import { useRef, useState } from 'react';
import { GripVertical, Plus, Trash2 } from 'lucide-react';
import { Link } from 'react-router';
import { Button } from '@/components/ui/button';
import { href } from '../routes';
import { CHOICES } from './AddComponentDialog';
import type { CanvasComponent, CanvasSection } from '../canvas';

/**
 * What is in one band, column by column.
 *
 * ── One list, two places ──
 *
 * The page's structure nests this under every band, and the band's own editor shows just its own.
 * They are the same list of the same things with the same actions, so they are the same component —
 * the carousels panel taught that lesson once already.
 *
 * ── Columns, because adding needs one ──
 *
 * A block goes IN a column, so a flat list cannot express adding one. A one-column band shows a single
 * button and never has to ask a question it has no answer to.
 *
 * A two-column band NAMES its columns. It used to leave them unlabelled and put the side on the
 * buttons — "Add left", "Add right" — and that reads as a flat list of blocks with two odd buttons
 * under it: a band whose only block was on the left looked like a band with nothing on the left and
 * two ways to fix it. The side belongs on the GROUP, which is the thing that has one; the buttons then
 * say what they do, and an empty column is visible as an empty column rather than inferred from the
 * absence of something.
 *
 * ── Reorder is within a column ──
 *
 * The write sends the column alongside the ids, and the query sets both — so dragging a block from one
 * column to the other is the same call, on the day the interface offers it. It does not yet: a list
 * per column has no gesture for crossing between them, and inventing one here would be guessing.
 */
export const BandBlocks = ({
  slug,
  section,
  busy,
  onAdd,
  onDelete,
  onReorder,
}: {
  slug: string;
  section: CanvasSection;
  busy: boolean;
  onAdd: (section: CanvasSection, column: number) => void;
  onDelete: (block: CanvasComponent) => void;
  onReorder: (section: CanvasSection, column: number, ids: number[]) => void;
}) => {
  const [dragged, setDragged] = useState<number | null>(null);
  const [order, setOrder] = useState<CanvasComponent[] | null>(null);
  const pending = useRef<CanvasComponent[] | null>(null);
  const columns = section.layout === 'two' ? 2 : 1;

  const blocksIn = (column: number) =>
    (order ?? section.components).filter((block) => block.column === column);

  const moveOver = (event: React.DragEvent, over: CanvasComponent) => {
    if (dragged === null) return;
    const all = order ?? section.components;
    const from = all.findIndex((one) => one.id === dragged);
    // Within a column only — see the note above. A drop on the other column is simply not accepted.
    if (from < 0 || all[from]!.column !== over.column) return;

    event.preventDefault();
    if (dragged === over.id) return;

    const next = [...all];
    const to = next.findIndex((one) => one.id === over.id);
    next.splice(to, 0, next.splice(from, 1)[0]!);
    pending.current = next;
    setOrder(next);
  };

  const commit = (column: number) => {
    const next = pending.current;
    setDragged(null);
    pending.current = null;
    // Dropped where it started, or outside the list. Nothing moved, so nothing is written.
    if (!next) return;
    setOrder(null);
    onReorder(section, column, next.filter((one) => one.column === column).map((one) => one.id));
  };

  return (
    <div className="flex flex-col gap-1">
      {Array.from({ length: columns }, (_, column) => (
        <div
          key={column}
          // Indented behind a rule when there are two, so where one column ends is something you see
          // rather than something you count.
          className={`flex flex-col gap-0.5 ${columns === 2 ? 'border-l border-border/60 pl-1.5' : ''}`}
        >
          {columns === 2 && (
            <span className="px-1 pt-0.5 text-[10px] font-medium tracking-wide text-muted-foreground/60 uppercase">
              {column === 0 ? 'Left' : 'Right'}
            </span>
          )}

          {blocksIn(column).map((block) => (
            <span
              key={block.id}
              onDragOver={(event) => moveOver(event, block)}
              onDrop={() => commit(column)}
              className={`flex items-center gap-1 ${dragged === block.id ? 'opacity-40' : ''}`}
            >
              <span
                draggable
                onDragStart={(event) => {
                  setDragged(block.id);
                  // Firefox starts no drag at all without data on the transfer. The value is unused.
                  event.dataTransfer.effectAllowed = 'move';
                  event.dataTransfer.setData('text/plain', String(block.id));
                }}
                onDragEnd={() => commit(column)}
                className="shrink-0 cursor-grab pl-1 text-muted-foreground/50 active:cursor-grabbing"
                aria-label="Reorder"
              >
                <GripVertical className="size-3.5" />
              </span>

              <Link
                to={href('pages', slug, String(section.id), String(block.id))}
                replace
                className="min-w-0 flex-1 truncate py-0.5 text-[11px] text-muted-foreground hover:text-foreground"
              >
                {CHOICES.find((choice) => choice.kind === block.kind)?.label ?? block.kind}
              </Link>

              <Button
                variant="ghost"
                size="sm"
                className="h-6 shrink-0 px-1 text-destructive"
                disabled={busy}
                onClick={() => onDelete(block)}
              >
                <Trash2 className="size-3" />
              </Button>
            </span>
          ))}

          <Button
            variant="ghost"
            size="sm"
            className="h-6 justify-start px-1 text-[11px] text-muted-foreground"
            disabled={busy}
            onClick={() => onAdd(section, column)}
          >
            <Plus className="size-3" />
            Add block
          </Button>
        </div>
      ))}
    </div>
  );
};