"use client";

import { useMemo, useRef, useState, type ReactNode } from "react";
import {
  DndContext,
  DragOverlay,
  KeyboardSensor,
  PointerSensor,
  closestCorners,
  useDroppable,
  useSensor,
  useSensors,
} from "@dnd-kit/core";
import type { DragEndEvent, DragStartEvent } from "@dnd-kit/core";
import {
  SortableContext,
  arrayMove,
  rectSortingStrategy,
  useSortable,
  verticalListSortingStrategy,
} from "@dnd-kit/sortable";
import { CSS } from "@dnd-kit/utilities";
import { toast } from "sonner";
import {
  CheckIcon,
  GripVerticalIcon,
  LayoutGridIcon,
  Maximize2Icon,
  Minimize2Icon,
  RotateCcwIcon,
} from "lucide-react";
import { Button } from "@/components/ui/button";
import { saveDashboardLayout } from "@/app/(frontend)/actions";
import {
  DEFAULT_DASHBOARD_LAYOUT,
  WIDGET_LABELS,
  effectiveSpan,
  type DashboardLayout,
  type DashboardWidgetId,
  type DashboardZone,
} from "@/lib/dashboard/layout";
import { cn } from "@/lib/utils";

export interface DashboardGridWidget {
  readonly id: DashboardWidgetId;
  readonly node: ReactNode;
}

interface DashboardGridProps {
  readonly layout: DashboardLayout;
  readonly widgets: readonly DashboardGridWidget[];
}

const ZONE_MAIN = "zone:main";
const ZONE_SIDEBAR = "zone:sidebar";

function zoneFromContainerId(id: string): DashboardZone | null {
  if (id === ZONE_MAIN) return "main";
  if (id === ZONE_SIDEBAR) return "sidebar";
  return null;
}

function findZone(layout: DashboardLayout, id: string): DashboardZone | null {
  if (layout.main.includes(id as DashboardWidgetId)) return "main";
  if (layout.sidebar.includes(id as DashboardWidgetId)) return "sidebar";
  return null;
}

/**
 * Computes the next layout for a drop, or null when the drop changes nothing.
 * Pure and driven only by the layout as of drag end, so there is no state
 * mutation during the drag itself (mutating layout in onDragOver re-renders
 * the grid and re-measures droppables mid-drag, which ping-pongs collision
 * detection and crashes React with "Maximum update depth exceeded").
 */
function placementFor(
  layout: DashboardLayout,
  activeId: string,
  overId: string,
): DashboardLayout | null {
  const from = findZone(layout, activeId);
  if (!from) return null;
  const toContainer = zoneFromContainerId(overId);
  const to = toContainer ?? findZone(layout, overId);
  if (!to) return null;

  if (to === from) {
    if (toContainer) return null;
    const items = layout[from];
    const fromIndex = items.indexOf(activeId as DashboardWidgetId);
    const toIndex = items.indexOf(overId as DashboardWidgetId);
    if (fromIndex < 0 || toIndex < 0 || fromIndex === toIndex) return null;
    return { ...layout, [from]: arrayMove(items, fromIndex, toIndex) };
  }

  const source = layout[from].filter((id) => id !== (activeId as DashboardWidgetId));
  const target = [...layout[to]];
  if (toContainer) {
    target.push(activeId as DashboardWidgetId);
  } else {
    const overIndex = target.indexOf(overId as DashboardWidgetId);
    target.splice(overIndex >= 0 ? overIndex : target.length, 0, activeId as DashboardWidgetId);
  }
  return { ...layout, [from]: source, [to]: target };
}

function SortableWidget({
  id,
  span,
  animate,
  resizable,
  onToggleSpan,
  children,
}: {
  id: string;
  span: 1 | 2;
  animate: boolean;
  resizable: boolean;
  onToggleSpan: () => void;
  children: ReactNode;
}) {
  const {
    attributes,
    listeners,
    setNodeRef,
    setActivatorNodeRef,
    transform,
    transition,
    isDragging,
    isOver,
  } = useSortable({ id });

  return (
    <div
      ref={setNodeRef}
      style={{
        transform: CSS.Transform.toString(animate && !isDragging ? transform : null),
        transition: animate ? transition : undefined,
      }}
      className={cn(
        "group relative flex min-w-0 [&>*]:flex-1 [&>*]:min-w-0",
        span === 2 && "lg:col-span-2",
        isDragging && "opacity-40",
        isOver && "outline-2 outline-dashed outline-primary/70",
      )}
    >
      {isOver && (
        <span
          aria-hidden
          className="absolute inset-x-0 -top-1.5 z-20 h-1 rounded bg-primary"
        />
      )}
      {children}
      {resizable && (
        <button
          type="button"
          onClick={onToggleSpan}
          title={span === 1 ? "Widen to full width" : "Shrink to half width"}
          aria-label={span === 1 ? `Widen widget ${id}` : `Shrink widget ${id}`}
          className="absolute right-8 top-1 z-20 rounded p-1 text-muted-foreground opacity-0 transition-opacity hover:bg-muted hover:text-foreground focus-visible:opacity-100 group-hover:opacity-100"
        >
          {span === 1 ? (
            <Maximize2Icon className="size-4" />
          ) : (
            <Minimize2Icon className="size-4" />
          )}
        </button>
      )}
      <button
        type="button"
        ref={setActivatorNodeRef}
        {...attributes}
        {...listeners}
        aria-label={`Drag widget ${id}`}
        className="absolute right-1 top-1 z-20 cursor-grab rounded p-1 text-muted-foreground opacity-0 transition-opacity hover:bg-muted hover:text-foreground focus-visible:opacity-100 group-hover:opacity-100 active:cursor-grabbing"
      >
        <GripVerticalIcon className="size-4" />
      </button>
    </div>
  );
}

function StaticWidget({ span, children }: { span: 1 | 2; children: ReactNode }) {
  return (
    <div className={cn("flex min-w-0 [&>*]:flex-1 [&>*]:min-w-0", span === 2 && "lg:col-span-2")}>
      {children}
    </div>
  );
}

function MainZone({
  layout,
  nodesById,
  editable,
  onToggleSpan,
}: {
  layout: DashboardLayout;
  nodesById: Map<DashboardWidgetId, ReactNode>;
  editable: boolean;
  onToggleSpan?: (id: DashboardWidgetId) => void;
}) {
  const { setNodeRef, isOver } = useDroppable({ id: ZONE_MAIN });
  const items = layout.main;

  const content = editable ? (
    <SortableContext items={items} strategy={rectSortingStrategy}>
      {items.map((id) => (
        <SortableWidget
          key={id}
          id={id}
          span={effectiveSpan(layout, id)}
          animate={false}
          resizable
          onToggleSpan={() => onToggleSpan?.(id)}
        >
          {nodesById.get(id) ?? null}
        </SortableWidget>
      ))}
    </SortableContext>
  ) : (
    items.map((id) => (
      <StaticWidget key={id} span={effectiveSpan(layout, id)}>
        {nodesById.get(id) ?? null}
      </StaticWidget>
    ))
  );

  return (
    <div
      ref={editable ? setNodeRef : undefined}
      aria-label="Main widgets"
      className={cn(
        "grid min-w-0 grid-cols-1 gap-4 lg:grid-cols-2",
        editable && "rounded-lg",
        editable && isOver && "ring-1 ring-primary/50",
      )}
    >
      {content}
    </div>
  );
}

function SidebarZone({
  layout,
  nodesById,
  editable,
  animate,
}: {
  layout: DashboardLayout;
  nodesById: Map<DashboardWidgetId, ReactNode>;
  editable: boolean;
  animate: boolean;
}) {
  const { setNodeRef, isOver } = useDroppable({ id: ZONE_SIDEBAR });
  const items = layout.sidebar;

  const content = editable ? (
    <SortableContext items={items} strategy={verticalListSortingStrategy}>
      {items.map((id) => (
        <SortableWidget
          key={id}
          id={id}
          span={1}
          animate={animate}
          resizable={false}
          onToggleSpan={() => undefined}
        >
          {nodesById.get(id) ?? null}
        </SortableWidget>
      ))}
    </SortableContext>
  ) : (
    items.map((id) => (
      <StaticWidget key={id} span={1}>
        {nodesById.get(id) ?? null}
      </StaticWidget>
    ))
  );

  return (
    <div
      ref={editable ? setNodeRef : undefined}
      aria-label="Sidebar widgets"
      className={cn(
        "flex min-w-0 flex-col gap-4",
        editable && "rounded-lg",
        editable && isOver && "ring-1 ring-primary/50",
      )}
    >
      {content}
    </div>
  );
}

export function DashboardGrid({ layout: initialLayout, widgets }: DashboardGridProps) {
  const [layout, setLayout] = useState<DashboardLayout>(initialLayout);
  const [editing, setEditing] = useState(false);
  const [saving, setSaving] = useState(false);
  const [activeDrag, setActiveDrag] = useState<{ id: string; width: number } | null>(null);
  const layoutRef = useRef(initialLayout);
  layoutRef.current = layout;

  const nodesById = useMemo(
    () => new Map(widgets.map((widget) => [widget.id, widget.node])),
    [widgets],
  );

  const sensors = useSensors(
    useSensor(PointerSensor, { activationConstraint: { distance: 6 } }),
    useSensor(KeyboardSensor),
  );

  const sidebarAnimate =
    !activeDrag || findZone(layout, activeDrag.id) === "sidebar";

  function commitLayout(next: DashboardLayout) {
    layoutRef.current = next;
    setLayout(next);
    setSaving(true);
    void saveDashboardLayout(next)
      .then((result) => {
        if (!result.success) {
          toast.error(result.error ?? "Could not save your dashboard layout.");
        }
      })
      .catch((error: unknown) => {
        toast.error(
          error instanceof Error ? error.message : "Could not save your dashboard layout.",
        );
      })
      .finally(() => setSaving(false));
  }

  function handleDragStart(event: DragStartEvent) {
    setActiveDrag({
      id: String(event.active.id),
      width: event.active.rect.current.initial?.width ?? 288,
    });
  }

  function handleDragEnd(event: DragEndEvent) {
    setActiveDrag(null);
    const { active, over } = event;
    if (!over || active.id === over.id) return;
    const next = placementFor(layoutRef.current, String(active.id), String(over.id));
    if (!next) return;
    commitLayout(next);
  }

  function handleDragCancel() {
    setActiveDrag(null);
  }

  function toggleSpan(id: DashboardWidgetId) {
    const current = layoutRef.current;
    const spans = { ...(current.spans ?? {}) };
    spans[id] = effectiveSpan(current, id) === 1 ? 2 : 1;
    commitLayout({ ...current, spans });
  }

  function resetLayout() {
    commitLayout(DEFAULT_DASHBOARD_LAYOUT);
  }

  return (
    <div className="flex flex-col gap-4">
      <div className="flex flex-wrap items-center justify-end gap-2">
        {editing && (
          <>
            {saving && (
              <span aria-live="polite" className="text-xs text-muted-foreground">
                Saving...
              </span>
            )}
            <Button variant="ghost" size="sm" onClick={resetLayout}>
              <RotateCcwIcon data-icon="inline-start" />
              Reset layout
            </Button>
          </>
        )}
        <Button
          variant={editing ? "default" : "outline"}
          size="sm"
          onClick={() => setEditing((value) => !value)}
        >
          {editing ? (
            <>
              <CheckIcon data-icon="inline-start" />
              Done
            </>
          ) : (
            <>
              <LayoutGridIcon data-icon="inline-start" />
              Customize
            </>
          )}
        </Button>
      </div>

      {editing ? (
        <DndContext
          sensors={sensors}
          collisionDetection={closestCorners}
          onDragStart={handleDragStart}
          onDragEnd={handleDragEnd}
          onDragCancel={handleDragCancel}
        >
          <div className="grid grid-cols-1 gap-6 xl:grid-cols-3">
            <div className="flex min-w-0 flex-col gap-4 xl:col-span-2">
            <MainZone layout={layout} nodesById={nodesById} editable onToggleSpan={toggleSpan} />
            </div>
            <SidebarZone
              layout={layout}
              nodesById={nodesById}
              editable
              animate={sidebarAnimate}
            />
          </div>
          <DragOverlay>
            {activeDrag ? (
              <div
                style={{ width: activeDrag.width }}
                className="flex items-center gap-2 rounded-lg border bg-card px-3 py-2.5 shadow-lg"
              >
                <GripVerticalIcon className="size-4 shrink-0 text-muted-foreground" />
                <span className="truncate text-sm font-medium">
                  {WIDGET_LABELS[activeDrag.id as DashboardWidgetId]}
                </span>
              </div>
            ) : null}
          </DragOverlay>
        </DndContext>
      ) : (
        <div className="grid grid-cols-1 gap-6 xl:grid-cols-3">
          <div className="flex min-w-0 flex-col gap-4 xl:col-span-2">
            <MainZone layout={layout} nodesById={nodesById} editable={false} />
          </div>
          <SidebarZone
            layout={layout}
            nodesById={nodesById}
            editable={false}
            animate={false}
          />
        </div>
      )}

      {editing && (
        <p className="text-xs text-muted-foreground">
          Drag cards by the handle to rearrange. Changes save automatically.
        </p>
      )}
    </div>
  );
}