Fake Draggable Sheet with Snapping

gistfile1.js

import React, { useRef, useState } from 'react';
import { Animated, FlatList, StyleSheet } from 'react-native';

import { Box, Button, Text, Touchable } from '@app/components';
import { Colors, Grid, Sizes } from '@app/utils/const/theme';
import { viewPort } from '@app/utils';

const initialPosition = viewPort.height.full - 300;

const MapSheet = ({
  children,
  debug,
}: {
  children: React.ReactElement;
  debug?: boolean;
}) => {
  const flatlistRef = useRef<FlatList>(null);
  const scrollOffsetY = useRef(new Animated.Value(0)).current;
  const [fullScreen, setFullscreen] = useState(false);

  const translateY = scrollOffsetY.interpolate({
    inputRange: [0, 250],
    outputRange: [initialPosition, 0],
    extrapolate: 'clamp',
  });

  const viewabilityConfig = useRef({ itemVisiblePercentThreshold: 75 }).current;

  const onViewableItemsChanged = useRef(({ viewableItems }) => {
    if (viewableItems.length > 0) {
      if (viewableItems?.[0].item === 2) setFullscreen(true);
      if (viewableItems?.[0].item === 1) setFullscreen(false); // Bugfix
    }
  }).current;

  const goFullScreen = () => {
    flatlistRef.current?.scrollToIndex({ index: 1, animated: true });
  };

  const returnToBeginning = () => {
    flatlistRef.current?.scrollToIndex({ index: 0, animated: true });
    setFullscreen(false);
  };

  const renderItem = ({ index }) => {
    return (
      <Touchable
        width="100%"
        height={viewPort.height.full - 300}
        onPress={goFullScreen}
        opacity={debug ? 0.5 : 0}
        backgroundColor={debug ? (index === 1 ? 'blue' : 'red') : 'transparent'}
        activeOpacity={0.5}
      />
    );
  };

  return (
    <Animated.View
      style={{
        flex: 1,
        backgroundColor: Colors.white,
        alignItems: 'center',
        transform: [{ translateY }],
      }}
    >
      <Box
        width={60}
        height={5}
        backgroundColor={Colors.gray400}
        borderRadius={100}
        marginTop={Sizes[3]}
      />
      {children}
      <Animated.FlatList
        ref={flatlistRef}
        data={[1, 2]}
        pointerEvents={fullScreen ? 'none' : 'auto'}
        renderItem={renderItem}
        scrollEventThrottle={16}
        decelerationRate="fast"
        snapToInterval={250}
        onViewableItemsChanged={onViewableItemsChanged}
        viewabilityConfig={viewabilityConfig}
        showsVerticalScrollIndicator={false}
        onScroll={Animated.event(
          [{ nativeEvent: { contentOffset: { y: scrollOffsetY } } }],
          { useNativeDriver: true }
        )}
        style={StyleSheet.absoluteFillObject}
      />
      <Button
        size="sm"
        position="absolute"
        bottom={Sizes[6]}
        onPress={returnToBeginning}
      >
        Map
      </Button>
    </Animated.View>
  );
};

export { MapSheet };