const express = require('express');
const db = require('../db');
const { buildSystemPrompt } = require('../systemPromptBuilder');
const { streamCompletion } = require('../lib/llm');
const { embedQuery, topK } = require('../lib/rag');
const { broadcastBuddy } = require('../lib/broadcast');
const router = express.Router();

// POST /api/chat/stream — SSE streaming endpoint
router.post('/stream', async (req, res) => {
  const { conversation_id, message, pdf_ids = [], attachment_texts = [] } = req.body;

  if (!conversation_id || !message) {
    return res.status(400).json({ error: 'conversation_id and message are required' });
  }

  const convId = parseInt(conversation_id, 10);
  if (Number.isNaN(convId)) {
    return res.status(400).json({ error: 'Invalid conversation_id' });
  }

  // Set SSE headers immediately
  res.setHeader('Content-Type', 'text/event-stream');
  res.setHeader('Cache-Control', 'no-cache');
  res.setHeader('Connection', 'keep-alive');
  res.setHeader('X-Accel-Buffering', 'no');
  res.flushHeaders();

  const sendEvent = (obj) => {
    res.write(`data: ${JSON.stringify(obj)}\n\n`);
  };

  try {
    // 1. Fetch conversation + model + progress + PDF contents
    const conv = db.prepare('SELECT * FROM conversations WHERE id = ?').get(convId);
    if (!conv) {
      sendEvent({ error: 'Conversation not found' });
      res.end();
      return;
    }

    let model = null;
    if (conv.model_id) {
      model = db.prepare('SELECT * FROM models WHERE id = ?').get(conv.model_id);
    }
    if (!model) {
      model = db.prepare('SELECT * FROM models WHERE is_default_main = 1 LIMIT 1').get();
    }
    if (!model) {
      sendEvent({ error: 'No model configured' });
      res.end();
      return;
    }

    const progressRows = db.prepare('SELECT * FROM progress').all();

    let pdfContents = [];
    if (pdf_ids.length > 0) {
      const validIds = pdf_ids.map(id => parseInt(id, 10)).filter(id => !Number.isNaN(id) && id > 0);
      if (validIds.length > 0) {
        const placeholders = validIds.map(() => '?').join(',');
        pdfContents = db.prepare(`SELECT * FROM pdfs WHERE id IN (${placeholders})`).all(...validIds);
      }
    }

    // 2. RAG: embed user message and fetch top-k chunks
    let ragChunks = [];
    let difficulty = 'normal';
    try {
      // First-topic match — picks first progress row whose topic appears in the message.
      // Multi-topic messages will match only the first topic found.
      const activeProgress = progressRows.find((r) => r.topic && message.toLowerCase().includes(r.topic.toLowerCase()));
      difficulty = activeProgress?.difficulty_level || 'normal';
    } catch (err) {
      console.error('[chat] difficulty detection error:', err.message);
      difficulty = 'normal';
    }

    if (pdf_ids.length > 0) {
      try {
        const queryVec = await embedQuery(message);
        const validPdfIds = pdf_ids.map(id => parseInt(id, 10)).filter(id => !Number.isNaN(id) && id > 0);
        if (validPdfIds.length > 0) {
          ragChunks = await topK(queryVec, validPdfIds, 3);
        }
      } catch (ragErr) {
        console.warn('[chat] RAG failed:', ragErr.message);
      }
    }

    // 2b. Build system prompt
    const systemPrompt = buildSystemPrompt(conv, progressRows, pdfContents, attachment_texts, ragChunks, difficulty);

    // 3. Load existing messages, removing consecutive duplicates
    const rawMessages = db.prepare(
      'SELECT id, role, content FROM messages WHERE conversation_id = ? ORDER BY id'
    ).all(convId);

    // Fix: only remove the VERY LAST message if it's a user message matching the current input
    const lastMsg = rawMessages[rawMessages.length - 1];
    if (lastMsg && lastMsg.role === 'user' && lastMsg.content === message) {
      rawMessages.pop();
      db.prepare('DELETE FROM messages WHERE id = ?').run(lastMsg.id);
    }

    // Filter: skip duplicate consecutive users (keep only the last in sequence)
    const existingMessages = [];
    for (let i = 0; i < rawMessages.length; i++) {
      const curr = rawMessages[i];
      if (curr.role === 'user' && i + 1 < rawMessages.length && rawMessages[i + 1].role === 'user') {
        db.prepare('DELETE FROM messages WHERE id = ?').run(curr.id);
        continue;
      }
      existingMessages.push({ role: curr.role, content: curr.content });
    }

    const messages = [
      ...existingMessages.filter(m => m.role === 'user' || m.role === 'assistant'),
      { role: 'user', content: message },
    ];

    // Save user message BEFORE streaming so it persists even if server crashes
    db.prepare('INSERT INTO messages (conversation_id, role, content) VALUES (?, ?, ?)')
      .run(convId, 'user', message);

    // 5. Stream via llm.streamCompletion()
    let assistantText = '';
    let errorOccurred = false;

    for await (const chunk of streamCompletion(model, messages, systemPrompt)) {
      if (chunk.error) {
        sendEvent({ error: chunk.error });
        errorOccurred = true;
        break;
      }
      if (chunk.token) {
        assistantText += chunk.token;
        sendEvent({ token: chunk.token });
      }
      if (chunk.done) {
        assistantText = chunk.fullText;
      }
    }

    if (errorOccurred) {
      sendEvent({ done: true, full_text: '' });
      res.end();
      return;
    }

    // 6. Parse exercise_logged JSON from response
    const exerciseLogs = [];
    const rawMatches = [];
    const fenceRegex = /```json\s*([\s\S]*?)\s*```/g;
    const fenceMatches = [...assistantText.matchAll(fenceRegex)];
    for (const fenceMatch of fenceMatches) {
      try {
        const parsed = JSON.parse(fenceMatch[1]);
        if (parsed && parsed.exercise_logged) {
          const entries = Array.isArray(parsed.exercise_logged)
            ? parsed.exercise_logged
            : [parsed.exercise_logged];
          for (const entry of entries) {
            if (entry && entry.topic) exerciseLogs.push(entry);
          }
          rawMatches.push(fenceMatch[0]);
        }
      } catch (e) {
        console.error('[chat] exercise JSON parse error:', e.message);
      }
    }

    // Alternative: inline JSON without fence
    const inlineRegex = /\{[^{}]*"exercise_logged"[^{}]*\}/g;
    const inlineMatches = [...assistantText.matchAll(inlineRegex)];
    for (const inlineMatch of inlineMatches) {
      try {
        const parsed = JSON.parse(inlineMatch[0]);
        if (parsed && parsed.exercise_logged) {
          const entries = Array.isArray(parsed.exercise_logged)
            ? parsed.exercise_logged
            : [parsed.exercise_logged];
          for (const entry of entries) {
            if (entry && entry.topic) exerciseLogs.push(entry);
          }
          rawMatches.push(inlineMatch[0]);
        }
      } catch (e) {
        // silent
      }
    }

    // Deduplicate exercises by topic+correct combination
    const seen = new Set();
    const dedupedLogs = [];
    for (const entry of exerciseLogs) {
      const key = `${entry.topic}|${entry.correct}`;
      if (!seen.has(key)) {
        seen.add(key);
        dedupedLogs.push(entry);
      }
    }

    // 7. Upsert progress table for each exercise + track streaks
    let lastSuggestedTopic = null;
    let difficultyChanged = false;
    let newDifficulty = difficulty;
    let newGlobalStreak = 0;

    for (const exerciseLogged of dedupedLogs) {
      const topic = exerciseLogged.topic;
      const correct = exerciseLogged.correct === true ? 1 : 0;
      const isWrong = correct === 0;

      const existing = db.prepare('SELECT * FROM progress WHERE topic = ?').get(topic);
      if (existing) {
        let newWrongStreak = isWrong ? (existing.wrong_streak || 0) + 1 : 0;
        newGlobalStreak = isWrong ? (existing.global_wrong_streak || 0) + 1 : Math.max(0, (existing.global_wrong_streak || 0) - 1);
        let newDiff = existing.difficulty_level || 'normal';

        // Difficulty adjustment based on global streak
        if (newGlobalStreak >= 3 && newDiff !== 'easy') {
          newDiff = 'easy';
          difficultyChanged = true;
        } else if (newGlobalStreak === 0 && existing.exercises_done > 0 && (existing.exercises_correct / existing.exercises_done) >= 0.8 && newDiff !== 'hard') {
          newDiff = 'hard';
          difficultyChanged = true;
        } else if (newGlobalStreak >= 1 && newGlobalStreak < 3 && newDiff === 'easy') {
          newDiff = 'normal';
          difficultyChanged = true;
        }

        newDifficulty = newDiff;

        db.prepare(`
          UPDATE progress SET
            exercises_done = exercises_done + 1,
            exercises_correct = exercises_correct + ?,
            last_session = datetime('now'),
            notes = ?,
            wrong_streak = ?,
            global_wrong_streak = ?,
            difficulty_level = ?
          WHERE topic = ?
        `).run(correct, existing.notes, newWrongStreak, newGlobalStreak, newDiff, topic);

        // Auto-fork suggest after 2 consecutive wrong answers on same topic
        if (isWrong && newWrongStreak >= 2) {
          lastSuggestedTopic = topic;
        }
      } else {
        let newWrongStreak = isWrong ? 1 : 0;
        newGlobalStreak = isWrong ? 1 : 0;
        let newDiff = isWrong ? 'normal' : 'normal';
        db.prepare(`
          INSERT INTO progress (topic, exercises_done, exercises_correct, last_session, notes, wrong_streak, global_wrong_streak, difficulty_level)
          VALUES (?, 1, ?, datetime('now'), '[]', ?, ?, ?)
        `).run(topic, correct, newWrongStreak, newGlobalStreak, newDiff);
        if (isWrong) {
          lastSuggestedTopic = topic;
        }
      }
    }

    // Also detect wrong answers from response text heuristics (fallback when no exercise_logged)
    const wrongHeuristic = /incorrect|incorrecta|no es correcto|mal|error/i.test(assistantText);
    if (wrongHeuristic && exerciseLogs.length === 0) {
      // Topic extracted from first sentence (fragile but functional enough for heuristic fallback)
      const topic = message.split(/[.!?\n]/)[0].slice(0, 50);
      const existing = db.prepare('SELECT * FROM progress WHERE topic = ?').get(topic);
      if (existing) {
        const newWrongStreak = (existing.wrong_streak || 0) + 1;
        const newGlobalStreak = (existing.global_wrong_streak || 0) + 1;
        db.prepare(`
          UPDATE progress SET wrong_streak = ?, global_wrong_streak = ?, exercises_done = exercises_done + 1 WHERE topic = ?
        `).run(newWrongStreak, newGlobalStreak, topic);
        if (newWrongStreak >= 2) {
          lastSuggestedTopic = topic;
        }
      }
    }

    // Strip JSON blocks from text before saving
    let cleanText = assistantText;
    for (const raw of rawMatches) {
      cleanText = cleanText.replace(raw, '');
    }
    cleanText = cleanText.trim();

    // Save assistant response
    const msgInfo = db.prepare('INSERT INTO messages (conversation_id, role, content) VALUES (?, ?, ?)')
      .run(convId, 'assistant', cleanText);
    const assistantMsgId = msgInfo.lastInsertRowid;

    // Update conversation updated_at
    db.prepare("UPDATE conversations SET updated_at = datetime('now') WHERE id = ?").run(convId);

    // Emit SSE events for streak/difficulty
    if (lastSuggestedTopic) {
      sendEvent({ auto_fork_suggest: { topic: lastSuggestedTopic, parent_id: convId, wrong_streak: 2 } });
    }
    if (difficultyChanged) {
      sendEvent({ difficulty_changed: { level: newDifficulty, global_wrong_streak: newGlobalStreak } });
    }

    // Broadcast buddy message if conversation has buddy_meta
    if (conv.buddy_meta) {
      try {
        broadcastBuddy({ type: 'buddy_msg', conv_id: convId, msg_id: assistantMsgId });
      } catch (e) {
        // silent
      }
    }

    sendEvent({ done: true, full_text: cleanText });
    res.end();
  } catch (err) {
    console.error('[chat] stream error:', err.message);
    sendEvent({ error: err.message });
    res.end();
  }
});

module.exports = router;