<!DOCTYPE html>
<title>CSS Cascade Layers: Empty layer statements before import rules</title>
<link rel="author" href="mailto:xiaochengh@chromium.org">
<link rel="help" href="https://www.w3.org/TR/css-cascade-5/#layering">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>

<div id="target"></div>
<div id="reference" style="color: green"></div>

<script>
// In all test cases, the 'color' property value of #target should be green.

const testCases = [
  {
    title: 'length and item',
    style: `
      @layer first, second;
      @import url(data:text/css,);
      @layer second {
        #target { color: green; }
      }
      @layer first {
        #target { color: red; }
      }
    `,
    operations: function(sheet) {
      assert_equals(sheet.cssRules.length, 4);
      assert_equals(sheet.cssRules.item(0).cssText, '@layer first, second;');
      assert_equals(sheet.cssRules.item(1).cssText, `@import url("data:text/css,");`);
      assert_equals(sheet.cssRules.item(2).cssText,
                    '@layer second {\n  #target { color: green; }\n}');
      assert_equals(sheet.cssRules.item(3).cssText,
                    '@layer first {\n  #target { color: red; }\n}');
    }
  },
  {
    title: 'insertRule before imports',
    style: `
      @import url(data:text/css,);
      @layer second {
        #target { color: green; }
      }
      @layer first {
        #target { color: red; }
      }
    `,
    operations: function(sheet) {
      sheet.insertRule('@layer first, second', 0);
    }
  },
  {
    title: 'insertRule after imports',
    style: `
      @layer first, second;
      @import url(data:text/css,);
      @layer first {
        #target { color: red; }
      }
    `,
    operations: function(sheet) {
      sheet.insertRule('@layer second { #target { color: green; } }', 2);
    }
  },
  {
    title: 'insert other rules to pre-import layer statements fails',
    style: `
      @layer first, second;
      @import url(data:text/css,);
      @layer second {
        #target { color: green; }
      }
      @layer first {
        #target { color: red; }
      }
    `,
    operations: function(sheet) {
      assert_throws_dom('HierarchyRequestError',
                        () => sheet.insertRule('#target { color: red !important; }', 0));
      assert_throws_dom('HierarchyRequestError',
                        () => sheet.insertRule('#target { color: red !important; }', 1));
    }
  },
  {
    title: 'insert other rules before the first layer statement without imports',
    style: `
      @layer first, second;
      @layer second {
        #target { color: red !important; }
      }
    `,
    operations: function(sheet) {
      sheet.insertRule(`@layer first {
        #target { color: green !important; }
      }`, 0);
    }
  },
  {
    title: 'deleteRule before imports',
    style: `
      @layer second, first;
      @import url(data:text/css,);
      @layer first {
        #target { color: red; }
      }
      @layer second {
        #target { color: green; }
      }
    `,
    operations: function(sheet) {
      sheet.deleteRule(0);
    }
  },
  {
    title: 'deleteRule after imports',
    style: `
      @layer first, second;
      @import url(data:text/css,);
      @layer second {
        #target { color: green; }
      }
      @layer first {
        #target { color: red; }
      }
      #target {
        color: red;
      }
    `,
    operations: function(sheet) {
      sheet.deleteRule(4);
    }
  },
];

const target = document.getElementById('target');
const reference = document.getElementById('reference');

for (let testCase of testCases) {
  promise_test(async t => {
    let styleElement = document.createElement('style');
    styleElement.textContent = testCase.style;
    await new Promise(resolve => {
      styleElement.onload = resolve;
      styleElement.onerror = resolve;
      document.head.append(styleElement);
    });
    let sheet = styleElement.sheet;

    try {
      testCase.operations(sheet);
      assert_equals(getComputedStyle(target).color, getComputedStyle(reference).color);
    } finally {
      styleElement.remove();
    }
  }, testCase.title);
}
</script>
