aymericbeaumet/metalsmith-redirect

const _ = require('lodash');
const normalize = require('./normalize');

module.exports = (files, options = {}) => {
    const getRedirectFrom = file =>
        _.get(file, options.frontmatter.redirectFrom || 'redirectFrom', null);
    const getRedirectTo = file =>
        _.get(file, options.frontmatter.redirectTo || 'redirectTo', null);

    return Object.entries(files).reduce((acc, [filepath, file]) => {
        const redirectFrom = getRedirectFrom(file);
        if (redirectFrom) {
            for (const source of _.castArray(redirectFrom)) {
                const normalizedDestination = normalize(filepath)
                    .relativeTo('/')
                    .get();
                const normalizedSource = normalize(source)
                    .appendHTMLIndexIfNeeded()
                    .ensureHTML(options)
                    .relativeTo(normalizedDestination)
                    .get();
                acc.push({normalizedSource, normalizedDestination});
            }
        }

        const redirectTo = getRedirectTo(file);
        if (redirectTo) {
            const normalizedSource = normalize(filepath)
                .appendHTMLIndexIfNeeded()
                .ensureHTML(options)
                .relativeTo('/')
                .get();
            const normalizedDestination = normalize(redirectTo)
                .relativeTo(normalizedSource)
                .get();
            acc.push({normalizedSource, normalizedDestination});
            delete files[filepath];
        }

        return acc;
    }, []);
};