const express = require('express');

const exercisesData = require('./data/exercises.json');

const OLLAMA_URL = process.env.OLLAMA_URL || 'http://localhost:11434';
const OLLAMA_MODEL = process.env.OLLAMA_MODEL || 'deepseek-v3.2:cloud';
const GEMINI_API_KEY = process.env.GOOGLE_API_KEY;
const OPENROUTER_API_KEY = process.env.OPENROUTER_API_KEY;
const OPENROUTER_BASE_URL = process.env.OPENROUTER_BASE_URL || 'https://openrouter.ai/api/v1';

const VALID_FITNESS_LEVELS = ['beginner', 'intermediate', 'advanced'];
const VALID_GOALS = ['strength', 'hypertrophy', 'fat_loss', 'endurance', 'mobility', 'general_fitness'];

const difficultyRank = {
  beginner: 1,
  intermediate: 2,
  advanced: 3
};

const normalizeGoals = (goals) => {
  if (!goals) return [];
  if (Array.isArray(goals)) {
    return goals.map((goal) => String(goal).trim()).filter(Boolean);
  }
  if (typeof goals === 'string') {
    return goals.split(',').map((goal) => goal.trim()).filter(Boolean);
  }
  return [];
};

const normalizeList = (value) => {
  if (!value) return [];
  if (Array.isArray(value)) {
    return value.map((item) => String(item).trim()).filter(Boolean);
  }
  if (typeof value === 'string') {
    return value.split(',').map((item) => item.trim()).filter(Boolean);
  }
  return [];
};

const validatePayload = (payload) => {
  const errors = [];
  const fitnessLevel = payload?.fitness_level;
  const goals = normalizeGoals(payload?.goals);
  const availableTime = Number(payload?.available_time);

  if (!fitnessLevel || typeof fitnessLevel !== 'string' || !VALID_FITNESS_LEVELS.includes(fitnessLevel)) {
    errors.push('fitness_level is required and must be beginner, intermediate, or advanced');
  }
  if (!goals.length) {
    errors.push('goals is required and must be a non-empty array or comma-separated string');
  } else {
    const invalidGoals = goals.filter((goal) => !VALID_GOALS.includes(goal));
    if (invalidGoals.length) {
      errors.push(`goals contains invalid values: ${invalidGoals.join(', ')}`);
    }
  }
  if (!Number.isFinite(availableTime) || availableTime <= 0) {
    errors.push('available_time is required and must be a positive number (minutes)');
  }

  return { errors, goals, availableTime };
};

const buildPrompt = ({ fitnessLevel, goals, availableTime, equipment, focusMuscles, limit, exercises }) => {
  const coachPersona = `Du är Coach, en erfaren styrke- och konditionscoach (15+ års erfarenhet).\n` +
    `- Direkt och tydlig, inga fluff.\n- Anpassar språk efter nivå.\n- Prioritera säkerhet.\n- Ge alltid alternativ.\n` +
    `Svara på svenska.`;

  const requestContext = {
    fitness_level: fitnessLevel,
    goals,
    available_time_minutes: availableTime,
    equipment,
    focus_muscles: focusMuscles,
    limit
  };

  const exerciseCatalog = exercises.map((exercise) => ({
    id: exercise.id,
    name: exercise.name,
    name_en: exercise.name_en,
    category: exercise.category,
    primary_muscles: exercise.primary_muscles,
    secondary_muscles: exercise.secondary_muscles,
    equipment: exercise.equipment,
    difficulty: exercise.difficulty,
    alternatives: exercise.alternatives
  }));

  return `${coachPersona}\n\n` +
    `Uppgift: Rekommendera övningar för användaren baserat på kontexten nedan.\n` +
    `- Välj endast från katalogen.\n- Anpassa set/reps/rest till mål och nivå.\n- Motivera kort varför varje övning passar.\n- Svara med exakt JSON enligt schema.\n\n` +
    `KONTEKST:\n${JSON.stringify(requestContext)}\n\n` +
    `KATALOG:\n${JSON.stringify(exerciseCatalog)}\n\n` +
    `SCHEMA:\n` +
    `{"recommendations":[{"id":"","sets":0,"reps":"","rest_seconds":0,"reason":"","alternatives":[]}],"notes":""}`;
};

const extractJsonPayload = (text) => {
  if (!text || typeof text !== 'string') {
    throw new Error('No response text to parse');
  }

  const start = text.indexOf('{');
  const end = text.lastIndexOf('}');
  if (start === -1 || end === -1 || end <= start) {
    throw new Error('No JSON object found in response');
  }

  const jsonString = text.slice(start, end + 1);
  return JSON.parse(jsonString);
};

const parseRecommendations = (payload, exerciseMap) => {
  if (!payload || !Array.isArray(payload.recommendations)) {
    throw new Error('Invalid recommendations payload');
  }

  const recommendations = payload.recommendations
    .map((rec) => {
      const exercise = exerciseMap.get(rec.id);
      if (!exercise) return null;
      return {
        id: exercise.id,
        name: exercise.name,
        name_en: exercise.name_en,
        sets: Number(rec.sets) || 3,
        reps: rec.reps || '8-12',
        rest_seconds: Number(rec.rest_seconds) || 90,
        reason: rec.reason || 'Bra match för ditt mål och din nivå.',
        alternatives: Array.isArray(rec.alternatives) && rec.alternatives.length
          ? rec.alternatives
          : exercise.alternatives || []
      };
    })
    .filter(Boolean);

  if (!recommendations.length) {
    throw new Error('No valid recommendations after parsing');
  }

  return {
    recommendations,
    notes: payload.notes || ''
  };
};

const buildHeuristicRecommendations = ({ fitnessLevel, goals, availableTime, equipment, focusMuscles, limit }) => {
  const maxDifficulty = difficultyRank[fitnessLevel] || 2;
  const equipmentSet = new Set((equipment || []).map((item) => item.toLowerCase()));
  const focusSet = new Set((focusMuscles || []).map((item) => item.toLowerCase()));

  const goalWeights = {
    strength: { compound: 3, isolation: 1 },
    hypertrophy: { compound: 2, isolation: 2 },
    fat_loss: { compound: 2, isolation: 1 },
    endurance: { compound: 1, isolation: 2 },
    mobility: { compound: 1, isolation: 2 },
    general_fitness: { compound: 2, isolation: 1 }
  };

  const filteredExercises = exercisesData.exercises.filter((exercise) => {
    const diffOk = (difficultyRank[exercise.difficulty] || 2) <= maxDifficulty;
    if (!diffOk) return false;

    if (equipmentSet.size === 0) return true;

    if (!exercise.equipment || exercise.equipment.length === 0) return true;
    return exercise.equipment.some((item) => equipmentSet.has(item.toLowerCase()));
  });

  const exercises = filteredExercises.length ? filteredExercises : exercisesData.exercises;

  const scored = exercises.map((exercise) => {
    let score = 0;
    goals.forEach((goal) => {
      const weights = goalWeights[goal] || goalWeights.general_fitness;
      score += weights[exercise.category] || 0;
    });

    if (focusSet.size) {
      if (exercise.primary_muscles?.some((muscle) => focusSet.has(muscle.toLowerCase()))) {
        score += 3;
      } else if (exercise.secondary_muscles?.some((muscle) => focusSet.has(muscle.toLowerCase()))) {
        score += 1;
      }
    }

    if (!exercise.equipment || exercise.equipment.length === 0) {
      score += 1;
    }

    return { exercise, score };
  });

  scored.sort((a, b) => b.score - a.score);

  const timeBasedLimit = availableTime <= 20
    ? 3
    : availableTime <= 35
      ? 4
      : availableTime <= 50
        ? 6
        : 8;

  const finalLimit = Math.min(limit || timeBasedLimit, 10);
  const selected = scored.slice(0, finalLimit);

  return selected.map(({ exercise }) => ({
    id: exercise.id,
    name: exercise.name,
    name_en: exercise.name_en,
    sets: exercise.category === 'compound' ? 4 : 3,
    reps: goals.includes('strength') ? '4-6' : '8-12',
    rest_seconds: exercise.category === 'compound' ? 120 : 60,
    reason: `Passar ${goals.join(', ')} med fokus på ${exercise.primary_muscles.join(', ')}.`,
    alternatives: exercise.alternatives || []
  }));
};

const extractProviderText = (provider, data) => {
  if (provider === 'ollama') {
    return data?.response || '';
  }
  if (provider === 'gemini') {
    return data?.candidates?.[0]?.content?.parts?.[0]?.text || '';
  }
  if (provider === 'openrouter') {
    return data?.choices?.[0]?.message?.content || '';
  }
  return '';
};

const generateRecommendationsWithFallback = async ({ prompt }) => {
  if (typeof fetch !== 'function') {
    throw new Error('Fetch API not available in this runtime');
  }

  // Tier 1: Ollama
  try {
    console.log(`📍 [Recommend] Tier 1: Ollama (${OLLAMA_MODEL})`);
    const response = await fetch(`${OLLAMA_URL}/api/generate`, {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({
        model: OLLAMA_MODEL,
        prompt,
        stream: false,
        temperature: 0.6
      }),
      timeout: 30000
    });

    if (response.ok) {
      const data = await response.json();
      console.log('✅ [Recommend] Ollama success');
      return { provider: 'ollama', data };
    }

    console.warn(`⚠️ [Recommend] Ollama error: ${response.status}`);
  } catch (err) {
    console.warn(`⚠️ [Recommend] Ollama failed: ${err.message}`);
  }

  // Tier 2: Gemini
  if (GEMINI_API_KEY) {
    try {
      console.log('📍 [Recommend] Tier 2: Gemini');
      const response = await fetch(
        `https://generativelanguage.googleapis.com/v1/models/gemini-pro:generateContent?key=${GEMINI_API_KEY}`,
        {
          method: 'POST',
          headers: { 'Content-Type': 'application/json' },
          body: JSON.stringify({
            contents: [{ parts: [{ text: prompt }] }],
            generationConfig: { temperature: 0.6 }
          })
        }
      );

      if (response.ok) {
        const data = await response.json();
        console.log('✅ [Recommend] Gemini success');
        return { provider: 'gemini', data };
      }

      if (response.status === 429 || response.status === 403) {
        console.warn('⚠️ [Recommend] Gemini quota exceeded');
      } else {
        console.warn(`⚠️ [Recommend] Gemini error: ${response.status}`);
      }
    } catch (err) {
      console.warn(`⚠️ [Recommend] Gemini failed: ${err.message}`);
    }
  }

  // Tier 3: OpenRouter
  if (OPENROUTER_API_KEY) {
    try {
      console.log('📍 [Recommend] Tier 3: OpenRouter');
      const response = await fetch(`${OPENROUTER_BASE_URL}/chat/completions`, {
        method: 'POST',
        headers: {
          'Authorization': `Bearer ${OPENROUTER_API_KEY}`,
          'Content-Type': 'application/json',
          'HTTP-Referer': 'https://gravl.app'
        },
        body: JSON.stringify({
          model: 'openai/gpt-4',
          messages: [{ role: 'user', content: prompt }],
          temperature: 0.6,
          max_tokens: 1200
        })
      });

      if (response.ok) {
        const data = await response.json();
        console.log('✅ [Recommend] OpenRouter success');
        return { provider: 'openrouter', data };
      }

      console.warn(`⚠️ [Recommend] OpenRouter error: ${response.status}`);
    } catch (err) {
      console.warn(`⚠️ [Recommend] OpenRouter failed: ${err.message}`);
    }
  }

  throw new Error('All recommendation providers failed (Ollama → Gemini → OpenRouter)');
};

const createExerciseRecommendationRouter = () => {
  const router = express.Router();
  const exerciseMap = new Map(exercisesData.exercises.map((exercise) => [exercise.id, exercise]));

  /**
   * POST /api/exercises/recommend
   * Request body:
   * {
   *   "fitness_level": "beginner" | "intermediate" | "advanced",
   *   "goals": ["strength" | "hypertrophy" | "fat_loss" | "endurance" | "mobility" | "general_fitness"],
   *   "available_time": 30,
   *   "equipment": ["barbell", "dumbbells"],
   *   "focus_muscles": ["chest", "back"],
   *   "limit": 6
   * }
   */
  router.post('/recommend', async (req, res) => {
    const { errors, goals, availableTime } = validatePayload(req.body);
    if (errors.length) {
      return res.status(400).json({ error: 'Validation failed', details: errors });
    }

    const fitnessLevel = req.body.fitness_level;
    const equipment = normalizeList(req.body.equipment);
    const focusMuscles = normalizeList(req.body.focus_muscles);
    const limit = Number.isFinite(Number(req.body.limit)) ? Math.min(Number(req.body.limit), 10) : null;

    const prompt = buildPrompt({
      fitnessLevel,
      goals,
      availableTime,
      equipment,
      focusMuscles,
      limit,
      exercises: exercisesData.exercises
    });

    try {
      const { provider, data } = await generateRecommendationsWithFallback({ prompt });
      const text = extractProviderText(provider, data);
      const parsedPayload = extractJsonPayload(text);
      const aiRecommendations = parseRecommendations(parsedPayload, exerciseMap);

      return res.json({
        recommendations: aiRecommendations.recommendations,
        notes: aiRecommendations.notes,
        provider,
        status: 'success'
      });
    } catch (err) {
      console.warn(`⚠️ [Recommend] Falling back to heuristic recommendations: ${err.message}`);
      const fallbackRecommendations = buildHeuristicRecommendations({
        fitnessLevel,
        goals,
        availableTime,
        equipment,
        focusMuscles,
        limit
      });

      return res.json({
        recommendations: fallbackRecommendations,
        notes: 'Fallback recommendations generated without AI provider.',
        provider: 'fallback',
        status: 'degraded'
      });
    }
  });

  return router;
};

module.exports = {
  createExerciseRecommendationRouter
};