
+  }
+}
+
+/**
+ * New device (no E2EE identity yet) starts a link session with its own ephemeral
+ * ECDH public key. Returns a linkId to encode as a QR — the already-linked device
+ * scans it, wraps its identity private key against this ephemeral key, and posts
+ * it back via `approveDeviceLink`. Server only ever stores/relays ciphertext.
+ */
+const startDeviceLink = async (req, res, next) => {
+  try {
+    const { ephemeralPublicKey } = req.body
+    if (
+      !ephemeralPublicKey ||
+      typeof ephemeralPublicKey !== 'string' ||
+      ephemeralPublicKey.length < 32 ||
+      ephemeralPublicKey.length > 2048
+    ) {
+      return res.status(422).json({ error: 'ephemeralPublicKey is required' })
+    }
+
+    const session = await DeviceLinkSessionModel.create({
+      user: req.user._id,
+      ephemeralPublicKeyB64: ephemeralPublicKey.trim(),
+      expiresAt: new Date(Date.now() + DEVICE_LINK_TTL_MS)
+    })
+
+    res.json({ linkId: String(session._id), expiresAt: session.expiresAt })
+  } catch (error) {
+    next(error)
+  }
+}
+
+/** Already-linked device fetches the new device's ephemeral public key to wrap the identity key against. */
+const getDeviceLinkSession = async (req, res, next) => {
+  try {
+    const session = await findOwnSession(req.params.linkId, req.user._id)
+    if (!session) {
+      return res.status(404).json({ error: 'Link not found or expired' })
+    }
+
+    res.json({
+      ephemeralPublicKey: session.ephemeralPublicKeyB64,
+      status: session.status
+    })
+  } catch (error) {
+    next(error)
+  }
+}
+
+/** Already-linked device submits the identity private key wrapped for the new device's ephemeral key. */
+const approveDeviceLink = async (req, res, next) => {
+  try {
+    const { wrappedIdentityKey } = req.body
+    if (!wrappedIdentityKey || typeof wrappedIdentityKey !== 'string') {
+      return res.status(422).json({ error: 'wrappedIdentityKey is required' })
+    }
+
+    const session = await findOwnSession(req.params.linkId, req.user._id)
+    if (!session) {
+      return res.status(404).json({ error: 'Link not found or expired' })
+    }
+
+    session.wrappedIdentityKey = wrappedIdentityKey
+    session.status = 'fulfilled'
+    await session.save()
+
+    res.json({ ok: true })
+  } catch (error) {
+    next(error)
+  }
+}
+
+/** New device polls until the wrapped key arrives. Single-use: the session is deleted once consumed. */
+const pollDeviceLink = async (req, res, next) => {
+  try {
+    const session = await findOwnSession(req.params.linkId, req.user._id)
+    if (!session) {
+      return res.status(404).json({ error: 'Link not found or expired' })
+    }
+
+    if (session.status !== 'fulfilled' || !session.wrappedIdentityKey) {
+      return res.json({ status: 'pending' })
+    }
+
+    const wrappedIdentityKey = session.wrappedIdentityKey
+    await DeviceLinkSessionModel.deleteOne({ _id: session._id })
+
+    res.json({ status: 'fulfilled', wrappedIdentityKey })
+  } catch (error) {
+    next(error)
+  }
+}
+
+module.exports = {
+  putMyPublicKey,
+  getPublicKeyByUserId,
+  startDeviceLink,
+  getDeviceLinkSession,
+  approveDeviceLink,
+  pollDeviceLink
+}