Merge branch 'zj-slash-commands-mattermost' into 'master'

Slash command for mattermost

Closes  #22540

## Does this MR meet the acceptance criteria?

- [x] [Changelog entry](https://docs.gitlab.com/ce/development/changelog.html) added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if it does - rebase it please)


See merge request !7438

5 files changed, 168 insertions, 0 deletions

diff --git a/lib/gitlab/chat_commands/base_command.rb b/lib/gitlab/chat_commands/base_command.rb
new file mode 100644
index 00000000000..e59d69b72b9
--- /dev/null
+++ b/lib/gitlab/chat_commands/base_command.rb
@@ -0,0 +1,49 @@
+module Gitlab
+  module ChatCommands
+    class BaseCommand
+      QUERY_LIMIT = 5
+
+      def self.match(_text)
+        raise NotImplementedError
+      end
+
+      def self.help_message
+        raise NotImplementedError
+      end
+
+      def self.available?(_project)
+        raise NotImplementedError
+      end
+
+      def self.allowed?(_user, _ability)
+        true
+      end
+
+      def self.can?(object, action, subject)
+        Ability.allowed?(object, action, subject)
+      end
+
+      def execute(_)
+        raise NotImplementedError
+      end
+
+      def collection
+        raise NotImplementedError
+      end
+
+      attr_accessor :project, :current_user, :params
+
+      def initialize(project, user, params = {})
+        @project, @current_user, @params = project, user, params.dup
+      end
+
+      private
+
+      def find_by_iid(iid)
+        resource = collection.find_by(iid: iid)
+
+        readable?(resource) ? resource : nil
+      end
+    end
+  end
+end
diff --git a/lib/gitlab/chat_commands/command.rb b/lib/gitlab/chat_commands/command.rb
new file mode 100644
index 00000000000..5f131703d40
--- /dev/null
+++ b/lib/gitlab/chat_commands/command.rb
@@ -0,0 +1,61 @@
+module Gitlab
+  module ChatCommands
+    class Command < BaseCommand
+      COMMANDS = [
+        Gitlab::ChatCommands::IssueShow,
+        Gitlab::ChatCommands::IssueCreate,
+      ].freeze
+
+      def execute
+        command, match = match_command
+
+        if command
+          if command.allowed?(project, current_user)
+            present command.new(project, current_user, params).execute(match)
+          else
+            access_denied
+          end
+        else
+          help(help_messages)
+        end
+      end
+
+      private
+
+      def match_command
+        match = nil
+        service = available_commands.find do |klass|
+          match = klass.match(command)
+        end
+
+        [service, match]
+      end
+
+      def help_messages
+        available_commands.map(&:help_message)
+      end
+
+      def available_commands
+        COMMANDS.select do |klass|
+          klass.available?(project)
+        end
+      end
+
+      def command
+        params[:text]
+      end
+
+      def help(messages)
+        Mattermost::Presenter.help(messages, params[:command])
+      end
+
+      def access_denied
+        Mattermost::Presenter.access_denied
+      end
+
+      def present(resource)
+        Mattermost::Presenter.present(resource)
+      end
+    end
+  end
+end
diff --git a/lib/gitlab/chat_commands/issue_command.rb b/lib/gitlab/chat_commands/issue_command.rb
new file mode 100644
index 00000000000..f1bc36239d5
--- /dev/null
+++ b/lib/gitlab/chat_commands/issue_command.rb
@@ -0,0 +1,17 @@
+module Gitlab
+  module ChatCommands
+    class IssueCommand < BaseCommand
+      def self.available?(project)
+        project.issues_enabled? && project.default_issues_tracker?
+      end
+
+      def collection
+        project.issues
+      end
+
+      def readable?(issue)
+        self.class.can?(current_user, :read_issue, issue)
+      end
+    end
+  end
+end
diff --git a/lib/gitlab/chat_commands/issue_create.rb b/lib/gitlab/chat_commands/issue_create.rb
new file mode 100644
index 00000000000..98338ebfa27
--- /dev/null
+++ b/lib/gitlab/chat_commands/issue_create.rb
@@ -0,0 +1,24 @@
+module Gitlab
+  module ChatCommands
+    class IssueCreate < IssueCommand
+      def self.match(text)
+        /\Aissue\s+create\s+(?<title>[^\n]*)\n*(?<description>.*)\z/.match(text)
+      end
+
+      def self.help_message
+        'issue create <title>\n<description>'
+      end
+
+      def self.allowed?(project, user)
+        can?(user, :create_issue, project)
+      end
+
+      def execute(match)
+        title = match[:title]
+        description = match[:description]
+
+        Issues::CreateService.new(project, current_user, title: title, description: description).execute
+      end
+    end
+  end
+end
diff --git a/lib/gitlab/chat_commands/issue_show.rb b/lib/gitlab/chat_commands/issue_show.rb
new file mode 100644
index 00000000000..f5bceb038e5
--- /dev/null
+++ b/lib/gitlab/chat_commands/issue_show.rb
@@ -0,0 +1,17 @@
+module Gitlab
+  module ChatCommands
+    class IssueShow < IssueCommand
+      def self.match(text)
+        /\Aissue\s+show\s+(?<iid>\d+)/.match(text)
+      end
+
+      def self.help_message
+        "issue show <id>"
+      end
+
+      def execute(match)
+        find_by_iid(match[:iid])
+      end
+    end
+  end
+end