"use client";

/**
 * useBlockSaveQueue — React binding for the shared per-page
 * BlockBatchQueue (lib/batch-queue.ts).
 *
 * `queueChange(blockId, content)` debounces (500 ms) into one
 * POST /blocks/batch. `saveNow(blockId, content)` persists a single block
 * immediately (blur fallback) and drops the queued copy of it so the final
 * state never depends on the debounce window closing. The shared queue is
 * also flushed on unmount.
 */
import { useCallback, useEffect, useRef } from "react";
import { useQueryClient } from "@tanstack/react-query";
import { blockApi, isApiError } from "@/lib/api";
import { getBlockBatchQueue } from "@/lib/batch-queue";

export function useBlockSaveQueue(pageId: string) {
  const qc = useQueryClient();
  const pageIdRef = useRef(pageId);
  pageIdRef.current = pageId;

  const invalidate = useCallback(
    (pid: string) => qc.invalidateQueries({ queryKey: ["pages", pid, "blocks"] }),
    [qc]
  );

  const queueChange = useCallback(
    (blockId: string, content: unknown) => {
      const id = pageIdRef.current;
      if (!id) return;
      getBlockBatchQueue(id).queue({ op: "update", blockId, patch: { content } });
    },
    []
  );

  const saveNow = useCallback(
    async (blockId: string, content: unknown) => {
      const id = pageIdRef.current;
      if (!id) return;
      try {
        await blockApi.update(blockId, { content });
        invalidate(id);
      } catch (err) {
        // TASK-0136: a 404 is NOT transient — the block is gone (the
        // delete-on-blur cleanup removed it while this blur save was
        // in flight, or a concurrent peer deleted it). Re-queueing would
        // poison the next batch flush (the batch endpoint 400s on a
        // missing id and aborts the whole batch). Drop it instead.
        if (isApiError(err) && err.status === 404) return;
        // Transient failure: re-queue so the next flush retries.
        getBlockBatchQueue(id).queue({ op: "update", blockId, patch: { content } });
      }
    },
    [invalidate]
  );

  // Flush pending ops when this page unmounts (no lost edits on navigation).
  useEffect(() => {
    const id = pageIdRef.current;
    return () => {
      if (!id) return;
      void getBlockBatchQueue(id).flush().then(() => invalidate(id));
    };
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [pageId]);

  // Exposed for property-only updates (e.g. the table grid's add/remove
  // row/col, which patch `properties` directly and otherwise leave the
  // ["pages", pageId, "blocks"] cache stale until the next refetch).
  return { queueChange, saveNow, invalidate };
}