// Copyright 2022 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

/**
 * `document.activeElement` will not enter shadow roots to find the element
 * that has focus; use this method if you need to traverse through any shadow
 * roots to find the actual, specific focused element.
 */
export function deepActiveElement(doc: Document): Element|null {
  let activeElement: Element|null = doc.activeElement;
  while (activeElement?.shadowRoot?.activeElement) {
    activeElement = activeElement.shadowRoot.activeElement;
  }
  return activeElement;
}

export function getEnclosingShadowRootForNode(node: Node): Node|null {
  let parentNode = node.parentNodeOrShadowHost();
  while (parentNode) {
    if (parentNode instanceof ShadowRoot) {
      return parentNode;
    }
    parentNode = parentNode.parentNodeOrShadowHost();
  }
  return null;
}

export function rangeOfWord(
    rootNode: Node, offset: number, stopCharacters: string, stayWithinNode: Node, direction?: string): Range {
  let startNode;
  let startOffset = 0;
  let endNode;
  let endOffset = 0;

  if (!stayWithinNode) {
    stayWithinNode = rootNode;
  }

  if (!direction || direction === 'backward' || direction === 'both') {
    let node: Node|null = rootNode;
    while (node) {
      if (node === stayWithinNode) {
        if (!startNode) {
          startNode = stayWithinNode;
        }
        break;
      }

      if (node.nodeType === Node.TEXT_NODE && node.nodeValue !== null) {
        const start = (node === rootNode ? (offset - 1) : (node.nodeValue.length - 1));
        for (let i = start; i >= 0; --i) {
          if (stopCharacters.indexOf(node.nodeValue[i]) !== -1) {
            startNode = node;
            startOffset = i + 1;
            break;
          }
        }
      }

      if (startNode) {
        break;
      }

      node = node.traversePreviousNode(stayWithinNode);
    }

    if (!startNode) {
      startNode = stayWithinNode;
      startOffset = 0;
    }
  } else {
    startNode = rootNode;
    startOffset = offset;
  }

  if (!direction || direction === 'forward' || direction === 'both') {
    let node: (Node|null)|Node = rootNode;
    while (node) {
      if (node === stayWithinNode) {
        if (!endNode) {
          endNode = stayWithinNode;
        }
        break;
      }

      if (node.nodeType === Node.TEXT_NODE && node.nodeValue !== null) {
        const start = (node === rootNode ? offset : 0);
        for (let i = start; i < node.nodeValue.length; ++i) {
          if (stopCharacters.indexOf(node.nodeValue[i]) !== -1) {
            endNode = node;
            endOffset = i;
            break;
          }
        }
      }

      if (endNode) {
        break;
      }

      node = node.traverseNextNode(stayWithinNode);
    }

    if (!endNode) {
      endNode = stayWithinNode;
      endOffset = stayWithinNode.nodeType === Node.TEXT_NODE ? stayWithinNode.nodeValue?.length || 0 :
                                                               stayWithinNode.childNodes.length;
    }
  } else {
    endNode = rootNode;
    endOffset = offset;
  }

  if (!rootNode.ownerDocument) {
    throw new Error('No `ownerDocument` found for rootNode');
  }
  const result = rootNode.ownerDocument.createRange();
  result.setStart(startNode, startOffset);
  result.setEnd(endNode, endOffset);

  return result;
}

/**
 * Appends the list of `styles` as individual `<style>` elements to the
 * given `node`.
 *
 * @param node the `Node` to append the `<style>` elements to.
 * @param styles an optional list of styles to append to the `node`.
 */
export function appendStyle(node: Node, ...styles: CSSInJS[]): void {
  for (const cssText of styles) {
    const style = (node.ownerDocument ?? document).createElement('style');
    style.textContent = cssText;
    node.appendChild(style);
  }
}