Merge branch 'markdowner' into 'master'

POC: Markdown shortcut buttons

## What does this MR do?
Adds markdown shortcut buttons to text area for comments. 

## Are there points in the code the reviewer needs to double check?
Because changing `textarea.val('something')` kills the natural browser undo stack, I had to implement a custom undo stack using state. You can't use the "undoable" state undo pattern because you need to go back to a previous state regardless of cursor position. The undo also adds an undo history item once you delete stuff or press enter.

You can also edit multiple textareas at once and it will keep an undo history for each textarea individually, so the undo state should not collide between textareas.

## Why was this MR needed?
It has been requested multiple times and the competition has it. https://gitlab.com/gitlab-org/gitlab-ce/issues/17185#note_12073433

Libraries are available that already implement this functionality but they are enormous and bloaty. I implemented this in very few lines of code and kept it very simple and as minimal as possible. This was also some competitions approach. I believe so as to not include too much JS. 

Adding extra buttons with new functionality **should only need new HTML and no new JS**.

Only extra complex thing was adding a overridden undo stack, which was made as simple as possible as well.

## What are the relevant issue numbers?
https://gitlab.com/gitlab-org/gitlab-ce/issues/17185#note_12073433

## Screenshots (if relevant)

**NOTE:** One thing you cannot see in this screenshot is that I am pressing <kbd>Cmd</kbd><kbd>Z</kbd> to undo and <kbd>Cmd</kbd><kbd>Shift</kbd><kbd>Z</kbd> to redo which is the undo/redo stack I implemented. <kbd>Ctrl</kbd><kbd>Y</kbd> also works for redo. 
![markdown-editor](/uploads/2517bfb1a7b4269da7fcc4003c88b7f6/markdown-editor.gif)

cc @dzaporozhets for UI

cc @iamphill @alfredo1 for JS review

cc @JobV if you like the idea.

Fixes: #17185

See merge request !4305

app/assets/javascripts/gl_form.js.coffee

@@ -34,6 +34,8 @@ class @GLForm
       # form and textarea event listeners
       @addEventListeners()
 
+      gl.text.init(@form)
+
     # hide discard button
     @form.find('.js-note-discard').hide()
 
@@ -42,6 +44,7 @@ class @GLForm
   clearEventListeners: ->
     @textarea.off 'focus'
     @textarea.off 'blur'
+    gl.text.removeListeners(@form)
 
   addEventListeners: ->
     @textarea.on 'focus', ->

app/assets/javascripts/lib/text_utility.js.coffee

+((w) ->
+  w.gl ?= {}
+  w.gl.text ?= {}
+
+  gl.text.randomString = -> Math.random().toString(36).substring(7)
+
+  gl.text.replaceRange = (s, start, end, substitute) ->
+    s.substring(0, start) + substitute + s.substring(end);
+
+  gl.text.selectedText = (text, textarea) ->
+    text.substring(textarea.selectionStart, textarea.selectionEnd)
+
+  gl.text.insertText = (textArea, text, tag, selected, wrap) ->
+    selectedSplit = selected.split('\n')
+    startChar = if not wrap and textArea.selectionStart > 0 then '\n' else ''
+
+    if selectedSplit.length > 1 and not wrap
+      insertText = selectedSplit.map((val) ->
+        if val.indexOf(tag) is 0
+          "#{val.replace(tag, '')}"
+        else
+          "#{tag}#{val}"
+      ).join('\n')
+    else
+      insertText = "#{startChar}#{tag}#{selected}#{if wrap then tag else ' '}"
+
+    if document.queryCommandSupported('insertText')
+      document.execCommand 'insertText', false, insertText
+    else
+      try
+        document.execCommand("ms-beginUndoUnit")
+
+      textArea.value = @replaceRange(
+          text,
+          textArea.selectionStart,
+          textArea.selectionEnd,
+          insertText)
+      try
+        document.execCommand("ms-endUndoUnit")
+
+    @moveCursor(textArea, tag, wrap)
+
+  gl.text.moveCursor = (textArea, tag, wrapped) ->
+    return unless textArea.setSelectionRange
+
+    if textArea.selectionStart is textArea.selectionEnd
+      if wrapped
+        pos = textArea.selectionStart - tag.length
+      else
+        pos = textArea.selectionStart
+
+      textArea.setSelectionRange pos, pos
+
+  gl.text.updateText = (textArea, tag, wrap) ->
+    $textArea = $(textArea)
+    oldVal = $textArea.val()
+    textArea = $textArea.get(0)
+    text = $textArea.val()
+    selected = @selectedText(text, textArea)
+    $textArea.focus()
+
+    @insertText(textArea, text, tag, selected, wrap)
+
+  gl.text.init = (form) ->
+    self = @
+    $('.js-md', form)
+      .off 'click'
+      .on 'click', ->
+        $this = $(@)
+        self.updateText(
+          $this.closest('.md-area').find('textarea'),
+          $this.data('md-tag'),
+          not $this.data('md-prepend')
+        )
+
+  gl.text.removeListeners = (form) ->
+    $('.js-md', form).off()
+
+) window

app/assets/stylesheets/framework/markdown_area.scss

@@ -65,6 +65,11 @@
     a {
       padding-top: 0;
       line-height: 1;
+      border-bottom: 1px solid $border-color;
+
+      &.btn.btn-xs {
+        padding: 2px 5px;
+      }
     }
   }
 }
@@ -99,3 +104,26 @@
     }
   }
 }
+
+.toolbar-group {
+  float: left;
+  margin-right: -5px;
+  margin-left: $gl-padding;
+
+  &:first-child {
+    margin-left: 0;
+  }
+}
+
+.toolbar-btn {
+  float: left;
+  padding: 0 5px;
+  color: #959494;
+  background: transparent;
+  border: 0;
+  outline: 0;
+
+  &:hover {
+    color: $gl-link-color;
+  }
+}

app/assets/stylesheets/pages/note_form.scss

@@ -179,6 +179,10 @@
   border-top: 1px solid $border-color;
 }
 
+.md-helper {
+  padding-top: 10px;
+}
+
 .toolbar-button {
   padding: 0;
   background: none;

app/helpers/gitlab_markdown_helper.rb

@@ -185,4 +185,17 @@ module GitlabMarkdownHelper
       ''
     end
   end
+
+  def markdown_toolbar_button(options = {})
+    data = options[:data].merge({ container: "body" })
+    content_tag :button,
+      type: "button",
+      class: "toolbar-btn js-md has-tooltip hidden-xs",
+      tabindex: -1,
+      data: data,
+      title: options[:title],
+      aria: { label: options[:title] } do
+      icon(options[:icon])
+    end
+  end
 end

app/views/projects/_md_preview.html.haml

@@ -14,8 +14,17 @@
           %span This is a confidential issue. Your comment will not be visible to the public.
           
       %li.pull-right
-        %button.zen-control.zen-control-full.js-zen-enter{ type: 'button', tabindex: -1 }
-          Go full screen
+        .toolbar-group
+          = markdown_toolbar_button({icon: "bold fw", data: { "md-tag" => "**" }, title: "Add bold text" })
+          = markdown_toolbar_button({icon: "italic fw", data: { "md-tag" => "*" }, title: "Add italic text" })
+          = markdown_toolbar_button({icon: "quote-right fw", data: { "md-tag" => "> ", "md-prepend" => true }, title: "Insert a quote" })
+          = markdown_toolbar_button({icon: "code fw", data: { "md-tag" => "`" }, title: "Insert code" })
+          = markdown_toolbar_button({icon: "list-ul fw", data: { "md-tag" => "* ", "md-prepend" => true }, title: "Add a bullet list" })
+          = markdown_toolbar_button({icon: "list-ol fw", data: { "md-tag" => "1. ", "md-prepend" => true }, title: "Add a numbered list" })
+          = markdown_toolbar_button({icon: "check-square-o fw", data: { "md-tag" => "* [ ] ", "md-prepend" => true }, title: "Add a task list" })
+        .toolbar-group
+          %button.toolbar-btn.js-zen-enter.has-tooltip.hidden-xs{ type: "button", tabindex: -1, aria: { label: "Go full screen" }, title: "Go full screen", data: { container: "body" } }
+            =icon("arrows-alt fw")
 
   .md-write-holder
     = yield
@@ -24,7 +33,7 @@
   - if defined?(referenced_users) && referenced_users
     %div.referenced-users.hide
       %span
-        = icon('exclamation-triangle')
+        = icon("exclamation-triangle")
         You are about to add
         %strong
           %span.js-referenced-users-count 0

spec/features/issues_spec.rb

@@ -22,7 +22,7 @@ describe 'Issues', feature: true do
 
     before do
       visit edit_namespace_project_issue_path(project.namespace, project, issue)
-      click_button "Go full screen"
+      find('.js-zen-enter').click
     end
 
     it 'should open new issue popup' do

spec/javascripts/issue_spec.js.coffee

+#= require lib/text_utility
 #= require issue
 
 describe 'Issue', ->