Add a SystemNoteService class

There's a lot of code in the Note model that only deals with creating
system notes, so we're going to split that into its own class.

6 files changed, 313 insertions, 8 deletions

diff --git a/app/services/issuable_base_service.rb b/app/services/issuable_base_service.rb
index 5e1906ad2ae..4d251cb30db 100644
--- a/app/services/issuable_base_service.rb
+++ b/app/services/issuable_base_service.rb
@@ -2,17 +2,17 @@ class IssuableBaseService < BaseService
   private
 
   def create_assignee_note(issuable)
-    Note.create_assignee_change_note(
+    SystemNoteService.assignee_change(
       issuable, issuable.project, current_user, issuable.assignee)
   end
 
   def create_milestone_note(issuable)
-    Note.create_milestone_change_note(
+    SystemNoteService.milestone_change(
       issuable, issuable.project, current_user, issuable.milestone)
   end
 
   def create_labels_note(issuable, added_labels, removed_labels)
-    Note.create_labels_change_note(
+    SystemNoteService.label_change(
       issuable, issuable.project, current_user, added_labels, removed_labels)
   end
 end
diff --git a/app/services/issues/close_service.rb b/app/services/issues/close_service.rb
index f670019cc63..bdc13685fd0 100644
--- a/app/services/issues/close_service.rb
+++ b/app/services/issues/close_service.rb
@@ -14,7 +14,7 @@ module Issues
     private
 
     def create_note(issue, current_commit)
-      Note.create_status_change_note(issue, issue.project, current_user, issue.state, current_commit)
+      SystemNoteService.status_change(issue, issue.project, current_user, issue.state, current_commit)
     end
   end
 end
diff --git a/app/services/issues/reopen_service.rb b/app/services/issues/reopen_service.rb
index 1e5c398516d..fbbf573e5a3 100644
--- a/app/services/issues/reopen_service.rb
+++ b/app/services/issues/reopen_service.rb
@@ -14,7 +14,7 @@ module Issues
     private
 
     def create_note(issue)
-      Note.create_status_change_note(issue, issue.project, current_user, issue.state, nil)
+      SystemNoteService.status_change(issue, issue.project, current_user, issue.state, nil)
     end
   end
 end
diff --git a/app/services/merge_requests/base_service.rb b/app/services/merge_requests/base_service.rb
index f6e1ae6f283..9b470880adf 100644
--- a/app/services/merge_requests/base_service.rb
+++ b/app/services/merge_requests/base_service.rb
@@ -2,7 +2,7 @@ module MergeRequests
   class BaseService < ::IssuableBaseService
 
     def create_note(merge_request)
-      Note.create_status_change_note(merge_request, merge_request.target_project, current_user, merge_request.state, nil)
+      SystemNoteService.status_change(merge_request, merge_request.target_project, current_user, merge_request.state, nil)
     end
 
     def hook_data(merge_request, action)
diff --git a/app/services/merge_requests/refresh_service.rb b/app/services/merge_requests/refresh_service.rb
index e9b526d1fb7..1d57fd11de7 100644
--- a/app/services/merge_requests/refresh_service.rb
+++ b/app/services/merge_requests/refresh_service.rb
@@ -82,8 +82,9 @@ module MergeRequests
           mr_commit_ids.include?(commit.id)
         end
 
-        Note.create_new_commits_note(merge_request, merge_request.project,
-                                     @current_user, new_commits, existing_commits, @oldrev)
+        SystemNoteService.commit_add(merge_request, merge_request.project,
+                                     @current_user, new_commits,
+                                     existing_commits, @oldrev)
       end
     end
 
diff --git a/app/services/system_note_service.rb b/app/services/system_note_service.rb
new file mode 100644
index 00000000000..2486360b261
--- /dev/null
+++ b/app/services/system_note_service.rb
@@ -0,0 +1,304 @@
+# SystemNoteService
+#
+# Used for creating system notes (e.g., when a user references a merge request
+# from an issue, an issue's assignee changes, an issue is closed, etc.)
+#
+# All methods creating notes should be named using a singular noun and
+# present-tense verb (e.g., "assignee_change" not "assignee_changed",
+# "label_change" not "labels_change").
+class SystemNoteService
+  # Called when the assignee of a Noteable is changed or removed
+  #
+  # noteable - Noteable object
+  # project  - Project owning noteable
+  # author   - User performing the change
+  # assignee - User being assigned, or nil
+  #
+  # Example Note text:
+  #
+  #   "Assignee removed"
+  #
+  #   "Reassigned to @rspeicher"
+  #
+  # Returns the created Note object
+  def self.assignee_change(noteable, project, author, assignee)
+    body = assignee.nil? ? 'Assignee removed' : "Reassigned to @#{assignee.username}"
+
+    create_note(noteable: noteable, project: project, author: author, note: body)
+  end
+
+  # Called when a Mentionable references a Noteable
+  #
+  # noteable  - Noteable object being referenced
+  # mentioner - Mentionable object
+  # author    - User performing the reference
+  #
+  # Example Note text:
+  #
+  #   "Mentioned in #1"
+  #
+  #   "Mentioned in !2"
+  #
+  #   "Mentioned in 54f7727c"
+  #
+  # See cross_reference_note_content.
+  #
+  # Returns the created Note object
+  def self.cross_reference(noteable, mentioner, author)
+    return if cross_reference_disallowed?(noteable, mentioner)
+
+    gfm_reference = mentioner_gfm_ref(noteable, mentioner)
+
+    note_options = {
+      project: noteable.project,
+      author:  author,
+      note:    cross_reference_note_content(gfm_reference)
+    }
+
+    if noteable.kind_of?(Commit)
+      note_options.merge!(noteable_type: 'Commit', commit_id: noteable.id)
+    else
+      note_options.merge!(noteable: noteable)
+    end
+
+    create_note(note_options)
+  end
+
+  # Called when one or more labels on a Noteable are added and/or removed
+  #
+  # noteable       - Noteable object
+  # project        - Project owning noteable
+  # author         - User performing the change
+  # added_labels   - Array of Labels added
+  # removed_labels - Array of Labels removed
+  #
+  # Example Note text:
+  #
+  #   "Added ~1 and removed ~2 ~3 labels"
+  #
+  #   "Added ~4 label"
+  #
+  #   "Removed ~5 label"
+  #
+  # Returns the created Note object
+  def self.label_change(noteable, project, author, added_labels, removed_labels)
+    labels_count = added_labels.count + removed_labels.count
+
+    references     = ->(label) { "~#{label.id}" }
+    added_labels   = added_labels.map(&references).join(' ')
+    removed_labels = removed_labels.map(&references).join(' ')
+
+    body = ''
+
+    if added_labels.present?
+      body << "added #{added_labels}"
+      body << ' and ' if removed_labels.present?
+    end
+
+    if removed_labels.present?
+      body << "removed #{removed_labels}"
+    end
+
+    body << ' ' << 'label'.pluralize(labels_count)
+    body = "#{body.capitalize}"
+
+    create_note(noteable: noteable, project: project, author: author, note: body)
+  end
+
+  # Called when the milestone of a Noteable is changed
+  #
+  # noteable  - Noteable object
+  # project   - Project owning noteable
+  # author    - User performing the change
+  # milestone - Milestone being assigned, or nil
+  #
+  # Example Note text:
+  #
+  #   "Milestone removed"
+  #
+  #   "Miletone changed to 7.11"
+  #
+  # Returns the created Note object
+  def self.milestone_change(noteable, project, author, milestone)
+    body = 'Milestone '
+    body += milestone.nil? ? 'removed' : "changed to #{milestone.title}"
+
+    create_note(noteable: noteable, project: project, author: author, note: body)
+  end
+
+  # Called when commits are added to a Merge Request
+  #
+  # noteable         - Noteable object
+  # project          - Project owning noteable
+  # author           - User performing the change
+  # new_commits      - Array of Commits added since last push
+  # existing_commits - Array of Commits added in a previous push
+  # oldrev           - TODO (rspeicher): I have no idea what this actually does
+  #
+  # See new_commit_summary and existing_commit_summary.
+  #
+  # Returns the created Note object
+  def self.commit_add(noteable, project, author, new_commits, existing_commits = [], oldrev = nil)
+    total_count  = new_commits.length + existing_commits.length
+    commits_text = "#{total_count} commit".pluralize(total_count)
+
+    body = "Added #{commits_text}:\n\n"
+    body << existing_commit_summary(noteable, existing_commits, oldrev)
+    body << new_commit_summary(new_commits).join("\n")
+
+    create_note(noteable: noteable, project: project, author: author, note: body)
+  end
+
+  # Called when the status of a Noteable is changed
+  #
+  # noteable - Noteable object
+  # project  - Project owning noteable
+  # author   - User performing the change
+  # status   - String status
+  # source   - Mentionable performing the change, or nil
+  #
+  # Example Note text:
+  #
+  #   "Status changed to merged"
+  #
+  #   "Status changed to closed by bc17db76"
+  #
+  # Returns the created Note object
+  def self.status_change(noteable, project, author, status, source)
+    body = "Status changed to #{status}"
+    body += " by #{source.gfm_reference}" if source
+
+    create_note(noteable: noteable, project: project, author: author, note: body)
+  end
+
+  def self.cross_reference?(note_text)
+    note_text.start_with?(cross_reference_note_prefix)
+  end
+
+  # Determine if cross reference note should be created.
+  # eg. mentioning a commit in MR comments which exists inside a MR
+  # should not create "mentioned in" note.
+  def self.cross_reference_disallowed?(noteable, mentioner)
+    if mentioner.kind_of?(MergeRequest)
+      mentioner.commits.map(&:id).include? noteable.id
+    end
+  end
+
+  def self.cross_reference_exists?(noteable, mentioner)
+    # Initial scope should be system notes of this noteable type
+    notes = Note.system.where(noteable_type: noteable.class)
+
+    if noteable.is_a?(Commit)
+      # Commits have non-integer IDs, so they're stored in `commit_id`
+      notes = notes.where(commit_id: noteable.id)
+    else
+      notes = notes.where(noteable_id: noteable.id)
+    end
+
+    gfm_reference = mentioner_gfm_ref(noteable, mentioner, true)
+    notes = notes.where('note like ?', cross_reference_note_pattern(gfm_reference))
+
+    notes.count > 0
+  end
+
+  private
+
+  def self.create_note(args = {})
+    Note.create(args.merge(system: true))
+  end
+
+  def self.cross_reference_note_prefix
+    'mentioned in '
+  end
+
+  # Prepend the mentioner's namespaced project path to the GFM reference for
+  # cross-project references.  For same-project references, return the
+  # unmodified GFM reference.
+  def self.mentioner_gfm_ref(noteable, mentioner, cross_reference = false)
+    if mentioner.is_a?(Commit) && cross_reference
+      return mentioner.gfm_reference.sub('commit ', 'commit %')
+    end
+
+    full_gfm_reference(mentioner.project, noteable.project, mentioner)
+  end
+
+  # Return the +mentioner+ GFM reference.  If the mentioner and noteable
+  # projects are not the same, add the mentioning project's path to the
+  # returned value.
+  def self.full_gfm_reference(mentioning_project, noteable_project, mentioner)
+    if mentioning_project == noteable_project
+      mentioner.gfm_reference
+    else
+      if mentioner.is_a?(Commit)
+        mentioner.gfm_reference.sub(
+          /(commit )/,
+          "\\1#{mentioning_project.path_with_namespace}@"
+        )
+      else
+        mentioner.gfm_reference.sub(
+          /(issue |merge request )/,
+          "\\1#{mentioning_project.path_with_namespace}"
+        )
+      end
+    end
+  end
+
+  def self.cross_reference_note_content(gfm_reference)
+    cross_reference_note_prefix + "#{gfm_reference}"
+  end
+
+  def self.cross_reference_note_pattern(gfm_reference)
+    # Older cross reference notes contained underscores for emphasis
+    "%" + cross_reference_note_content(gfm_reference) + "%"
+  end
+
+  # Build an Array of lines detailing each commit added in a merge request
+  #
+  # new_commits - Array of new Commit objects
+  #
+  # Returns an Array of Strings
+  def self.new_commit_summary(new_commits)
+    new_commits.collect do |commit|
+      "* #{commit.short_id} - #{commit.title}"
+    end
+  end
+
+  # Build a single line summarizing existing commits being added in a merge
+  # request
+  #
+  # noteable         - MergeRequest object
+  # existing_commits - Array of existing Commit objects
+  # oldrev           - Optional String SHA of ... TODO (rspeicher): I have no idea what this actually does.
+  #
+  # Examples:
+  #
+  #   "* ea0f8418...2f4426b7 - 24 commits from branch `master`"
+  #
+  #   "* ea0f8418..4188f0ea - 15 commits from branch `fork:master`"
+  #
+  #   "* ea0f8418 - 1 commit from branch `feature`"
+  #
+  # Returns a newline-terminated String
+  def self.existing_commit_summary(noteable, existing_commits, oldrev = nil)
+    return '' if existing_commits.empty?
+
+    count = existing_commits.size
+
+    commit_ids = if count == 1
+                   existing_commits.first.short_id
+                 else
+                   if oldrev
+                     "#{Commit.truncate_sha(oldrev)}...#{existing_commits.last.short_id}"
+                   else
+                     "#{existing_commits.first.short_id}..#{existing_commits.last.short_id}"
+                   end
+                 end
+
+    commits_text = "#{count} commit".pluralize(count)
+
+    branch = noteable.target_branch
+    branch = "#{noteable.target_project_namespace}:#{branch}" if noteable.for_fork?
+
+    "* #{commit_ids} - #{commits_text} from branch `#{branch}`\n"
+  end
+end