content: import React from 'react';
  import PropTypes from 'prop-types';
  import classNames from 'classnames';
  import { LoadingBar } from 'react-redux-loading-bar';
  import ZoomableImage from './zoomable_image';
  
  export default class ImageLoader extends React.PureComponent {
  
    static propTypes = {
      alt: PropTypes.string,
      src: PropTypes.string.isRequired,
      previewSrc: PropTypes.string,
      width: PropTypes.number,
      height: PropTypes.number,
      onClick: PropTypes.func,
    }
  
    static defaultProps = {
      alt: '',
      width: null,
      height: null,
    };
  
    state = {
      loading: true,
      error: false,
      width: null,
    }
  
    removers = [];
    canvas = null;
  
    get canvasContext() {
      if (!this.canvas) {
        return null;
      }
      this._canvasContext = this._canvasContext || this.canvas.getContext('2d');
      return this._canvasContext;
    }
  
    componentDidMount () {
      this.loadImage(this.props);
    }
  
    componentWillReceiveProps (nextProps) {
      if (this.props.src !== nextProps.src) {
        this.loadImage(nextProps);
      }
    }
  
    componentWillUnmount () {
      this.removeEventListeners();
    }
  
    loadImage (props) {
      this.removeEventListeners();
      this.setState({ loading: true, error: false });
      Promise.all([
        props.previewSrc && this.loadPreviewCanvas(props),
        this.hasSize() && this.loadOriginalImage(props),
      ].filter(Boolean))
        .then(() => {
          this.setState({ loading: false, error: false });
          this.clearPreviewCanvas();
        })
        .catch(() => this.setState({ loading: false, error: true }));
    }
  
    loadPreviewCanvas = ({ previewSrc, width, height }) => new Promise((resolve, reject) => {
      const image = new Image();
      const removeEventListeners = () => {
        image.removeEventListener('error', handleError);
        image.removeEventListener('load', handleLoad);
      };
      const handleError = () => {
        removeEventListeners();
        reject();
      };
      const handleLoad = () => {
        removeEventListeners();
        this.canvasContext.drawImage(image, 0, 0, width, height);
        resolve();
      };
      image.addEventListener('error', handleError);
      image.addEventListener('load', handleLoad);
      image.src = previewSrc;
      this.removers.push(removeEventListeners);
    })
  
    clearPreviewCanvas () {
      const { width, height } = this.canvas;
      this.canvasContext.clearRect(0, 0, width, height);
    }
  
    loadOriginalImage = ({ src }) => new Promise((resolve, reject) => {
      const image = new Image();
      const removeEventListeners = () => {
        image.removeEventListener('error', handleError);
        image.removeEventListener('load', handleLoad);
      };
      const handleError = () => {
        removeEventListeners();
        reject();
      };
      const handleLoad = () => {
        removeEventListeners();
        resolve();
      };
      image.addEventListener('error', handleError);
      image.addEventListener('load', handleLoad);
      image.src = src;
      this.removers.push(removeEventListeners);
    });
  
    removeEventListeners () {
      this.removers.forEach(listeners => listeners());
      this.removers = [];
    }
  
    hasSize () {
      const { width, height } = this.props;
      return typeof width === 'number' && typeof height === 'number';
    }
  
    setCanvasRef = c => {
      this.canvas = c;
      if (c) this.setState({ width: c.offsetWidth });
    }
  
    render () {
      const { alt, src, width, height, onClick } = this.props;
      const { loading } = this.state;
  
      const className = classNames('image-loader', {
        'image-loader--loading': loading,
        'image-loader--amorphous': !this.hasSize(),
      });
  
      return (
        <div className={className}>
          <LoadingBar loading={loading ? 1 : 0} className='loading-bar' style={{ width: this.state.width || width }} />
          {loading ? (
            <canvas
              className='image-loader__preview-canvas'
              ref={this.setCanvasRef}
              width={width}
              height={height}
            />
          ) : (
            <ZoomableImage
              alt={alt}
              src={src}
              onClick={onClick}
            />
          )}
        </div>
      );
    }
  
  }
  