aubade/src/artisan/frontmatter/index.js

filesystem-based content processor

export function matter(raw, memo = {}) {
    if (!/[:\-\[\]|#]/gm.test(raw))
        return coerce(raw.trim());
    if (/^(".*"|'.*')$/.test(raw.trim()))
        return raw.trim().slice(1, -1);
    const PATTERN = /(^[^:\s]+):(?!\/)\r?\n?([\s\S]*?(?=^\S)|[\s\S]*$)/gm;
    let match;
    while ((match = PATTERN.exec(raw))) {
        const [, key, value] = match;
        const data = matter(outdent(value), memo[key]);
        if (Array.isArray(data) || typeof data !== 'object')
            memo[key] = data;
        else
            memo[key] = { ...memo[key], ...data };
    }
    if (Object.keys(memo).length)
        return memo;
    const cleaned = raw.replace(/#.*$/gm, '').trim();
    switch (cleaned[0]) {
        case '-': {
            const sequence = cleaned.split(/^- /gm).filter((v) => v);
            const tabbed = sequence.map((v) => v.replace(/\n( +)/g, (_, s) => '\n' + '\t'.repeat(s.length / 2)));
            // @ts-expect-error - `FrontMatter` is assignable to itself
            return tabbed.map((v) => matter(outdent(` ${v}`)));
        }
        case '[': {
            const pruned = cleaned.slice(1, -1);
            return pruned.split(',').map(coerce);
        }
        case '|': {
            return outdent(cleaned.slice(1).replace('\n', ''));
        }
        default: {
            return coerce(cleaned.trim());
        }
    }
}
function coerce(u) {
    const v = u.trim(); // argument can be passed as-is
    const map = { true: true, false: false, null: null };
    if (v in map)
        return map[v];
    // if (!Number.isNaN(Number(v))) return Number(v);
    return /^(".*"|'.*')$/.test(v) ? v.slice(1, -1) : v;
}
function outdent(input) {
    const lines = input.split(/\r?\n/).filter((l) => l.trim());
    const { length } = (/^\s*/.exec(lines[0]) || [''])[0];
    return lines.map((l) => l.slice(length)).join('\n');
}