Date highlight script for Google Docs

gistfile1.js

function numToCol(c) {
  var r = '';
  if (c > 25) {
    r = String.fromCharCode('A'.charCodeAt(0) + parseInt(c / 26, 10) - 1);
  }
  r = r + String.fromCharCode('A'.charCodeAt(0) + parseInt(c % 26, 10));
  return r;
}

function getCellForDate_(d) {
  if (!d) d = new Date();
  // not a weekday? highlight nothing
  if (d.getDay() == 0 || d.getDay() > 5) {
    return '';
  }
  // E = 04-Jul = 0
  // F = 05-Jul = 1
  // G = 06-Jul = 2
  // H = 07-Jul = 3
  // I = 08-Jul = 4
  // J = [WEEKEND]
  // K = 11-Jul = 6
  // Q = 18-Jul = 12
  // W = 25-Jul = 18
  // ...

  // so... (E+ ((days since 04-Jul) - ((days since 04-Jul) % 7))) ?
  
  var d_ref = new Date(2011, 6, 4, 6, 0, 0);
  var d_now = new Date(d.getFullYear(), d.getMonth(), d.getDate(), 8, 0, 0);
  var days_since = (d_now.getTime() - d_ref.getTime()) / ( 24 * 3600 * 1000 );
  var col_offset = days_since - parseInt(days_since / 7, 10);
  var col = numToCol(4+col_offset);

  return col+'2';
}

function highlightTodayOnSheet(sheet) {
  var vals = sheet.getRange('E2:ZZ2').getValues();
  var colors = sheet.getRange('E2:ZZ2').getBackgroundColors();
  for (var i=0, l=vals[0].length; i<l; ++i) {
    colors[0][i] = vals[0][i] ? 'white' : '#C2D1F0';
  }
  sheet.getRange('E2:ZZ2').setBackgroundColors(colors);
  var today_cell = getCellForDate_();
  if (today_cell) {
    sheet.getRange(today_cell).setBackgroundColor('#ff0');
  }
  SpreadsheetApp.flush();
}

function highlightToday(e) {
  var spreadsheet = SpreadsheetApp.getActiveSpreadsheet();
  var sheets = spreadsheet.getSheets();
  // NB: skip sheet zero, as it's the example sheet
  for (var i=1, l=sheets.length; i < l; ++i) {
    highlightTodayOnSheet(sheets[i]);
  }
}