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.

lib/build_failure_notifier.rb

@@ -0,0 +1,98 @@
+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_uri    => api_url && URI(api_url)
+                  }
+
+                  Gitter::API::Client.new(client_settings)
+                end
+  end
+
+  def self.repo_room_map
+    settings = Settings.travis_branch_monitor
+    repo_map = settings.included_repos.to_h.merge(settings.excluded_repos.to_h)
+
+    repo_map.stringify_keys!
+    repo_map.each do |repo, room_uri|
+      repo_map[repo] = repo if room_uri.nil?
+    end
+  end
+
+  attr_reader :branch, :build, :repo, :repo_path, :room
+
+  def initialize(branch)
+    @branch    = branch
+    @repo_path = branch.repo.name
+    @repo      = Travis::Repository.find(repo_path)
+    @room      = repo_room_map[repo_path]
+    @build     = repo.session.find_one(Travis::Client::Build, branch.travis_build_failure_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
+
+  def report_passing
+    notification_msg = <<~MSG
+      > ### :green_heart: #{repo_branches_markdown_url} now passing!
+    MSG
+
+    gitter_room.send_message(notification_msg)
+  end
+
+  private
+
+  def gitter
+    self.class.gitter
+  end
+
+  def repo_room_map
+    self.class.repo_room_map
+  end
+
+  # join room if needed, otherwise returns room
+  def gitter_room
+    @gitter_room ||= gitter.join_room(room)
+  end
+
+  def travis_build_url
+    "https://travis-ci.org/#{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/#{repo_path}/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

spec/lib/build_failure_notifier_spec.rb

@@ -0,0 +1,37 @@
+describe BuildFailureNotifier do
+  include IncludedReposConfigMethods
+
+  describe "#repo_room_map (private)" do
+    it "builds a map from a hash of only keys" do
+      stub_settings included_repos_keys_only
+      expected_map = {
+        "ManageIQ/manageiq" => "ManageIQ/manageiq",
+        "ManageIQ/miq_bot"  => "ManageIQ/miq_bot"
+      }
+
+      expect(described_class.repo_room_map).to eq(expected_map)
+    end
+
+    it "builds a map from a hash of keys with values" do
+      stub_settings included_repos_keys_and_values
+      expected_map = {
+        "ManageIQ/manageiq-ui-classic"   => "ManageIQ/ui",
+        "ManageIQ/manageiq-gems-pending" => "ManageIQ/core"
+      }
+
+      expect(described_class.repo_room_map).to eq(expected_map)
+    end
+
+    it "builds a map from a mixed hash with keys and some values" do
+      stub_settings included_repos_mixed_keys_with_some_values
+      expected_map = {
+        "ManageIQ/manageiq-ui-classic"   => "ManageIQ/ui",
+        "ManageIQ/manageiq-gems-pending" => "ManageIQ/core",
+        "ManageIQ/manageiq"              => "ManageIQ/manageiq",
+        "ManageIQ/miq_bot"               => "ManageIQ/miq_bot"
+      }
+
+      expect(described_class.repo_room_map).to eq(expected_map)
+    end
+  end
+end

spec/support/travis_branch_monitor_helper.rb

@@ -0,0 +1,33 @@
+require 'yaml'
+
+module IncludedReposConfigMethods
+  def included_repos_keys_only
+    YAML.safe_load <<~YAML
+      ---
+      travis_branch_monitor:
+        included_repos:
+          ManageIQ/manageiq:
+          ManageIQ/miq_bot:
+    YAML
+  end
+
+  def included_repos_keys_and_values
+    YAML.safe_load <<~YAML
+      travis_branch_monitor:
+        included_repos:
+          ManageIQ/manageiq-ui-classic: ManageIQ/ui
+          ManageIQ/manageiq-gems-pending: ManageIQ/core
+    YAML
+  end
+
+  def included_repos_mixed_keys_with_some_values
+    YAML.safe_load <<~YAML
+      travis_branch_monitor:
+        included_repos:
+          ManageIQ/manageiq-ui-classic: ManageIQ/ui
+          ManageIQ/manageiq-gems-pending: ManageIQ/core
+          ManageIQ/manageiq:
+          ManageIQ/miq_bot:
+    YAML
+  end
+end