135 lines
3.2 KiB
JavaScript
135 lines
3.2 KiB
JavaScript
// @flow
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import * as React from "react";
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import styled from "styled-components";
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import breakpoint from "styled-components-breakpoint";
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import HelpText from "components/HelpText";
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import useWindowScrollPosition from "hooks/useWindowScrollPosition";
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const HEADING_OFFSET = 20;
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type Props = {
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headings: { title: string, level: number, id: string }[],
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};
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export default function Contents({ headings }: Props) {
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const [activeSlug, setActiveSlug] = React.useState();
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const position = useWindowScrollPosition({ throttle: 100 });
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React.useEffect(() => {
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for (let key = 0; key < headings.length; key++) {
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const heading = headings[key];
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const element = window.document.getElementById(
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decodeURIComponent(heading.id)
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);
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if (element) {
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const bounding = element.getBoundingClientRect();
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if (bounding.top > HEADING_OFFSET) {
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const last = headings[Math.max(0, key - 1)];
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setActiveSlug(last.id);
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return;
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}
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}
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}
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}, [position, headings]);
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// calculate the minimum heading level and adjust all the headings to make
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// that the top-most. This prevents the contents from being weirdly indented
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// if all of the headings in the document are level 3, for example.
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const minHeading = headings.reduce(
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(memo, heading) => (heading.level < memo ? heading.level : memo),
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Infinity
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);
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const headingAdjustment = minHeading - 1;
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return (
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<div>
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<Wrapper>
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<Heading>Contents</Heading>
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{headings.length ? (
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<List>
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{headings.map((heading) => (
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<ListItem
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key={heading.id}
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level={heading.level - headingAdjustment}
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active={activeSlug === heading.id}
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>
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<Link href={`#${heading.id}`}>{heading.title}</Link>
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</ListItem>
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))}
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</List>
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) : (
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<Empty>Headings you add to the document will appear here</Empty>
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)}
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</Wrapper>
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</div>
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);
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}
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const Wrapper = styled("div")`
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display: none;
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position: sticky;
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top: 80px;
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max-height: calc(100vh - 80px);
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box-shadow: 1px 0 0 ${(props) => props.theme.divider};
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margin-top: 40px;
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margin-right: 3.2em;
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min-height: 40px;
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overflow-y: auto;
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${breakpoint("desktopLarge")`
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margin-left: -16em;
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`};
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${breakpoint("tablet")`
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display: block;
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`};
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`;
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const Heading = styled("h3")`
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font-size: 11px;
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font-weight: 600;
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text-transform: uppercase;
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color: ${(props) => props.theme.sidebarText};
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letter-spacing: 0.04em;
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`;
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const Empty = styled(HelpText)`
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margin: 1em 0 4em;
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padding-right: 2em;
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min-width: 16em;
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width: 16em;
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font-size: 14px;
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`;
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const ListItem = styled("li")`
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margin-left: ${(props) => (props.level - 1) * 10}px;
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margin-bottom: 8px;
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padding-right: 2em;
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line-height: 1.3;
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border-right: 3px solid
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${(props) => (props.active ? props.theme.divider : "transparent")};
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a {
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color: ${(props) =>
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props.active ? props.theme.primary : props.theme.text};
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}
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`;
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const Link = styled("a")`
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color: ${(props) => props.theme.text};
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font-size: 14px;
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&:hover {
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color: ${(props) => props.theme.primary};
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}
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`;
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const List = styled("ol")`
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min-width: 14em;
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width: 14em;
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padding: 0;
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list-style: none;
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`;
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