mattermost-mobile/app/hooks/header.ts

// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
// See LICENSE.txt for license information.

import React, {useCallback, useMemo, useState} from 'react';
import Animated, {runOnJS, scrollTo, useAnimatedRef, useAnimatedScrollHandler, useDerivedValue, useSharedValue, withTiming} from 'react-native-reanimated';
import {useSafeAreaInsets} from 'react-native-safe-area-context';

import ViewConstants from '@constants/view';
import {useIsTablet} from '@hooks/device';

import type {NativeScrollEvent} from 'react-native';

type HeaderScrollContext = {
    dragging?: boolean;
    momentum?: string;
    start?: number;
};

export const MAX_OVERSCROLL = 80;

export const useDefaultHeaderHeight = () => {
    const insets = useSafeAreaInsets();
    const isTablet = useIsTablet();

    let headerHeight = ViewConstants.DEFAULT_HEADER_HEIGHT;
    if (isTablet) {
        headerHeight = ViewConstants.TABLET_HEADER_HEIGHT;
    }
    return headerHeight + insets.top;
};

export const useLargeHeaderHeight = () => {
    let largeHeight = useDefaultHeaderHeight();
    largeHeight += ViewConstants.LARGE_HEADER_TITLE_HEIGHT;
    largeHeight += ViewConstants.SUBTITLE_HEIGHT;
    return largeHeight;
};

export const useHeaderHeight = () => {
    const defaultHeight = useDefaultHeaderHeight();
    const largeHeight = useLargeHeaderHeight();
    const headerOffset = largeHeight - defaultHeight;
    return useMemo(() => ({
        defaultHeight,
        largeHeight,
        headerOffset,
    }), [defaultHeight, headerOffset, largeHeight]);
};

export const useCollapsibleHeader = <T>(isLargeTitle: boolean, onSnap?: (offset: number) => void) => {
    const insets = useSafeAreaInsets();
    const animatedRef = useAnimatedRef<Animated.ScrollView>();
    const {largeHeight, defaultHeight, headerOffset} = useHeaderHeight();
    const scrollValue = useSharedValue(0);
    const [lockValue, setLockValue] = useState<number>(0);
    const autoScroll = useSharedValue(false);
    const snapping = useSharedValue(false);
    const scrollEnabled = useSharedValue(true);

    const headerHeight = useDerivedValue(() => {
        const value = -(scrollValue.value);
        const heightWithScroll = (isLargeTitle ? largeHeight : defaultHeight) + value;
        let height = Math.max(heightWithScroll, defaultHeight);
        if (value > insets.top) {
            height = Math.min(heightWithScroll, largeHeight + MAX_OVERSCROLL);
        }
        return height;
    });

    function snapIfNeeded(dir: string, offset: number) {
        'worklet';
        if (onSnap && !snapping.value) {
            snapping.value = true;
            if (dir === 'down' && offset < largeHeight) {
                runOnJS(onSnap)(0);
            } else if (dir === 'up' && offset < (defaultHeight)) {
                runOnJS(onSnap)(headerOffset);
            }
            snapping.value = Boolean(withTiming(0, {duration: 100}));
        }
    }

    const setAutoScroll = (enabled: boolean) => {
        autoScroll.value = enabled;
    };

    const onScroll = useAnimatedScrollHandler({
        onBeginDrag: (e: NativeScrollEvent, ctx: HeaderScrollContext) => {
            ctx.start = e.contentOffset.y;
            ctx.dragging = true;
        },
        onScroll: (e, ctx) => {
            if (!scrollEnabled.value) {
                scrollTo(animatedRef, 0, headerOffset, false);
                return;
            }

            if (ctx?.dragging || autoScroll.value || snapping.value) {
                scrollValue.value = e.contentOffset.y;
            } else {
                // here we want to ensure that the scroll position
                // always start at 0 if the user has not dragged
                // the scrollview manually
                scrollTo(animatedRef, 0, scrollValue.value, false);
            }
        },
        onEndDrag: (e, ctx) => {
            if (ctx?.start !== undefined) {
                const dir = e.contentOffset.y < ctx.start ? 'down' : 'up';
                const offset = Math.abs(e.contentOffset.y);
                snapIfNeeded(dir, offset);
            }
        },
        onMomentumBegin: (e, ctx) => {
            if (ctx) {
                ctx.momentum = e.contentOffset.y < (ctx.start || 0) ? 'down' : 'up';
            }
        },
        onMomentumEnd: (e, ctx) => {
            if (ctx) {
                ctx.start = undefined;
                ctx.dragging = false;
                if (ctx.momentum === 'down') {
                    const offset = Math.abs(e.contentOffset.y);

                    if (onSnap && offset < largeHeight) {
                        runOnJS(onSnap)(0);
                    }
                    ctx.momentum = undefined;
                }
            }
        },
    }, [insets, defaultHeight, largeHeight, animatedRef]);

    const hideHeader = useCallback((lock = false) => {
        if (lock) {
            // by disabling scroll, this prevent the scrollValue from being updated needlessly as observed in iOS simulators
            scrollEnabled.value = false;
            setLockValue(defaultHeight);
        }

        const offset = headerOffset;
        if (animatedRef?.current && Math.abs((scrollValue.value)) <= insets.top) {
            autoScroll.value = true;
            if ('scrollTo' in animatedRef.current) {
                animatedRef.current.scrollTo({y: offset, animated: true});
            } else if ('scrollToOffset' in animatedRef.current) {
                (animatedRef.current as any).scrollToOffset({
                    offset,
                    animated: true,
                });
            } else {
                // No scroll for section lists?
            }
        }
    }, [largeHeight, defaultHeight]);

    const unlock = useCallback(() => {
        scrollEnabled.value = true;
        setLockValue(0);
    }, []);

    return {
        defaultHeight,
        largeHeight,
        scrollPaddingTop: (isLargeTitle ? largeHeight : defaultHeight),
        scrollRef: animatedRef as unknown as React.RefObject<T>,
        scrollValue,
        onScroll,
        hideHeader,
        lockValue,
        unlock,
        headerHeight,
        headerOffset,
        scrollEnabled,
        setAutoScroll,
    };
};

export default useHeaderHeight;