source: imaps-frontend/node_modules/clean-css/lib/optimizer/level-2/merge-media-queries.js

var canReorder = require('./reorderable').canReorder;
var canReorderSingle = require('./reorderable').canReorderSingle;
var extractProperties = require('./extract-properties');
var rulesOverlap = require('./rules-overlap');

var serializeRules = require('../../writer/one-time').rules;
var OptimizationLevel = require('../../options/optimization-level').OptimizationLevel;
var Token = require('../../tokenizer/token');

function mergeMediaQueries(tokens, context) {
  var mergeSemantically = context.options.level[OptimizationLevel.Two].mergeSemantically;
  var specificityCache = context.cache.specificity;
  var candidates = {};
  var reduced = [];

  for (var i = tokens.length - 1; i >= 0; i--) {
    var token = tokens[i];
    if (token[0] != Token.NESTED_BLOCK) {
      continue;
    }

    var key = serializeRules(token[1]);
    var candidate = candidates[key];
    if (!candidate) {
      candidate = [];
      candidates[key] = candidate;
    }

    candidate.push(i);
  }

  for (var name in candidates) {
    var positions = candidates[name];

    positionLoop:
    for (var j = positions.length - 1; j > 0; j--) {
      var positionOne = positions[j];
      var tokenOne = tokens[positionOne];
      var positionTwo = positions[j - 1];
      var tokenTwo = tokens[positionTwo];

      directionLoop:
      for (var direction = 1; direction >= -1; direction -= 2) {
        var topToBottom = direction == 1;
        var from = topToBottom ? positionOne + 1 : positionTwo - 1;
        var to = topToBottom ? positionTwo : positionOne;
        var delta = topToBottom ? 1 : -1;
        var source = topToBottom ? tokenOne : tokenTwo;
        var target = topToBottom ? tokenTwo : tokenOne;
        var movedProperties = extractProperties(source);

        while (from != to) {
          var traversedProperties = extractProperties(tokens[from]);
          from += delta;

          if (mergeSemantically
            && allSameRulePropertiesCanBeReordered(movedProperties, traversedProperties, specificityCache)
          ) {
            continue;
          }

          if (!canReorder(movedProperties, traversedProperties, specificityCache)) { continue directionLoop; }
        }

        target[2] = topToBottom
          ? source[2].concat(target[2])
          : target[2].concat(source[2]);
        source[2] = [];

        reduced.push(target);
        continue positionLoop;
      }
    }
  }

  return reduced;
}

function allSameRulePropertiesCanBeReordered(movedProperties, traversedProperties, specificityCache) {
  var movedProperty;
  var movedRule;
  var traversedProperty;
  var traversedRule;
  var i, l;
  var j, m;

  for (i = 0, l = movedProperties.length; i < l; i++) {
    movedProperty = movedProperties[i];
    movedRule = movedProperty[5];

    for (j = 0, m = traversedProperties.length; j < m; j++) {
      traversedProperty = traversedProperties[j];
      traversedRule = traversedProperty[5];

      if (rulesOverlap(movedRule, traversedRule, true)
        && !canReorderSingle(movedProperty, traversedProperty, specificityCache)) {
        return false;
      }
    }
  }

  return true;
}

module.exports = mergeMediaQueries;