From ad0f638487c45ad2f79375e38220b051ada5dfae Mon Sep 17 00:00:00 2001
From: Pavel Djundik <github@xpaw.me>
Date: Wed, 18 Jul 2018 21:31:51 +0300
Subject: [PATCH] Add jump-to-bottom arrow when scrolled up

---
 client/components/MessageList.vue  | 41 ++++++++++++++++----
 client/css/style.css               | 60 ++++++++++++++++++++++++++++++
 client/js/socket-events/init.js    |  2 +
 client/js/socket-events/network.js |  2 +
 4 files changed, 98 insertions(+), 7 deletions(-)

diff --git a/client/components/MessageList.vue b/client/components/MessageList.vue
index a42f2be1..7ca57ed0 100644
--- a/client/components/MessageList.vue
+++ b/client/components/MessageList.vue
@@ -55,6 +55,18 @@
 					@linkPreviewToggle="onLinkPreviewToggle"/>
 			</template>
 		</div>
+
+		<transition name="fade">
+			<div
+				v-if="!channel.scrolledToBottom"
+				class="scroll-down"
+				@click="jumpToBottom()">
+				<div class="scroll-down-arrow"/>
+				<div
+					v-if="unreadMessages > 0"
+					class="scroll-down-number">{{ unreadMessages }}</div>
+			</div>
+		</transition>
 	</div>
 </template>
 
@@ -125,10 +137,23 @@ export default {
 
 			return condensed;
 		},
+		unreadMessages() {
+			let unread = 0;
+
+			for (let id = this.condensedMessages.length - 1; id > 0; id--) {
+				if (this.channel.firstUnread >= this.condensedMessages[id].id) {
+					break;
+				}
+
+				unread++;
+			}
+
+			return unread;
+		},
 	},
 	watch: {
 		"channel.id"() {
-			this.$set(this.channel, "scrolledToBottom", true);
+			this.channel.scrolledToBottom = true;
 		},
 		"channel.messages"() {
 			this.keepScrollPosition();
@@ -153,7 +178,7 @@ export default {
 			}
 
 			this.channel.scrolledToBottom = true;
-			this.$refs.chat.scrollTop = this.$refs.chat.scrollHeight;
+			this.jumpToBottom();
 		});
 	},
 	mounted() {
@@ -261,7 +286,7 @@ export default {
 			this.isWaitingForNextTick = true;
 			this.$nextTick(() => {
 				this.isWaitingForNextTick = false;
-				el.scrollTop = el.scrollHeight;
+				this.jumpToBottom();
 			});
 		},
 		handleScroll() {
@@ -275,12 +300,14 @@ export default {
 		},
 		handleResize() {
 			// Keep message list scrolled to bottom on resize
-			const el = this.$refs.chat;
-
-			if (el && this.channel.scrolledToBottom) {
-				el.scrollTop = el.scrollHeight;
+			if (this.channel.scrolledToBottom) {
+				this.jumpToBottom();
 			}
 		},
+		jumpToBottom() {
+			const el = this.$refs.chat;
+			el.scrollTop = el.scrollHeight;
+		},
 	},
 };
 </script>
diff --git a/client/css/style.css b/client/css/style.css
index e1b5d44b..201d8f82 100644
--- a/client/css/style.css
+++ b/client/css/style.css
@@ -259,6 +259,7 @@ kbd {
 #chat .action .from::before,
 #chat .toggle-button::after,
 #chat .toggle-content .more-caret::before,
+#chat .scroll-down-arrow::after,
 #version-checker::before,
 .context-menu-item::before,
 #help .website-link::before,
@@ -1082,6 +1083,65 @@ background on hover (unless active) */
 	margin: 0;
 }
 
+.scroll-down.fade-leave-active,
+.scroll-down.fade-enter-active {
+	opacity: 0;
+	transform: translateY(16px);
+	transition: opacity .3s, transform .3s;
+}
+
+.scroll-down.fade-enter-to {
+	opacity: 1;
+	transform: none;
+}
+
+.scroll-down {
+	position: absolute;
+
+	bottom: 16px;
+	right: 16px;
+	z-index: 2;
+	transition: right 0.2s ease-in-out;
+	cursor: pointer;
+}
+
+.scroll-down-number {
+	background: #84ce88;
+	border-radius: 50%;
+	text-align: center;
+	width: 30px;
+	height: 30px;
+	line-height: 30px;
+	font-size: 12px;
+	margin-left: 9px;
+	z-index: 23;
+	position: absolute;
+	top: -20px;
+	font-weight: bold;
+}
+
+.scroll-down-arrow {
+	width: 48px;
+	height: 48px;
+	line-height: 48px;
+	border-radius: 50%;
+	background: #fff;
+	border: 1px solid #84ce88;
+	text-align: center;
+}
+
+.scroll-down:hover .scroll-down-arrow {
+	background: #84ce88;
+}
+
+.scroll-down-arrow::after {
+	content: "\f107"; /* https://fontawesome.com/icons/angle-down?style=solid */
+}
+
+.userlist-open #chat .scroll-down {
+	right: 196px;
+}
+
 #chat .messages {
 	padding: 10px 0;
 	touch-action: pan-y;
diff --git a/client/js/socket-events/init.js b/client/js/socket-events/init.js
index 1e807700..2e9347ee 100644
--- a/client/js/socket-events/init.js
+++ b/client/js/socket-events/init.js
@@ -47,6 +47,8 @@ socket.on("init", function(data) {
 		}
 
 		for (const channel of network.channels) {
+			channel.scrolledToBottom = true;
+
 			if (channel.type === "channel") {
 				channel.usersOutdated = true;
 			}
diff --git a/client/js/socket-events/network.js b/client/js/socket-events/network.js
index e5c1d80c..67f19ba7 100644
--- a/client/js/socket-events/network.js
+++ b/client/js/socket-events/network.js
@@ -14,6 +14,8 @@ socket.on("network", function(data) {
 	network.isCollapsed = false;
 
 	for (const channel of network.channels) {
+		channel.scrolledToBottom = true;
+
 		if (channel.type === "channel") {
 			channel.usersOutdated = true;
 		}