const { extractFromHtml } = require("@extractus/article-extractor");
const db = require("./db");
const config = require("./config");
const { fetchWithPolicy } = require("./http");
const { getSharedBrowserSession } = require("./sources/browserCrawler");
const { validateExtractedArticle } = require("./contentValidation");
const {
  getEffectivePolicy,
  recordPlainSuccess,
  recordPlainFailure,
  recordBrowserSuccess,
  recordBrowserFailure,
} = require("./domainPolicy");


const MAX_PLAIN_HTML_LENGTH = 1_500_000;
const PLAIN_FETCH_TIMEOUT = 12000;
const BROWSER_FETCH_TIMEOUT = 20000;
const HEAD_PRECHECK_TIMEOUT = 6000;

const VALIDATION_RETRY_AFTER_MS = 24 * 60 * 60 * 1000;
const TRANSIENT_RETRY_AFTER_MS = 6 * 60 * 60 * 1000;
const MAX_TERMINAL_ATTEMPTS = 3;

// flaky domains get a HEAD precheck before we waste a body fetch. only kicks
// in once a domain has accumulated some failure history; pristine domains
// skip the round trip
const HEAD_PRECHECK_FAILURE_THRESHOLD = 2;


const updateArticleAssets = db.prepare(`
  UPDATE articles
  SET content = ?, content_status = 'ready', content_error = NULL,
      content_attempted_at = ?, content_attempt_count = content_attempt_count + 1,
      content_retry_after = NULL
  WHERE id = ?
`);
const updateArticleTitleDescription = db.prepare(`
  UPDATE articles
  SET title = ?, description = ?
  WHERE id = ?
`);
const markContentSkipped = db.prepare(`
  UPDATE articles
  SET content_status = 'skipped', content_error = ?, content_attempted_at = ?,
      content_attempt_count = content_attempt_count + 1, content_retry_after = NULL
  WHERE id = ?
`);
const markContentFailed = db.prepare(`
  UPDATE articles
  SET content_status = 'failed', content_error = ?, content_attempted_at = ?,
      content_attempt_count = content_attempt_count + 1, content_retry_after = NULL
  WHERE id = ?
`);
const markContentPending = db.prepare(`
  UPDATE articles
  SET content_status = 'pending', content_error = ?, content_attempted_at = ?,
      content_attempt_count = content_attempt_count + 1, content_retry_after = ?
  WHERE id = ?
`);

// pulls a partition of pending articles. workerIndex/workerCount partitions
// by article id (deterministic) so multiple workers never see the same row.
// also round-robins by source so no single domain dominates the queue
const selectPartitionedArticlesMissingContent = db.prepare(`
  SELECT id, url, title, description
  FROM (
    SELECT id, url, title, description, source, pub_date_effective,
      ROW_NUMBER() OVER (PARTITION BY source ORDER BY pub_date_effective DESC, id DESC) AS rn
    FROM articles
    WHERE (content IS NULL OR TRIM(content) = '')
      AND (content_status IS NULL OR content_status = 'pending')
      AND (content_retry_after IS NULL OR content_retry_after <= datetime('now'))
      AND (id % ?) = ?
  )
  WHERE rn <= ?
  ORDER BY pub_date_effective DESC, rn, source
`);

const selectAttemptCount = db.prepare(`
  SELECT content_attempt_count AS attempts FROM articles WHERE id = ?
`);


// shared semaphore — tracks both plain and browser pool occupancy across all
// workers. defining at module scope so the limits are global, not per-worker
function makeSemaphore(limit) {
  let active = 0;
  const waiters = [];

  return {
    async acquire() {
      if (active < limit) {
        active += 1;
        return;
      }
      await new Promise((resolve) => waiters.push(resolve));
      active += 1;
    },
    release() {
      active = Math.max(0, active - 1);
      const next = waiters.shift();
      if (next) next();
    },
    inFlight() {
      return active;
    },
  };
}

const PLAIN_CONCURRENCY = Number(config.contentBackfill?.plainConcurrency) || 50;
const BROWSER_CONCURRENCY = Number(config.contentBackfill?.browserConcurrency) || 8;

const plainSemaphore = makeSemaphore(PLAIN_CONCURRENCY);
const browserSemaphore = makeSemaphore(BROWSER_CONCURRENCY);


function getErrorStatus(error) {
  if (error && Number.isInteger(error.status)) {
    return error.status;
  }

  const match = String((error && error.message) || "").match(/\b(401|403|404|408|429|5\d\d)\b/);
  return match ? Number(match[1]) : null;
}

function nowIso() {
  return new Date().toISOString();
}

function futureIso(ms) {
  return new Date(Date.now() + ms).toISOString();
}


// cheap HEAD check before pulling the body. only used on domains we already
// know are unreliable. if HEAD says 404/410/451, skip the body fetch entirely
async function headPrecheck(url) {
  try {
    const response = await fetchWithPolicy(url, {
      method: "HEAD",
      timeout: HEAD_PRECHECK_TIMEOUT,
      retries: 0,
    });
    return { status: response.status, finalUrl: response.url || url };
  } catch (error) {
    return { status: getErrorStatus(error), error };
  }
}


async function fetchPlainHtml(url) {
  await plainSemaphore.acquire();
  try {
    const response = await fetchWithPolicy(url, {
      timeout: PLAIN_FETCH_TIMEOUT,
      retries: 1,
    });

    if (!response.ok) {
      const error = new Error(`plain fetch returned ${response.status}`);
      error.status = response.status;
      throw error;
    }

    const contentType = String(response.headers.get("content-type") || "").toLowerCase();
    if (contentType && !contentType.includes("html") && !contentType.includes("xml")) {
      throw new Error(`plain fetch returned non-html content-type: ${contentType}`);
    }

    const text = await response.text();
    return {
      html: text.slice(0, MAX_PLAIN_HTML_LENGTH),
      finalUrl: response.url || url,
    };
  } finally {
    plainSemaphore.release();
  }
}


async function fetchBrowserHtml(url) {
  await browserSemaphore.acquire();
  try {
    const maxConcurrentPages = Number(config.browser?.maxConcurrentPages) || 8;
    const session = await getSharedBrowserSession({
      requestTimeout: BROWSER_FETCH_TIMEOUT,
      maxConcurrentPages,
    });

    const html = await session.fetchRenderedHtml(url, { timeout: BROWSER_FETCH_TIMEOUT });
    return { html, finalUrl: url };
  } finally {
    browserSemaphore.release();
  }
}


function stripHtmlContent(value) {
  if (typeof value !== "string") return null;
  const stripped = value.replace(/<[^>]+>/g, " ").replace(/\s+/g, " ").trim();
  return stripped || null;
}


async function attemptFetch(url, fetcher) {
  let html;
  let finalUrl;
  try {
    const result = await fetcher(url);
    html = result.html;
    finalUrl = result.finalUrl;
  } catch (error) {
    return { ok: false, reason: `fetch-error:${error.message || "unknown"}`, error };
  }

  if (!html) {
    return { ok: false, reason: "empty-html" };
  }

  let extracted;
  try {
    extracted = await extractFromHtml(html, finalUrl || url);
  } catch (error) {
    return { ok: false, reason: `extractor-error:${error.message || "unknown"}` };
  }

  if (extracted) {
    extracted = {
      ...extracted,
      content: stripHtmlContent(extracted.content),
    };
  }

  const validation = validateExtractedArticle({ article: extracted, html, finalUrl });
  if (!validation.ok) {
    return { ok: false, reason: validation.reason, retryable: validation.retryable, html, finalUrl };
  }

  return { ok: true, article: extracted, html, finalUrl };
}


function getAttemptCount(id) {
  const row = selectAttemptCount.get(id);
  return row ? row.attempts || 0 : 0;
}


// shouldPrecheck: domains with at least N consecutive plain or browser failures
// in their policy entry get a HEAD check first. we read the row directly here
// rather than threading through the policy module
const selectFailureCounts = db.prepare(`
  SELECT consecutive_plain_failures, consecutive_browser_failures
  FROM domain_fetch_policy WHERE domain = ?
`);

function shouldPrecheck(url) {
  try {
    const domain = new URL(url).hostname.toLowerCase();
    const row = selectFailureCounts.get(domain);
    if (!row) return false;
    return (row.consecutive_plain_failures + row.consecutive_browser_failures) >= HEAD_PRECHECK_FAILURE_THRESHOLD;
  } catch {
    return false;
  }
}


async function fetchAndStoreContent(id, url, storedTitle, storedDescription) {
  const policy = getEffectivePolicy(url);

  if (policy.policy === "blocked") {
    markContentPending.run(
      `domain blocked by policy`,
      nowIso(),
      futureIso(TRANSIENT_RETRY_AFTER_MS),
      id
    );
    return;
  }

  // HEAD precheck for known-flaky domains. if it returns 404/410/451 we mark
  // terminal-failed without burning a body fetch. transient errors fall through
  if (shouldPrecheck(url)) {
    const head = await headPrecheck(url);
    if (head.status === 404 || head.status === 410 || head.status === 451) {
      markContentFailed.run(`head ${head.status}`, nowIso(), id);
      return;
    }
  }

  const tryPlainFirst = policy.policy === "auto" || policy.policy === "plain_only";
  let plainResult = null;
  let browserResult = null;


  if (tryPlainFirst) {
    plainResult = await attemptFetch(url, fetchPlainHtml);

    if (plainResult.ok) {
      recordPlainSuccess(url);
      commitArticle(id, url, plainResult, storedTitle, storedDescription);
      return;
    }

    recordPlainFailure(url);

    const status = plainResult.error && getErrorStatus(plainResult.error);
    if (status === 408 || status === 429 || (status && status >= 500)) {
      markContentPending.run(
        `plain ${status}`,
        nowIso(),
        futureIso(TRANSIENT_RETRY_AFTER_MS),
        id
      );
      return;
    }
  }

  if (policy.policy === "plain_only") {
    recordValidationFailure(id, plainResult);
    return;
  }


  browserResult = await attemptFetch(url, fetchBrowserHtml);

  if (browserResult.ok) {
    recordBrowserSuccess(url);
    commitArticle(id, url, browserResult, storedTitle, storedDescription);
    return;
  }

  recordBrowserFailure(url);

  const browserStatus = browserResult.error && getErrorStatus(browserResult.error);
  if (browserStatus === 408 || browserStatus === 429 || (browserStatus && browserStatus >= 500)) {
    markContentPending.run(
      `browser ${browserStatus}`,
      nowIso(),
      futureIso(TRANSIENT_RETRY_AFTER_MS),
      id
    );
    return;
  }

  recordValidationFailure(id, browserResult);
}


function recordValidationFailure(id, result) {
  const reason = result?.reason || "unknown";
  const retryable = result?.retryable !== false;
  const attempts = getAttemptCount(id);

  if (!retryable || attempts + 1 >= MAX_TERMINAL_ATTEMPTS) {
    markContentFailed.run(reason, nowIso(), id);
    return;
  }

  markContentPending.run(reason, nowIso(), futureIso(VALIDATION_RETRY_AFTER_MS), id);
}


function commitArticle(id, url, result, storedTitle, storedDescription) {
  const { article } = result;
  const content = article.content || null;

  const titleLooksLikeUrl = storedTitle && /^https?:\/\//i.test(storedTitle.trim());
  if (titleLooksLikeUrl) {
    const scrapedTitle = typeof article.title === "string" ? article.title.trim() : null;
    const scrapedDescription = typeof article.description === "string" ? article.description.trim() : null;
    if (scrapedTitle) {
      updateArticleTitleDescription.run(scrapedTitle, scrapedDescription || storedDescription || null, id);
    }
  }

  updateArticleAssets.run(content, nowIso(), id);

  // embedding generation is no longer kicked off here — runEmbeddingLoop
  // in scheduler.js batches them in its own pipeline. that decouples slow
  // openrouter calls from content fetch throughput
}


// runs one worker pass — pulls its partition slice, fires N concurrent fetches
// from a single backfill loop. multiple workers share the plain/browser
// semaphores so total concurrency stays bounded regardless of worker count
async function runBackfillWorker({ workerIndex, workerCount, perSource, batchSize }) {
  const rows = selectPartitionedArticlesMissingContent.all(workerCount, workerIndex, perSource);
  if (rows.length === 0) return 0;

  // dispatch in chunks of batchSize so we don't allocate thousands of unawaited
  // promises at once. the semaphores throttle inside fetchAndStoreContent
  for (let i = 0; i < rows.length; i += batchSize) {
    const batch = rows.slice(i, i + batchSize);
    await Promise.all(batch.map((row) =>
      fetchAndStoreContent(row.id, row.url, row.title, row.description).catch((error) => {
        console.error(`backfill worker ${workerIndex} failed on ${row.url}:`, error.message || error);
      })
    ));
  }

  return rows.length;
}


function hasPendingContent() {
  return Boolean(db.prepare(`
    SELECT 1 FROM articles
    WHERE (content IS NULL OR TRIM(content) = '')
      AND (content_status IS NULL OR content_status = 'pending')
      AND (content_retry_after IS NULL OR content_retry_after <= datetime('now'))
    LIMIT 1
  `).get());
}


// kept for backwards compat with scheduler/runAllIngestions one-shot runs
async function backfillMissingContent(perSource = 50, concurrency = 50) {
  await runBackfillWorker({
    workerIndex: 0,
    workerCount: 1,
    perSource,
    batchSize: concurrency,
  });
}


module.exports = {
  fetchAndStoreContent,
  backfillMissingContent,
  runBackfillWorker,
  hasPendingContent,
};