const express = require('express');
const crypto = require('crypto');
const db = require('../db');
const { buildSystemPrompt } = require('../systemPromptBuilder');
const { streamCompletion } = require('../lib/llm');
const router = express.Router();

// POST /api/conversations — create main or fork
router.post('/', (req, res) => {
  const { title, type = 'main', parent_id, model_id, topic } = req.body;
  if (!title) {
    return res.status(400).json({ error: 'title is required' });
  }

  try {
    const info = db.prepare(`
      INSERT INTO conversations (title, type, parent_id, model_id)
      VALUES (?, ?, ?, ?)
    `).run(title, type, parent_id || null, model_id || null);

    const row = db.prepare('SELECT * FROM conversations WHERE id = ?').get(info.lastInsertRowid);
    res.status(201).json(row);
  } catch (err) {
    console.error('[conversations] create error:', err.message);
    res.status(500).json({ error: err.message });
  }
});

// GET /api/conversations — list all, order by updated_at desc
router.get('/', (req, res) => {
  try {
    const rows = db.prepare('SELECT * FROM conversations ORDER BY updated_at DESC').all();
    res.json(rows);
  } catch (err) {
    console.error('[conversations] list error:', err.message);
    res.status(500).json({ error: err.message });
  }
});

// GET /api/conversations/:id/messages — chat history
router.get('/:id/messages', (req, res) => {
  const id = parseInt(req.params.id, 10);
  if (Number.isNaN(id)) {
    return res.status(400).json({ error: 'Invalid conversation id' });
  }

  try {
    const conv = db.prepare('SELECT * FROM conversations WHERE id = ?').get(id);
    if (!conv) {
      return res.status(404).json({ error: 'Conversation not found' });
    }

    const messages = db.prepare(
      'SELECT * FROM messages WHERE conversation_id = ? ORDER BY created_at, id'
    ).all(id);

    const forkPointRow = db.prepare('SELECT value FROM config WHERE key = ?').get(`fork_point_${id}`);
    const forkPoint = forkPointRow ? parseInt(forkPointRow.value, 10) : undefined;

    res.json({ conversation: { ...conv, fork_point: forkPoint }, messages });
  } catch (err) {
    console.error('[conversations] messages error:', err.message);
    res.status(500).json({ error: err.message });
  }
});

// DELETE /api/conversations/:id
router.delete('/:id', (req, res) => {
  const id = parseInt(req.params.id, 10);
  if (Number.isNaN(id)) {
    return res.status(400).json({ error: 'Invalid conversation id' });
  }

  try {
    const info = db.prepare('DELETE FROM conversations WHERE id = ?').run(id);
    if (info.changes === 0) {
      return res.status(404).json({ error: 'Conversation not found' });
    }
    res.json({ deleted: true });
  } catch (err) {
    console.error('[conversations] delete error:', err.message);
    res.status(500).json({ error: err.message });
  }
});

// POST /api/conversations/:id/fork — create child conversation with new topic+model, no message inheritance
router.post('/:id/fork', (req, res) => {
  const parentId = parseInt(req.params.id, 10);
  if (Number.isNaN(parentId)) {
    return res.status(400).json({ error: 'Invalid conversation id' });
  }

  const { topic, model_id } = req.body;
  if (!topic) {
    return res.status(400).json({ error: 'topic is required' });
  }

  try {
    const parent = db.prepare('SELECT * FROM conversations WHERE id = ?').get(parentId);
    if (!parent) {
      return res.status(404).json({ error: 'Parent conversation not found' });
    }

    // Get last message id as fork_point
    const lastMsg = db.prepare(
      'SELECT id FROM messages WHERE conversation_id = ? ORDER BY id DESC LIMIT 1'
    ).get(parentId);
    const forkPoint = lastMsg ? lastMsg.id : 0;

    const info = db.prepare(`
      INSERT INTO conversations (title, type, parent_id, model_id)
      VALUES (?, ?, ?, ?)
    `).run(topic, 'fork', parentId, model_id || parent.model_id || null);

    const newId = info.lastInsertRowid;

    // Persist fork_point in config table
    // TODO: migrate fork_point to a dedicated column on conversations table instead of config
    db.prepare('INSERT OR REPLACE INTO config (key, value) VALUES (?, ?)')
      .run(`fork_point_${newId}`, String(forkPoint));

    const row = db.prepare('SELECT * FROM conversations WHERE id = ?').get(newId);
    res.status(201).json({ ...row, fork_point: forkPoint });
  } catch (err) {
    console.error('[conversations] fork error:', err.message);
    res.status(500).json({ error: err.message });
  }
});

// POST /api/conversations/:id/merge — generate summary via LLM, save context_merge message in parent
router.post('/:id/merge', async (req, res) => {
  const forkId = parseInt(req.params.id, 10);
  if (Number.isNaN(forkId)) {
    return res.status(400).json({ error: 'Invalid conversation id' });
  }

  try {
    const fork = db.prepare('SELECT * FROM conversations WHERE id = ?').get(forkId);
    if (!fork) {
      return res.status(404).json({ error: 'Fork conversation not found' });
    }
    if (fork.type !== 'fork') {
      return res.status(400).json({ error: 'Conversation is not a fork' });
    }

    const parentId = fork.parent_id;
    if (!parentId) {
      return res.status(400).json({ error: 'Fork has no parent' });
    }

    const forkMessages = db.prepare(
      'SELECT role, content FROM messages WHERE conversation_id = ? ORDER BY id'
    ).all(forkId);

    if (forkMessages.length === 0) {
      return res.status(400).json({ error: 'Fork has no messages to merge' });
    }

    // Get model for summarization
    let model = null;
    if (fork.model_id) {
      model = db.prepare('SELECT * FROM models WHERE id = ?').get(fork.model_id);
    }
    if (!model) {
      model = db.prepare('SELECT * FROM models WHERE is_default_fork = 1 LIMIT 1').get();
    }
    if (!model) {
      model = db.prepare('SELECT * FROM models WHERE is_default_main = 1 LIMIT 1').get();
    }
    if (!model) {
      return res.status(500).json({ error: 'No model available for summarization' });
    }

    // Truncate to last 50 messages to avoid exceeding context window
    const recentMessages = forkMessages.slice(-50);
    const transcript = recentMessages.map(m => `${m.role}: ${m.content}`).join('\n\n');
    const summarizePrompt = `Resume en 2-3 oraciones qué aprendió el usuario en esta sesión sobre ${fork.title}:\n\n${transcript}`;

    let summary = '';
    for await (const chunk of streamCompletion(model, [{ role: 'user', content: summarizePrompt }], undefined)) {
      if (chunk.error) {
        return res.status(502).json({ error: chunk.error });
      }
      if (chunk.done) {
        summary = chunk.fullText;
      }
    }

    // Max 200 tokens ~ 1500 chars
    const truncated = summary.length > 1500 ? summary.slice(0, 1500) : summary;

    // Insert context_merge into parent
    const info = db.prepare(`
      INSERT INTO messages (conversation_id, role, content)
      VALUES (?, ?, ?)
    `).run(parentId, 'context_merge', `[Resumen de fork: ${fork.title}]\n\n${truncated}`);

    res.json({ parent_id: parentId, merged_message_id: info.lastInsertRowid, chars: truncated.length });
  } catch (err) {
    console.error('[conversations] merge error:', err.message);
    res.status(500).json({ error: err.message });
  }
});

// POST /api/conversations/:id/share — generate a share token for buddy mode
router.post('/:id/share', (req, res) => {
  const convId = parseInt(req.params.id, 10);
  if (Number.isNaN(convId)) {
    return res.status(400).json({ error: 'Invalid conversation id' });
  }

  const { role_label = 'compañero' } = req.body;

  try {
    const conv = db.prepare('SELECT * FROM conversations WHERE id = ?').get(convId);
    if (!conv) {
      return res.status(404).json({ error: 'Conversation not found' });
    }

    const token = crypto.randomBytes(16).toString('hex');
    db.prepare('INSERT INTO shared_conversations (token, conv_id, role_label) VALUES (?, ?, ?)')
      .run(token, convId, role_label);

    const shareUrl = `${req.protocol}://${req.get('host')}/shared/${token}`;
    res.json({ token, share_url: shareUrl, role_label });
  } catch (err) {
    console.error('[conversations] share error:', err.message);
    res.status(500).json({ error: err.message });
  }
});

// GET /api/conversations/shared/:token — get shared conversation data
router.get('/shared/:token', (req, res) => {
  const { token } = req.params;
  if (!token) {
    return res.status(400).json({ error: 'token is required' });
  }

  try {
    const shared = db.prepare('SELECT * FROM shared_conversations WHERE token = ?').get(token);
    if (!shared) {
      return res.status(404).json({ error: 'Shared conversation not found' });
    }

    const conv = db.prepare('SELECT * FROM conversations WHERE id = ?').get(shared.conv_id);
    if (!conv) {
      return res.status(404).json({ error: 'Conversation not found' });
    }

    const messages = db.prepare(
      'SELECT * FROM messages WHERE conversation_id = ? ORDER BY created_at, id'
    ).all(shared.conv_id);

    // Find counterpart label (if there are 2 shared entries for same conv)
    const allShared = db.prepare('SELECT * FROM shared_conversations WHERE conv_id = ?').all(shared.conv_id);
    const counterpart = allShared.find((s) => s.token !== token);

    res.json({
      conversation: conv,
      messages,
      role_label: shared.role_label,
      counterpart_label: counterpart?.role_label || 'compañero',
    });
  } catch (err) {
    console.error('[conversations] shared get error:', err.message);
    res.status(500).json({ error: err.message });
  }
});

// POST /api/conversations/join — join a shared conversation by token
router.post('/join', (req, res) => {
  const { share_token, user_name } = req.body;
  if (!share_token || !user_name) {
    return res.status(400).json({ error: 'share_token and user_name are required' });
  }

  try {
    const shared = db.prepare('SELECT * FROM shared_conversations WHERE token = ?').get(share_token);
    if (!shared) {
      return res.status(404).json({ error: 'Shared conversation not found' });
    }

    const conv = db.prepare('SELECT * FROM conversations WHERE id = ?').get(shared.conv_id);
    if (!conv) {
      return res.status(404).json({ error: 'Conversation not found' });
    }

    // Track participant
    db.prepare('INSERT INTO conversation_participants (conversation_id, user_name) VALUES (?, ?)')
      .run(shared.conv_id, user_name);

    const messages = db.prepare(
      'SELECT * FROM messages WHERE conversation_id = ? ORDER BY created_at, id'
    ).all(shared.conv_id);

    res.json({
      conversation: conv,
      messages,
      role_label: shared.role_label,
      share_token,
    });
  } catch (err) {
    console.error('[conversations] join error:', err.message);
    res.status(500).json({ error: err.message });
  }
});

module.exports = router;