;(function(win, lib) {

    var doc = win.document;

    var docEl = doc.documentElement;

    var metaEl = doc.querySelector('meta[name="viewport"]');

    var flexibleEl = doc.querySelector('meta[name="flexible"]');

    var dpr = 0;

    var scale = 0;

    var tid;

    var flexible = lib.flexible || (lib.flexible = {});

    if (metaEl) {

        console.warn('将根据已有的meta标签来设置缩放比例');

        var match = metaEl.getAttribute('content').match(/initial\-scale=([\d\.]+)/);

        if (match) {

            scale = parseFloat(match[1]);

            dpr = parseInt(1 / scale);

        }

    } else if (flexibleEl) {

        var content = flexibleEl.getAttribute('content');

        if (content) {

            var initialDpr = content.match(/initial\-dpr=([\d\.]+)/);

            var maximumDpr = content.match(/maximum\-dpr=([\d\.]+)/);

            if (initialDpr) {

                dpr = parseFloat(initialDpr[1]);

                scale = parseFloat((1 / dpr).toFixed(2));

            }

            if (maximumDpr) {

                dpr = parseFloat(maximumDpr[1]);

                scale = parseFloat((1 / dpr).toFixed(2));

            }

        }

    }

    if (!dpr && !scale) {

        var isAndroid = win.navigator.appVersion.match(/android/gi);

        var isIPhone = win.navigator.appVersion.match(/iphone/gi);

        var devicePixelRatio = win.devicePixelRatio;

        if (isIPhone) {

            // iOS下，对于2和3的屏，用2倍的方案，其余的用1倍方案

            if (devicePixelRatio >= 3 && (!dpr || dpr >= 3)) {

                dpr = 3;

            } else if (devicePixelRatio >= 2 && (!dpr || dpr >= 2)){

                dpr = 2;

            } else {

                dpr = 1;

            }

        } else {

            // 其他设备下，仍旧使用1倍的方案

            dpr = 1;

        }

        scale = 1 / dpr;

    }

    docEl.setAttribute('data-dpr', dpr);

    if (!metaEl) {

        metaEl = doc.createElement('meta');

        metaEl.setAttribute('name', 'viewport');

        metaEl.setAttribute('content', 'initial-scale=' + scale + ', maximum-scale=' + scale + ', minimum-scale=' + scale + ', user-scalable=no');

        if (docEl.firstElementChild) {

            docEl.firstElementChild.appendChild(metaEl);

        } else {

            var wrap = doc.createElement('div');

            wrap.appendChild(metaEl);

            doc.write(wrap.innerHTML);

        }

    }

    function refreshRem(){

        var width = docEl.getBoundingClientRect().width;

        if (width / dpr > 540) {

            width = 540 * dpr;

        }

        var rem = width / 10;

        docEl.style.fontSize = rem + 'px';

        flexible.rem = win.rem = rem;

    }

    win.addEventListener('resize', function() {

        clearTimeout(tid);

        tid = setTimeout(refreshRem, 300);

    }, false);

    win.addEventListener('pageshow', function(e) {

        if (e.persisted) {

            clearTimeout(tid);

            tid = setTimeout(refreshRem, 300);

        }

    }, false);

    if (doc.readyState === 'complete') {

        doc.body.style.fontSize = 12 * dpr + 'px';

    } else {

        doc.addEventListener('DOMContentLoaded', function(e) {

            doc.body.style.fontSize = 12 * dpr + 'px';

        }, false);

    }

    refreshRem();

    flexible.dpr = win.dpr = dpr;

    flexible.refreshRem = refreshRem;

    flexible.rem2px = function(d) {

        var val = parseFloat(d) * this.rem;

        if (typeof d === 'string' && d.match(/rem$/)) {

            val += 'px';

        }

        return val;

    }

    flexible.px2rem = function(d) {

        var val = parseFloat(d) / this.rem;

        if (typeof d === 'string' && d.match(/px$/)) {

            val += 'rem';

        }

        return val;

    }

})(window, window['lib'] || (window['lib'] = {}));