/**
 * Analyzes HTTP caching headers
 *
 * @see https://developers.google.com/speed/docs/best-practices/caching
 */

exports.version = '0.2.a';

exports.module = function(phantomas) {
    'use strict';
    
    var cacheControlRegExp = /max-age=(\d+)/;

    function getCachingTime(url, headers) {
        // false means "no caching"
        var ttl = false,
            headerName,
            now = new Date(),
            headerDate;

        for (headerName in headers) {
            var value = headers[headerName];

            switch (headerName.toLowerCase()) {
                // parse max-age=...
                //
                // max-age=2592000
                // public, max-age=300, must-revalidate
                case 'cache-control':
                    var matches = value.match(cacheControlRegExp);

                    if (matches) {
                        ttl = parseInt(matches[1], 10);
                    }
                    break;

                    // catch Expires and Pragma headers
                case 'expires':
                case 'pragma':
                    // and Varnish specific headers
                case 'x-pass-expires':
                case 'x-pass-cache-control':
                    phantomas.incrMetric('oldCachingHeaders'); // @desc number of responses with old, HTTP 1.0 caching headers (Expires and Pragma)
                    phantomas.addOffender('oldCachingHeaders', url + ' - ' + headerName + ': ' + value);
                    headerDate = Date.parse(value);
                    if (headerDate) ttl = Math.round((headerDate - now) / 1000);
                    break;
            }
        }

        //console.log(JSON.stringify(headers)); console.log("TTL: " + ttl + ' s');

        return ttl;
    }

    phantomas.setMetric('cachingNotSpecified'); // @desc number of responses with no caching header sent (no Cache-Control header)
    phantomas.setMetric('cachingTooShort'); // @desc number of responses with too short (less than a week) caching time
    phantomas.setMetric('cachingDisabled'); // @desc number of responses with caching disabled (max-age=0)

    phantomas.setMetric('oldCachingHeaders');

    phantomas.on('recv', function(entry, res) {
        var ttl = getCachingTime(entry.url, entry.headers);

        // static assets
        if (entry.isImage || entry.isJS || entry.isCSS) {
            if (ttl === false) {
                phantomas.incrMetric('cachingNotSpecified');
                phantomas.addOffender('cachingNotSpecified', entry.url);
            } else if (ttl <= 0) {
                phantomas.incrMetric('cachingDisabled');
                phantomas.addOffender('cachingDisabled', entry.url);
            } else if (ttl < 7 * 86400) {
                phantomas.incrMetric('cachingTooShort');
                phantomas.addOffender('cachingTooShort', entry.url + ' cached for ' + ttl + ' s');
            }
        }
    });
};