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app_vue/node_modules/csso/lib/restructure/7-mergeRuleset.js

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+var walk = require('css-tree').walk;
+var utils = require('./utils');
+
+/*
+    At this step all rules has single simple selector. We try to join by equal
+    declaration blocks to first rule, e.g.
+
+    .a { color: red }
+    b { ... }
+    .b { color: red }
+    ->
+    .a, .b { color: red }
+    b { ... }
+*/
+
+function processRule(node, item, list) {
+    var selectors = node.prelude.children;
+    var declarations = node.block.children;
+    var nodeCompareMarker = selectors.first().compareMarker;
+    var skippedCompareMarkers = {};
+
+    list.nextUntil(item.next, function(next, nextItem) {
+        // skip non-ruleset node if safe
+        if (next.type !== 'Rule') {
+            return utils.unsafeToSkipNode.call(selectors, next);
+        }
+
+        if (node.pseudoSignature !== next.pseudoSignature) {
+            return true;
+        }
+
+        var nextFirstSelector = next.prelude.children.head;
+        var nextDeclarations = next.block.children;
+        var nextCompareMarker = nextFirstSelector.data.compareMarker;
+
+        // if next ruleset has same marked as one of skipped then stop joining
+        if (nextCompareMarker in skippedCompareMarkers) {
+            return true;
+        }
+
+        // try to join by selectors
+        if (selectors.head === selectors.tail) {
+            if (selectors.first().id === nextFirstSelector.data.id) {
+                declarations.appendList(nextDeclarations);
+                list.remove(nextItem);
+                return;
+            }
+        }
+
+        // try to join by properties
+        if (utils.isEqualDeclarations(declarations, nextDeclarations)) {
+            var nextStr = nextFirstSelector.data.id;
+
+            selectors.some(function(data, item) {
+                var curStr = data.id;
+
+                if (nextStr < curStr) {
+                    selectors.insert(nextFirstSelector, item);
+                    return true;
+                }
+
+                if (!item.next) {
+                    selectors.insert(nextFirstSelector);
+                    return true;
+                }
+            });
+
+            list.remove(nextItem);
+            return;
+        }
+
+        // go to next ruleset if current one can be skipped (has no equal specificity nor element selector)
+        if (nextCompareMarker === nodeCompareMarker) {
+            return true;
+        }
+
+        skippedCompareMarkers[nextCompareMarker] = true;
+    });
+}
+
+module.exports = function mergeRule(ast) {
+    walk(ast, {
+        visit: 'Rule',
+        enter: processRule
+    });
+};