Update to Imgur API v3

Version 2 of Imgur's API is deprecated. Their documentation for v2 is no
longer online, and applications can only be registered under version 3.
Version 3 of their API has a slightly different endpoint but, more
importantly, uses a Client ID/Secret pair instead of an API Key.

This PR updates Discourse to use the new version of Imgur's API.

Signed-off-by: David Celis <me@davidcel.is>

spec/components/imgur_spec.rb

@@ -0,0 +1,55 @@
+require 'spec_helper'
+require 'imgur'
+
+describe Imgur do
+
+  describe "upload_file" do
+
+    let(:file) { Rails.root.join('app', 'assets', 'images', 'logo.png') }
+    let(:params) { [SiteSetting.imgur_endpoint, { image: Base64.encode64(file.read) }, { 'Authorization' => "Client-ID #{SiteSetting.imgur_client_id}" }] }
+
+    it 'returns JSON of the Imgur upload if successful' do
+      json = {
+        data: {
+          id: 'fake',
+          link: 'http://imgur.com/fake.png',
+          deletehash: 'a3kaoad30'
+        },
+        success: true,
+        status: 200
+      }.to_json
+
+      response = mock
+      response.expects(:body).returns(json)
+
+      image_info = {
+        url: 'http://imgur.com/fake.png',
+        filesize: File.size(file)
+      }
+
+      RestClient.expects(:post).with(*params).returns(response)
+      result = Imgur.upload_file(file)
+
+      # Not testing what width/height actually are because ImageSizer is already tested
+      result[:url].should eq(image_info[:url])
+      result[:filesize].should eq(image_info[:filesize])
+      result[:width].should_not be_nil
+      result[:height].should_not be_nil
+    end
+
+    it 'returns nil if the request fails' do
+      json = {
+        success: false,
+        status: 400
+      }.to_json
+
+      response = mock
+      response.expects(:body).returns(json)
+      RestClient.expects(:post).with(*params).returns(response)
+
+      Imgur.upload_file(file).should be_nil
+    end
+
+  end
+
+end