Initial code.

.travis.yml

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+language: php
+php:
+    - "5.4"
+    - "5.3"
+    - "5.5"
+    - "5.6"
+    - "7.0"
+    - "nightly"
+    - hhvm
+script: phpunit .
+sudo: false
+

composer.json

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+{
+    "name": "jelle-s/cssoptimizer",
+    "description": "Optimizes & minifies css files or strings.",
+    "type": "library",
+    "require": {
+        "sabberworm/php-css-parser": "^8.1",
+        "nicmart/Tree": "^0.2.7",
+        "jelle-s/arraykeycombiner": "^1.0"
+    },
+    "license": "GPL-3.0+",
+    "authors": [
+        {
+            "name": "Jelle Sebreghts",
+            "email": "[email protected]"
+        }
+    ],
+    "minimum-stability": "stable",
+    "autoload": {
+      "psr-4": {"Jelle_S\\CssOptimizer\\": "src/"}
+    }
+}

example/example.php

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+<?php
+
+include_once '../vendor/autoload.php';
+$css = <<<EOT
+div {
+  display:block;
+  background: transparent;
+}
+div .black-with-border {
+  border: 1px solid black;
+  color: black;
+  font-weight: bold;
+  text-decoration: underline;
+  margin: 0;
+}
+
+div .black-with-border-and-margin {
+  border: 1px solid black;
+  color: black;
+  font-weight: bold;
+  text-decoration: underline;
+  margin: 5px 0;
+}
+
+h1 {
+  font-weight: bold;
+  text-decoration: underline;
+  padding: 5px;
+  color: #d3d3d3;
+  margin: 0;
+  text-align: left;
+}
+
+h2 {
+  font-weight: bold;
+  text-decoration: underline;
+  padding: 5px;
+  color: #d3d3d3;
+  margin: 0;
+  text-align: right;
+}
+
+h3 {
+  font-weight: bold;
+  text-decoration: underline;
+  padding: 5px;
+  color: #d3d3d3;
+  margin: 3px;
+  text-align: right;
+}
+
+@media only screen and (min-width:16.5em) {
+  div .black-with-border {
+    border: 1px solid black;
+    color: black;
+    font-weight: bold;
+    text-decoration: underline;
+    margin: 0;
+  }
+
+  div .black-with-border-and-margin {
+    border: 1px solid black;
+    color: black;
+    font-weight: bold;
+    text-decoration: underline;
+    margin: 5px 0;
+  }
+}
+
+@media only screen and (min-width:36em) {
+  div .black-with-border {
+    border: 1px solid black;
+    color: black;
+    font-weight: bold;
+    text-decoration: underline;
+    margin: 0;
+  }
+
+  div .black-with-border-and-margin {
+    border: 1px solid black;
+    color: black;
+    font-weight: bold;
+    text-decoration: underline;
+    margin: 5px 0;
+  }
+}
+EOT;
+$optimizer = new Jelle_S\CssOptimizer\CssOptimizer($css, 3);
+file_put_contents('style.min.css', $optimizer->renderMinifiedCSS());
+
+
+$optimizer = new Jelle_S\CssOptimizer\CssOptimizer($css, 3);
+file_put_contents('style.scss', $optimizer->renderSCSS());

example/style.scss

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+div{display:block;background:transparent none repeat 0% 0% scroll;.black-with-border{color:black;font-weight:bold;text-decoration:underline;margin:0;border:1px black;}.black-with-border-and-margin{color:black;font-weight:bold;text-decoration:underline;margin:5px 0;border:1px black;}}h1{font-weight:bold;text-decoration:underline;color:#d3d3d3;text-align:left;margin:0;padding:5px;}h2{font-weight:bold;text-decoration:underline;color:#d3d3d3;text-align:right;margin:0;padding:5px;}h3{font-weight:bold;text-decoration:underline;color:#d3d3d3;text-align:right;margin:3px;padding:5px;}@media only screen and (min-width:16.5em){div{.black-with-border{color:black;font-weight:bold;text-decoration:underline;margin:0;border:1px black;}.black-with-border-and-margin{color:black;font-weight:bold;text-decoration:underline;margin:5px 0;border:1px black;}}}@media only screen and (min-width:36em){div{.black-with-border{color:black;font-weight:bold;text-decoration:underline;margin:0;border:1px black;}.black-with-border-and-margin{color:black;font-weight:bold;text-decoration:underline;margin:5px 0;border:1px black;}}}

src/CssOptimizer.php

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+<?php
+
+namespace Jelle_S\CssOptimizer;
+
+use Jelle_S\CssOptimizer\Tree\CssNode;
+use Jelle_S\Util\Combiner\ArrayKeyCombiner;
+use Sabberworm\CSS\CSSList\CSSList;
+use Sabberworm\CSS\OutputFormat;
+use Sabberworm\CSS\Parser;
+use Sabberworm\CSS\Property\AtRule;
+use Sabberworm\CSS\RuleSet\AtRuleSet;
+use Sabberworm\CSS\RuleSet\DeclarationBlock;
+use Sabberworm\CSS\RuleSet\RuleSet;
+use SebastianBergmann\CodeCoverage\Exception;
+
+/**
+ * Optimize css by minifying and combining selectors.
+ *
+ * @author Jelle Sebreghts
+ */
+class CssOptimizer {
+
+  /**
+   * The css parser.
+   *
+   * @var \Sabberworm\CSS\Parser
+   */
+  protected $cssParser;
+
+  /**
+   * Selector tree.
+   *
+   * @var \Jelle_S\CssOptimizer\Tree\CssNode
+   */
+  protected $selectorTree;
+
+  /**
+   * The maximum number of combinations to try for finding intersections.
+   *
+   * @var int
+   */
+  protected $combinationLimit;
+
+  /**
+   * The threshold. The minimum size of the intersections to search for.
+   *
+   * @var int
+   */
+  protected $threshold;
+
+  /**
+   * Creates a CssOptimizer.
+   *
+   * @param string $css
+   *   The raw css or path to the css file to optimize.
+   * @param int $threshold
+   *   The threshold. The minimum size of the intersections to search for.
+   * @param int $combinationLimit
+   *   The maximum number of combinations to try for finding intersections.
+   */
+  public function __construct($css, $threshold = 5, $combinationLimit = NULL) {
+    $this->threshold = $threshold;
+    if (is_file($css)) {
+      $css = file_get_contents($css);
+    }
+    // Try to keep some sort of sane default based on the amount of data we get.
+    if (is_null($combinationLimit)) {
+      $combinationLimit = round(PHP_INT_MAX / pow((strlen($css) * 10) / $this->threshold, 3));
+    }
+    $this->combinationLimit = $combinationLimit;
+    $this->cssParser = new Parser($css);
+    $this->selectorTree = new CssNode();
+  }
+
+  /**
+   * Optimizes the given css using the contructor parameters.
+   */
+  protected function optimize() {
+    $this->buildSelectorTree();
+    $flattened = $this->asFlattenedArray();
+    $arrays_to_optimize = array();
+    foreach ($flattened as $key => $flat) {
+      if (is_array(reset($flat))) {
+        $arrays_to_optimize[$key] = $flat;
+      }
+      else {
+        $arrays_to_optimize['_main'][$key] = $flat;
+      }
+    }
+    $optimized_arrs = [];
+    foreach ($arrays_to_optimize as $key => $arrs) {
+      $optimized_arrs[$key] = $this->optimizeArrays($arrs);
+    }
+    if (isset($optimized_arrs['_main'])) {
+      $optimized_arrs += $optimized_arrs['_main'];
+      unset($optimized_arrs['_main']);
+    }
+    $css = '';
+    foreach ($optimized_arrs as $key => $arr) {
+      $css .= $key . '{';
+      foreach ($arr as $k => $a) {
+        if (is_array($a)) {
+          $css .= $k . '{';
+          foreach ($a as $prop => $val) {
+            $css .= $prop . ':' . $val . ';';
+          }
+          $css .= '}';
+        }
+        else {
+          $css .= $k . ':' . $a . ';';
+        }
+      }
+      $css .= '}';
+    }
+    $this->cssParser = new Parser($css);
+  }
+
+  /**
+   * Helper function to optimize array representing css.
+   *
+   * @param array $arrs
+   *   An array of arrays representing css blocks.
+   *
+   * @return array
+   *   The optimized arrays.
+   */
+  protected function optimizeArrays($arrs) {
+    $combiner = new ArrayKeyCombiner($arrs, $this->threshold, $this->combinationLimit);
+    return $combiner->combine();
+  }
+
+  /**
+   * Get the current css tree as a flattened array
+   *
+   * @return array
+   *   The flattened array.
+   */
+  protected function asFlattenedArray() {
+    return $this->selectorTree->asFlattenedArray();
+  }
+
+  /**
+   * Render the current css tree.
+   *
+   * @return string
+   *   The current css tree rendered as a css string.
+   */
+  public function renderMinifiedCSS() {
+    $this->optimize();
+    $doc = $this->cssParser->parse();
+    $doc->createShorthands();
+    return $doc->render(OutputFormat::createCompact());
+  }
+
+  /**
+   * Render the current css tree as SCSS.
+   *
+   * @return string
+   *   The current css tree rendered as a scss string.
+   */
+  public function renderSCSS() {
+    $this->buildSelectorTree();
+    return $this->selectorTree->renderSCSS();
+  }
+
+  /**
+   * Build the css tree for a list.
+   *
+   * @param \Sabberworm\CSS\CSSList\CSSList $list
+   *   The css list to create the tree for.
+   * @param \Jelle_S\CssOptimizer\Tree\CssNode $parent
+   *   The parent to attach the built tree to.
+   *
+   * @throws Exception
+   *   When we encounter an unsupported css element.
+   */
+  protected function buildSelectorTree(CSSList $list = NULL, CssNode $parent = NULL) {
+    if (is_null($list)) {
+      $list = $this->cssParser->parse();
+    }
+    if (is_null($parent)) {
+      $parent = $this->selectorTree;
+    }
+    foreach ($list->getContents() as $content) {
+      switch (TRUE) {
+        case $content instanceof CSSList:
+          if ($content instanceof AtRule) {
+            $child = $parent->find(["@{$content->atRuleName()} {$content->atRuleArgs()}"]);
+            $child->setBlock(TRUE);
+            $this->buildSelectorTree($content, $child);
+          }
+          else {
+            throw new Exception('Not supported');
+          }
+          break;
+        case $content instanceof RuleSet:
+          $this->addRuleSetToSelectorTree($content, $parent);
+          break;
+      }
+    }
+  }
+
+  /**
+   * Add a css rule set to the css tree.
+   *
+   * @param \Sabberworm\CSS\RuleSet\RuleSet $ruleset
+   *   The rule set to add.
+   * @param \Jelle_S\CssOptimizer\Tree\CssNode $parent
+   *   The parent to add it to.
+   *
+   * @throws \Exception
+   *   When we encounter an unsupported ruleset.
+   */
+  protected function addRuleSetToSelectorTree(RuleSet $ruleset, CssNode $parent) {
+    if ($ruleset instanceof AtRuleSet) {
+      $child = $parent->find(["@{$ruleset->atRuleName()} {$ruleset->atRuleArgs()}"]);
+      $child->setBlock(TRUE);
+      $child->addData($ruleset);
+    }
+    else if ($ruleset instanceof DeclarationBlock) {
+      $ruleset->expandShorthands();
+      foreach ($ruleset->getSelectors() as $selector) {
+        // Remove spaces around:
+        //   - child selector: '>'
+        //   - sibling selector: '~'
+        //   - adjacent selector: '+'
+        $selector = preg_replace("/\s*([\>\~\+])\s*/", "$1", (string) $selector);
+        $child = $parent->find(array_filter(explode(' ', $selector)));
+        $child->addData($ruleset);
+      }
+    }
+    else {
+      throw new Exception('Not supported');
+    }
+  }
+}