parse-css-classes.js

import fs from 'fs';
import path from 'path';
import postcss from 'postcss';
import getCustomPropertiesFromRoot from './get-custom-properties-from-root';

/* Get Custom Properties from CSS File
/* ========================================================================== */

async function getCustomPropertiesFromCSSFile(from) {
    const css = await readFile(from);
    const root = postcss.parse(css, { from });

    return await getCustomPropertiesFromRoot(root);
}

/* Get Custom Properties from Object
/* ========================================================================== */

function getCustomPropertiesFromObject(object) {
    const customProperties = Object.assign(
        {},
        Object(object).customProperties,
        Object(object)['custom-properties']
    );

    return customProperties;
}

/* Get Custom Properties from JSON file
/* ========================================================================== */

async function getCustomPropertiesFromJSONFile(from) {
    const object = await readJSON(from);

    return getCustomPropertiesFromObject(object);
}

/* Get Custom Properties from JS file
/* ========================================================================== */

async function getCustomPropertiesFromJSFile(from) {
    const object = await import(from);

    return getCustomPropertiesFromObject(object);
}

/* Get Custom Properties from Sources
/* ========================================================================== */

export default function getCustomPropertiesFromSources(sources) {
    return sources.map(source => {
        if (source instanceof Promise) {
            return source;
        } else if (source instanceof Function) {
            return source();
        }

        // read the source as an object
        const opts = source === Object(source) ? source : { from: String(source) };

        // skip objects with Custom Properties
        if (opts.customProperties || opts['custom-properties']) {
            return opts
        }

        // source pathname
        const from = path.resolve(String(opts.from || ''));

        // type of file being read from
        const type = (opts.type || path.extname(from).slice(1)).toLowerCase();

        return { type, from };
    }).reduce(async (customProperties, source) => {
        const { type, from } = await source;

        if (type === 'css') {
            return Object.assign(await customProperties, await getCustomPropertiesFromCSSFile(from));
        }

        if (type === 'js') {
            return Object.assign(await customProperties, await getCustomPropertiesFromJSFile(from));
        }

        if (type === 'json') {
            return Object.assign(await customProperties, await getCustomPropertiesFromJSONFile(from));
        }

        return Object.assign(await customProperties, await getCustomPropertiesFromObject(await source));
    }, {});
}

/* Promise-ified utilities
/* ========================================================================== */

const readFile = from => new Promise((resolve, reject) => {
    fs.readFile(from, 'utf8', (error, result) => {
        if (error) {
            reject(error);
        } else {
            resolve(result);
        }
    });
});

const readJSON = async from => JSON.parse(await readFile(from));