(function () {
    var canvas, gl, glRenderer, models,
        devices = [
            ['a7', '640x1136', ['iPhone 5', 'iPhone 5s']],
            ['a7', '1536x2048', ['iPad Air', 'iPad Mini 2', 'iPad Mini 3']],
            ['a8', '640x1136', ['iPod touch (6th gen)']],
            ['a8', '750x1334', ['iPhone 6']],
            ['a8', '1242x2208', ['iPhone 6 Plus']],
            ['a8', '1536x2048', ['iPad Air 2', 'iPad Mini 4']],
            ['a9', '640x1136', ['iPhone SE']],
            ['a9', '750x1334', ['iPhone 6s']],
            ['a9', '1242x2208', ['iPhone 6s Plus']],
            ['a9x', '1536x2048', ['iPad Pro (1st gen 9.7-inch)']],
            ['a9x', '2048x2732', ['iPad Pro (1st gen 12.9-inch)']],
            ['a10', '750x1334', ['iPhone 7']],
            ['a10', '1242x2208', ['iPhone 7 Plus']],
            ['a10x', '1668x2224', ['iPad Pro (2th gen 10.5-inch)']],
            ['a10x', '2048x2732', ['iPad Pro (2th gen 12.9-inch)']],
            ['a11', '750x1334', ['iPhone 8']],
            ['a11', '1242x2208', ['iPhone 8 Plus']],
            ['a11', '1125x2436', ['iPhone X']],
            ['a12', '828x1792', ['iPhone Xr']],
            ['a12', '1125x2436', ['iPhone Xs']],
            ['a12', '1242x2688', ['iPhone Xs Max']],
            ['a12x', '1668x2388', ['iPad Pro (3rd gen 11-inch)']],
            ['a12x', '2048x2732', ['iPad Pro (3rd gen 12.9-inch)']]
        ];

    function getCanvas() {
        if (canvas == null) {
            canvas = document.createElement('canvas');
        }

        return canvas;
    }

    function getGl() {
        if (gl == null) {
            gl = getCanvas().getContext('experimental-webgl');
        }

        return gl;
    }

    function getResolution() {
        var ratio = window.devicePixelRatio || 1;
        return (Math.min(screen.width, screen.height) * ratio)
            + 'x' + (Math.max(screen.width, screen.height) * ratio);
    }

    function getGlRenderer() {
        if (glRenderer == null) {
            debugInfo = getGl().getExtension('WEBGL_debug_renderer_info');
            glRenderer = debugInfo == null ? 'unknown' : getGl().getParameter(debugInfo.UNMASKED_RENDERER_WEBGL);
        }

        return glRenderer;
    }

    function getModels() {
        if (models == null) {
            var gpu = getGlRenderer(),
                matches = gpu.match(/^apple\s+([_a-z0-9-]+)\s+gpu$/i),
                res = getResolution();
            
            models = ['unknown'];

            if (matches) {
                for (var i = 0; i < devices.length; i ++) {
                    var device = devices[i];

                    if (matches[1].toLowerCase() == device[0]
                        && res == device[1]) {
                        models = device[2];
                        break;
                    }
                }
            }
        }

        return models;
    }

    if (window.MobileDevice == undefined) {
        window.MobileDevice = {};
    }

    window.MobileDevice.getGlRenderer = getGlRenderer;
    window.MobileDevice.getModels = getModels;
    window.MobileDevice.getResolution = getResolution;

    window.MobileDevice.is = function (match) {
        var currentModels = getModels();
        match = match.toLowerCase().replace(/\s+$/, '') + ' ';

        for (var i = 0; i < currentModels.length; i ++) {
            var model = currentModels[i].toLowerCase() + ' ';

            if (0 === model.indexOf(math)) {
                return true;
            }
        }

        return false;
    };
})();