/**
 * Copyright 2019 Google Inc. All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

const {helper, assert, debugError} = require('./helper');
const path = require('path');

function createJSHandle(context, remoteObject) {
  const frame = context.frame();
  if (remoteObject.subtype === 'node' && frame) {
    const frameManager = frame._frameManager;
    return new ElementHandle(context, context._client, remoteObject, frameManager.page(), frameManager);
  }
  return new JSHandle(context, context._client, remoteObject);
}

class JSHandle {
  /**
   * @param {!Puppeteer.ExecutionContext} context
   * @param {!Puppeteer.CDPSession} client
   * @param {!Protocol.Runtime.RemoteObject} remoteObject
   */
  constructor(context, client, remoteObject) {
    this._context = context;
    this._client = client;
    this._remoteObject = remoteObject;
    this._disposed = false;
  }

  /**
   * @return {!Puppeteer.ExecutionContext}
   */
  executionContext() {
    return this._context;
  }

  /**
   * @param {string} propertyName
   * @return {!Promise<?JSHandle>}
   */
  /* async */ getProperty(propertyName) {return (fn => {
  const gen = fn.call(this);
  return new Promise((resolve, reject) => {
    function step(key, arg) {
      let info, value;
      try {
        info = gen[key](arg);
        value = info.value;
      } catch (error) {
        reject(error);
        return;
      }
      if (info.done) {
        resolve(value);
      } else {
        return Promise.resolve(value).then(
            value => {
              step('next', value);
            },
            err => {
              step('throw', err);
            });
      }
    }
    return step('next');
  });
})(function*(){
    const objectHandle = (yield this._context.evaluateHandle((object, propertyName) => {
      const result = {__proto__: null};
      result[propertyName] = object[propertyName];
      return result;
    }, this, propertyName));
    const properties = (yield objectHandle.getProperties());
    const result = properties.get(propertyName) || null;
    (yield objectHandle.dispose());
    return result;
  });}

  /**
   * @return {!Promise<!Map<string, !JSHandle>>}
   */
  /* async */ getProperties() {return (fn => {
  const gen = fn.call(this);
  return new Promise((resolve, reject) => {
    function step(key, arg) {
      let info, value;
      try {
        info = gen[key](arg);
        value = info.value;
      } catch (error) {
        reject(error);
        return;
      }
      if (info.done) {
        resolve(value);
      } else {
        return Promise.resolve(value).then(
            value => {
              step('next', value);
            },
            err => {
              step('throw', err);
            });
      }
    }
    return step('next');
  });
})(function*(){
    const response = (yield this._client.send('Runtime.getProperties', {
      objectId: this._remoteObject.objectId,
      ownProperties: true
    }));
    const result = new Map();
    for (const property of response.result) {
      if (!property.enumerable)
        continue;
      result.set(property.name, createJSHandle(this._context, property.value));
    }
    return result;
  });}

  /**
   * @return {!Promise<?Object>}
   */
  /* async */ jsonValue() {return (fn => {
  const gen = fn.call(this);
  return new Promise((resolve, reject) => {
    function step(key, arg) {
      let info, value;
      try {
        info = gen[key](arg);
        value = info.value;
      } catch (error) {
        reject(error);
        return;
      }
      if (info.done) {
        resolve(value);
      } else {
        return Promise.resolve(value).then(
            value => {
              step('next', value);
            },
            err => {
              step('throw', err);
            });
      }
    }
    return step('next');
  });
})(function*(){
    if (this._remoteObject.objectId) {
      const response = (yield this._client.send('Runtime.callFunctionOn', {
        functionDeclaration: 'function() { return this; }',
        objectId: this._remoteObject.objectId,
        returnByValue: true,
        awaitPromise: true,
      }));
      return helper.valueFromRemoteObject(response.result);
    }
    return helper.valueFromRemoteObject(this._remoteObject);
  });}

  /**
   * @return {?Puppeteer.ElementHandle}
   */
  asElement() {
    return null;
  }

  /* async */ dispose() {return (fn => {
  const gen = fn.call(this);
  return new Promise((resolve, reject) => {
    function step(key, arg) {
      let info, value;
      try {
        info = gen[key](arg);
        value = info.value;
      } catch (error) {
        reject(error);
        return;
      }
      if (info.done) {
        resolve(value);
      } else {
        return Promise.resolve(value).then(
            value => {
              step('next', value);
            },
            err => {
              step('throw', err);
            });
      }
    }
    return step('next');
  });
})(function*(){
    if (this._disposed)
      return;
    this._disposed = true;
    (yield helper.releaseObject(this._client, this._remoteObject));
  });}

  /**
   * @override
   * @return {string}
   */
  toString() {
    if (this._remoteObject.objectId) {
      const type =  this._remoteObject.subtype || this._remoteObject.type;
      return 'JSHandle@' + type;
    }
    return 'JSHandle:' + helper.valueFromRemoteObject(this._remoteObject);
  }
}

class ElementHandle extends JSHandle {
  /**
   * @param {!Puppeteer.ExecutionContext} context
   * @param {!Puppeteer.CDPSession} client
   * @param {!Protocol.Runtime.RemoteObject} remoteObject
   * @param {!Puppeteer.Page} page
   * @param {!Puppeteer.FrameManager} frameManager
   */
  constructor(context, client, remoteObject, page, frameManager) {
    super(context, client, remoteObject);
    this._client = client;
    this._remoteObject = remoteObject;
    this._page = page;
    this._frameManager = frameManager;
    this._disposed = false;
  }

  /**
   * @override
   * @return {?ElementHandle}
   */
  asElement() {
    return this;
  }

  /**
   * @return {!Promise<?Puppeteer.Frame>}
   */
  /* async */ contentFrame() {return (fn => {
  const gen = fn.call(this);
  return new Promise((resolve, reject) => {
    function step(key, arg) {
      let info, value;
      try {
        info = gen[key](arg);
        value = info.value;
      } catch (error) {
        reject(error);
        return;
      }
      if (info.done) {
        resolve(value);
      } else {
        return Promise.resolve(value).then(
            value => {
              step('next', value);
            },
            err => {
              step('throw', err);
            });
      }
    }
    return step('next');
  });
})(function*(){
    const nodeInfo = (yield this._client.send('DOM.describeNode', {
      objectId: this._remoteObject.objectId
    }));
    if (typeof nodeInfo.node.frameId !== 'string')
      return null;
    return this._frameManager.frame(nodeInfo.node.frameId);
  });}

  /* async */ _scrollIntoViewIfNeeded() {return (fn => {
  const gen = fn.call(this);
  return new Promise((resolve, reject) => {
    function step(key, arg) {
      let info, value;
      try {
        info = gen[key](arg);
        value = info.value;
      } catch (error) {
        reject(error);
        return;
      }
      if (info.done) {
        resolve(value);
      } else {
        return Promise.resolve(value).then(
            value => {
              step('next', value);
            },
            err => {
              step('throw', err);
            });
      }
    }
    return step('next');
  });
})(function*(){
    const error = (yield this.executionContext().evaluate(/* async */(element, pageJavascriptEnabled) => {return (fn => {
  const gen = fn.call(this);
  return new Promise((resolve, reject) => {
    function step(key, arg) {
      let info, value;
      try {
        info = gen[key](arg);
        value = info.value;
      } catch (error) {
        reject(error);
        return;
      }
      if (info.done) {
        resolve(value);
      } else {
        return Promise.resolve(value).then(
            value => {
              step('next', value);
            },
            err => {
              step('throw', err);
            });
      }
    }
    return step('next');
  });
})(function*(){
      if (!element.isConnected)
        return 'Node is detached from document';
      if (element.nodeType !== Node.ELEMENT_NODE)
        return 'Node is not of type HTMLElement';
      // force-scroll if page's javascript is disabled.
      if (!pageJavascriptEnabled) {
        element.scrollIntoView({block: 'center', inline: 'center', behavior: 'instant'});
        return false;
      }
      const visibleRatio = (yield new Promise(resolve => {
        const observer = new IntersectionObserver(entries => {
          resolve(entries[0].intersectionRatio);
          observer.disconnect();
        });
        observer.observe(element);
      }));
      if (visibleRatio !== 1.0)
        element.scrollIntoView({block: 'center', inline: 'center', behavior: 'instant'});
      return false;
    });}, this, this._page._javascriptEnabled));
    if (error)
      throw new Error(error);
  });}

  /**
   * @return {!Promise<!{x: number, y: number}>}
   */
  /* async */ _clickablePoint() {return (fn => {
  const gen = fn.call(this);
  return new Promise((resolve, reject) => {
    function step(key, arg) {
      let info, value;
      try {
        info = gen[key](arg);
        value = info.value;
      } catch (error) {
        reject(error);
        return;
      }
      if (info.done) {
        resolve(value);
      } else {
        return Promise.resolve(value).then(
            value => {
              step('next', value);
            },
            err => {
              step('throw', err);
            });
      }
    }
    return step('next');
  });
})(function*(){
    const result = (yield this._client.send('DOM.getContentQuads', {
      objectId: this._remoteObject.objectId
    }).catch(debugError));
    if (!result || !result.quads.length)
      throw new Error('Node is either not visible or not an HTMLElement');
    // Filter out quads that have too small area to click into.
    const quads = result.quads.map(quad => this._fromProtocolQuad(quad)).filter(quad => computeQuadArea(quad) > 1);
    if (!quads.length)
      throw new Error('Node is either not visible or not an HTMLElement');
    // Return the middle point of the first quad.
    const quad = quads[0];
    let x = 0;
    let y = 0;
    for (const point of quad) {
      x += point.x;
      y += point.y;
    }
    return {
      x: x / 4,
      y: y / 4
    };
  });}

  /**
   * @return {!Promise<void|Protocol.DOM.getBoxModelReturnValue>}
   */
  _getBoxModel() {
    return this._client.send('DOM.getBoxModel', {
      objectId: this._remoteObject.objectId
    }).catch(error => debugError(error));
  }

  /**
   * @param {!Array<number>} quad
   * @return {!Array<{x: number, y: number}>}
   */
  _fromProtocolQuad(quad) {
    return [
      {x: quad[0], y: quad[1]},
      {x: quad[2], y: quad[3]},
      {x: quad[4], y: quad[5]},
      {x: quad[6], y: quad[7]}
    ];
  }

  /* async */ hover() {return (fn => {
  const gen = fn.call(this);
  return new Promise((resolve, reject) => {
    function step(key, arg) {
      let info, value;
      try {
        info = gen[key](arg);
        value = info.value;
      } catch (error) {
        reject(error);
        return;
      }
      if (info.done) {
        resolve(value);
      } else {
        return Promise.resolve(value).then(
            value => {
              step('next', value);
            },
            err => {
              step('throw', err);
            });
      }
    }
    return step('next');
  });
})(function*(){
    (yield this._scrollIntoViewIfNeeded());
    const {x, y} = (yield this._clickablePoint());
    (yield this._page.mouse.move(x, y));
  });}

  /**
   * @param {!{delay?: number, button?: "left"|"right"|"middle", clickCount?: number}=} options
   */
  /* async */ click(options) {return (fn => {
  const gen = fn.call(this);
  return new Promise((resolve, reject) => {
    function step(key, arg) {
      let info, value;
      try {
        info = gen[key](arg);
        value = info.value;
      } catch (error) {
        reject(error);
        return;
      }
      if (info.done) {
        resolve(value);
      } else {
        return Promise.resolve(value).then(
            value => {
              step('next', value);
            },
            err => {
              step('throw', err);
            });
      }
    }
    return step('next');
  });
})(function*(){
    (yield this._scrollIntoViewIfNeeded());
    const {x, y} = (yield this._clickablePoint());
    (yield this._page.mouse.click(x, y, options));
  });}

  /**
   * @param {!Array<string>} filePaths
   */
  /* async */ uploadFile(...filePaths) {return (fn => {
  const gen = fn.call(this);
  return new Promise((resolve, reject) => {
    function step(key, arg) {
      let info, value;
      try {
        info = gen[key](arg);
        value = info.value;
      } catch (error) {
        reject(error);
        return;
      }
      if (info.done) {
        resolve(value);
      } else {
        return Promise.resolve(value).then(
            value => {
              step('next', value);
            },
            err => {
              step('throw', err);
            });
      }
    }
    return step('next');
  });
})(function*(){
    const files = filePaths.map(filePath => path.resolve(filePath));
    const objectId = this._remoteObject.objectId;
    (yield this._client.send('DOM.setFileInputFiles', { objectId, files }));
  });}

  /* async */ tap() {return (fn => {
  const gen = fn.call(this);
  return new Promise((resolve, reject) => {
    function step(key, arg) {
      let info, value;
      try {
        info = gen[key](arg);
        value = info.value;
      } catch (error) {
        reject(error);
        return;
      }
      if (info.done) {
        resolve(value);
      } else {
        return Promise.resolve(value).then(
            value => {
              step('next', value);
            },
            err => {
              step('throw', err);
            });
      }
    }
    return step('next');
  });
})(function*(){
    (yield this._scrollIntoViewIfNeeded());
    const {x, y} = (yield this._clickablePoint());
    (yield this._page.touchscreen.tap(x, y));
  });}

  /* async */ focus() {return (fn => {
  const gen = fn.call(this);
  return new Promise((resolve, reject) => {
    function step(key, arg) {
      let info, value;
      try {
        info = gen[key](arg);
        value = info.value;
      } catch (error) {
        reject(error);
        return;
      }
      if (info.done) {
        resolve(value);
      } else {
        return Promise.resolve(value).then(
            value => {
              step('next', value);
            },
            err => {
              step('throw', err);
            });
      }
    }
    return step('next');
  });
})(function*(){
    (yield this.executionContext().evaluate(element => element.focus(), this));
  });}

  /**
   * @param {string} text
   * @param {{delay: (number|undefined)}=} options
   */
  /* async */ type(text, options) {return (fn => {
  const gen = fn.call(this);
  return new Promise((resolve, reject) => {
    function step(key, arg) {
      let info, value;
      try {
        info = gen[key](arg);
        value = info.value;
      } catch (error) {
        reject(error);
        return;
      }
      if (info.done) {
        resolve(value);
      } else {
        return Promise.resolve(value).then(
            value => {
              step('next', value);
            },
            err => {
              step('throw', err);
            });
      }
    }
    return step('next');
  });
})(function*(){
    (yield this.focus());
    (yield this._page.keyboard.type(text, options));
  });}

  /**
   * @param {string} key
   * @param {!{delay?: number, text?: string}=} options
   */
  /* async */ press(key, options) {return (fn => {
  const gen = fn.call(this);
  return new Promise((resolve, reject) => {
    function step(key, arg) {
      let info, value;
      try {
        info = gen[key](arg);
        value = info.value;
      } catch (error) {
        reject(error);
        return;
      }
      if (info.done) {
        resolve(value);
      } else {
        return Promise.resolve(value).then(
            value => {
              step('next', value);
            },
            err => {
              step('throw', err);
            });
      }
    }
    return step('next');
  });
})(function*(){
    (yield this.focus());
    (yield this._page.keyboard.press(key, options));
  });}

  /**
   * @return {!Promise<?{x: number, y: number, width: number, height: number}>}
   */
  /* async */ boundingBox() {return (fn => {
  const gen = fn.call(this);
  return new Promise((resolve, reject) => {
    function step(key, arg) {
      let info, value;
      try {
        info = gen[key](arg);
        value = info.value;
      } catch (error) {
        reject(error);
        return;
      }
      if (info.done) {
        resolve(value);
      } else {
        return Promise.resolve(value).then(
            value => {
              step('next', value);
            },
            err => {
              step('throw', err);
            });
      }
    }
    return step('next');
  });
})(function*(){
    const result = (yield this._getBoxModel());

    if (!result)
      return null;

    const quad = result.model.border;
    const x = Math.min(quad[0], quad[2], quad[4], quad[6]);
    const y = Math.min(quad[1], quad[3], quad[5], quad[7]);
    const width = Math.max(quad[0], quad[2], quad[4], quad[6]) - x;
    const height = Math.max(quad[1], quad[3], quad[5], quad[7]) - y;

    return {x, y, width, height};
  });}

  /**
   * @return {!Promise<?BoxModel>}
   */
  /* async */ boxModel() {return (fn => {
  const gen = fn.call(this);
  return new Promise((resolve, reject) => {
    function step(key, arg) {
      let info, value;
      try {
        info = gen[key](arg);
        value = info.value;
      } catch (error) {
        reject(error);
        return;
      }
      if (info.done) {
        resolve(value);
      } else {
        return Promise.resolve(value).then(
            value => {
              step('next', value);
            },
            err => {
              step('throw', err);
            });
      }
    }
    return step('next');
  });
})(function*(){
    const result = (yield this._getBoxModel());

    if (!result)
      return null;

    const {content, padding, border, margin, width, height} = result.model;
    return {
      content: this._fromProtocolQuad(content),
      padding: this._fromProtocolQuad(padding),
      border: this._fromProtocolQuad(border),
      margin: this._fromProtocolQuad(margin),
      width,
      height
    };
  });}

  /**
   *
   * @param {!Object=} options
   * @returns {!Promise<string|!Buffer>}
   */
  /* async */ screenshot(options = {}) {return (fn => {
  const gen = fn.call(this);
  return new Promise((resolve, reject) => {
    function step(key, arg) {
      let info, value;
      try {
        info = gen[key](arg);
        value = info.value;
      } catch (error) {
        reject(error);
        return;
      }
      if (info.done) {
        resolve(value);
      } else {
        return Promise.resolve(value).then(
            value => {
              step('next', value);
            },
            err => {
              step('throw', err);
            });
      }
    }
    return step('next');
  });
})(function*(){
    let needsViewportReset = false;

    let boundingBox = (yield this.boundingBox());
    assert(boundingBox, 'Node is either not visible or not an HTMLElement');

    const viewport = this._page.viewport();

    if (viewport && (boundingBox.width > viewport.width || boundingBox.height > viewport.height)) {
      const newViewport = {
        width: Math.max(viewport.width, Math.ceil(boundingBox.width)),
        height: Math.max(viewport.height, Math.ceil(boundingBox.height)),
      };
      (yield this._page.setViewport(Object.assign({}, viewport, newViewport)));

      needsViewportReset = true;
    }

    (yield this._scrollIntoViewIfNeeded());

    boundingBox = (yield this.boundingBox());
    assert(boundingBox, 'Node is either not visible or not an HTMLElement');
    assert(boundingBox.width !== 0, 'Node has 0 width.');
    assert(boundingBox.height !== 0, 'Node has 0 height.');

    const { layoutViewport: { pageX, pageY } } = (yield this._client.send('Page.getLayoutMetrics'));

    const clip = Object.assign({}, boundingBox);
    clip.x += pageX;
    clip.y += pageY;

    const imageData = (yield this._page.screenshot(Object.assign({}, {
      clip
    }, options)));

    if (needsViewportReset)
      (yield this._page.setViewport(viewport));

    return imageData;
  });}

  /**
   * @param {string} selector
   * @return {!Promise<?ElementHandle>}
   */
  /* async */ $(selector) {return (fn => {
  const gen = fn.call(this);
  return new Promise((resolve, reject) => {
    function step(key, arg) {
      let info, value;
      try {
        info = gen[key](arg);
        value = info.value;
      } catch (error) {
        reject(error);
        return;
      }
      if (info.done) {
        resolve(value);
      } else {
        return Promise.resolve(value).then(
            value => {
              step('next', value);
            },
            err => {
              step('throw', err);
            });
      }
    }
    return step('next');
  });
})(function*(){
    const handle = (yield this.executionContext().evaluateHandle(
        (element, selector) => element.querySelector(selector),
        this, selector
    ));
    const element = handle.asElement();
    if (element)
      return element;
    (yield handle.dispose());
    return null;
  });}

  /**
   * @param {string} selector
   * @return {!Promise<!Array<!ElementHandle>>}
   */
  /* async */ $$(selector) {return (fn => {
  const gen = fn.call(this);
  return new Promise((resolve, reject) => {
    function step(key, arg) {
      let info, value;
      try {
        info = gen[key](arg);
        value = info.value;
      } catch (error) {
        reject(error);
        return;
      }
      if (info.done) {
        resolve(value);
      } else {
        return Promise.resolve(value).then(
            value => {
              step('next', value);
            },
            err => {
              step('throw', err);
            });
      }
    }
    return step('next');
  });
})(function*(){
    const arrayHandle = (yield this.executionContext().evaluateHandle(
        (element, selector) => element.querySelectorAll(selector),
        this, selector
    ));
    const properties = (yield arrayHandle.getProperties());
    (yield arrayHandle.dispose());
    const result = [];
    for (const property of properties.values()) {
      const elementHandle = property.asElement();
      if (elementHandle)
        result.push(elementHandle);
    }
    return result;
  });}

  /**
   * @param {string} selector
   * @param {Function|String} pageFunction
   * @param {!Array<*>} args
   * @return {!Promise<(!Object|undefined)>}
   */
  /* async */ $eval(selector, pageFunction, ...args) {return (fn => {
  const gen = fn.call(this);
  return new Promise((resolve, reject) => {
    function step(key, arg) {
      let info, value;
      try {
        info = gen[key](arg);
        value = info.value;
      } catch (error) {
        reject(error);
        return;
      }
      if (info.done) {
        resolve(value);
      } else {
        return Promise.resolve(value).then(
            value => {
              step('next', value);
            },
            err => {
              step('throw', err);
            });
      }
    }
    return step('next');
  });
})(function*(){
    const elementHandle = (yield this.$(selector));
    if (!elementHandle)
      throw new Error(`Error: failed to find element matching selector "${selector}"`);
    const result = (yield this.executionContext().evaluate(pageFunction, elementHandle, ...args));
    (yield elementHandle.dispose());
    return result;
  });}

  /**
   * @param {string} selector
   * @param {Function|String} pageFunction
   * @param {!Array<*>} args
   * @return {!Promise<(!Object|undefined)>}
   */
  /* async */ $$eval(selector, pageFunction, ...args) {return (fn => {
  const gen = fn.call(this);
  return new Promise((resolve, reject) => {
    function step(key, arg) {
      let info, value;
      try {
        info = gen[key](arg);
        value = info.value;
      } catch (error) {
        reject(error);
        return;
      }
      if (info.done) {
        resolve(value);
      } else {
        return Promise.resolve(value).then(
            value => {
              step('next', value);
            },
            err => {
              step('throw', err);
            });
      }
    }
    return step('next');
  });
})(function*(){
    const arrayHandle = (yield this.executionContext().evaluateHandle(
        (element, selector) => Array.from(element.querySelectorAll(selector)),
        this, selector
    ));

    const result = (yield this.executionContext().evaluate(pageFunction, arrayHandle, ...args));
    (yield arrayHandle.dispose());
    return result;
  });}

  /**
   * @param {string} expression
   * @return {!Promise<!Array<!ElementHandle>>}
   */
  /* async */ $x(expression) {return (fn => {
  const gen = fn.call(this);
  return new Promise((resolve, reject) => {
    function step(key, arg) {
      let info, value;
      try {
        info = gen[key](arg);
        value = info.value;
      } catch (error) {
        reject(error);
        return;
      }
      if (info.done) {
        resolve(value);
      } else {
        return Promise.resolve(value).then(
            value => {
              step('next', value);
            },
            err => {
              step('throw', err);
            });
      }
    }
    return step('next');
  });
})(function*(){
    const arrayHandle = (yield this.executionContext().evaluateHandle(
        (element, expression) => {
          const document = element.ownerDocument || element;
          const iterator = document.evaluate(expression, element, null, XPathResult.ORDERED_NODE_ITERATOR_TYPE);
          const array = [];
          let item;
          while ((item = iterator.iterateNext()))
            array.push(item);
          return array;
        },
        this, expression
    ));
    const properties = (yield arrayHandle.getProperties());
    (yield arrayHandle.dispose());
    const result = [];
    for (const property of properties.values()) {
      const elementHandle = property.asElement();
      if (elementHandle)
        result.push(elementHandle);
    }
    return result;
  });}

  /**
   * @returns {!Promise<boolean>}
   */
  isIntersectingViewport() {
    return this.executionContext().evaluate(/* async */ element => {return (fn => {
  const gen = fn.call(this);
  return new Promise((resolve, reject) => {
    function step(key, arg) {
      let info, value;
      try {
        info = gen[key](arg);
        value = info.value;
      } catch (error) {
        reject(error);
        return;
      }
      if (info.done) {
        resolve(value);
      } else {
        return Promise.resolve(value).then(
            value => {
              step('next', value);
            },
            err => {
              step('throw', err);
            });
      }
    }
    return step('next');
  });
})(function*(){
      const visibleRatio = (yield new Promise(resolve => {
        const observer = new IntersectionObserver(entries => {
          resolve(entries[0].intersectionRatio);
          observer.disconnect();
        });
        observer.observe(element);
      }));
      return visibleRatio > 0;
    });}, this);
  }
}

function computeQuadArea(quad) {
  // Compute sum of all directed areas of adjacent triangles
  // https://en.wikipedia.org/wiki/Polygon#Simple_polygons
  let area = 0;
  for (let i = 0; i < quad.length; ++i) {
    const p1 = quad[i];
    const p2 = quad[(i + 1) % quad.length];
    area += (p1.x * p2.y - p2.x * p1.y) / 2;
  }
  return Math.abs(area);
}

/**
 * @typedef {Object} BoxModel
 * @property {!Array<!{x: number, y: number}>} content
 * @property {!Array<!{x: number, y: number}>} padding
 * @property {!Array<!{x: number, y: number}>} border
 * @property {!Array<!{x: number, y: number}>} margin
 * @property {number} width
 * @property {number} height
 */

module.exports = {createJSHandle, JSHandle, ElementHandle};