Tension Stack

import type { PropsWithChildren } from "react";import type { StyleProp, ViewStyle } from "react-native";import Animated, {  Extrapolation,  interpolate,  type SharedValue,  useAnimatedStyle,} from "react-native-reanimated";type TensionCardProps = PropsWithChildren<{  className?: string;  depth: number;  moving?: boolean;  style?: StyleProp<ViewStyle>;  translateX: SharedValue<number>;  width: SharedValue<number>;}>;export function TensionCard({  children,  className,  depth,  moving = false,  style,  translateX,  width,}: TensionCardProps) {  const animatedStyle = useAnimatedStyle(() => {    const progress = Math.min(      Math.abs(translateX.get()) / Math.max(width.get(), 1),      1,    );    const restingScale = 1 - depth * 0.055;    const restingY = depth * 13;    if (depth === 0) {      if (!moving) {        return {          opacity: 1,          transform: [            { translateX: 0 },            { rotate: "0deg" },          ],        };      }      return {        opacity: 1,        transform: [          { translateX: translateX.get() },          {            rotate: `${interpolate(              translateX.get(),              [-Math.max(width.get(), 1), 0, Math.max(width.get(), 1)],              [-7, 0, 7],              Extrapolation.CLAMP,            )}deg`,          },        ],      };    }    return {      opacity: interpolate(        progress,        [0, 1],        [1 - depth * 0.16, 1 - (depth - 1) * 0.16],        Extrapolation.CLAMP,      ),      transform: [        {          translateY: interpolate(            progress,            [0, 1],            [restingY, Math.max(0, restingY - 13)],            Extrapolation.CLAMP,          ),        },        {          scale: interpolate(            progress,            [0, 1],            [restingScale, restingScale + 0.055],            Extrapolation.CLAMP,          ),        },      ],    };  });  return (    <Animated.View      className={className}      pointerEvents={depth === 0 ? "auto" : "none"}      style={[style, animatedStyle]}    >      {children}    </Animated.View>  );}

import type { ReactNode } from "react";export type TensionStackItem = {  accessibilityLabel?: string;  children: ReactNode;  id: string;};export type TensionStackItemProps = TensionStackItem;export type TensionStackBaseProps = {  accessibilityLabel?: string;  autoAdvanceInterval?: number;  defaultIndex?: number;  disabled?: boolean;  children: ReactNode;  index?: number;  loop?: boolean;  maxVisible?: number;  onDismiss?: (id: string, index: number) => void;  onIndexChange?: (index: number) => void;  threshold?: number;};

import {  Children,  isValidElement,} from "react";import { View } from "react-native";import { GestureDetector } from "react-native-gesture-handler";import type { SlotsToClasses } from "#shared/types/slots";import { TensionCard } from "../card";import type {  TensionStackBaseProps,  TensionStackItem,  TensionStackItemProps,} from "../types";import { useTensionStack } from "../use-tension-stack";import {  tensionStackVariants,  type TensionStackSlot,} from "./variants";export type TensionStackProps = TensionStackBaseProps & {  className?: string;  classNames?: SlotsToClasses<TensionStackSlot>;};function TensionStackItem({  children,}: TensionStackItemProps) {  return children;}function TensionStackRoot({  accessibilityLabel = "Swipe the top card to continue",  autoAdvanceInterval,  children,  className,  classNames,  defaultIndex,  disabled,  index,  loop,  maxVisible,  onDismiss,  onIndexChange,  threshold,}: TensionStackProps) {  const items = Children.toArray(children).flatMap<TensionStackItem>(    (child) =>      isValidElement<TensionStackItemProps>(child) &&      child.type === TensionStackItem        ? [child.props]        : [],  );  const {    activeIndex,    gesture,    movingItemId,    onLayout,    translateX,    visibleItems,    width,  } = useTensionStack({    autoAdvanceInterval,    defaultIndex,    disabled,    index,    items,    loop,    maxVisible,    onDismiss,    onIndexChange,    threshold,  });  const { card, root } = tensionStackVariants({ disabled });  return (    <View      accessibilityLabel={accessibilityLabel}      accessibilityRole="adjustable"      accessibilityValue={{        max: items.length,        min: items.length > 0 ? 1 : 0,        now: items.length > 0 ? activeIndex + 1 : 0,      }}      className={root({        className: [className, classNames?.root],      })}      onLayout={onLayout}    >      <GestureDetector gesture={gesture}>        <View className="absolute inset-0">          {visibleItems.map(({ depth, item }) => (            <TensionCard              key={item.id}              className={card({                className: classNames?.card,              })}              depth={depth}              moving={item.id === movingItemId}              translateX={translateX}              width={width}            >              {item.children}            </TensionCard>          ))}        </View>      </GestureDetector>    </View>  );}export const TensionStack = Object.assign(TensionStackRoot, {  Item: TensionStackItem,});

import { tv } from "tailwind-variants";export const tensionStackSlots = {  card: "absolute inset-0 overflow-hidden",  root: "relative h-full w-full",} as const;export type TensionStackSlot = keyof typeof tensionStackSlots;export const tensionStackVariants = tv({  slots: tensionStackSlots,  variants: {    disabled: {      true: {        root: "opacity-[0.45]",      },    },  },});

import {  useCallback,  useEffect,  useLayoutEffect,  useMemo,  useState,} from "react";import type { LayoutChangeEvent } from "react-native";import { Gesture } from "react-native-gesture-handler";import {  runOnJS,  useReducedMotion,  useSharedValue,  withSpring,  withTiming,} from "react-native-reanimated";import { TENSION_STACK_CONFIG } from "./config";import type {  TensionStackBaseProps,  TensionStackItem,} from "./types";type UseTensionStackProps = Omit<  TensionStackBaseProps,  "accessibilityLabel" | "children"> & {  items: readonly TensionStackItem[];};export function useTensionStack({  autoAdvanceInterval,  defaultIndex = 0,  disabled = false,  index,  items,  loop = false,  maxVisible = TENSION_STACK_CONFIG.maxVisible,  onDismiss,  onIndexChange,  threshold = TENSION_STACK_CONFIG.threshold,}: UseTensionStackProps) {  if (threshold <= 0 || threshold >= 1) {    throw new Error(      "TensionStack requires threshold to be between zero and one.",    );  }  if (maxVisible < 1) {    throw new Error("TensionStack requires maxVisible to be at least one.");  }  const isControlled = index !== undefined;  const [internalIndex, setInternalIndex] = useState(defaultIndex);  const [movingItemId, setMovingItemId] = useState(    items[index ?? defaultIndex]?.id,  );  const activeIndex = index ?? internalIndex;  const translateX = useSharedValue(0);  const width = useSharedValue(0);  const reducedMotion = useReducedMotion();  const commitDismiss = useCallback(    () => {      const item = items[activeIndex];      if (!item) {        return;      }      const nextIndex =        activeIndex === items.length - 1          ? loop            ? 0            : activeIndex          : activeIndex + 1;      onDismiss?.(item.id, activeIndex);      if (nextIndex !== activeIndex) {        if (!isControlled) {          setInternalIndex(nextIndex);        }        onIndexChange?.(nextIndex);      }    },    [      activeIndex,      isControlled,      items,      loop,      onDismiss,      onIndexChange,    ],  );  const canAdvance =    items.length > 0 &&    (activeIndex < items.length - 1 || loop);  useLayoutEffect(() => {    translateX.set(0);    setMovingItemId(items[activeIndex]?.id);  }, [activeIndex, items, translateX]);  const dismiss = useCallback(    (direction: -1 | 1 = 1) => {      if (disabled || !canAdvance) {        return;      }      const distance = Math.max(width.get(), 320) * 1.18;      translateX.set(        reducedMotion          ? direction * distance          : withTiming(              direction * distance,              { duration: TENSION_STACK_CONFIG.dismissDuration },              (finished) => {                if (finished) {                  runOnJS(commitDismiss)();                }              },            ),      );      if (reducedMotion) {        commitDismiss();      }    },    [      commitDismiss,      disabled,      canAdvance,      reducedMotion,      translateX,      width,    ],  );  useEffect(() => {    if (!autoAdvanceInterval || disabled || items.length < 2) {      return;    }    const timer = setInterval(() => {      dismiss(1);    }, autoAdvanceInterval);    return () => {      clearInterval(timer);    };  }, [autoAdvanceInterval, disabled, dismiss, items.length]);  const onLayout = useCallback(    (event: LayoutChangeEvent) => {      width.set(event.nativeEvent.layout.width);    },    [width],  );  const gesture = useMemo(    () =>      Gesture.Pan()        .enabled(!disabled && items.length > 0)        .minDistance(3)        .onUpdate((event) => {          const distance = event.translationX;          const boundary = width.get() * 0.55;          if (Math.abs(distance) <= boundary) {            translateX.set(distance);            return;          }          const overflow = Math.abs(distance) - boundary;          translateX.set(            Math.sign(distance) *              (boundary + overflow * TENSION_STACK_CONFIG.resistance),          );        })        .onEnd((event) => {          const stackWidth = width.get();          const projected =            translateX.get() + event.velocityX * 0.12;          const shouldDismiss =            Math.abs(projected) >= stackWidth * threshold ||            Math.abs(event.velocityX) >=              TENSION_STACK_CONFIG.velocityThreshold;          if (shouldDismiss && canAdvance) {            const direction = projected < 0 ? -1 : 1;            const distance = Math.max(stackWidth, 320) * 1.18;            translateX.set(              withTiming(                direction * distance,                { duration: TENSION_STACK_CONFIG.dismissDuration },                (finished) => {                  if (finished) {                    runOnJS(commitDismiss)();                  }                },              ),            );            return;          }          translateX.set(            withSpring(0, {              damping: 18,              mass: 0.72,              stiffness: 210,            }),          );        }),    [      commitDismiss,      canAdvance,      disabled,      items.length,      threshold,      translateX,      width,    ],  );  const visibleItems = Array.from(    {      length: Math.min(        loop ? items.length : items.length - activeIndex,        maxVisible,      ),    },    (_, depth) => {      const itemIndex = loop        ? (activeIndex + depth) % items.length        : activeIndex + depth;      return {        depth,        item: items[itemIndex] as TensionStackItem,      };    },  ).reverse();  return {    activeIndex,    gesture,    movingItemId,    onLayout,    translateX,    visibleItems,    width,  };}