const cron = require("node-cron");
const dbApi = require("./db.js");
const {
  fetchSeriesChapters,
  resolveCbzPath,
  cbzExists,
} = require("./sources.js");

/**
 * Sync a title's chapter list from the source site and enqueue missing downloads.
 * @param {import("better-sqlite3").Database} db - Database handle.
 * @param {import("./queue.js").DownloadQueue} queue - Download queue.
 * @param {number} titleId - Title to sync.
 * @param {string} dataDir - Absolute data root for CBZ paths.
 * @param {{ enqueue?: boolean }} [opts] - Options; `enqueue` defaults to true.
 * @returns {Promise<{ added: number, enqueued: number, total: number }>} Sync summary.
 */
async function syncTitle(db, queue, titleId, dataDir, opts = {}) {
  const title = dbApi.getTitle(db, titleId);
  if (!title) {
    throw new Error(`Title ${String(titleId)} not found.`);
  }

  const syncJobId = dbApi.createJob(db, {
    type: "watch_sync",
    title_id: titleId,
    message: `Syncing ${title.title}`,
  });
  dbApi.updateJob(db, syncJobId, { status: "running" });

  try {
    const series = await fetchSeriesChapters(title.url, title.source);
    let added = 0;

    for (const ch of series.chapters) {
      const cbzPath = resolveCbzPath(
        title.source,
        series.comicTitle || title.title,
        ch.url,
        dataDir,
      );
      const exists = cbzExists(cbzPath);
      const { inserted } = dbApi.upsertChapter(db, {
        title_id: titleId,
        chapter_key: ch.chapter_key,
        chapter_number: ch.chapter_number,
        label: ch.title,
        url: ch.url,
        status: exists ? "downloaded" : "pending",
        cbz_path: cbzPath,
      });
      if (inserted) {
        added += 1;
      }

      // Heal statuses without interrupting an in-flight download
      const row = db
        .prepare(
          "SELECT id, status, cbz_path FROM chapters WHERE title_id = ? AND chapter_key = ?",
        )
        .get(titleId, ch.chapter_key);
      if (row && row.status === "downloading") {
        continue;
      }
      if (row && row.status === "downloaded" && !cbzExists(row.cbz_path)) {
        dbApi.updateChapter(db, row.id, {
          status: "pending",
          error: "CBZ missing on disk",
        });
      }
      if (row && exists && row.status !== "downloaded") {
        dbApi.updateChapter(db, row.id, {
          status: "downloaded",
          cbz_path: cbzPath,
          downloaded_at: new Date().toISOString(),
          error: null,
        });
      }
    }

    // Refresh comic title if site provides a better one
    if (series.comicTitle && series.comicTitle !== title.title) {
      dbApi.updateTitle(db, titleId, { title: series.comicTitle });
    }

    dbApi.touchTitleChecked(db, titleId);

    let enqueued = 0;
    if (opts.enqueue !== false) {
      enqueued = queue.enqueueMissingForTitle(titleId, { alsoMissingFiles: true });
    }

    dbApi.updateJob(db, syncJobId, {
      status: "done",
      message: `Sync complete: +${String(added)} chapter(s), ${String(enqueued)} queued`,
      finished_at: new Date().toISOString(),
    });

    return {
      added,
      enqueued,
      total: series.chapters.length,
    };
  } catch (err) {
    const msg = err instanceof Error ? err.message : String(err);
    dbApi.updateJob(db, syncJobId, {
      status: "failed",
      message: msg,
      finished_at: new Date().toISOString(),
    });
    throw err;
  }
}

/**
 * Watches titles on a schedule. Each tick syncs at most one due title
 * (oldest `last_checked_at` first), so titles are staggered instead of
 * all hitting the source sites at once. Default cadence is hourly wake +
 * 24h per-title cooldown → each title roughly once per day, unlimited count.
 * @param {import("better-sqlite3").Database} db - Database handle.
 * @param {import("./queue.js").DownloadQueue} queue - Download queue.
 * @param {string} dataDir - Absolute data root.
 * @param {string} cronExpr - node-cron expression.
 * @param {{ titleIntervalHours?: number }} [opts] - Per-title cooldown in hours.
 * @returns {{ stop: () => void }} Handle to stop the cron task.
 */
function startWatcher(db, queue, dataDir, cronExpr, opts = {}) {
  if (!cron.validate(cronExpr)) {
    throw new Error(`Invalid WATCH_CRON expression: ${cronExpr}`);
  }

  const titleIntervalHours =
    Number(opts.titleIntervalHours) > 0 ? Number(opts.titleIntervalHours) : 24;

  let busy = false;

  const task = cron.schedule(cronExpr, () => {
    if (busy) {
      console.warn("[watcher] previous sync still running; skipping this tick");
      return;
    }
    busy = true;
    void (async () => {
      try {
        const title = dbApi.pickNextTitleDue(db, titleIntervalHours);
        if (!title) {
          console.info("[watcher] no titles due this tick");
          return;
        }
        console.info(
          `[watcher] syncing 1 title: ${title.title} (${title.source})`,
        );
        await syncTitle(db, queue, title.id, dataDir, { enqueue: true });
      } catch (err) {
        console.error(
          "[watcher] sync failed:",
          err instanceof Error ? err.message : err,
        );
      } finally {
        busy = false;
      }
    })();
  });

  return {
    stop() {
      task.stop();
    },
  };
}

module.exports = { syncTitle, startWatcher };