Enforce header file changes

Dangerfile

@@ -1,7 +1,17 @@
+#DO NOT COMMIT
+require 'pp'
+
+source_pattern = /(\.m|\.mm|\.h)$/
+
 # Sometimes it's a README fix, or something like that - which isn't relevant for
 # including in a project's CHANGELOG for example
 declared_trivial = github.pr_title.include? "#trivial"
-has_source_changes = !git.modified_files.grep(/Source/).empty?
+has_changes_in_source_directory = !git.modified_files.grep(/Source/).empty?
+
+modified_source_files = git.modified_files.grep(source_pattern)
+has_modified_source_files = !modified_source_files.empty?
+added_source_files = git.added_files.grep(source_pattern)
+has_added_source_files = !added_source_files.empty?
 
 # Make it more obvious that a PR is a work in progress and shouldn't be merged yet
 warn("PR is classed as Work in Progress") if github.pr_title.include? "[WIP]"
@@ -11,6 +21,79 @@ warn("This is a big PR, please consider splitting it up to ease code review.") i
 
 # Changelog entries are required for changes to source files.
 no_changelog_entry = !git.modified_files.include?("CHANGELOG.md")
-if has_source_changes && no_changelog_entry && not_declared_trivial
-  fail("Any source code changes should have an entry in CHANGELOG.md.")
+if has_changes_in_source_directory && no_changelog_entry && not_declared_trivial
+  fail("Any source code changes should have an entry in CHANGELOG.md or have #trivial in their title.")
+end
+
+def check_file_header(files_to_check, license)
+  repo_name = github.pr_json["base"]["repo"]["full_name"]
+  pr_number = github.pr_json["number"]
+  files = github.api.pull_request_files(repo_name, pr_number)
+  files.each do |file|
+    if files_to_check.include?(file["filename"])
+      filename = File.basename(file["filename"])
+      license_header = <<-HEREDOC
+//
+      HEREDOC
+      license_header += "//  " + filename + "\n"
+      license_header += <<-HEREDOC
+//  Texture
+//
+      HEREDOC
+      license_header += license
+
+      data = ""
+      contents = github.api.get file["contents_url"]
+      open(contents["download_url"]) { |io|
+        data += io.read
+      }
+      if !data.start_with?(license_header)
+        fail ("Please ensure new source files begin with: \n" + license_header)
+      end
+    end
+  end
 end
+
+# Ensure new files have proper header
+new_source_license_header = <<-HEREDOC
+//  Copyright (c) 2017-present, Pinterest, Inc.  All rights reserved.
+//  Licensed under the Apache License, Version 2.0 (the "License");
+//  you may not use this file except in compliance with the License.
+//  You may obtain a copy of the License at
+//  
+//      http://www.apache.org/licenses/LICENSE-2.0
+//  
+//  Unless required by applicable law or agreed to in writing, software
+//  distributed under the License is distributed on an "AS IS" BASIS,
+//  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//  See the License for the specific language governing permissions and
+//  limitations under the License.
+//
+HEREDOC
+if has_added_source_files
+  check_file_header(added_source_files, new_source_license_header)
+end
+
+# Ensure modified files have proper header
+modified_source_license_header = <<-HEREDOC
+//  Copyright (c) 2014-present, Facebook, Inc.  All rights reserved.
+//  This source code is licensed under the BSD-style license found in the
+//  LICENSE file in the root directory of this source tree. An additional grant
+//  of patent rights can be found in the PATENTS file in the same directory.
+//  Modifications to this file made after 4/13/2017 are: Copyright (c) 2017-present,
+//  Pinterest, Inc.  Licensed under the Apache License, Version 2.0 (the "License");
+//  you may not use this file except in compliance with the License.
+//  You may obtain a copy of the License at
+//  
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+//  Unless required by applicable law or agreed to in writing, software
+//  distributed under the License is distributed on an "AS IS" BASIS,
+//  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//  See the License for the specific language governing permissions and
+//  limitations under the License.
+//
+HEREDOC
+if has_modified_source_files
+  check_file_header(modified_source_files, modified_source_license_header)
+end