import { useCallback, useEffect, useRef, useState } from 'react';
import { useSearchParams } from 'react-router';
import { Images, Loader2, Plus, Trash2 } from 'lucide-react';
import { useClient } from 'hooks/useClient';
import { Button } from '@/components/ui/button';
import { Input } from '@/components/ui/input';
import { readableError } from '../errors';
import { useEditorSlot } from '../useEditorSlot';
import { GalleryItems } from './GalleryItems';

/**
 * Galleries — named, ordered sets of media, reusable anywhere on the site.
 *
 * ── Why a gallery is not a list on a page ──
 *
 * The home page had one, as rows hanging off its own content. That works for exactly one. The moment a
 * second page wants the same photographs in the same order, a list-per-page means choosing them again
 * and keeping two copies in step by hand.
 *
 * ── The server owns the shape ──
 *
 * Every write answers with the whole gallery and this never patches its own state from what it sent.
 * That matters most here: reordering renumbers everything, adding appends after whatever was there,
 * and deleting closes a gap. A client keeping its own copy drifts on the first of those with no way to
 * notice.
 */

type Item = { id: number; url: string; alt: string | null; sort_order: number };
type Gallery = { id: number; name: string; slug: string; items: Item[] };

export const GalleriesPanel = () => {
  const client = useClient();
  const clientRef = useRef(client);
  clientRef.current = client;

  const [galleries, setGalleries] = useState<Gallery[] | null>(null);
  const [openId, setOpenId] = useState<number | null>(null);
  const [name, setName] = useState('');
  /** Paths handed over by the context menu, waiting for a name. */
  const [pending, setPending] = useState<string[]>([]);
  const [busy, setBusy] = useState<string | null>(null);
  const [error, setError] = useState<string | null>(null);
  const [params, setParams] = useSearchParams();

  const load = useCallback(async () => {
    try {
      const response = await clientRef.current.get<{ data: Gallery[] }>('/fofos-admin/galleries');
      setGalleries(response.data);
    } catch (failure) {
      setError(readableError(failure));
      setGalleries([]);
    }
  }, []);

  useEffect(() => {
    void load();
  }, [load]);

  /*
    The selected gallery's contents, handed to the editor column.

    Announced rather than rendered, because that panel is a SIBLING — see useEditorSlot. `onChanged`
    reloads the list here, so the item count beside the name is never one behind what is in it.

    The dependency list is everything the editor DISPLAYS: an element captures the props it was built
    with, so one left out reads as a control that has stopped responding rather than as an error.
  */
  const [, setEditor] = useEditorSlot();
  const setEditorRef = useRef(setEditor);
  setEditorRef.current = setEditor;

  useEffect(() => {
    setEditorRef.current(
      openId === null ? null : <GalleryItems galleryId={openId} onChanged={() => void load()} />,
    );
  }, [openId, load]);

  // Cleared on unmount, or the panel goes on offering a gallery over somebody else's screen.
  useEffect(() => () => setEditorRef.current(null), []);

  /*
    Arriving from "Create Gallery" in the file browser.

    The action puts the chosen paths in the URL and sends you here rather than opening its own dialog:
    naming a gallery, seeing the slug it gets and watching the items land belongs on the screen that
    owns galleries. Consumed once and removed from the URL — a `?from=` left behind would recreate the
    gallery on every refresh, which somebody discovers as four copies.
  */
  const arriving = params.get('from');
  useEffect(() => {
    if (arriving === null) return;
    const urls = arriving.split('\n').filter(Boolean);
    const suggested = params.get('create') ?? '';
    setParams(
      (current) => {
        const next = new URLSearchParams(current);
        next.delete('from');
        next.delete('create');
        return next;
      },
      { replace: true },
    );
    // Pre-filled rather than created: the name is somebody's to choose and a folder name is only a
    // suggestion. Nothing is written until Create.
    setName(suggested);
    setPending(urls);
  }, [arriving, params, setParams]);

  const send = async (label: string, call: () => Promise<unknown>) => {
    setBusy(label);
    setError(null);
    try {
      await call();
      await load();
    } catch (failure) {
      setError(readableError(failure));
    } finally {
      setBusy(null);
    }
  };

  const create = () =>
    send('create', async () => {
      // `urls` in the same request, so creating from a selection is one action — splitting it would
      // leave an empty gallery behind whenever the second call failed.
      await clientRef.current.post('/fofos-admin/galleries', { name: name.trim(), urls: pending });
      setName('');
      setPending([]);
    });

  if (!galleries) return <div className="p-5 text-xs text-muted-foreground">{error ?? 'Loading…'}</div>;

  return (
    <div className="flex size-full flex-col gap-4 overflow-auto p-5">
      <section className="flex flex-col gap-3 rounded-lg border border-border p-4">
        <h3 className="text-sm font-medium">Galleries</h3>

        {error && <p className="text-xs text-destructive">{error}</p>}

        {/* What the context menu sent, so what is about to be created is not a mystery. */}
        {pending.length > 0 && (
          <p className="text-xs text-muted-foreground/80">
            {pending.length} item{pending.length === 1 ? '' : 's'} ready — name it and press Create.
          </p>
        )}

        <div className="flex gap-2">
          <Input
            autoFocus={pending.length > 0}
            value={name}
            onChange={(event) => setName(event.target.value)}
            placeholder="Name a new gallery"
            className="min-w-0 flex-1 text-xs"
            onKeyDown={(event) => {
              if (event.key === 'Enter' && name.trim()) void create();
            }}
          />
          <Button
            variant="outline"
            size="sm"
            className="w-24 shrink-0 justify-center"
            onClick={() => void create()}
            disabled={busy !== null || !name.trim()}
          >
            {busy === 'create' ? <Loader2 className="size-3.5 animate-spin" /> : <Plus className="size-3.5" />}
            Create
          </Button>
        </div>
      </section>

      {/*
        The list, and only the list.

        The contents of a gallery — its pictures, their order, their captions — are announced to the
        editor column and drawn by `GalleryItems`, which is the same component a gallery BLOCK on a
        page uses. Two copies of that list existed for a day and this is the one that went.

        So this panel is what a master list should be: which galleries there are, making one, deleting
        one. What is inside the selected one is a different question, answered beside it.
      */}
      {galleries.map((gallery) => {
        const open = openId === gallery.id;
        return (
          <section
            key={gallery.id}
            className={`flex items-center gap-3 rounded-lg border p-4 ${
              open ? 'border-primary/60 bg-muted/40' : 'border-border'
            }`}
          >
            <button
              type="button"
              className="flex min-w-0 flex-1 items-center gap-2 text-left"
              onClick={() => setOpenId(open ? null : gallery.id)}
            >
              <Images className="size-4 shrink-0" />
              <span className="min-w-0 space-y-1">
                <span className="block truncate text-sm font-medium">{gallery.name}</span>
                <span className="block truncate font-mono text-xs text-muted-foreground/70">
                  {gallery.slug} · {gallery.items.length} item{gallery.items.length === 1 ? '' : 's'}
                </span>
              </span>
            </button>

            <Button
              variant="ghost"
              size="sm"
              className="shrink-0"
              onClick={() =>
                void send(`gallery:${gallery.id}`, () =>
                  clientRef.current.delete(`/fofos-admin/galleries/${gallery.id}`),
                )
              }
              disabled={busy !== null}
            >
              <Trash2 className="size-3.5 text-destructive" />
            </Button>
          </section>
        );
      })}

    </div>
  );
};