Add BuildFailureNotifier lib

This class is a service class in charge of the logistics of sending a
message to a configured gitter channel for a given repo, notifying there
has been a failure.

Author: NickLaMuro

lib/build_failure_notifier.rb

@@ -0,0 +1,82 @@
+require 'travis'
+require 'gitter/api'
+
+class BuildFailureNotifier
+  def self.gitter
+    @gitter ||= begin
+                  api_url = Settings.gitter.api_url
+                  client_settings = {
+                    :token      => Settings.gitter_credentials.token,
+                    :api_prefix => Settings.gitter.api_prefix,
+                    :api_url    => api_url && URI(api_url)
+                  }
+
+                  Gitter::API::Client.new(client_settings)
+                end
+  end
+
+  attr_reader :build, :build_failure, :repo, :room
+
+  alias repo_path room
+
+  def initialize(build_failure)
+    @build_failure = build_failure
+
+    @room  = build_failure.repo.name
+    @repo  = Travis::Repository.find(room)
+    @build = v3_client.repo_build(build_failure.travis_build_id)
+  end
+
+  def post_failure
+    notification_msg = <<~MSG
+      > ### :red_circle: Build Failure in #{repo_branches_markdown_url}!
+      >
+      > **Travis Build**:  #{travis_build_url}
+    MSG
+    notification_msg << "> **Failure PR**:    #{offending_pr}\n" if offending_pr
+    notification_msg << "> **Commit**:        #{commit_url}\n"   if commit_url
+    notification_msg << "> **Compare**:       #{compare_url}\n"  if compare_url
+
+    gitter_room.send_message(notification_msg)
+  end
+
+  private
+
+  def gitter
+    self.class.gitter
+  end
+
+  # join room if needed, otherwise returns room
+  def gitter_room
+    @gitter_room ||= gitter.join_room(room)
+  end
+
+  def v3_client
+    @v3_client ||= TravisV3Client.new(:repo => @repo)
+  end
+
+  def travis_build_url
+    "#{Travis::Client::ORG_URI}#{repo_path}/builds/#{build.id}"
+  end
+
+  # find the PR that caused this mess...
+  def offending_pr
+    if build.commit && build.commit.message =~ /^Merge pull request #(\d+)/
+      "https://github.com/#{repo_path}/issues/#{$1}"
+    end
+  end
+
+  def commit_url
+    if build.commit
+      "https://github.com/ManageIQ/manageiq/commit/#{build.commit.sha[0, 8]}"
+    end
+  end
+
+  def compare_url
+    build.commit.compare_url if build.commit && build.commit.compare_url
+  end
+
+  def repo_branches_markdown_url
+    "[`#{repo_path}`](https://travis-ci.org/#{repo_path}/branches)"
+  end
+end