const DEFAULT_CACHE_TTL_SECONDS = 600;

function jsonResponse(data, init = {}) {
  return new Response(JSON.stringify(data), {
    ...init,
    headers: {
      'Content-Type': 'application/json; charset=utf-8',
      ...init.headers,
    },
  });
}

function getCorsHeaders(request, env) {
  const origin = request.headers.get('Origin') || '';
  const allowedOrigin = env.ALLOWED_ORIGIN || 'https://blog.biss.click';
  const allowOrigin = origin === allowedOrigin ? origin : allowedOrigin;

  return {
    'Access-Control-Allow-Origin': allowOrigin,
    'Access-Control-Allow-Methods': 'GET, OPTIONS',
    'Access-Control-Allow-Headers': 'Content-Type',
    'Vary': 'Origin',
  };
}

function normalizeBaseUrl(value) {
  return String(value || 'https://umami.biss.click').replace(/\/+$/, '');
}

function getShareId(env) {
  if (env.UMAMI_SHARE_ID) return env.UMAMI_SHARE_ID;
  if (!env.UMAMI_SHARE_URL) return '';

  try {
    const url = new URL(env.UMAMI_SHARE_URL);
    const parts = url.pathname.split('/').filter(Boolean);
    const shareIndex = parts.indexOf('share');
    return shareIndex >= 0 ? parts[shareIndex + 1] || '' : parts.at(-1) || '';
  } catch {
    return env.UMAMI_SHARE_URL.split('/').filter(Boolean).at(-1) || '';
  }
}

async function getShareData(env) {
  const baseUrl = normalizeBaseUrl(env.UMAMI_BASE_URL);
  const shareId = getShareId(env);

  if (!shareId) {
    throw new Error('Missing UMAMI_SHARE_ID or UMAMI_SHARE_URL');
  }

  const response = await fetch(`${baseUrl}/api/share/${shareId}`, {
    headers: { Accept: 'application/json' },
  });

  if (!response.ok) {
    throw new Error(`Umami share lookup failed: ${response.status}`);
  }

  const data = await response.json();
  if (!data.websiteId || !data.token) {
    throw new Error('Umami share response did not include websiteId or token');
  }

  return data;
}

async function fetchUmamiStats(env, shareData) {
  const baseUrl = normalizeBaseUrl(env.UMAMI_BASE_URL);
  const websiteId = env.UMAMI_WEBSITE_ID || shareData.websiteId;

  const startAt = Number(env.STATS_START_AT || 0);
  const endAt = Date.now();
  const url = `${baseUrl}/api/websites/${websiteId}/stats?startAt=${startAt}&endAt=${endAt}`;

  return fetch(url, {
    headers: {
      Accept: 'application/json',
      'x-umami-share-context': '1',
      'x-umami-share-token': shareData.token,
    },
  });
}

async function getStats(env) {
  const shareData = await getShareData(env);
  const response = await fetchUmamiStats(env, shareData);

  if (!response.ok) {
    throw new Error(`Umami stats failed: ${response.status}`);
  }

  const stats = await response.json();

  return {
    visitors: stats.visitors ?? 0,
    pageviews: stats.pageviews ?? 0,
    visits: stats.visits ?? 0,
    updatedAt: Date.now(),
  };
}

export default {
  async fetch(request, env, ctx) {
    const corsHeaders = getCorsHeaders(request, env);

    if (request.method === 'OPTIONS') {
      return new Response(null, { status: 204, headers: corsHeaders });
    }

    if (request.method !== 'GET') {
      return jsonResponse({ error: 'Method not allowed' }, { status: 405, headers: corsHeaders });
    }

    const cacheTtl = Number(env.CACHE_TTL_SECONDS || DEFAULT_CACHE_TTL_SECONDS);
    const cache = caches.default;
    const cacheKey = new Request(
      `https://site-stats-cache.local/umami-site-stats/${getShareId(env) || 'default'}`,
    );
    const cached = await cache.match(cacheKey);

    if (cached) {
      return new Response(cached.body, {
        status: cached.status,
        headers: {
          ...Object.fromEntries(cached.headers),
          ...corsHeaders,
          'X-Stats-Cache': 'HIT',
        },
      });
    }

    try {
      const stats = await getStats(env);
      const response = jsonResponse(stats, {
        headers: {
          ...corsHeaders,
          'Cache-Control': `public, max-age=${cacheTtl}`,
          'X-Stats-Cache': 'MISS',
        },
      });

      ctx.waitUntil(cache.put(cacheKey, response.clone()));
      return response;
    } catch (error) {
      return jsonResponse(
        {
          error: 'Failed to fetch stats',
          message: error instanceof Error ? error.message : String(error),
        },
        { status: 502, headers: corsHeaders },
      );
    }
  },
};