Add draggable switch example

stories/3 - Examples/FormElements/Switch/Switch.module.css

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+$switch-border-radius: 50px;
+$switch-track-length: 50px;
+$switch-track-height: 32px;
+$switch-track-border: 2px;
+$switch-thumb-diameter: 28px;
+$switch-thumb-offset-left: 1px;
+$switch-thumb-offset-right: $switch-track-length - $switch-thumb-diameter -
+  $switch-thumb-offset-left - $switch-track-border;
+
+.Switch {
+  --color: rgba(70, 70, 70, 0.5);
+  --background-color: rgba(0, 0, 0, 0.02);
+  --cursor: grab;
+
+  position: relative;
+  appearance: none;
+  background-color: var(--background-color);
+  border: 0;
+  border-radius: $switch-border-radius;
+  cursor: pointer;
+  display: inline-block;
+  padding: 0;
+  margin: 0 1rem;
+  user-select: none;
+  box-sizing: border-box;
+  outline: none;
+
+  &:focus-visible {
+    box-shadow: 0 0 3px 2px #4c9ffe;
+  }
+
+  &::after {
+    border-radius: $switch-border-radius;
+  }
+
+  &.checked:not(.off):not(.disabled),
+  &.on {
+    --color: #2389ff;
+    --background-color: #56a1f8;
+  }
+
+  &.disabled {
+    --color: rgba(34, 33, 81, 0.5);
+  }
+
+  &.dragging {
+    --cursor: grabbing;
+    cursor: var(--cursor);
+  }
+
+  &:not(.disabled) .Thumb {
+    cursor: var(--cursor);
+  }
+
+  &:hover:not(.disabled, .dragging) .Track {
+    background-color: rgba(0, 0, 0, 0.05);
+  }
+}
+
+.Track {
+  display: block;
+  box-sizing: border-box;
+  border-radius: $switch-border-radius;
+  height: $switch-track-height;
+  width: $switch-track-length;
+  border: $switch-track-border solid var(--color);
+  transition: background-color 150ms ease;
+}
+
+.ThumbWrapper {
+  position: absolute;
+  top: $switch-track-border;
+  left: $switch-thumb-offset-left;
+  bottom: $switch-track-border;
+  right: $switch-track-border;
+}
+
+.Thumb {
+  position: absolute;
+  top: 0;
+  left: 0;
+  display: block;
+  box-sizing: border-box;
+  background-color: #fff;
+  border: 0.1em solid var(--color);
+  border-radius: 50%;
+  width: $switch-thumb-diameter;
+  height: $switch-thumb-diameter;
+  transition: transform 150ms ease;
+  transform: translate3d(var(--transform), 0, 0);
+
+  .checked & {
+    transform: translate3d(
+      calc($switch-thumb-offset-right + var(--transform)),
+      0,
+      0
+    );
+  }
+
+  .checked:not(.off) &,
+  .on & {
+    border-color: transparent;
+    transform: translateX($switch-thumb-offset-right);
+  }
+}
+
+.OnRegion,
+.OffRegion {
+  position: absolute;
+  top: 0;
+  bottom: 0;
+  width: 50%;
+  pointer-events: none;
+}
+
+.OnRegion {
+  right: 0;
+}
+
+.OffRegion {
+  left: 0;
+}
+
+.disabled {
+  cursor: not-allowed;
+  opacity: 0.5;
+}
+
+.Label {
+  display: block;
+  color: #666;
+  padding: 1rem;
+}

stories/3 - Examples/FormElements/Switch/Switch.story.tsx

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+import React, {ComponentProps, useState} from 'react';
+
+import {Switch} from './Switch';
+
+export default {
+  title: 'Examples/Form Elements/Switch',
+};
+
+type Props = Pick<ComponentProps<typeof Switch>, 'disabled' | 'label'>;
+
+function SwitchExample({disabled, label}: Props) {
+  const [checked, setChecked] = useState(false);
+
+  return (
+    <div style={{padding: 40}}>
+      <Switch
+        checked={checked}
+        label={label}
+        onChange={setChecked}
+        disabled={disabled}
+      />
+    </div>
+  );
+}
+
+export const BasicSetup = () => <SwitchExample label="Draggable switch" />;
+export const Disabled = () => (
+  <SwitchExample label="Disabled switch" disabled />
+);

stories/3 - Examples/FormElements/Switch/Switch.tsx

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+import React, {useState} from 'react';
+import {
+  DndContext,
+  DragEndEvent,
+  DragOverEvent,
+  getBoundingClientRect,
+  MeasuringConfiguration,
+  PointerSensor,
+  useSensor,
+  useSensors,
+} from '@dnd-kit/core';
+import {
+  restrictToHorizontalAxis,
+  restrictToParentElement,
+} from '@dnd-kit/modifiers';
+import classNames from 'classnames';
+
+import {State} from './constants';
+import {Thumb} from './Thumb';
+import {Track} from './Track';
+import styles from './Switch.module.css';
+
+export interface Props {
+  accessibilityLabel?: string;
+  disabled?: boolean;
+  id?: string;
+  label?: string;
+  checked: boolean;
+  onChange: (checked: boolean) => void;
+}
+
+const modifiers = [restrictToParentElement, restrictToHorizontalAxis];
+const measuring: MeasuringConfiguration = {
+  draggable: {
+    measure: getBoundingClientRect,
+  },
+};
+
+export function Switch({
+  accessibilityLabel = '',
+  label = '',
+  disabled = false,
+  id,
+  checked,
+  onChange,
+}: Props) {
+  const [overId, setOverId] = useState<string | null>(null);
+  const sensors = useSensors(
+    useSensor(PointerSensor, {
+      activationConstraint: {
+        distance: 2,
+      },
+    })
+  );
+
+  const markup = (
+    <>
+      {label ? (
+        <label className={styles.Label} htmlFor={id}>
+          {label}
+        </label>
+      ) : null}
+      <button
+        id={id}
+        type="button"
+        className={classNames(styles.Switch, {
+          [styles.checked]: checked,
+          [styles.dragging]: overId != null,
+          [styles.on]: overId === State.On,
+          [styles.off]: overId === State.Off,
+          [styles.disabled]: disabled,
+        })}
+        onClick={disabled ? undefined : handleClick}
+        aria-pressed={checked}
+        aria-label={accessibilityLabel}
+        disabled={disabled}
+      >
+        <Track />
+        <Thumb />
+      </button>
+    </>
+  );
+
+  return disabled ? (
+    markup
+  ) : (
+    <DndContext
+      autoScroll={false}
+      measuring={measuring}
+      modifiers={modifiers}
+      sensors={sensors}
+      onDragOver={handleDragOver}
+      onDragEnd={handleDragEnd}
+      onDragCancel={handleDragCancel}
+    >
+      {markup}
+    </DndContext>
+  );
+
+  function handleClick() {
+    onChange(!checked);
+  }
+
+  function handleDragOver({over}: DragOverEvent) {
+    setOverId(over?.id ?? null);
+  }
+
+  function handleDragEnd({over}: DragEndEvent) {
+    if (over) {
+      const checked = over.id === State.On;
+      onChange(checked);
+    }
+
+    setOverId(null);
+  }
+
+  function handleDragCancel() {
+    setOverId(null);
+  }
+}

stories/3 - Examples/FormElements/Switch/Thumb.tsx

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+import React from 'react';
+import {useDraggable} from '@dnd-kit/core';
+import classNames from 'classnames';
+
+import styles from './Switch.module.css';
+
+export function Thumb() {
+  const {isDragging, listeners, transform, setNodeRef} = useDraggable({
+    id: 'thumb',
+  });
+
+  return (
+    <span className={styles.ThumbWrapper} {...listeners}>
+      <span
+        ref={setNodeRef}
+        className={classNames(styles.Thumb, isDragging && styles.dragging)}
+        style={
+          {
+            '--transform': `${transform?.x ?? 0}px`,
+          } as React.CSSProperties
+        }
+      />
+    </span>
+  );
+}

stories/3 - Examples/FormElements/Switch/Track.tsx

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+import React from 'react';
+import {useDroppable} from '@dnd-kit/core';
+
+import {State} from './constants';
+import styles from './Switch.module.css';
+
+export function Track() {
+  const {setNodeRef: setOnRegionNodeRef} = useDroppable({
+    id: State.On,
+  });
+  const {setNodeRef: setOffRegionNodeRef} = useDroppable({
+    id: State.Off,
+  });
+
+  return (
+    <span className={styles.Track}>
+      <span ref={setOffRegionNodeRef} className={styles.OffRegion} />
+      <span ref={setOnRegionNodeRef} className={styles.OnRegion} />
+    </span>
+  );
+}

stories/3 - Examples/FormElements/Switch/constants.ts

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+export enum State {
+  On = 'on',
+  Off = 'off',
+}