Image Compare

// Shared motion tokens. Easing curves mirror the CSS custom properties in
// globals.css; springs are the canonical physics used across components.
// Strong custom variants — defaults like `ease-in`/`ease-out` feel weak.

export const EASE_OUT = [0.16, 1, 0.3, 1] as const;
export const EASE_IN_OUT = [0.77, 0, 0.175, 1] as const;
export const EASE_DRAWER = [0.32, 0.72, 0, 1] as const;

/** CSS string form of EASE_OUT for inline style transitions. */
export const EASE_OUT_CSS = "cubic-bezier(0.16, 1, 0.3, 1)";

/** Press feedback on buttons and other tappable surfaces. */
export const SPRING_PRESS = {
  type: "spring",
  stiffness: 500,
  damping: 30,
  mass: 0.6,
} as const;

/** Content swaps — label/icon slots trading places inside a control. */
export const SPRING_SWAP = {
  type: "spring",
  stiffness: 460,
  damping: 30,
  mass: 0.55,
} as const;

/** Overlay panel entrances — modals and sheets summoned by pointer. */
export const SPRING_PANEL = {
  type: "spring",
  stiffness: 420,
  damping: 40,
  mass: 0.5,
} as const;

/** Shared-layout glides — pills, indicators and panels morphing between positions. */
export const SPRING_LAYOUT = {
  type: "spring",
  stiffness: 360,
  damping: 32,
  mass: 0.6,
} as const;

/** Cursor-follow physics for decorative mouse tracking (magnetic, tilt, dock). */
export const SPRING_MOUSE = {
  stiffness: 200,
  damping: 15,
  mass: 0.3,
} as const;

/** Dragged handles and fills (sliders) — critically damped `useSpring` config,
 * so the value follows the pointer butterily and never rebounds off an end. */
export const SPRING_GLIDE = {
  stiffness: 700,
  damping: 50,
  mass: 0.5,
} as const;

// Shared touch primitives. iOS and iPadOS run their own gestures on top of the
// page — the long-press selection callout and the selection it drags in with
// it — and they win: once the platform claims a touch it cancels ours
// mid-gesture, so a press-and-hold or a drag simply dies. Surfaces that own
// their gesture have to opt out.
//
// What the two classes below cover, precisely:
// - `-webkit-touch-callout: none` stops iOS's long-press callout. WebKit-only:
//   it is not a property other engines have, so it is inert everywhere else.
// - `user-select: none` stops the long-press selection on every engine,
//   Android included, and stops a drag from painting a selection under the
//   cursor. It is inherited, so it reaches every descendant — which is why the
//   two classes differ only in whether they apply it unconditionally.
// What neither covers:
// - Chrome for Android's long-press menu on a link or an image. No CSS
//   suppresses it; a gesture surface that wraps one needs its own
//   `onContextMenu` with `preventDefault()`.
// - The native drag of an `<img>` or `<a>` descendant. `-webkit-user-drag` is
//   not inherited and plain divs and buttons are not drag sources, so setting
//   it on the surface does nothing — the child itself needs `draggable={false}`.

/**
 * Classes for a surface that *is* the control: a thumb, a drum, a stage, a
 * handle, a hold button. Selection is suppressed on every input, because a
 * drag that highlights the control's own label is wrong on a mouse too.
 * Compose with `touch-none` when the surface also owns the scroll axis — leave
 * it off when the page must still scroll from there.
 */
export const TOUCH_GESTURE_CLASS = "select-none [-webkit-touch-callout:none]";

/**
 * The same opt-out for a gesture surface that wraps content the consumer owns:
 * a scroller, a context-menu trigger, a sheet header, a list row. Selection is
 * suppressed only where the platform runs its own press gestures — a coarse
 * pointer — so a mouse user can still select and copy that content. If the
 * gesture itself would paint a selection under the cursor, add `select-none`
 * for the duration of the gesture rather than reaching for
 * `TOUCH_GESTURE_CLASS`.
 *
 * `pointer: coarse` describes the *primary* pointer and nothing else, so a
 * hybrid machine reads it wrong in both directions: a tablet with a mouse
 * plugged in keeps touch as primary and loses mouse selection, and a laptop
 * with a touchscreen keeps the mouse as primary and leaves selection live
 * under a finger. No media query can answer per interaction — the query is
 * about the device, and the question is about the gesture in progress. The
 * default stays here because it is right on the machines that are one thing or
 * the other, and losing a selection is a nuisance; where the miss costs a
 * *gesture* instead, the surface pairs it with `holdSelection` on the press.
 */
export const TOUCH_GESTURE_CONTENT_CLASS =
  "[-webkit-touch-callout:none] pointer-coarse:select-none";

/**
 * Grow a small control's *hit area* to at least 44×44px (WCAG 2.5.5, Apple
 * HIG) on a coarse pointer, without changing what it looks like or the space
 * it takes in layout. An invisible `::after` box, centered on the control and
 * `max(100%, 2.75rem)` on each axis, catches the taps: a 32px icon button
 * reaches 6px past each edge, a wide 40px button only grows vertically, and a
 * control already 44px or larger is left as it is. Hit-testing a pseudo
 * element lands on its owner, so handlers, focus and `:active` all behave.
 *
 * Mouse and trackpad rendering is untouched — nothing here applies outside
 * `pointer: coarse`. Requirements on the element it goes on:
 * - It must be the containing block: add `relative` (and keep it mergeable, so
 *   a consumer's `absolute` still wins through `cn`).
 * - It must not clip itself (`overflow-hidden`), or the overhang is clipped
 *   away along with its hit area.
 * - It must render children: `<input>` and other void elements have no
 *   `::after`. Put it on the wrapper or label instead.
 * - It must not already use `::after` for something visible.
 *
 * Centered 44px means two 32px buttons with a 4px gap overlap by 8px; the
 * later one wins that strip, which still ends well short of the earlier
 * button's visual center. Below a ~32px pitch the later neighbour starts
 * eating into that center — use `TOUCH_TARGET_Y_CLASS` for such dense rows.
 *
 * The overhang is real geometry: inside a scroll container it counts as
 * scrollable overflow, so a control flush against a scroller's edge can add a
 * few pixels of scroll on touch screens. Give such a scroller a little padding
 * on that side.
 */
export const TOUCH_TARGET_CLASS =
  "pointer-coarse:after:absolute pointer-coarse:after:top-1/2 pointer-coarse:after:left-1/2 pointer-coarse:after:size-[max(100%,2.75rem)] pointer-coarse:after:-translate-x-1/2 pointer-coarse:after:-translate-y-1/2 pointer-coarse:after:content-['']";

/**
 * `TOUCH_TARGET_CLASS` on the vertical axis only, for controls packed tighter
 * than ~32px apart in a row (pagination dots, dense swatches), where growing
 * sideways would hand most of each control to its neighbour. Same rules.
 */
export const TOUCH_TARGET_Y_CLASS =
  "pointer-coarse:after:absolute pointer-coarse:after:inset-x-0 pointer-coarse:after:top-1/2 pointer-coarse:after:h-[max(100%,2.75rem)] pointer-coarse:after:-translate-y-1/2 pointer-coarse:after:content-['']";

/**
 * Suppress selection on `element` for as long as a gesture is running on it,
 * whatever the primary pointer of the machine happens to be. Returns the
 * release. Inline, so it wins over the class above and is gone again the
 * moment the gesture ends.
 *
 * For the press gestures a native selection would otherwise steal — a
 * long-press that opens a menu. Elsewhere prefer the classes: a surface that
 * takes selection away for the whole session is a surface whose text nobody
 * can copy.
 */
export function holdSelection(element: HTMLElement) {
  element.style.setProperty("user-select", "none");
  element.style.setProperty("-webkit-user-select", "none");
  return () => {
    element.style.removeProperty("user-select");
    element.style.removeProperty("-webkit-user-select");
  };
}

/**
 * Pointer capture, best effort. WebKit throws `NotFoundError` when the pointer
 * is already gone by the time the handler runs — routine on iOS, where the
 * system can claim the touch first — and an uncaught throw takes the rest of
 * the handler, the gesture included, down with it. Touch pointers carry
 * implicit capture anyway, so losing it is never fatal.
 */
export function capturePointer(element: Element, pointerId: number) {
  try {
    element.setPointerCapture(pointerId);
  } catch {
    // Pointer is no longer active — implicit capture still applies on touch.
  }
}

/** Release a capture taken with `capturePointer`, ignoring a stale pointer. */
export function releasePointer(element: Element, pointerId: number) {
  try {
    if (element.hasPointerCapture(pointerId)) {
      element.releasePointerCapture(pointerId);
    }
  } catch {
    // Capture was already dropped by the browser.
  }
}

/**
 * Whether this event came from a pointer that is *hovering*: not a touch, and
 * not currently pressed. Which input the user is holding right now is not
 * something a device capability can answer — a touchscreen laptop hovers and
 * taps, and iPadOS reports a fine hovering pointer for a finger — so both
 * paths stay live and each handler branches on the event it was given.
 *
 * A pen resting on the glass is making contact, not hovering: `buttons` is the
 * tell, and it sends a pen tap down the same route a finger takes.
 *
 * This answers what an *enter* asks. A leave is the other half of a pair and
 * has to be read against the enter that started it — `useHoverGesture` in
 * `lib/hooks/use-hover-gesture` does that, and hover surfaces should use it
 * rather than asking this question twice.
 */
export const isHoveringPointer = (event: {
  pointerType: string;
  buttons: number;
}) => event.pointerType !== "touch" && event.buttons === 0;

import { clsx, type ClassValue } from "clsx"
import { twMerge } from "tailwind-merge"

export function cn(...inputs: ClassValue[]) {
  return twMerge(clsx(inputs))
}

"use client";
// karaui.kamisama-v0.my.id/components/motion/image-compare

import { ChevronLeft, ChevronRight } from "lucide-react";
import {
  motion,
  useMotionTemplate,
  useMotionValue,
  useReducedMotion,
  useSpring,
  useTransform,
} from "motion/react";
import {
  type KeyboardEvent,
  type PointerEvent,
  type ReactNode,
  useCallback,
  useEffect,
  useRef,
  useState,
} from "react";

import { SPRING_GLIDE, SPRING_PRESS } from "@/lib/ease";
import {
  capturePointer,
  isHoveringPointer,
  releasePointer,
  TOUCH_GESTURE_CLASS,
} from "@/lib/touch";
import { cn } from "@/lib/utils";

export interface ImageCompareProps {
  /** Left / underneath layer. An image URL or any node. */
  before: ReactNode | string;
  /** Right / clipped top layer. An image URL or any node. */
  after: ReactNode | string;
  /** Alt text when `before` is a URL. */
  beforeAlt?: string;
  /** Alt text when `after` is a URL. */
  afterAlt?: string;
  /** Divider position in percent (controlled). */
  value?: number;
  defaultValue?: number;
  onValueChange?: (value: number) => void;
  /** Divider follows the pointer while hovering instead of needing a drag. */
  hover?: boolean;
  beforeLabel?: ReactNode;
  afterLabel?: ReactNode;
  showLabels?: boolean;
  "aria-label"?: string;
  className?: string;
}

const KEY_STEP = 1;
const KEY_STEP_LARGE = 10;

const clamp = (v: number) => Math.min(100, Math.max(0, v));

function Layer({ content, alt }: { content: ReactNode | string; alt?: string }) {
  if (typeof content === "string") {
    return (
      // biome-ignore lint/performance/noImgElement: keeps the component framework-agnostic and both layers pixel-aligned.
      <img
        src={content}
        alt={alt ?? ""}
        draggable={false}
        className="absolute inset-0 size-full object-cover"
      />
    );
  }
  return <div className="absolute inset-0 size-full">{content}</div>;
}

export function ImageCompare({
  before,
  after,
  beforeAlt,
  afterAlt,
  value,
  defaultValue = 50,
  onValueChange,
  hover = false,
  beforeLabel = "Before",
  afterLabel = "After",
  showLabels = true,
  "aria-label": ariaLabel = "Comparison divider",
  className,
}: ImageCompareProps) {
  const reduce = useReducedMotion();
  const stageRef = useRef<HTMLDivElement>(null);
  const handleRef = useRef<HTMLDivElement>(null);
  const [internal, setInternal] = useState(clamp(defaultValue));
  const controlled = value !== undefined;
  const percent = clamp(controlled ? value : internal);
  const [dragging, setDragging] = useState(false);

  const target = useMotionValue(percent);
  useEffect(() => {
    target.set(percent);
  }, [percent, target]);
  const smooth = useSpring(target, SPRING_GLIDE);
  const pos = reduce ? target : smooth;

  // Clip the top ("after") layer from the left edge up to the divider.
  const clipPath = useMotionTemplate`inset(0 0 0 ${pos}%)`;
  const left = useMotionTemplate`${pos}%`;
  // Chips fade as their side shrinks toward the edge.
  const beforeOpacity = useTransform(pos, [4, 18], [0, 1]);
  const afterOpacity = useTransform(pos, [82, 96], [1, 0]);

  const setValue = useCallback(
    (next: number) => {
      const v = Math.round(clamp(next) * 10) / 10;
      if (!controlled) setInternal(v);
      onValueChange?.(v);
    },
    [controlled, onValueChange],
  );

  const fromPointer = (clientX: number) => {
    const rect = stageRef.current?.getBoundingClientRect();
    if (!rect?.width) return;
    setValue(((clientX - rect.left) / rect.width) * 100);
  };

  const onPointerDown = (event: PointerEvent<HTMLDivElement>) => {
    if (event.pointerType === "mouse" && event.button !== 0) return;
    event.preventDefault();
    capturePointer(event.currentTarget, event.pointerId);
    handleRef.current?.focus({ preventScroll: true });
    setDragging(true);
    fromPointer(event.clientX);
  };

  const onPointerMove = (event: PointerEvent<HTMLDivElement>) => {
    if (dragging || (hover && isHoveringPointer(event))) {
      fromPointer(event.clientX);
    }
  };

  const endDrag = (event: PointerEvent<HTMLDivElement>) => {
    releasePointer(event.currentTarget, event.pointerId);
    setDragging(false);
  };

  const onKeyDown = (event: KeyboardEvent<HTMLDivElement>) => {
    const step = event.shiftKey ? KEY_STEP_LARGE : KEY_STEP;
    let next: number | null = null;
    switch (event.key) {
      case "ArrowLeft":
      case "ArrowDown":
        next = percent - step;
        break;
      case "ArrowRight":
      case "ArrowUp":
        next = percent + step;
        break;
      case "PageDown":
        next = percent - KEY_STEP_LARGE;
        break;
      case "PageUp":
        next = percent + KEY_STEP_LARGE;
        break;
      case "Home":
        next = 0;
        break;
      case "End":
        next = 100;
        break;
      default:
        return;
    }
    event.preventDefault();
    setValue(next);
  };

  return (
    <div
      ref={stageRef}
      data-dragging={dragging || undefined}
      onPointerDown={onPointerDown}
      onPointerMove={onPointerMove}
      onPointerUp={endDrag}
      onPointerCancel={endDrag}
      className={cn(
        "relative isolate aspect-video w-full touch-pan-y overflow-hidden rounded-2xl bg-muted",
        TOUCH_GESTURE_CLASS,
        hover ? "cursor-ew-resize" : "cursor-grab data-dragging:cursor-grabbing",
        className,
      )}
    >
      <Layer content={before} alt={beforeAlt} />
      <motion.div className="absolute inset-0" style={{ clipPath }}>
        <Layer content={after} alt={afterAlt} />
      </motion.div>

      {showLabels ? (
        <>
          <motion.span
            aria-hidden
            style={{ opacity: beforeOpacity }}
            className="pointer-events-none absolute top-3 left-3 rounded-full bg-black/55 px-2.5 py-1 text-[11px] font-medium text-white backdrop-blur-sm"
          >
            {beforeLabel}
          </motion.span>
          <motion.span
            aria-hidden
            style={{ opacity: afterOpacity }}
            className="pointer-events-none absolute top-3 right-3 rounded-full bg-black/55 px-2.5 py-1 text-[11px] font-medium text-white backdrop-blur-sm"
          >
            {afterLabel}
          </motion.span>
        </>
      ) : null}

      <motion.div
        aria-hidden
        className="pointer-events-none absolute inset-y-0 w-0.5 -translate-x-1/2 bg-white shadow-[0_0_0_1px_rgba(0,0,0,0.12)]"
        style={{ left }}
      />
      <motion.div
        ref={handleRef}
        role="slider"
        tabIndex={0}
        aria-label={ariaLabel}
        aria-orientation="horizontal"
        aria-valuemin={0}
        aria-valuemax={100}
        aria-valuenow={Math.round(percent)}
        aria-valuetext={`${Math.round(percent)}% before, ${Math.round(100 - percent)}% after`}
        onKeyDown={onKeyDown}
        style={{ left }}
        animate={{ scale: dragging && !reduce ? 1.08 : 1 }}
        transition={SPRING_PRESS}
        className={cn(
          "absolute top-1/2 grid size-10 -translate-x-1/2 -translate-y-1/2 grid-flow-col place-items-center rounded-full bg-white text-neutral-900 shadow-lg outline-none",
          "ring-offset-2 focus-visible:ring-2 focus-visible:ring-white/90",
        )}
      >
        <ChevronLeft aria-hidden className="-mr-1 size-4" />
        <ChevronRight aria-hidden className="-ml-1 size-4" />
      </motion.div>
    </div>
  );
}