/* Reddit Scraper written by Amit Agarwal */
/* January 9, 2013 */

/* Replace LifeProTips with the Subreddit Name */
var REDDIT = 'LifeProTips';

function run() {
  deleteTriggers_();

  /* Fetch Reddit posts every 5 minutes to avoid hitting
     the reddit and Google Script quotas */
  ScriptApp.newTrigger('scrapReddit').timeBased().everyMinutes(5).create();
}

function scrapReddit() {
  // Process 20 Reddit posts in a batch
  var url = 'http://www.reddit.com/r/' + REDDIT + '/new.xml?limit=20' + getLastID_();

  // Reddit API returns the results in XML format
  var response = UrlFetchApp.fetch(url);
  var doc = XmlService.parse(response.getContentText());
  var entries = doc.getRootElement().getChildren('channel')[0].getChildren('item');

  var data = new Array();

  for (var i = 0; i < entries.length; i++) {
    /* Extract post date, title, description and link from Reddit */

    var date = entries[i].getChild('pubDate').getText();
    var title = entries[i].getChild('title').getText();
    var desc = entries[i].getChild('description').getText();
    var link = entries[i].getChild('link').getText();

    data[i] = new Array(date, title, desc, link);
  }

  if (data.length == 0) {
    /* There's no data so stop the background trigger */
    deleteTriggers_();
  } else {
    writeData_(data);
  }
}

/* Write the scrapped data in a batch to the
   Google Spreadsheet since this is more efficient */
function writeData_(data) {
  if (data.length === 0) {
    return;
  }

  var ss = SpreadsheetApp.getActiveSpreadsheet();
  var sheet = ss.getSheets()[0];
  var row = sheet.getLastRow();
  var col = sheet.getLastColumn();

  var range = sheet.getRange(row + 1, 1, data.length, 4);
  try {
    range.setValues(data);
  } catch (e) {
    Logger.log(e.toString());
  }
}

/* Use the ID of the last processed post from Reddit as token */
function getLastID_() {
  var ss = SpreadsheetApp.getActiveSpreadsheet();
  var sheet = ss.getSheets()[0];
  var row = sheet.getLastRow();
  var col = sheet.getLastColumn();

  var url = sheet.getRange(row, col).getValue().toString();
  var pattern = /.*comments\/([^\/]*).*/;
  var id = url.match(pattern);

  return id ? '&after=t3_' + id[1] : '';
}

/* Posts Extracted, Delete the Triggers */
function deleteTriggers_() {
  var triggers = ScriptApp.getProjectTriggers();
  for (var i = 0; i < triggers.length; i++) {
    ScriptApp.deleteTrigger(triggers[i]);
  }
}