support label filtering

README.md

@@ -55,6 +55,9 @@ resource_types:
 * `disable_forks`: *Optional.* If set to `true`, it will filter out pull requests that
   were created via users that forked from your repo.
 
+* `label`: *Optional.* If set to a string it will only return pull requests that have been
+marked with that specific label. It is case insensitive.
+
 * `username`: *Optional.* Username for HTTP(S) auth when pulling/pushing.
   This is needed when only HTTP/HTTPS protocol for git is available (which does not support private key auth)
   and auth is required.

assets/lib/filters/label.rb

@@ -0,0 +1,20 @@
+module Filters
+  class Label
+    def initialize(pull_requests:, input: Input.instance)
+      @pull_requests = pull_requests
+      @input = input
+    end
+
+    def pull_requests
+      if @input.source.label
+        @memoized ||= @pull_requests.select do |pr|
+          issue  = Octokit.issue(@input.source.repo, pr.id)
+          labels = issue[:labels] || []
+          labels.find { |l| l['name'].to_s.casecmp(@input.source.label.to_s.downcase).zero? }
+        end
+      else
+        @pull_requests
+      end
+    end
+  end
+end

assets/lib/repository.rb

@@ -1,11 +1,12 @@
 require_relative 'filters/all'
 require_relative 'filters/fork'
+require_relative 'filters/label'
 require_relative 'filters/path'
 
 class Repository
   attr_reader :name
 
-  def initialize(name:, input: Input.instance, filters: [Filters::All, Filters::Path, Filters::Fork])
+  def initialize(name:, input: Input.instance, filters: [Filters::All, Filters::Path, Filters::Fork, Filters::Label])
     @filters = filters
     @name    = name
     @input   = input

spec/filters/label_spec.rb

@@ -0,0 +1,43 @@
+require_relative '../../assets/lib/filters/label'
+require_relative '../../assets/lib/pull_request'
+require 'webmock/rspec'
+
+describe Filters::Label do
+  let(:ignore_pr) do
+    PullRequest.new(pr: { 'number' => 1 })
+  end
+
+  let(:pr) do
+    PullRequest.new(pr: { 'number' => 2 })
+  end
+
+  let(:pull_requests) { [ignore_pr, pr] }
+
+  def stub_json(uri, body)
+    stub_request(:get, uri)
+      .to_return(headers: { 'Content-Type' => 'application/json' }, body: body.to_json)
+  end
+
+  context 'when no label is specified' do
+    it 'does not filter' do
+      payload = { 'source' => { 'repo' => 'user/repo' } }
+      filter = described_class.new(pull_requests: pull_requests, input: Input.instance(payload: payload))
+
+      expect(filter.pull_requests).to eq pull_requests
+    end
+  end
+
+  context 'when the label for filtering is provided' do
+    before do
+      stub_json(%r{https://api.github.com/repos/user/repo/issues/1}, 'labels' => [{ 'name' => 'feature' }])
+      stub_json(%r{https://api.github.com/repos/user/repo/issues/2}, 'labels' => [{ 'name' => 'bug' }])
+    end
+
+    it 'only returns PRs with that label' do
+      payload = { 'source' => { 'repo' => 'user/repo', 'label' => 'bug' } }
+      filter = described_class.new(pull_requests: pull_requests, input: Input.instance(payload: payload))
+
+      expect(filter.pull_requests).to eq [pr]
+    end
+  end
+end