const crypto = require('crypto');
const jwt = require('jsonwebtoken');
const redis = require('../config/redis');
const dataPageCache = require('../services/dataPageCache');

const CACHE_BUSTER_KEYS = new Set([
  '_',
  '_t',
  't',
  'timestamp',
  'cacheBust',
  'cacheBuster',
  'nocache',
]);
const DEFAULT_REDIS_TTL_SECONDS = Math.max(
  Number(process.env.PAGE_RESPONSE_CACHE_REDIS_TTL_SECONDS) || 300,
  30
);
const MAX_RECENT_EVENTS = 200;
const pageCacheStats = {
  total: 0,
  hits: 0,
  misses: 0,
  stores: 0,
  bypasses: 0,
  invalidations: 0,
  labels: new Map(),
  recentEvents: [],
  lastResetAt: new Date().toISOString(),
};

function hashValue(value) {
  if (!value) return '';
  return crypto.createHash('sha256').update(String(value)).digest('hex');
}

function normalizeQuery(query = {}) {
  return Object.keys(query || {})
    .filter((key) => !CACHE_BUSTER_KEYS.has(key))
    .sort()
    .reduce((acc, key) => {
      acc[key] = query[key];
      return acc;
    }, {});
}

function buildUserScope(req) {
  if (req.user) {
    return {
      sub: req.user.sub || req.user.id || '',
      role: req.user.role || '',
    };
  }

  return {
    authHash: hashValue(req.headers.authorization || ''),
  };
}

function verifyAuthHeaderIfPresent(req) {
  if (req.user) {
    return true;
  }

  const authHeader = String(req.headers.authorization || '');
  if (!authHeader) {
    return true;
  }

  if (!authHeader.startsWith('Bearer ')) {
    return false;
  }

  try {
    req.user = jwt.verify(authHeader.substring(7), process.env.CUBEJS_SECRET);
    return true;
  } catch (_error) {
    return false;
  }
}

function getNamespacePrefix(namespace) {
  return `page-response:${namespace}:`;
}

function buildCacheKey(req, namespace, version) {
  return dataPageCache.buildHashedCacheKey(
    getNamespacePrefix(namespace),
    {
      method: req.method,
      path: `${req.baseUrl || ''}${req.path || ''}`,
      query: normalizeQuery(req.query),
      user: buildUserScope(req),
      acceptLanguage: req.headers['accept-language'] || '',
    },
    version
  );
}

function isCacheBypassed(req) {
  const cacheControl = String(req.headers['cache-control'] || '').toLowerCase();
  return (
    cacheControl.includes('no-cache')
    || cacheControl.includes('no-store')
    || req.query?._refresh === '1'
    || req.query?.refresh === '1'
  );
}

function defaultShouldCacheBody(body) {
  if (body === undefined) return false;
  if (body?.success === false) return false;
  return true;
}

function recordPageCacheEvent(namespace, hit, details = {}) {
  pageCacheStats.total += 1;
  if (hit === 'redis') pageCacheStats.hits += 1;
  if (hit === 'miss') pageCacheStats.misses += 1;
  if (hit === 'store') pageCacheStats.stores += 1;
  if (hit === 'bypass') pageCacheStats.bypasses += 1;
  if (hit === 'invalidate') pageCacheStats.invalidations += 1;

  const labelStats = pageCacheStats.labels.get(namespace) || {
    label: namespace,
    total: 0,
    hits: 0,
    misses: 0,
    stores: 0,
    bypasses: 0,
    invalidations: 0,
    lastHit: null,
    lastSeenAt: null,
  };
  labelStats.total += 1;
  labelStats.lastHit = hit;
  labelStats.lastSeenAt = new Date().toISOString();
  if (hit === 'redis') labelStats.hits += 1;
  if (hit === 'miss') labelStats.misses += 1;
  if (hit === 'store') labelStats.stores += 1;
  if (hit === 'bypass') labelStats.bypasses += 1;
  if (hit === 'invalidate') labelStats.invalidations += 1;
  pageCacheStats.labels.set(namespace, labelStats);

  pageCacheStats.recentEvents.unshift({
    namespace,
    hit,
    path: details.path || '',
    timestamp: new Date().toISOString(),
  });
  if (pageCacheStats.recentEvents.length > MAX_RECENT_EVENTS) {
    pageCacheStats.recentEvents.length = MAX_RECENT_EVENTS;
  }
}

function getPageDataCacheStats() {
  return {
    total: pageCacheStats.total,
    hits: pageCacheStats.hits,
    misses: pageCacheStats.misses,
    stores: pageCacheStats.stores,
    bypasses: pageCacheStats.bypasses,
    invalidations: pageCacheStats.invalidations,
    hitRate: pageCacheStats.total ? Number((pageCacheStats.hits * 100 / pageCacheStats.total).toFixed(2)) : 0,
    lastResetAt: pageCacheStats.lastResetAt,
    labels: Array.from(pageCacheStats.labels.values()).sort((a, b) => b.total - a.total),
    recentEvents: pageCacheStats.recentEvents,
  };
}

function resetPageDataCacheStats() {
  pageCacheStats.total = 0;
  pageCacheStats.hits = 0;
  pageCacheStats.misses = 0;
  pageCacheStats.stores = 0;
  pageCacheStats.bypasses = 0;
  pageCacheStats.invalidations = 0;
  pageCacheStats.labels.clear();
  pageCacheStats.recentEvents = [];
  pageCacheStats.lastResetAt = new Date().toISOString();
}

function createPageDataCache(options = {}) {
  const namespace = options.namespace || 'default';
  const version = options.version || 'v1';
  const redisTtlSeconds = Math.max(Number(options.redisTtlSeconds) || DEFAULT_REDIS_TTL_SECONDS, 30);
  const enabled = options.enabled !== false;
  const invalidateOnMutations = options.invalidateOnMutations !== false;
  const shouldHandleRequest = typeof options.shouldHandleRequest === 'function'
    ? options.shouldHandleRequest
    : () => true;
  const shouldCacheBody = typeof options.shouldCacheBody === 'function'
    ? options.shouldCacheBody
    : defaultShouldCacheBody;

  return async (req, res, next) => {
    if (!enabled || !shouldHandleRequest(req)) {
      recordPageCacheEvent(namespace, 'bypass', { path: req.originalUrl });
      return next();
    }

    if (req.method !== 'GET') {
      if (invalidateOnMutations) {
        res.on('finish', () => {
          if (res.statusCode >= 200 && res.statusCode < 300) {
            dataPageCache.deleteByPrefix(getNamespacePrefix(namespace)).catch((error) => {
              console.warn(`[PageDataCache] ${namespace} invalidation failed:`, error.message);
            });
            recordPageCacheEvent(namespace, 'invalidate', { path: req.originalUrl });
          }
        });
      }
      return next();
    }

    if (!verifyAuthHeaderIfPresent(req) || isCacheBypassed(req)) {
      recordPageCacheEvent(namespace, 'bypass', { path: req.originalUrl });
      res.set('X-Page-Cache', 'bypass');
      return next();
    }

    const cacheKey = buildCacheKey(req, namespace, version);
    const cachedPayload = await redis.get(cacheKey);
    if (cachedPayload?.body !== undefined) {
      recordPageCacheEvent(namespace, 'redis', { path: req.originalUrl });
      res.set('X-Page-Cache', 'redis');
      return res.status(cachedPayload.statusCode || 200).json(cachedPayload.body);
    }

    recordPageCacheEvent(namespace, 'miss', { path: req.originalUrl });
    res.set('X-Page-Cache', 'miss');

    const originalJson = res.json.bind(res);
    res.json = (body) => {
      if (res.statusCode >= 200 && res.statusCode < 300 && shouldCacheBody(body, req)) {
        redis.setex(cacheKey, redisTtlSeconds, {
          statusCode: res.statusCode,
          body,
          cachedAt: new Date().toISOString(),
        }).then((stored) => {
          if (stored) {
            recordPageCacheEvent(namespace, 'store', { path: req.originalUrl });
          }
        }).catch((error) => {
          console.warn(`[PageDataCache] ${namespace} store failed:`, error.message);
        });
      }

      return originalJson(body);
    };

    return next();
  };
}

module.exports = {
  createPageDataCache,
  getPageDataCacheStats,
  resetPageDataCacheStats,
};