Step 13.5: Create PictureService with utils for files

src/services/picture.ts

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+import { Injectable } from '@angular/core';
+import { Platform } from 'ionic-angular';
+import { ImagePicker } from '@ionic-native/image-picker';
+import { UploadFS } from 'meteor/jalik:ufs';
+
+@Injectable()
+export class PictureService {
+  constructor(private platform: Platform,
+              private imagePicker: ImagePicker) {
+  }
+
+  select(): Promise<File> {
+    if (!this.platform.is('cordova') || !this.platform.is('mobile')) {
+      return new Promise((resolve, reject) => {
+        try {
+          UploadFS.selectFile((file: File) => {
+            resolve(file);
+          });
+        }
+        catch (e) {
+          reject(e);
+        }
+      });
+    }
+
+    return this.imagePicker.getPictures({maximumImagesCount: 1}).then((URL: string) => {
+      return this.convertURLtoBlob(URL);
+    });
+  }
+
+  convertURLtoBlob(url: string, options = {}): Promise<File> {
+    return new Promise((resolve, reject) => {
+      const image = document.createElement('img');
+
+      image.onload = () => {
+        try {
+          const dataURI = this.convertImageToDataURI(image, options);
+          const blob = this.convertDataURIToBlob(dataURI);
+          const pathname = (new URL(url)).pathname;
+          const filename = pathname.substring(pathname.lastIndexOf('/') + 1);
+          const file = new File([blob], filename);
+
+          resolve(file);
+        }
+        catch (e) {
+          reject(e);
+        }
+      };
+
+      image.src = url;
+    });
+  }
+
+  convertImageToDataURI(image: HTMLImageElement, {MAX_WIDTH = 400, MAX_HEIGHT = 400} = {}): string {
+    // Create an empty canvas element
+    const canvas = document.createElement('canvas');
+
+    var width = image.width, height = image.height;
+
+    if (width > height) {
+      if (width > MAX_WIDTH) {
+        height *= MAX_WIDTH / width;
+        width = MAX_WIDTH;
+      }
+    } else {
+      if (height > MAX_HEIGHT) {
+        width *= MAX_HEIGHT / height;
+        height = MAX_HEIGHT;
+      }
+    }
+
+    canvas.width = width;
+    canvas.height = height;
+
+    // Copy the image contents to the canvas
+    const context = canvas.getContext('2d');
+    context.drawImage(image, 0, 0, width, height);
+
+    // Get the data-URL formatted image
+    // Firefox supports PNG and JPEG. You could check image.src to
+    // guess the original format, but be aware the using 'image/jpg'
+    // will re-encode the image.
+    const dataURL = canvas.toDataURL('image/png');
+
+    return dataURL.replace(/^data:image\/(png|jpg);base64,/, '');
+  }
+
+  convertDataURIToBlob(dataURI): Blob {
+    const binary = atob(dataURI);
+
+    // Write the bytes of the string to a typed array
+    const charCodes = Object.keys(binary)
+      .map<number>(Number)
+      .map<number>(binary.charCodeAt.bind(binary));
+
+    // Build blob with typed array
+    return new Blob([new Uint8Array(charCodes)], {type: 'image/jpeg'});
+  }
+}