From 784625559e17cd2debee94d5931e39ab69a8c25c Mon Sep 17 00:00:00 2001
From: Alexander Ebert <ebert@woltlab.com>
Date: Mon, 17 Aug 2020 18:54:40 +0200
Subject: [PATCH] Overflow handling for reaction popovers on smartphones

Closes #3518
---
 .../WoltLabSuite/Core/Ui/Reaction/Handler.js  | 49 +++++++++++++++++--
 .../install/files/style/ui/reactions.scss     | 45 +++++++++++++++++
 2 files changed, 89 insertions(+), 5 deletions(-)

diff --git a/wcfsetup/install/files/js/WoltLabSuite/Core/Ui/Reaction/Handler.js b/wcfsetup/install/files/js/WoltLabSuite/Core/Ui/Reaction/Handler.js
index 7e0a60363c..5aad47ce22 100644
--- a/wcfsetup/install/files/js/WoltLabSuite/Core/Ui/Reaction/Handler.js
+++ b/wcfsetup/install/files/js/WoltLabSuite/Core/Ui/Reaction/Handler.js
@@ -23,6 +23,8 @@ define(
 	{
 		"use strict";
 		
+		var UiScreen = require('Ui/Screen');
+		
 		/**
 		 * @constructor
 		 */
@@ -175,6 +177,24 @@ define(
 					if (~~elData(reactionTypeButton, 'is-assignable') === 0) {
 						elShow(reactionTypeButton);
 					}
+					
+					this._scrollReactionIntoView(reactionTypeButton);
+				}
+			},
+			
+			_scrollReactionIntoView: function (reactionTypeButton) {
+				var scrollableContainer = elBySel('.reactionPopoverContent', this._getPopover());
+				
+				// Do not scroll if the button is located in the upper 75%.
+				if (reactionTypeButton.offsetTop < scrollableContainer.clientHeight * 0.75) {
+					scrollableContainer.scrollTop = 0;
+				}
+				else {
+					// `Element.scrollTop` permits arbitrary values and will always clamp them to
+					// the maximum possible offset value. We can abuse this behavior by calculating
+					// the values to place the selected reaction in the center of the popover,
+					// regardless of the offset being out of range.
+					scrollableContainer.scrollTop = reactionTypeButton.offsetTop + reactionTypeButton.clientHeight / 2 - scrollableContainer.clientHeight / 2;
 				}
 			},
 			
@@ -221,20 +241,30 @@ define(
 				}
 				
 				this._popoverCurrentObjectId = objectId;
-				this._markReactionAsActive();
 				
 				UiAlignment.set(this._getPopover(), element, {
 					pointer: true,
-					horizontal: (this._options.isButtonGroupNavigation) ? 'left' :'center',
-					vertical: 'top'
+					horizontal: (this._options.isButtonGroupNavigation) ? 'left' : 'center',
+					vertical: UiScreen.is('screen-xs') ? 'bottom' : 'top'
 				});
 				
 				if (this._options.isButtonGroupNavigation) {
 					element.closest('nav').style.setProperty('opacity', '1', '');
 				}
 				
-				this._getPopover().classList.remove('forceHide');
-				this._getPopover().classList.add('active');
+				var popover = this._getPopover();
+				
+				// The popover could be rendered below the input field on mobile, in which case
+				// the "first" button is displayed at the bottom and thus farthest away. Reversing
+				// the display order will restore the logic by placing the "first" button as close
+				// to the react button as possible.
+				var inverseOrder = popover.style.getPropertyValue('bottom') === 'auto';
+				popover.classList[inverseOrder ? 'add' : 'remove']('inverseOrder');
+				
+				this._markReactionAsActive();
+				
+				popover.classList.remove('forceHide');
+				popover.classList.add('active');
 			},
 			
 			/**
@@ -251,6 +281,7 @@ define(
 					_popoverContent.className = 'reactionPopoverContent';
 					
 					var popoverContentHTML = elCreate('ul');
+					popoverContentHTML.className = 'reactionTypeButtonList';
 					
 					var sortedReactionTypes = this._getSortedReactionTypes();
 					
@@ -286,6 +317,14 @@ define(
 					}
 					
 					_popoverContent.appendChild(popoverContentHTML);
+					_popoverContent.addEventListener('scroll', function () {
+						var hasTopOverflow = _popoverContent.scrollTop > 0;
+						_popoverContent.classList[hasTopOverflow ? 'add' : 'remove']('overflowTop');
+						
+						var hasBottomOverflow = _popoverContent.scrollTop + _popoverContent.clientHeight < _popoverContent.scrollHeight;
+						_popoverContent.classList[hasBottomOverflow ? 'add' : 'remove']('overflowBottom');
+					}, {passive: true});
+					
 					this._popover.appendChild(_popoverContent);
 					
 					var pointer = elCreate('span');
diff --git a/wcfsetup/install/files/style/ui/reactions.scss b/wcfsetup/install/files/style/ui/reactions.scss
index b22db4f6ef..18e4c4ed12 100644
--- a/wcfsetup/install/files/style/ui/reactions.scss
+++ b/wcfsetup/install/files/style/ui/reactions.scss
@@ -4,6 +4,7 @@
 	background-color: $wcfContentBackground;
 	border-radius: 2px;
 	box-shadow: 0 2px 6px rgba(0,0,0,0.16), 0 3px 6px rgba(0,0,0,0.23);
+	overflow: hidden;
 	position: absolute;
 	top: 0;
 	vertical-align: middle;
@@ -23,6 +24,12 @@
 	> .elementPointer {
 		display: none;
 	}
+	
+	@include screen-xs {
+		&.inverseOrder .reactionTypeButtonList {
+			flex-direction: column-reverse;
+		}
+	}
 }
 
 .reactionType {
@@ -86,6 +93,39 @@
 		}
 	}
 	
+	@include screen-xs {
+		max-height: 200px;
+		overflow: auto;
+		
+		&::after,
+		&::before {
+			content: "";
+			height: 40px;
+			left: 0;
+			opacity: 0;
+			pointer-events: none;
+			position: absolute;
+			right: 0;
+			transition: opacity .12s linear;
+		}
+		
+		&::after {
+			background-image: linear-gradient(to bottom, transparent, $wcfContentBackground);
+			bottom: 0;
+		}
+		&.overflowBottom::after {
+			opacity: 1;
+		}
+		
+		&::before {
+			background-image: linear-gradient(to top, transparent, $wcfContentBackground);
+			top: 0;
+		}
+		&.overflowTop::before {
+			opacity: 1;
+		}
+	}
+	
 	@include screen-md-down {
 		padding: 5px 0;
 		
@@ -140,6 +180,11 @@
 	}
 }
 
+.reactionTypeButtonList {
+	display: flex;
+	flex-direction: column;
+}
+
 @include screen-lg {
 	html.touch .reactionPopoverContent .reactionTypeButton {
 		display: block;
-- 
2.20.1