let compatibilityStyles = null;

/**
 * Returns a list of stylesheets that target the editor canvas. A stylesheet is
 * considered targetting the editor a canvas if it contains the
 * `editor-styles-wrapper`, `wp-block`, or `wp-block-*` class selectors.
 *
 * Ideally, this hook should be removed in the future and styles should be added
 * explicitly as editor styles.
 */
export function getCompatibilityStyles() {
  if (compatibilityStyles) {
    return compatibilityStyles;
  }

  // Only memoize the result once on load, since these stylesheets should not
  // change.
  compatibilityStyles = Array.from(document.styleSheets).reduce((accumulator, styleSheet) => {
    try {
      // May fail for external styles.
      // eslint-disable-next-line no-unused-expressions
      styleSheet.cssRules;
    } catch (e) {
      return accumulator;
    }
    const {
      ownerNode,
      cssRules
    } = styleSheet;

    // Stylesheet is added by another stylesheet. See
    // https://developer.mozilla.org/en-US/docs/Web/API/StyleSheet/ownerNode#notes.
    if (ownerNode === null) {
      return accumulator;
    }
    if (!cssRules) {
      return accumulator;
    }

    // Don't try to add the reset styles, which were removed as a dependency
    // from `edit-blocks` for the iframe since we don't need to reset admin
    // styles.
    if (ownerNode.id === 'wp-reset-editor-styles-css') {
      return accumulator;
    }

    // Don't try to add styles without ID. Styles enqueued via the WP dependency system will always have IDs.
    if (!ownerNode.id) {
      return accumulator;
    }
    function matchFromRules(_cssRules) {
      return Array.from(_cssRules).find(({
        selectorText,
        conditionText,
        cssRules: __cssRules
      }) => {
        // If the rule is conditional then it will not have selector text.
        // Recurse into child CSS ruleset to determine selector eligibility.
        if (conditionText) {
          return matchFromRules(__cssRules);
        }
        return selectorText && (selectorText.includes('.editor-styles-wrapper') || selectorText.includes('.wp-block'));
      });
    }
    if (matchFromRules(cssRules)) {
      const isInline = ownerNode.tagName === 'STYLE';
      if (isInline) {
        // If the current target is inline,
        // it could be a dependency of an existing stylesheet.
        // Look for that dependency and add it BEFORE the current target.
        const mainStylesCssId = ownerNode.id.replace('-inline-css', '-css');
        const mainStylesElement = document.getElementById(mainStylesCssId);
        if (mainStylesElement) {
          accumulator.push(mainStylesElement.cloneNode(true));
        }
      }
      accumulator.push(ownerNode.cloneNode(true));
      if (!isInline) {
        // If the current target is not inline,
        // we still look for inline styles that could be relevant for the current target.
        // If they exist, add them AFTER the current target.
        const inlineStylesCssId = ownerNode.id.replace('-css', '-inline-css');
        const inlineStylesElement = document.getElementById(inlineStylesCssId);
        if (inlineStylesElement) {
          accumulator.push(inlineStylesElement.cloneNode(true));
        }
      }
    }
    return accumulator;
  }, []);
  return compatibilityStyles;
}
//# sourceMappingURL=get-compatibility-styles.js.map