aubade/src/transform/chain.js

markdown, orchestrated.

export function chain(items, options) {
    const { key = 'flank', group = () => 'default', sorter, breakpoint, transform = ({ slug, title }) => ({ slug, title }), finalize = (groups) => Object.values(groups).flat(), } = options;
    const groups = {};
    for (const item of items) {
        const key = group(item);
        if (key == null)
            continue;
        groups[key] = groups[key] || [];
        groups[key].push(item);
    }
    for (const name in groups) {
        sorter && groups[name].sort(sorter(name));
        groups[name] = process(groups[name]);
    }
    return finalize(groups);
    function process(array) {
        for (let idx = 0; idx < array.length; idx++) {
            const [back, next] = [array[idx - 1], array[idx + 1]];
            if (!back && !next)
                continue;
            array[idx][key] = array[idx][key] || {};
            if (back)
                array[idx][key].back = transform(back);
            if (breakpoint && breakpoint(next))
                return array;
            if (next)
                array[idx][key].next = transform(next);
        }
        return array;
    }
}