subsequent-plugins.js

const fs = require('fs');
const path = require('path');
const postcss = require('postcss');
const rootPath = require('app-root-path').path;

class SubsequentPlugins {
    constructor() {
        this.config = {};
        this.updateConfig();
    }

    /**
     * (Re)init with current postcss config
     */
    _init() {
        this.allNames = this.config.plugins ? Object.keys(this.config.plugins) : [];
        this.subsequentNames = this.allNames.slice(this.allNames.indexOf('postcss-extract-media-query') + 1);
        this.subsequentPlugins = this.subsequentNames.map(name => ({
            name,
            mod: this.config.pluginsSrc && this.config.pluginsSrc[name] || require(name),
            opts: this.config.plugins[name]
        }));
    }

    /**
     * Updates the postcss config by resolving file path
     * or by using the config file object
     * 
     * @param {string|Object} file
     * @returns {Object}
     */
    updateConfig(file) {
        if (typeof file === 'object') {
            this.config = file;
            this._init();
            return this.config;
        }
        if (typeof file === 'string' && !path.isAbsolute(file)) {
            file = path.join(rootPath, file);
        }
        const filePath = file || path.join(rootPath, 'postcss.config.js');

        if (fs.existsSync(filePath)) {
            this.config = require(filePath);
        }
        this._init();
        return this.config;
    }

    /**
     * Apply all subsequent plugins to the (extracted) css
     * 
     * @param {string} css 
     * @param {string} filePath
     * @returns {string}
     */
    applyPlugins(css, filePath) {
        const plugins = this.subsequentPlugins.map(plugin => plugin.mod(plugin.opts));

        if (plugins.length) {
            return new Promise(resolve => {
                postcss(plugins)
                    .process(css, { from: filePath, to: filePath })
                    .then(result => {
                        resolve(result.css);
                    });
            });
        }
        return Promise.resolve(css);
    }
}

module.exports = SubsequentPlugins;