import OpenAI from 'openai';
import { safeSend, broadcastToUser } from './helpers.js';
import { LIGHTNING_BASE, PUBLIC_URL } from './config.js';
import { sessionStore, deviceSessionStore } from './sessionStore.js';
import { rateLimiter } from './rateLimiter.js';
import { initGuestRequestLimiter, consumeGuestRequest } from './guestRequestLimiter.js';
import {
  verifySupabaseToken, getUserSettings, saveUserSettings,
  getUserProfile, setUsername, getSubscriptionInfo,
  getTierConfig, getUsageInfo,
} from './auth.js';
import { streamChat } from './chatStream.js';
import { mediaStore } from './mediaStore.js';
import { memoryStore } from './memoryStore.js';
import { chatTrashStore } from './chatTrashStore.js';
import { systemPromptStore } from './systemPromptStore.js';
import { getWebSearchUsage } from './webSearchUsageStore.js';
import crypto from 'crypto';
import path from 'path';

/**
 * Message Structure: Tree-based with versioned tails
 * 
 * Each message has versions, and each version has a complete tail of subsequent messages.
 * Messages only exist within parent tails (no separate flat array).
 * 
 * {
 *   id: "msg-123",
 *   role: "user" | "assistant",
 *   content: string | array,
 *   timestamp: number,
 *   versions: [
 *     {
 *       content: string | array,
 *       tail: [  // Full message objects
 *         { id, role, content, timestamp, versions: [...], currentVersionIdx, ... },
 *         ...
 *       ],
 *       timestamp: number
 *     },
 *     ...
 *   ],
 *   currentVersionIdx: 0,
 *   toolCalls?: [...]
 * }
 */

const activeStreams = new Map();
const VERSION_META_FIELDS = ['toolCalls', 'responseEdits', 'responseSegments', 'error'];
const CONTINUE_ASSISTANT_PROMPT =
  'Continue your previous response exactly where it left off. Do not restart, summarize, or repeat the opening. Preserve the same formatting and only add the missing continuation.';
const FREE_WEB_SEARCH_LIMIT = 15;

export function abortActiveStream(ws) {
  if (!activeStreams.has(ws)) return;
  activeStreams.get(ws).abort();
  activeStreams.delete(ws);
}

initGuestRequestLimiter().catch(err => console.error('Failed to initialize guest request limiter:', err));

function usageOwnerKey(client, clientId = '') {
  if (client?.userId) return `user:${client.userId}`;
  return `guest:${clientId || client?.tempId || 'anonymous'}`;
}

function isFreeSearchPlan(client, usageInfo) {
  if (!client?.userId) return true;
  const planKey = usageInfo?.plan_key || usageInfo?.planKey || null;
  return planKey === 'free';
}

async function buildUsagePayload(client, clientId = '') {
  const usageInfo = await getUsageInfo(client?.accessToken, clientId);
  const webSearchDaily = await getWebSearchUsage(usageOwnerKey(client, clientId), FREE_WEB_SEARCH_LIMIT);
  return {
    ...(usageInfo || {}),
    usage: {
      ...(usageInfo?.usage || {}),
      webSearchDaily,
    },
  };
}

export async function handleWsMessage(ws, msg, wsClients) {
  const client = wsClients.get(ws); if (!client) return;
  // Require turnstile verification for most message types
  if (!client.verified && msg.type !== 'ping' && msg.type !== 'turnstile:verify') {
    return safeSend(ws, { type: 'error', message: 'turnstile:required' });
  }

  const bypassDeviceValidation = new Set([
    'ping',
    'turnstile:verify',
    'auth:login',
    'auth:guest',
    'auth:logout',
  ]);
  if (client.userId && client.deviceToken && !bypassDeviceValidation.has(msg.type)) {
    const activeDeviceSession = await deviceSessionStore.validate(client.deviceToken);
    if (!activeDeviceSession) {
      const priorUserId = client.userId;
      Object.assign(client, { userId: null, authenticated: false, accessToken: null, deviceToken: null });
      sessionStore.markOffline(priorUserId, ws);
      return safeSend(ws, { type: 'auth:forcedLogout', reason: 'Session revoked by another device' });
    }
  }

  const h = handlers[msg.type];
  if (h) return h(ws, msg, client, wsClients);
  safeSend(ws, { type: 'error', message: `Unknown: ${msg.type}` });
}

function bcast(wsClients, userId, data, excludeWs) {
  broadcastToUser(wsClients, userId, data, excludeWs);
}

const handlers = {
  'ping': (ws) => { safeSend(ws, { type: 'pong' }); },

  'turnstile:verify': async (ws, msg, client) => {
    try {
      const token = msg?.token;
      const secret = process.env.TURNSTILE_SECRET_KEY;
      if (!token || !secret) return safeSend(ws, { type: 'turnstile:error', message: 'Missing token or server not configured' });
      const params = new URLSearchParams(); params.append('secret', secret); params.append('response', token);
      if (client.ip) params.append('remoteip', client.ip);
      const r = await fetch('https://challenges.cloudflare.com/turnstile/v0/siteverify', { method: 'POST', body: params });
      const j = await r.json();
      if (j?.success) { client.verified = true; return safeSend(ws, { type: 'turnstile:ok' }); }
      return safeSend(ws, { type: 'turnstile:error', message: 'Verification failed' });
    } catch (e) { console.error('ws turnstile verify', e); return safeSend(ws, { type: 'turnstile:error', message: 'Server error' }); }
  },

  'auth:login': async (ws, msg, client, wsClients) => {
    const { accessToken, tempId: clientTempId, deviceToken: requestedDeviceToken } = msg;
    if (!accessToken) return safeSend(ws, { type: 'auth:error', message: 'Missing token' });
    const user = await verifySupabaseToken(accessToken);
    if (!user) return safeSend(ws, { type: 'auth:error', message: 'Invalid token' });

    let nextDeviceToken = null;
    let reusedDeviceSession = false;
    if (requestedDeviceToken) {
      const existingDevice = await deviceSessionStore.validate(requestedDeviceToken);
      if (existingDevice?.userId === user.id) {
        existingDevice.ip = client.ip;
        existingDevice.userAgent = client.userAgent;
        nextDeviceToken = existingDevice.token;
        reusedDeviceSession = true;
      }
    }
    if (!nextDeviceToken) {
      nextDeviceToken = await deviceSessionStore.create(user.id, client.ip, client.userAgent);
    }
    if (client.deviceToken && client.deviceToken !== nextDeviceToken) {
      await deviceSessionStore.revoke(client.deviceToken);
    }
    client.userId = user.id; client.accessToken = accessToken; client.authenticated = true;
    client.deviceToken = nextDeviceToken;
    sessionStore.markOnline(user.id, ws);

    if (clientTempId) client.tempId = clientTempId;
    const tId = client.tempId;
    await sessionStore.transferTempToUser(tId, user.id, accessToken);

    const [sessions, settings, profile, subscription] = await Promise.all([
      sessionStore.loadUserSessions(user.id, accessToken),
      getUserSettings(user.id, accessToken),
      getUserProfile(user.id, accessToken),
      getSubscriptionInfo(accessToken),
    ]);

    const authOkMsg = { type: 'auth:ok', userId: user.id, email: user.email,
      deviceToken: client.deviceToken, sessions: sessions.map(ser), settings, profile, subscription };
    safeSend(ws, authOkMsg);

    if (!reusedDeviceSession) {
      bcast(wsClients, user.id, { type: 'auth:newLogin', message: 'New login on your account.',
        ip: client.ip, userAgent: client.userAgent, timestamp: new Date().toISOString() }, ws);
    }
  },

  'auth:logout': async (ws, msg, client) => {
    const priorUserId = client.userId;
    if (client.deviceToken) await deviceSessionStore.revoke(client.deviceToken);
    Object.assign(client, { userId: null, authenticated: false, accessToken: null, deviceToken: null });
    if (priorUserId) sessionStore.markOffline(priorUserId, ws);
    safeSend(ws, { type: 'auth:loggedOut' });
  },

  'auth:guest': async (ws, msg, client) => {
    const t = msg.tempId || client.tempId;
    client.tempId = t;
    sessionStore.initTemp(t);
    const sessions = await sessionStore.getTempSessions(t);
    safeSend(ws, { type: 'auth:guestOk', tempId: t, sessions: sessions.map(ser) });
  },

  'sessions:list': async (ws, msg, client) => {
    const list = client.userId
      ? sessionStore.getUserSessions(client.userId)
      : await sessionStore.getTempSessions(client.tempId);
    list.sort((a, b) => b.created - a.created);
    safeSend(ws, { type: 'sessions:list', sessions: list.map(ser) });
  },

  'sessions:create': async (ws, msg, client) => {
    const s = client.userId
      ? await sessionStore.createUserSession(client.userId, client.accessToken)
      : await sessionStore.createTempSession(client.tempId);
    safeSend(ws, { type: 'sessions:created', session: ser(s) });
  },

  'sessions:delete': async (ws, msg, client) => {
    const owner = getClientOwner(client);
    const session = client.userId
      ? sessionStore.getUserSession(client.userId, msg.sessionId)
      : await sessionStore.getTempSession(client.tempId, msg.sessionId);
    if (!session) return safeSend(ws, { type: 'error', message: 'Session not found' });

    await chatTrashStore.add(owner, JSON.parse(JSON.stringify(session)));
    if (client.userId) {
      await sessionStore.deleteUserSession(client.userId, client.accessToken, msg.sessionId);
      await sessionStore.deleteTempSessionEverywhere(msg.sessionId);
    } else {
      await sessionStore.deleteTempSession(client.tempId, msg.sessionId);
    }
    safeSend(ws, { type: 'sessions:deleted', sessionId: msg.sessionId });
    safeSend(ws, { type: 'trash:chats:changed' });
  },

  'sessions:deleteAll': async (ws, msg, client) => {
    const owner = getClientOwner(client);
    const sessions = client.userId
      ? sessionStore.getUserSessions(client.userId)
      : await sessionStore.getTempSessions(client.tempId);
    for (const session of sessions) {
      await chatTrashStore.add(owner, JSON.parse(JSON.stringify(session)));
      if (client.userId) await sessionStore.deleteTempSessionEverywhere(session.id);
    }
    if (client.userId) await sessionStore.deleteAllUserSessions(client.userId, client.accessToken);
    else await sessionStore.deleteTempAll(client.tempId);
    safeSend(ws, { type: 'sessions:deletedAll' });
    safeSend(ws, { type: 'trash:chats:changed' });
  },

  'sessions:rename': async (ws, msg, client) => {
    const name = (msg.name || '').trim(); if (!name) return;
    if (client.userId)
      await sessionStore.updateUserSession(client.userId, client.accessToken, msg.sessionId, { name });
    else await sessionStore.updateTempSession(client.tempId, msg.sessionId, { name });
    safeSend(ws, { type: 'sessions:renamed', sessionId: msg.sessionId, name });
  },

  'sessions:get': async (ws, msg, client) => {
    const s = client.userId
      ? sessionStore.getUserSession(client.userId, msg.sessionId)
      : await sessionStore.getTempSession(client.tempId, msg.sessionId);
    if (!s) return safeSend(ws, { type: 'error', message: 'Session not found' });
    safeSend(ws, { type: 'sessions:data', session: ser(s) });
  },

  'sessions:share': async (ws, msg, client) => {
    if (!client.userId) return safeSend(ws, { type: 'error', message: 'Sign in to share' });
    const token = await sessionStore.createShareToken(client.userId, client.accessToken, msg.sessionId);
    if (!token) return safeSend(ws, { type: 'error', message: 'Share failed' });
    safeSend(ws, { type: 'sessions:shareUrl', url: `${PUBLIC_URL}/?share=${token}`, sessionId: msg.sessionId });
  },

  'sessions:import': async (ws, msg, client) => {
    if (!client.userId) return safeSend(ws, { type: 'error', message: 'Sign in to import' });
    const s = await sessionStore.importSharedSession(client.userId, client.accessToken, msg.token);
    if (!s) return safeSend(ws, { type: 'error', message: 'Invalid share link' });
    safeSend(ws, { type: 'sessions:imported', session: ser(s) });
  },

  'trash:chats:list': async (ws, msg, client) => {
    const owner = getClientOwner(client);
    const items = await chatTrashStore.list(owner);
    safeSend(ws, { type: 'trash:chats:list', items });
  },

  'trash:chats:restore': async (ws, msg, client) => {
    const owner = getClientOwner(client);
    const restored = await chatTrashStore.restore(owner, msg.ids || []);
    const sessions = [];
    for (const snapshot of restored) {
      const restoredSession = await restoreDeletedSession(client, snapshot);
      if (restoredSession) sessions.push(ser(restoredSession));
    }
    safeSend(ws, { type: 'trash:chats:restored', sessions });
    safeSend(ws, { type: 'trash:chats:changed' });
  },

  'trash:chats:deleteForever': async (ws, msg, client) => {
    const owner = getClientOwner(client);
    const removedIds = await chatTrashStore.deleteForever(owner, msg.ids || []);
    safeSend(ws, { type: 'trash:chats:deletedForever', ids: removedIds });
    safeSend(ws, { type: 'trash:chats:changed' });
  },

  'chat:send': async (ws, msg, client) => {
    const { sessionId, content, tools } = msg;
    const owner = getClientOwner(client);
    if (!client.userId) {
      const allowed = await consumeGuestRequest(client.ip || 'unknown');
      if (!allowed) return safeSend(ws, { type: 'guest:rateLimit', message: 'Guest request limit exceeded' });
      if (!await sessionStore.tempCanSend(client.tempId)) return safeSend(ws, { type: 'chat:limitReached' });
      await sessionStore.tempBump(client.tempId);
    }
    const session = client.userId
      ? sessionStore.getUserSession(client.userId, sessionId)
      : await sessionStore.getTempSession(client.tempId, sessionId);
    if (!session) return safeSend(ws, { type: 'error', message: 'Session not found' });

    abortActiveStream(ws);
    const abort = new AbortController();
    activeStreams.set(ws, abort);
    safeSend(ws, { type: 'chat:start', sessionId });

    let fullText = '';
    const assetsCollected = [], toolCallsCollected = [];

    // Extract flat history from tree structure
    const rootMessage = session.history?.[0];
    const flatHistory = rootMessage ? extractFlatHistory(rootMessage) : [];

    if (Array.isArray(msg.linkedMediaIds) && msg.linkedMediaIds.length) {
      await mediaStore.attachToSession(owner, msg.linkedMediaIds, sessionId).catch((err) => {
        console.error('Failed to link uploaded media to session:', err);
      });
    }

    const usagePayload = await buildUsagePayload(client, msg.clientId || '');
    const webSearchLimit = isFreeSearchPlan(client, usagePayload)
      ? { key: usageOwnerKey(client, msg.clientId || ''), limit: FREE_WEB_SEARCH_LIMIT }
      : null;

    await streamChat({
      sessionId,
      model: session.model,
      history: flatHistory,
      userMessage: content,
      tools: tools || {},
      accessToken: client.accessToken,
      clientId: msg.clientId,
      webSearchLimit,
      owner,
      sessionName: session.name,
      abortSignal: abort.signal,
      onToken(t) { fullText += t; safeSend(ws, { type: 'chat:token', token: t, sessionId }); },
      onToolCall(call) {
        safeSend(ws, { type: 'chat:toolCall', call, sessionId });
        if (call.state === 'resolved' || call.state === 'canceled') toolCallsCollected.push(call);
      },
      onNewAsset(asset) {
        safeSend(ws, { type: 'chat:asset', asset, sessionId });
        assetsCollected.push(asset);
        safeSend(ws, { type: 'media:changed' });
      },
      onDraftEdit(edit, draftText) {
        safeSend(ws, { type: 'chat:draftEdited', edit, text: draftText, sessionId });
      },
      async onDone(text, toolCalls, aborted, sessionNameFromTag, responseEdits = [], responseSegments = []) {
        activeStreams.delete(ws);
        const finalText = text || fullText;

        // Only create user entry if content was actually provided
        const hasContent = content !== undefined && content !== null && content !== '' &&
          !(Array.isArray(content) && content.length === 0);
        const userEntry = hasContent
          ? buildEntry('user', content)
          : null;

        const resolvedMap = new Map(toolCallsCollected.map(c => [c.id, c]));
        const mergedCalls = (toolCalls || []).map(c => {
          const resolved = resolvedMap.get(c.id) || {};
          return { ...c, state: resolved.state || 'resolved', result: resolved.result };
        });
        const asstEntry = buildEntry('assistant', finalText, mergedCalls, {
          responseEdits,
          responseSegments,
        });

        const mediaEntries = assetsCollected.map((asset) =>
          buildMediaEntry(asset.role, {
            assetId: asset.id,
            mimeType: asset.mimeType,
            name: asset.name,
          })
        );

        const generatedFiles = extractAssistantGeneratedFiles(finalText);
        for (const file of generatedFiles) {
          await mediaStore.storeBuffer(owner, {
            name: file.name,
            mimeType: file.mimeType,
            buffer: file.buffer,
            sessionId,
            source: 'assistant_generated',
            kind: file.kind,
          }).catch((err) => console.error('Failed to store generated text asset:', err));
        }
        if (generatedFiles.length) safeSend(ws, { type: 'media:changed' });

        // Rebuild tree structure with new messages appended to the active branch leaf.
        let newRootMessage = rootMessage ? cloneAndRepairTree(rootMessage) : null;

        if (!newRootMessage) {
          // First message in session - must have user entry
          if (!userEntry) return safeSend(ws, { type: 'error', message: 'No content for first message' });
          newRootMessage = userEntry;
          newRootMessage.versions[0].tail = [{ ...asstEntry }, ...mediaEntries];
        } else if (userEntry) {
          appendConversationTurn(newRootMessage, userEntry, asstEntry, mediaEntries);
        } else {
          const appendedEntries = [
            asstEntry,
            ...mediaEntries,
          ];
          appendEntriesToActiveLeaf(newRootMessage, appendedEntries);
        }

        const newHistory = [newRootMessage];

        let newName = session.name;
        if (sessionNameFromTag) {
          newName = sessionNameFromTag;
        } else if (!session.history?.length || session.name === 'New Chat') {
          newName = session.name;
        }

        if (client.userId)
          await sessionStore.updateUserSession(client.userId, client.accessToken, sessionId, { history: newHistory, name: newName });
        else await sessionStore.updateTempSession(client.tempId, sessionId, { history: newHistory, name: newName });

        safeSend(ws, { type: aborted ? 'chat:aborted' : 'chat:done', sessionId, name: newName, history: extractFlatHistory(newRootMessage) });
      },
      onError(err) {
        activeStreams.delete(ws);
        console.error('streamChat error:', err);
        safeSend(ws, { type: 'chat:error', error: String(err), sessionId });
        safeSend(ws, { type: 'chat:aborted', sessionId, reason: 'error' });
      },
    });
  },

  'chat:stop': (ws) => { abortActiveStream(ws); },

  'chat:editMessage': async (ws, msg, client) => {
    const { sessionId, messageIndex, newContent } = msg;
    const session = client.userId
      ? sessionStore.getUserSession(client.userId, sessionId)
      : await sessionStore.getTempSession(client.tempId, sessionId);
    if (!session) return safeSend(ws, { type: 'error', message: 'Session not found' });
    
    const rootMessage = session.history?.[0];
    if (!rootMessage) return safeSend(ws, { type: 'error', message: 'No history' });
    
    const flatHistory = extractFlatHistory(rootMessage);
    const targetMsg = flatHistory[messageIndex];
    if (!targetMsg) {
      console.error(`chat:editMessage: Message at index ${messageIndex} not found. History length: ${flatHistory.length}`);
      return safeSend(ws, { type: 'error', message: 'Message not found' });
    }
    
    // Find the target message in the tree and add new version
    const newRoot = cloneAndRepairTree(rootMessage);
    const context = findMessageContext(newRoot, targetMsg.id);
    if (!context?.message) return safeSend(ws, { type: 'error', message: 'Message not found in tree' });

    const found = findAndUpdateMessage(newRoot, targetMsg.id, (msgInTree) => {
      if (msgInTree.role === 'user' && Array.isArray(context.parentTail) && context.index >= 0) {
        const trailing = context.parentTail.splice(context.index + 1);
        if (trailing.length) {
          const currentVersion = getActiveVersion(msgInTree);
          currentVersion.tail = [...(currentVersion.tail || []), ...trailing];
        }
      }
      // Add new version with EMPTY tail (no responses yet for this edited version)
      msgInTree.versions.push({
        content: newContent,
        tail: [],  // New version starts fresh, no tail
        timestamp: Date.now()
      });
      msgInTree.currentVersionIdx = msgInTree.versions.length - 1;
      msgInTree.content = newContent;
    });
    
    if (!found) return;
    
    const newHistory = [newRoot];
    if (client.userId) {
      await sessionStore.updateUserSession(client.userId, client.accessToken, sessionId, { history: newHistory });
    } else {
      await sessionStore.updateTempSession(client.tempId, sessionId, { history: newHistory });
    }
    
    // Send back the updated message with its ID and the full flat history
    const updatedFlatHistory = extractFlatHistory(newRoot);
    const updatedTargetMsg = updatedFlatHistory[messageIndex];
    
    if (!updatedTargetMsg) {
      console.error(`chat:editMessage: Updated message not found at index ${messageIndex}. Updated history length: ${updatedFlatHistory.length}`);
      return safeSend(ws, { type: 'error', message: 'Failed to apply edit - message lost' });
    }
    
    safeSend(ws, { type: 'chat:messageEdited', sessionId, messageId: targetMsg.id, messageIndex, message: updatedTargetMsg, history: updatedFlatHistory });
  },

  'chat:selectVersion': async (ws, msg, client) => {
    const { sessionId, messageIndex, versionIdx } = msg;
    const session = client.userId
      ? sessionStore.getUserSession(client.userId, sessionId)
      : await sessionStore.getTempSession(client.tempId, sessionId);
    if (!session) return;
    
    const rootMessage = session.history?.[0];
    if (!rootMessage) return;
    
    const flatHistory = extractFlatHistory(rootMessage);
    const targetMsg = flatHistory[messageIndex];
    if (!targetMsg || !targetMsg.versions || versionIdx >= targetMsg.versions.length) return;
    
    // Find and update the message in tree, switching to specified version
    const newRoot = cloneAndRepairTree(rootMessage);
    const found = findAndUpdateMessage(newRoot, targetMsg.id, (msgInTree) => {
      msgInTree.currentVersionIdx = versionIdx;
      msgInTree.content = msgInTree.versions[versionIdx].content;
      // Tail is automatically correct since each version has its own tail
    });
    
    if (!found) return;
    
    const newHistory = [newRoot];
    if (client.userId) {
      await sessionStore.updateUserSession(client.userId, client.accessToken, sessionId, { history: newHistory });
    } else {
      await sessionStore.updateTempSession(client.tempId, sessionId, { history: newHistory });
    }
    
    // Send back with messageId for clarity
    safeSend(ws, { type: 'chat:versionSelected', sessionId, messageId: targetMsg.id, messageIndex, history: extractFlatHistory(newRoot) });
  },

  'chat:assistantAction': async (ws, msg, client) => {
    const { sessionId, messageIndex } = msg;
    const action = msg.action === 'continue' ? 'continue' : 'regenerate';
    const session = client.userId
      ? sessionStore.getUserSession(client.userId, sessionId)
      : await sessionStore.getTempSession(client.tempId, sessionId);
    if (!session) return safeSend(ws, { type: 'error', message: 'Session not found' });

    const rootMessage = session.history?.[0];
    if (!rootMessage) return safeSend(ws, { type: 'error', message: 'No history' });

    const flatHistory = extractFlatHistory(rootMessage);
    const targetMsg = flatHistory[messageIndex];
    if (!targetMsg || targetMsg.role !== 'assistant') {
      return safeSend(ws, { type: 'error', message: 'Assistant message not found' });
    }

    abortActiveStream(ws);
    const abort = new AbortController();
    activeStreams.set(ws, abort);

    const owner = getClientOwner(client);
    const historyBeforeTarget = flatHistory.slice(0, messageIndex);
    const baseAssistantText = stripSessionTagText(targetMsg.content || '');
    const actionHistory = action === 'continue'
      ? [...historyBeforeTarget, { role: 'assistant', content: baseAssistantText }]
      : historyBeforeTarget;
    const actionUserMessage = action === 'continue' ? CONTINUE_ASSISTANT_PROMPT : null;

    safeSend(ws, {
      type: 'chat:start',
      sessionId,
      streamKind: 'assistantAction',
      action,
      messageIndex,
      prefillText: action === 'continue' ? baseAssistantText : '',
    });

    let fullText = '';
    const assetsCollected = [];
    const toolCallsCollected = [];
    const usagePayload = await buildUsagePayload(client, msg.clientId || '');
    const webSearchLimit = isFreeSearchPlan(client, usagePayload)
      ? { key: usageOwnerKey(client, msg.clientId || ''), limit: FREE_WEB_SEARCH_LIMIT }
      : null;

    await streamChat({
      sessionId,
      model: session.model,
      history: actionHistory,
      userMessage: actionUserMessage,
      tools: msg.tools || {},
      accessToken: client.accessToken,
      clientId: msg.clientId,
      webSearchLimit,
      owner,
      sessionName: session.name,
      abortSignal: abort.signal,
      onToken(t) {
        fullText += t;
        safeSend(ws, { type: 'chat:token', token: t, sessionId });
      },
      onToolCall(call) {
        safeSend(ws, { type: 'chat:toolCall', call, sessionId });
        if (call.state === 'resolved' || call.state === 'canceled') toolCallsCollected.push(call);
      },
      onNewAsset(asset) {
        safeSend(ws, { type: 'chat:asset', asset, sessionId });
        assetsCollected.push(asset);
        safeSend(ws, { type: 'media:changed' });
      },
      onDraftEdit(edit, draftText) {
        safeSend(ws, { type: 'chat:draftEdited', edit, text: draftText, sessionId });
      },
      async onDone(text, toolCalls, aborted, sessionNameFromTag, responseEdits = [], responseSegments = []) {
        activeStreams.delete(ws);
        if (aborted) {
          return safeSend(ws, { type: 'chat:aborted', sessionId });
        }

        const rawAssistantText = text || fullText;
        const resolvedMap = new Map(toolCallsCollected.map((call) => [call.id, call]));
        const mergedCalls = (toolCalls || []).map((call) => {
          const resolved = resolvedMap.get(call.id) || {};
          return { ...call, state: resolved.state || 'resolved', result: resolved.result };
        });

        let finalText = rawAssistantText;
        let finalSegments = responseSegments;

        if (action === 'continue') {
          const { continuationText, overlapLength } = stripContinuationOverlap(baseAssistantText, rawAssistantText);
          finalText = baseAssistantText + continuationText;
          finalSegments = [
            ...(baseAssistantText ? [{ type: 'text', text: baseAssistantText }] : []),
            ...trimLeadingTextFromSegments(responseSegments, overlapLength),
          ];
        }

        const mediaEntries = assetsCollected.map((asset) =>
          buildMediaEntry(asset.role, {
            assetId: asset.id,
            mimeType: asset.mimeType,
            name: asset.name,
          })
        );

        const generatedFiles = extractAssistantGeneratedFiles(finalText);
        for (const file of generatedFiles) {
          await mediaStore.storeBuffer(owner, {
            name: file.name,
            mimeType: file.mimeType,
            buffer: file.buffer,
            sessionId,
            source: 'assistant_generated',
            kind: file.kind,
          }).catch((err) => console.error('Failed to store generated text asset:', err));
        }
        if (generatedFiles.length) safeSend(ws, { type: 'media:changed' });

        const newRoot = cloneAndRepairTree(rootMessage);
        const found = findAndUpdateMessage(newRoot, targetMsg.id, (msgInTree) => {
          const nextVersion = buildVersionRecord(finalText, {
            tail: mediaEntries,
            toolCalls: mergedCalls,
            responseEdits,
            responseSegments: finalSegments,
          });
          applyVersionToMessage(msgInTree, nextVersion);
        });
        if (!found) {
          return safeSend(ws, { type: 'error', message: 'Assistant branch could not be updated' });
        }

        let newName = session.name;
        if (sessionNameFromTag) {
          newName = sessionNameFromTag;
        }

        const newHistory = [newRoot];
        if (client.userId) {
          await sessionStore.updateUserSession(client.userId, client.accessToken, sessionId, { history: newHistory, name: newName });
        } else {
          await sessionStore.updateTempSession(client.tempId, sessionId, { history: newHistory, name: newName });
        }

        safeSend(ws, { type: 'chat:done', sessionId, name: newName, history: extractFlatHistory(newRoot) });
      },
      onError(err) {
        activeStreams.delete(ws);
        console.error('assistant action streamChat error:', err);
        safeSend(ws, { type: 'chat:error', error: String(err), sessionId });
        safeSend(ws, { type: 'chat:aborted', sessionId, reason: 'error' });
      },
    });
  },

  'settings:get': async (ws, msg, client) => {
    const s = client.userId
      ? await getUserSettings(client.userId, client.accessToken)
      : { theme: 'dark', webSearch: true, imageGen: true, videoGen: true, audioGen: true };
    safeSend(ws, { type: 'settings:data', settings: s });
  },
  'settings:save': async (ws, msg, client, wsClients) => {
    if (!client.userId) return;
    await saveUserSettings(client.userId, client.accessToken, msg.settings);
    safeSend(ws, { type: 'settings:saved' });
    bcast(wsClients, client.userId, { type: 'settings:updated', settings: msg.settings }, ws);
  },

  'personalization:get': async (ws, msg, client) => {
    const defaultPrompt = await systemPromptStore.getDefaultPrompt();
    const personalization = client.userId
      ? await systemPromptStore.getPersonalization(client.userId)
      : {
          defaultPrompt,
          customPrompt: null,
          resolvedPrompt: defaultPrompt,
          isCustom: false,
          updatedAt: null,
          canEdit: false,
        };
    safeSend(ws, { type: 'personalization:data', personalization });
  },
  'personalization:saveSystemPrompt': async (ws, msg, client, wsClients) => {
    if (!client.userId) return safeSend(ws, { type: 'personalization:error', message: 'Sign in to customize your system prompt' });
    try {
      const personalization = await systemPromptStore.setUserPrompt(client.userId, msg.markdown);
      safeSend(ws, { type: 'personalization:updated', personalization });
      bcast(wsClients, client.userId, { type: 'personalization:updated', personalization }, ws);
    } catch (err) {
      safeSend(ws, { type: 'personalization:error', message: err.message || 'Unable to save system prompt' });
    }
  },
  'personalization:resetSystemPrompt': async (ws, msg, client, wsClients) => {
    if (!client.userId) return safeSend(ws, { type: 'personalization:error', message: 'Sign in to customize your system prompt' });
    try {
      const personalization = await systemPromptStore.resetUserPrompt(client.userId);
      safeSend(ws, { type: 'personalization:updated', personalization });
      bcast(wsClients, client.userId, { type: 'personalization:updated', personalization }, ws);
    } catch (err) {
      safeSend(ws, { type: 'personalization:error', message: err.message || 'Unable to reset system prompt' });
    }
  },

  'memories:list': async (ws, msg, client) => {
    const owner = getClientOwner(client);
    const items = await memoryStore.list(owner);
    safeSend(ws, { type: 'memories:list', items });
  },

  'memories:create': async (ws, msg, client, wsClients) => {
    const owner = getClientOwner(client);
    const memory = await memoryStore.create(owner, {
      content: msg.content,
      sessionId: msg.sessionId || null,
      source: msg.source || 'manual',
    });
    safeSend(ws, { type: 'memories:created', memory });
    if (client.userId) bcast(wsClients, client.userId, { type: 'memories:changed' }, ws);
  },

  'memories:update': async (ws, msg, client, wsClients) => {
    const owner = getClientOwner(client);
    const memory = await memoryStore.update(owner, msg.id, msg.content);
    safeSend(ws, { type: 'memories:updated', memory });
    if (client.userId) bcast(wsClients, client.userId, { type: 'memories:changed' }, ws);
  },

  'memories:delete': async (ws, msg, client, wsClients) => {
    const owner = getClientOwner(client);
    const ok = await memoryStore.delete(owner, msg.id);
    safeSend(ws, { type: 'memories:deleted', id: ok ? msg.id : null });
    if (client.userId) bcast(wsClients, client.userId, { type: 'memories:changed' }, ws);
  },

  'account:getProfile':      async (ws, msg, c) => { if (!c.userId) return; safeSend(ws, { type: 'account:profile', profile: await getUserProfile(c.userId, c.accessToken) }); },
  'account:setUsername':     async (ws, msg, c) => { if (!c.userId) return; safeSend(ws, { type: 'account:usernameResult', ...await setUsername(c.userId, c.accessToken, msg.username) }); },
  'account:getSubscription': async (ws, msg, c) => { 
    if (!c.userId) return console.warn('[Account] getSubscription called without userId');
    const subInfo = await getSubscriptionInfo(c.accessToken);
    safeSend(ws, { type: 'account:subscription', info: subInfo });
  },
  'account:getUsage':        async (ws, msg, c) => { safeSend(ws, { type: 'account:usage', usage: await buildUsagePayload(c, msg.clientId || '') }); },
  'account:getTierConfig':   async (ws)          => { safeSend(ws, { type: 'account:tierConfig', config: await getTierConfig() }); },
  'account:getSessions':     async (ws, msg, c)   => {
    if (!c.userId) return;
    safeSend(ws, {
      type: 'account:deviceSessions',
      sessions: await deviceSessionStore.getForUser(c.userId),
      currentToken: c.deviceToken,
    });
  },
  'account:revokeSession':   async (ws, msg, c, wsClients) => {
    if (!c.userId || !msg.token) return;
    const revoked = await deviceSessionStore.revoke(msg.token);
    if (revoked) {
      const activeSessions = await deviceSessionStore.getForUser(c.userId);
      for (const [ows, oc] of wsClients) {
        if (oc.userId !== c.userId) continue;
        if (oc.deviceToken === msg.token) {
          safeSend(ows, { type: 'auth:forcedLogout', reason: 'Session revoked by another device' });
          sessionStore.markOffline(oc.userId, ows);
          Object.assign(oc, { userId: null, authenticated: false, accessToken: null, deviceToken: null });
          continue;
        }
        safeSend(ows, {
          type: 'account:deviceSessions',
          sessions: activeSessions,
          currentToken: oc.deviceToken,
        });
      }
    }
    safeSend(ws, { type: 'account:sessionRevoked', token: msg.token });
  },
  'account:revokeAllOthers': async (ws, msg, c, wsClients) => {
    if (!c.userId) return;
    await deviceSessionStore.revokeAllExcept(c.userId, c.deviceToken);
    const activeSessions = await deviceSessionStore.getForUser(c.userId);
    for (const [ows, oc] of wsClients) {
      if (oc.userId !== c.userId) continue;
      if (oc.deviceToken && oc.deviceToken !== c.deviceToken) {
        safeSend(ows, { type: 'auth:forcedLogout', reason: 'Session revoked by another device' });
        sessionStore.markOffline(oc.userId, ows);
        Object.assign(oc, { userId: null, authenticated: false, accessToken: null, deviceToken: null });
        continue;
      }
      safeSend(ows, {
        type: 'account:deviceSessions',
        sessions: activeSessions,
        currentToken: oc.deviceToken,
      });
    }
    safeSend(ws, { type: 'account:allOthersRevoked' });
  },
};

function ser(s) { return { id: s.id, name: s.name, created: s.created, history: s.history || [], model: s.model }; }

function getClientOwner(client) {
  return client.userId
    ? { type: 'user', id: client.userId }
    : { type: 'guest', id: client.tempId };
}

async function restoreDeletedSession(client, snapshot) {
  if (!snapshot) return null;
  const restored = JSON.parse(JSON.stringify(snapshot));
  const existing = client.userId
    ? sessionStore.getUserSession(client.userId, restored.id)
    : await sessionStore.getTempSession(client.tempId, restored.id);
  if (existing) restored.id = crypto.randomUUID();
  restored.created = restored.created || Date.now();
  if (client.userId) {
    return sessionStore.restoreUserSession(client.userId, client.accessToken, restored);
  }
  return sessionStore.restoreTempSession(client.tempId, restored);
}

function generateMessageId() {
  return `msg-${Date.now()}-${Math.random().toString(36).substr(2, 9)}`;
}

function buildEntry(role, content, toolCalls = [], extraFields = {}) {
  const normalizedCalls = toolCalls.map(c => ({
    id:     c.id,
    name:   c.name || c.function?.name,
    args:   c.args ?? (c.function?.arguments ? (() => { try { return JSON.parse(c.function.arguments); } catch { return c.function.arguments; } })() : {}),
    state:  c.state || 'resolved',
    result: c.result,
  }));
  const validContent = (content === undefined || content === null) ? '' : content;
  const versionMeta = {};
  const topLevelExtraFields = { ...extraFields };
  VERSION_META_FIELDS.forEach((key) => {
    if (key in topLevelExtraFields) {
      versionMeta[key] = topLevelExtraFields[key];
      delete topLevelExtraFields[key];
    }
  });
  return { 
    id: generateMessageId(),
    role, 
    content: validContent, 
    timestamp: Date.now(),
    versions: [{
      content: validContent,
      tail: [],
      timestamp: Date.now(),
      ...(normalizedCalls.length ? { toolCalls: normalizedCalls } : {}),
      ...versionMeta,
    }],
    currentVersionIdx: 0,
    ...(normalizedCalls.length ? { toolCalls: normalizedCalls } : {}),
    ...versionMeta,
    ...topLevelExtraFields,
  };
}

function buildMediaEntry(role, content) {
  return {
    id: generateMessageId(),
    role,
    content,
    timestamp: Date.now(),
    versions: [{ content, tail: [], timestamp: Date.now() }],
    currentVersionIdx: 0,
  };
}

function buildVersionRecord(content, extraFields = {}) {
  const validContent = content === undefined || content === null ? '' : content;
  const version = {
    content: validContent,
    tail: Array.isArray(extraFields.tail) ? extraFields.tail : [],
    timestamp: Date.now(),
  };
  VERSION_META_FIELDS.forEach((key) => {
    if (extraFields[key] !== undefined && extraFields[key] !== null) {
      version[key] = extraFields[key];
    }
  });
  return version;
}

function applyVersionToMessage(message, versionRecord) {
  if (!message?.versions || !Array.isArray(message.versions)) {
    message.versions = [];
  }
  message.versions.push(versionRecord);
  message.currentVersionIdx = message.versions.length - 1;
  syncMessageFromActiveVersion(message);
  return message;
}

function stripSessionTagText(content) {
  return typeof content === 'string'
    ? content.replace(/<session_name>[\s\S]*?<\/session_name>/gi, '').trim()
    : content;
}

function stripContinuationOverlap(baseText = '', generatedText = '') {
  const base = String(baseText || '');
  const generated = String(generatedText || '');
  if (!base) return { continuationText: generated, overlapLength: 0 };
  if (!generated) return { continuationText: '', overlapLength: 0 };
  if (generated.startsWith(base)) {
    return { continuationText: generated.slice(base.length), overlapLength: base.length };
  }

  const maxWindow = Math.min(base.length, generated.length, 400);
  for (let size = maxWindow; size > 0; size--) {
    if (base.slice(-size) === generated.slice(0, size)) {
      return { continuationText: generated.slice(size), overlapLength: size };
    }
  }

  return { continuationText: generated, overlapLength: 0 };
}

function trimLeadingTextFromSegments(segments = [], overlapLength = 0) {
  let remaining = Math.max(0, overlapLength);
  const trimmedSegments = [];

  for (const segment of segments || []) {
    if (!segment || segment.type !== 'text' || remaining <= 0) {
      trimmedSegments.push(segment);
      continue;
    }

    const text = String(segment.text || '');
    if (remaining >= text.length) {
      remaining -= text.length;
      continue;
    }

    trimmedSegments.push({
      ...segment,
      text: text.slice(remaining),
    });
    remaining = 0;
  }

  return trimmedSegments.filter((segment) => segment && (segment.type !== 'text' || segment.text));
}

function extractAssistantGeneratedFiles(text) {
  if (!text || typeof text !== 'string') return [];
  const files = [];
  const detailsRe = /<details><summary>([^<]+?)<\/summary>\s*```(?:\w*)\n([\s\S]*?)\n```\s*<\/details>/g;
  const svgRe = /```svg\n([\s\S]*?)\n```/g;
  let match;

  while ((match = detailsRe.exec(text)) !== null) {
    const name = String(match[1] || '').trim();
    const ext = path.extname(name).toLowerCase();
    files.push({
      name: name || 'generated-file.txt',
      mimeType: ext === '.html' || ext === '.htm' ? 'text/html' : 'text/plain',
      kind: ext === '.html' || ext === '.htm' ? 'rich_text' : 'text',
      buffer: Buffer.from(match[2], 'utf8'),
    });
  }

  let svgIndex = 1;
  while ((match = svgRe.exec(text)) !== null) {
    files.push({
      name: `generated-image-${svgIndex++}.svg`,
      mimeType: 'image/svg+xml',
      kind: 'image',
      buffer: Buffer.from(match[1], 'utf8'),
    });
  }

  return files;
}

/**
 * Validate and repair tree structure after cloning/modification
 * Ensures all messages and versions have valid content property
 */
function validateAndRepairTree(rootMessage) {
  const repair = (msg) => {
    if (!msg) return;
    // Ensure message has content
    if (msg.content === undefined || msg.content === null) {
      msg.content = '';
    }
    // Ensure versions array and each version's content
    if (msg.versions && Array.isArray(msg.versions)) {
      for (const version of msg.versions) {
        if (version.content === undefined || version.content === null) {
          version.content = '';
        }
        // Recursively repair tail messages
        if (version.tail && Array.isArray(version.tail)) {
          for (const tailMsg of version.tail) {
            repair(tailMsg);
          }
        }
      }
    }
  };
  repair(rootMessage);
  return rootMessage;
}

function cloneAndRepairTree(rootMessage) {
  return validateAndRepairTree(JSON.parse(JSON.stringify(rootMessage)));
}

function getActiveVersion(message) {
  if (!message) return null;
  const versions = Array.isArray(message.versions) ? message.versions : [];
  if (!versions.length) {
    message.versions = [{ content: message.content ?? '', tail: [], timestamp: Date.now() }];
    message.currentVersionIdx = 0;
    return message.versions[0];
  }
  const currentVersionIdx = Number.isInteger(message.currentVersionIdx)
    ? Math.max(0, Math.min(message.currentVersionIdx, versions.length - 1))
    : 0;
  message.currentVersionIdx = currentVersionIdx;
  if (!Array.isArray(message.versions[currentVersionIdx].tail)) {
    message.versions[currentVersionIdx].tail = [];
  }
  if (message.versions[currentVersionIdx].content === undefined || message.versions[currentVersionIdx].content === null) {
    message.versions[currentVersionIdx].content = message.content ?? '';
  }
  return message.versions[currentVersionIdx];
}

function cloneVersionMetaValue(value) {
  if (value === undefined) return undefined;
  return JSON.parse(JSON.stringify(value));
}

function syncMessageFromActiveVersion(message) {
  if (!message) return message;
  const currentVersion = getActiveVersion(message);
  if (!currentVersion) return message;
  message.content = currentVersion.content ?? message.content ?? '';
  VERSION_META_FIELDS.forEach((key) => {
    if (key in currentVersion) {
      message[key] = cloneVersionMetaValue(currentVersion[key]);
    } else {
      delete message[key];
    }
  });
  return message;
}

function getActiveLeafMessage(rootMessage) {
  let current = rootMessage;
  while (current) {
    const currentVersion = getActiveVersion(current);
    const tail = Array.isArray(currentVersion?.tail) ? currentVersion.tail : [];
    if (!tail.length) return current;
    current = tail[tail.length - 1];
  }
  return rootMessage;
}

function appendEntriesToActiveLeaf(rootMessage, entries = []) {
  if (!rootMessage || !entries.length) return rootMessage;
  const leaf = getActiveLeafMessage(rootMessage);
  const currentVersion = getActiveVersion(leaf);
  currentVersion.tail = [...(currentVersion.tail || []), ...entries];
  return rootMessage;
}

function appendConversationTurn(rootMessage, userEntry, assistantEntry, mediaEntries = []) {
  if (!rootMessage || !userEntry) return rootMessage;
  const leaf = getActiveLeafMessage(rootMessage);
  const currentVersion = getActiveVersion(leaf);
  const userVersion = getActiveVersion(userEntry);
  userVersion.tail = [
    ...(assistantEntry ? [assistantEntry] : []),
    ...(Array.isArray(mediaEntries) ? mediaEntries : []),
  ];
  syncMessageFromActiveVersion(userEntry);
  currentVersion.tail = [...(currentVersion.tail || []), userEntry];
  return rootMessage;
}

function extractFlatHistory(rootMessage) {
  if (!rootMessage) return [];
  
  // Helper to ensure message has valid content
  const ensureValidContent = (msg) => {
    if (msg.content === undefined || msg.content === null) {
      msg.content = '';
    }
    return syncMessageFromActiveVersion(msg);
  };
  
  const history = [ensureValidContent(rootMessage)];
  const currentVerIdx = rootMessage.currentVersionIdx ?? 0;
  
  if (!Array.isArray(rootMessage.versions)) {
    console.warn(`extractFlatHistory: Root message ${rootMessage.id} missing versions array`);
    return history;
  }
  
  if (currentVerIdx >= rootMessage.versions.length) {
    console.warn(`extractFlatHistory: Root message currentVersionIdx ${currentVerIdx} out of bounds (${rootMessage.versions.length} versions)`);
    return history;
  }
  
  const currentTail = rootMessage.versions[currentVerIdx]?.tail;
  
  if (currentTail && Array.isArray(currentTail)) {
    const walkTail = (tail) => {
      for (let i = 0; i < tail.length; i++) {
        const msg = tail[i];
        history.push(ensureValidContent(msg));
        const ver = msg.versions?.[msg.currentVersionIdx ?? 0];
        if (ver?.tail && Array.isArray(ver.tail)) {
          walkTail(ver.tail);
        }
        if (msg.role === 'user' && Array.isArray(msg.versions) && msg.versions.length > 1) {
          break;
        }
      }
    };
    walkTail(currentTail);
  }
  return history;
}

function findMessageContext(rootMessage, targetId) {
  if (!rootMessage) return null;
  if (rootMessage.id === targetId) {
    return { message: rootMessage, parent: null, parentTail: null, index: -1 };
  }

  const search = (msg) => {
    const verIdx = msg.currentVersionIdx ?? 0;
    const tail = msg.versions?.[verIdx]?.tail;
    if (!tail || !Array.isArray(tail)) return null;

    for (let i = 0; i < tail.length; i++) {
      const child = tail[i];
      if (child.id === targetId) {
        return { message: child, parent: msg, parentTail: tail, index: i };
      }
      const nested = search(child);
      if (nested) return nested;
    }
    return null;
  };

  return search(rootMessage);
}

function findAndUpdateMessage(rootMessage, targetId, updateFn) {
  if (rootMessage.id === targetId) {
    updateFn(rootMessage);
    return true;
  }
  
  const search = (msg) => {
    const verIdx = msg.currentVersionIdx ?? 0;
    const tail = msg.versions?.[verIdx]?.tail;
    if (!tail || !Array.isArray(tail)) return false;
    
    for (const child of tail) {
      if (child.id === targetId) {
        updateFn(child);
        return true;
      }
      if (search(child)) return true;
    }
    return false;
  };
  
  return search(rootMessage);
}