1 files changed, 168 insertions, 0 deletions
diff --git a/app/javascript/mastodon/features/ui/components/image_loader.jsx b/app/javascript/mastodon/features/ui/components/image_loader.jsx
new file mode 100644
index 000000000..92aeef5c4
--- /dev/null
+++ b/app/javascript/mastodon/features/ui/components/image_loader.jsx
@@ -0,0 +1,168 @@
+import classNames from 'classnames';
+import PropTypes from 'prop-types';
+import React, { PureComponent } from 'react';
+import { LoadingBar } from 'react-redux-loading-bar';
+import ZoomableImage from './zoomable_image';
+
+export default class ImageLoader extends PureComponent {
+
+  static propTypes = {
+    alt: PropTypes.string,
+    src: PropTypes.string.isRequired,
+    previewSrc: PropTypes.string,
+    width: PropTypes.number,
+    height: PropTypes.number,
+    onClick: PropTypes.func,
+    zoomButtonHidden: PropTypes.bool,
+  };
+
+  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);
+  }
+
+  UNSAFE_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}>
+        {loading ? (
+          <>
+            <div className='loading-bar__container' style={{ width: this.state.width || width }}>
+              <LoadingBar className='loading-bar' loading={1} />
+            </div>
+            <canvas
+              className='image-loader__preview-canvas'
+              ref={this.setCanvasRef}
+              width={width}
+              height={height}
+            />
+          </>
+        ) : (
+          <ZoomableImage
+            alt={alt}
+            src={src}
+            onClick={onClick}
+            width={width}
+            height={height}
+            zoomButtonHidden={this.props.zoomButtonHidden}
+          />
+        )}
+      </div>
+    );
+  }
+
+}