const express = require('express');
const router = express.Router();
const { getDatabase } = require('../db/init');

/**
 * getAncestorMap(db, dogId, maxGen)
 * Returns Map<id, [{ id, name, generation }, ...]>
 * INCLUDES dogId itself at generation 0 so direct parent-offspring
 * pairings are correctly detected by calculateCOI.
 */
function getAncestorMap(db, dogId, maxGen = 6) {
  const map = new Map();

  function recurse(id, gen) {
    if (gen > maxGen) return;
    const dog = db.prepare('SELECT id, name FROM dogs WHERE id = ?').get(id);
    if (!dog) return;
    if (!map.has(id)) map.set(id, []);
    map.get(id).push({ id: dog.id, name: dog.name, generation: gen });
    // Only walk parents on first encounter to prevent exponential blowup
    if (map.get(id).length === 1) {
      const parents = db.prepare(`
        SELECT p.parent_id FROM parents p WHERE p.dog_id = ?
      `).all(id);
      parents.forEach(p => recurse(p.parent_id, gen + 1));
    }
  }

  recurse(parseInt(dogId), 0);
  return map;
}

/**
 * isDirectRelation(db, sireId, damId)
 * Checks within 3 generations whether one dog is a direct ancestor
 * of the other. Returns { related, relationship }.
 */
function isDirectRelation(db, sireId, damId) {
  const sid = parseInt(sireId);
  const did = parseInt(damId);
  const sireMap = getAncestorMap(db, sid, 3);
  const damMap  = getAncestorMap(db, did, 3);

  if (damMap.has(sid)) {
    const gen = damMap.get(sid)[0].generation;
    const label = gen === 1 ? 'parent' : gen === 2 ? 'grandparent' : `generation-${gen} ancestor`;
    return { related: true, relationship: `Sire is the ${label} of the selected dam` };
  }
  if (sireMap.has(did)) {
    const gen = sireMap.get(did)[0].generation;
    const label = gen === 1 ? 'parent' : gen === 2 ? 'grandparent' : `generation-${gen} ancestor`;
    return { related: true, relationship: `Dam is the ${label} of the selected sire` };
  }
  return { related: false, relationship: null };
}

/**
 * calculateCOI(db, sireId, damId)
 * Wright Path Coefficient method.
 * sire/dam included at gen 0 in their own maps so parent x offspring
 * yields the correct 25% COI instead of 0%.
 *
 * Per path: COI += (0.5)^(sireGen + damGen + 1)
 * Parent x offspring: sireGen=0, damGen=1 => (0.5)^2 = 0.25 = 25%
 */
function calculateCOI(db, sireId, damId) {
  const sid = parseInt(sireId);
  const did = parseInt(damId);
  const sireMap = getAncestorMap(db, sid);
  const damMap  = getAncestorMap(db, did);

  // Common ancestors excluding the pair themselves
  const commonIds = [...sireMap.keys()].filter(
    id => damMap.has(id) && id !== sid && id !== did
  );

  let coi = 0;
  const processedPaths = new Set();
  const commonAncestorList = [];

  commonIds.forEach(ancId => {
    const sireOccs = sireMap.get(ancId);
    const damOccs  = damMap.get(ancId);

    sireOccs.forEach(so => {
      damOccs.forEach(do_ => {
        const key = `${ancId}-${so.generation}-${do_.generation}`;
        if (!processedPaths.has(key)) {
          processedPaths.add(key);
          coi += Math.pow(0.5, so.generation + do_.generation + 1);
        }
      });
    });

    const closestSire = sireOccs.reduce((a, b) => a.generation < b.generation ? a : b);
    const closestDam  = damOccs.reduce((a, b)  => a.generation < b.generation ? a : b);
    commonAncestorList.push({
      id:      ancId,
      name:    sireOccs[0].name,
      sireGen: closestSire.generation,
      damGen:  closestDam.generation
    });
  });

  return {
    coefficient:     Math.round(coi * 10000) / 100,
    commonAncestors: commonAncestorList
  };
}

// ── GET pedigree tree ─────────────────────────────────────────────────────────
router.get('/:id', (req, res) => {
  try {
    const db = getDatabase();
    const generations = parseInt(req.query.generations) || 5;

    function buildTree(dogId, currentGen = 0) {
      if (currentGen >= generations) return null;
      const dog = db.prepare('SELECT * FROM dogs WHERE id = ?').get(dogId);
      if (!dog) return null;
      dog.photo_urls = dog.photo_urls ? JSON.parse(dog.photo_urls) : [];
      const parents = db.prepare('SELECT parent_type, parent_id FROM parents WHERE dog_id = ?').all(dogId);
      const sire = parents.find(p => p.parent_type === 'sire');
      const dam  = parents.find(p => p.parent_type === 'dam');
      return {
        ...dog,
        generation: currentGen,
        sire: sire ? buildTree(sire.parent_id, currentGen + 1) : null,
        dam:  dam  ? buildTree(dam.parent_id,  currentGen + 1) : null
      };
    }

    const tree = buildTree(req.params.id);
    if (!tree) return res.status(404).json({ error: 'Dog not found' });
    res.json(tree);
  } catch (error) {
    res.status(500).json({ error: error.message });
  }
});

// ── GET descendants ───────────────────────────────────────────────────────────
router.get('/:id/descendants', (req, res) => {
  try {
    const db = getDatabase();
    const generations = parseInt(req.query.generations) || 3;

    function buildDescendantTree(dogId, currentGen = 0) {
      if (currentGen >= generations) return null;
      const dog = db.prepare('SELECT * FROM dogs WHERE id = ?').get(dogId);
      if (!dog) return null;
      dog.photo_urls = dog.photo_urls ? JSON.parse(dog.photo_urls) : [];
      const offspring = db.prepare(`
        SELECT DISTINCT d.id, d.name, d.sex, d.birth_date
        FROM dogs d JOIN parents p ON d.id = p.dog_id
        WHERE p.parent_id = ? AND d.is_active = 1
      `).all(dogId);
      return {
        ...dog,
        generation: currentGen,
        offspring: offspring.map(c => buildDescendantTree(c.id, currentGen + 1))
      };
    }

    const tree = buildDescendantTree(req.params.id);
    if (!tree) return res.status(404).json({ error: 'Dog not found' });
    res.json(tree);
  } catch (error) {
    res.status(500).json({ error: error.message });
  }
});

// ── GET direct-relation check (used by frontend before simulate) ──────────────
// GET /api/pedigree/relations/:sireId/:damId
router.get('/relations/:sireId/:damId', (req, res) => {
  try {
    const db = getDatabase();
    res.json(isDirectRelation(db, req.params.sireId, req.params.damId));
  } catch (error) {
    res.status(500).json({ error: error.message });
  }
});

// ── POST trial pairing ────────────────────────────────────────────────────────
router.post('/trial-pairing', (req, res) => {
  try {
    const { sire_id, dam_id } = req.body;
    if (!sire_id || !dam_id) {
      return res.status(400).json({ error: 'Both sire_id and dam_id are required' });
    }

    const db = getDatabase();
    const sire = db.prepare("SELECT * FROM dogs WHERE id = ? AND sex = 'male'").get(sire_id);
    const dam  = db.prepare("SELECT * FROM dogs WHERE id = ? AND sex = 'female'").get(dam_id);

    if (!sire || !dam) {
      return res.status(404).json({ error: 'Invalid sire or dam — check sex values in database' });
    }

    const relation = isDirectRelation(db, sire_id, dam_id);
    const result   = calculateCOI(db, sire_id, dam_id);

    res.json({
      sire:           { id: sire.id, name: sire.name },
      dam:            { id: dam.id,  name: dam.name  },
      coi:            result.coefficient,
      commonAncestors: result.commonAncestors,
      directRelation: relation.related ? relation.relationship : null,
      recommendation: result.coefficient < 5  ? 'Low risk'
                    : result.coefficient < 10 ? 'Moderate risk'
                    :                           'High risk'
    });
  } catch (error) {
    res.status(500).json({ error: error.message });
  }
});

module.exports = router;