index.js

/*
Copyright (c) 2014, Yahoo! Inc. All rights reserved.
Copyrights licensed under the New BSD License.
See the accompanying LICENSE file for terms.
*/

'use strict';

exports.match = matchQuery;
exports.parse = parseQuery;

// -----------------------------------------------------------------------------

var RE_MEDIA_QUERY     = /^(?:(only|not)?\s*([_a-z][_a-z0-9-]*)|(\([^\)]+\)))(?:\s*and\s*(.*))?$/i,
    RE_MQ_EXPRESSION   = /^\(\s*([_a-z-][_a-z0-9-]*)\s*(?:\:\s*([^\)]+))?\s*\)$/,
    RE_MQ_FEATURE      = /^(?:(min|max)-)?(.+)/,
    RE_LENGTH_UNIT     = /(em|rem|px|cm|mm|in|pt|pc)?\s*$/,
    RE_RESOLUTION_UNIT = /(dpi|dpcm|dppx)?\s*$/;

function matchQuery(mediaQuery, values) {
    return parseQuery(mediaQuery).some(function (query) {
        var inverse = query.inverse;

        // Either the parsed or specified `type` is "all", or the types must be
        // equal for a match.
        var typeMatch = query.type === 'all' || values.type === query.type;

        // Quit early when `type` doesn't match, but take "not" into account.
        if ((typeMatch && inverse) || !(typeMatch || inverse)) {
            return false;
        }

        var expressionsMatch = query.expressions.every(function (expression) {
            var feature  = expression.feature,
                modifier = expression.modifier,
                expValue = expression.value,
                value    = values[feature];

            // Missing or falsy values don't match.
            if (!value) { return false; }

            switch (feature) {
                case 'orientation':
                case 'scan':
                    return value.toLowerCase() === expValue.toLowerCase();

                case 'width':
                case 'height':
                case 'device-width':
                case 'device-height':
                    expValue = toPx(expValue);
                    value    = toPx(value);
                    break;

                case 'resolution':
                    expValue = toDpi(expValue);
                    value    = toDpi(value);
                    break;

                case 'aspect-ratio':
                case 'device-aspect-ratio':
                case /* Deprecated */ 'device-pixel-ratio':
                    expValue = toDecimal(expValue);
                    value    = toDecimal(value);
                    break;

                case 'grid':
                case 'color':
                case 'color-index':
                case 'monochrome':
                    expValue = parseInt(expValue, 10) || 1;
                    value    = parseInt(value, 10) || 0;
                    break;
            }

            switch (modifier) {
                case 'min': return value >= expValue;
                case 'max': return value <= expValue;
                default   : return value === expValue;
            }
        });

        return (expressionsMatch && !inverse) || (!expressionsMatch && inverse);
    });
}

function parseQuery(mediaQuery) {
    return mediaQuery.split(',').map(function (query) {
        query = query.trim();

        var captures = query.match(RE_MEDIA_QUERY);

        // Media Query must be valid.
        if (!captures) {
            throw new SyntaxError('Invalid CSS media query: "' + query + '"');
        }

        var modifier    = captures[1],
            type        = captures[2],
            expressions = ((captures[3] || '') + (captures[4] || '')).trim(),
            parsed      = {};

        parsed.inverse = !!modifier && modifier.toLowerCase() === 'not';
        parsed.type    = type ? type.toLowerCase() : 'all';

        // Check for media query expressions.
        if (!expressions) {
            parsed.expressions = [];
            return parsed;
        }

        // Split expressions into a list.
        expressions = expressions.match(/\([^\)]+\)/g);

        // Media Query must be valid.
        if (!expressions) {
            throw new SyntaxError('Invalid CSS media query: "' + query + '"');
        }

        parsed.expressions = expressions.map(function (expression) {
            var captures = expression.match(RE_MQ_EXPRESSION);

            // Media Query must be valid.
            if (!captures) {
                throw new SyntaxError('Invalid CSS media query: "' + query + '"');
            }

            var feature = captures[1].toLowerCase().match(RE_MQ_FEATURE);

            return {
                modifier: feature[1],
                feature : feature[2],
                value   : captures[2]
            };
        });

        return parsed;
    });
}

// -- Utilities ----------------------------------------------------------------

function toDecimal(ratio) {
    var decimal = Number(ratio),
        numbers;

    if (!decimal) {
        numbers = ratio.match(/^(\d+)\s*\/\s*(\d+)$/);
        decimal = numbers[1] / numbers[2];
    }

    return decimal;
}

function toDpi(resolution) {
    var value = parseFloat(resolution),
        units = String(resolution).match(RE_RESOLUTION_UNIT)[1];

    switch (units) {
        case 'dpcm': return value / 2.54;
        case 'dppx': return value * 96;
        default    : return value;
    }
}

function toPx(length) {
    var value = parseFloat(length),
        units = String(length).match(RE_LENGTH_UNIT)[1];

    switch (units) {
        case 'em' : return value * 16;
        case 'rem': return value * 16;
        case 'cm' : return value * 96 / 2.54;
        case 'mm' : return value * 96 / 2.54 / 10;
        case 'in' : return value * 96;
        case 'pt' : return value * 72;
        case 'pc' : return value * 72 / 12;
        default   : return value;
    }
}