text: var utils = require('./utils.js');
  var walkRules = require('../../utils/walk.js').rules;
  
  function processRuleset(node, item, list) {
      var selectors = node.selector.selectors;
      var declarations = node.block.declarations;
  
      list.prevUntil(item.prev, function(prev) {
          // skip non-ruleset node if safe
          if (prev.type !== 'Ruleset') {
              return utils.unsafeToSkipNode.call(selectors, prev);
          }
  
          var prevSelectors = prev.selector.selectors;
          var prevDeclarations = prev.block.declarations;
  
          // try to join rulesets with equal pseudo signature
          if (node.pseudoSignature === prev.pseudoSignature) {
              // try to join by selectors
              if (utils.isEqualLists(prevSelectors, selectors)) {
                  prevDeclarations.appendList(declarations);
                  list.remove(item);
                  return true;
              }
  
              // try to join by declarations
              if (utils.isEqualDeclarations(declarations, prevDeclarations)) {
                  utils.addSelectors(prevSelectors, selectors);
                  list.remove(item);
                  return true;
              }
          }
  
          // go to prev ruleset if has no selector similarities
          return utils.hasSimilarSelectors(selectors, prevSelectors);
      });
  };
  
  // NOTE: direction should be left to right, since rulesets merge to left
  // ruleset. When direction right to left unmerged rulesets may prevent lookup
  // TODO: remove initial merge
  module.exports = function initialMergeRuleset(ast) {
      walkRules(ast, function(node, item, list) {
          if (node.type === 'Ruleset') {
              processRuleset(node, item, list);
          }
      });
  };
  