this.recline = this.recline || {};
this.recline.Backend = this.recline.Backend || {};
this.recline.Backend.GDocs = this.recline.Backend.GDocs || {};

(function($, my) {
  my.__type__ = 'gdocs';

  // ## Google spreadsheet backend
  // 
  // Fetch data from a Google Docs spreadsheet.
  //
  // Dataset must have a url attribute pointing to the Gdocs or its JSON feed e.g.
  // <pre>
  // var dataset = new recline.Model.Dataset({
  //     url: 'https://docs.google.com/spreadsheet/ccc?key=0Aon3JiuouxLUdGlQVDJnbjZRSU1tUUJWOUZXRG53VkE#gid=0'
  //   },
  //   'gdocs'
  // );
  //
  // var dataset = new recline.Model.Dataset({
  //     url: 'https://spreadsheets.google.com/feeds/list/0Aon3JiuouxLUdDQwZE1JdV94cUd6NWtuZ0IyWTBjLWc/od6/public/values?alt=json'
  //   },
  //   'gdocs'
  // );
  // </pre>
  //
  // @return object with two attributes
  //
  // * fields: array of Field objects
  // * records: array of objects for each row
  my.fetch = function(dataset) {
    var dfd = $.Deferred(); 
    var url = my.getSpreadsheetAPIUrl(dataset.url);
    
    $.getJSON(url, function(d) {
      var result = my.parseData(d);
      var fields = _.map(result.fields, function(fieldId) {
        return {id: fieldId};
      });
      dfd.resolve({
        records: result.records,
        fields: fields,
        useMemoryStore: true
      });
    });

    return dfd.promise();
  };

  // ## parseData
  //
  // Parse data from Google Docs API into a reasonable form
  //
  // :options: (optional) optional argument dictionary:
  // columnsToUse: list of columns to use (specified by field names)
  // colTypes: dictionary (with column names as keys) specifying types (e.g. range, percent for use in conversion).
  // :return: tabular data object (hash with keys: field and data).
  // 
  // Issues: seems google docs return columns in rows in random order and not even sure whether consistent across rows.
  my.parseData = function(gdocsSpreadsheet, options) {
    var options  = options || {};
    var colTypes = options.colTypes || {};
    var results = {
      fields : [],
      records: []
    };
    var entries = gdocsSpreadsheet.feed.entry || [];
    var key;
    var colName;
    // percentage values (e.g. 23.3%)
    var rep = /^([\d\.\-]+)\%$/;

    for(key in entries[0]) {
      // it's barely possible it has inherited keys starting with 'gsx$'
      if(/^gsx/.test(key)) {
        colName = key.substr(4);
        results.fields.push(colName);
      }
    }

    // converts non numberical values that should be numerical (22.3%[string] -> 0.223[float])
    results.records = _.map(entries, function(entry) {
      var row = {};

      _.each(results.fields, function(col) {
        var _keyname = 'gsx$' + col;
        var value = entry[_keyname].$t;
        var num;
 
        // TODO cover this part of code with test
        // TODO use the regexp only once
        // if labelled as % and value contains %, convert
        if(colTypes[col] === 'percent' && rep.test(value)) {
          num   = rep.exec(value)[1];
          value = parseFloat(num) / 100;
        }

        row[col] = value;
      });

      return row;
    });

    return results;
  };

  // Convenience function to get GDocs JSON API Url from standard URL
  my.getSpreadsheetAPIUrl = function(url) {
    // https://docs.google.com/spreadsheet/ccc?key=XXXX#gid=YYY
    var regex = /.*spreadsheet\/ccc?.*key=([^#?&+]+).*gid=([\d]+).*/;
    var matches = url.match(regex);
    var key;
    var worksheet;
    
    if(!!matches) {
        key       = matches[1];
        // the gid in url is 0-based and feed url is 1-based
        worksheet = parseInt(matches[2]) + 1;
        url = 'https://spreadsheets.google.com/feeds/list/'+ key +'/'+ worksheet +'/public/values?alt=json';
    }
    return url;
  };
}(jQuery, this.recline.Backend.GDocs));