flow like the river

BACK_BACK/node_modules/csso/lib/restructure/prepare/index.js

@@ -0,0 +1,43 @@
+var resolveKeyword = require('css-tree').keyword;
+var walk = require('css-tree').walk;
+var generate = require('css-tree').generate;
+var createDeclarationIndexer = require('./createDeclarationIndexer');
+var processSelector = require('./processSelector');
+
+module.exports = function prepare(ast, options) {
+    var markDeclaration = createDeclarationIndexer();
+
+    walk(ast, {
+        visit: 'Rule',
+        enter: function processRule(node) {
+            node.block.children.each(markDeclaration);
+            processSelector(node, options.usage);
+        }
+    });
+
+    walk(ast, {
+        visit: 'Atrule',
+        enter: function(node) {
+            if (node.prelude) {
+                node.prelude.id = null; // pre-init property to avoid multiple hidden class for generate
+                node.prelude.id = generate(node.prelude);
+            }
+
+            // compare keyframe selectors by its values
+            // NOTE: still no clarification about problems with keyframes selector grouping (issue #197)
+            if (resolveKeyword(node.name).basename === 'keyframes') {
+                node.block.avoidRulesMerge = true;  /* probably we don't need to prevent those merges for @keyframes
+                                                       TODO: need to be checked */
+                node.block.children.each(function(rule) {
+                    rule.prelude.children.each(function(simpleselector) {
+                        simpleselector.compareMarker = simpleselector.id;
+                    });
+                });
+            }
+        }
+    });
+
+    return {
+        declaration: markDeclaration
+    };
+};