const cssom = require('cssom');

/**
* Returns an array of the selectors.
*
* @license Sizzle CSS Selector Engine - MIT
* @param {String} selectorText from cssom
* @api public
*/

function extract(selectorText) {
    let attr = 0;
    const sels = [];
    let sel = '';
    let i;
    let c;
    const l = selectorText.length;

    for (i = 0; i < l; i++) {
        c = selectorText.charAt(i);

        if (attr) {
            if (c === '[' || c === '(') {
                attr--;
            }
            sel += c;
        } else if (c === ',') {
            sels.push(sel);
            sel = '';
        } else {
            if (c === '[' || c === '(') {
                attr++;
            }
            if (sel.length || (c !== ',' && c !== '\n' && c !== ' ')) {
                sel += c;
            }
        }
    }

    if (sel.length) {
        sels.push(sel);
    }

    return sels;
}

/**
 * Returns a parse tree for a CSS source.
 * If it encounters multiple selectors separated by a comma, it splits the
 * tree.
 *
 * @param {String} css source
 * @api public
 */

module.exports = css => {
    const rules = cssom.parse(css).cssRules || [];
    const ret = [];
    let i;
    const l = rules.length;
    let rule;
    let selectors;
    let ii;
    let ll;

    for (i = 0; i < l; i++) {
        if (rules[i].selectorText) { // media queries don't have selectorText
            rule = rules[i];
            selectors = extract(rule.selectorText);
            ll = selectors.length;

            for (ii = 0; ii < ll; ii++) {
                ret.push([ selectors[ii], rule.style ]);
            }
        }
    }

    return ret;
};