feathermost/js/view/messages.js

function transformMessageText(message) {
	return message
		.split(/(?<=:|\W|^)(:[a-z0-9_+-]+:)(?=:|\W|$)/)
		.map((x, i) => i % 2
			?  emoji[x.slice(1, -1)] || x
			: x)
		.join("");
}


function shouldShowTime(lastShownTime, time) {
	const sim = dateSimilarity(lastShownTime, time);
	if (sim < DATE_SIMILARITY.date) {
		return {date: true, time: true};
	}
	const minutesSinceLastShown = (time - lastShownTime) / 1000 / 60;
	if (minutesSinceLastShown >= 15) {
		return {date: false, time: true};
	}
	return {date: false, time: false};
}


async function createMessageElement(client, post, lastTime, lastAuthor) {
	let nodes = [];

	const users = await client.getUsers();
	const isThreadReply = !!post.parent_id;

	const createAt = new Date(post.create_at);
	let createAtLocalized = createAt;
	let lastTimeLocalized = lastTime;
	try {
		if (client.me.timezone.useAutomaticTimezone !== "true") {
			createAtLocalized = toTimeZone(createAt, client.me.timezone.manualTimezone);
			lastTimeLocalized = toTimeZone(lastTime, client.me.timezone.manualTimezone);
		}
	} catch(e) {}
	const showTime = shouldShowTime(lastTimeLocalized, createAtLocalized);
	if (showTime.time) {
		lastTime = createAt;
	}

	const postDiv = document.createElement("div");
	postDiv.className = "post";
	if (post.type !== "") {
		postDiv.className += " special";
	}

	if (showTime.date) {
		const dateElement = document.createElement("div");
		dateElement.className = "date_separator";
		dateElement.innerText = formatYyyyMmDdWeekday(createAtLocalized);
		nodes.push(dateElement);
	}

	if (showTime.time) {
		postDiv.className += " show_time";
	}

	const messageDiv = document.createElement("div");
	messageDiv.className = "message";
	messageDiv.innerText = transformMessageText(post.message);

	const createAtDiv = document.createElement("time");
	createAtDiv.className = "create_at";
	let createAtText = formatHhMm(createAtLocalized);
	createAtDiv.title = createAt.toString();
	createAtDiv.innerText = createAtText;
	createAtDiv.dateTime = createAt.toISOString();

	const authorName = users[post.user_id] ? users[post.user_id].username : post.user_id;
	const authorDiv = document.createElement("div");
	authorDiv.className = "author";
	authorDiv.innerText = authorName;

	if (lastAuthor === post.user_id) {
		postDiv.className += " same_author";
	}
	lastAuthor = post.user_id;

	postDiv.dataset["id"] = post.id;
	postDiv.appendChild(authorDiv);
	postDiv.appendChild(createAtDiv);
	postDiv.appendChild(messageDiv);

	if (post.metadata && (post.metadata.files || []).length > 0) {
		const attachmentsUl = document.createElement("ul");
		attachmentsUl.className = "attachments";
		for (let file of post.metadata.files || []) {
			const attachmentLi = document.createElement("li");
			attachmentLi.dataset["id"] = file.id;

			const attachmentA = document.createElement("a");
			client.filePublicLink(file.id).then(link => attachmentA.href = link);
			attachmentA.target = "_blank";
			attachmentA.innerText = file.name;

			if (file.mini_preview) {
				const attachmentImg = document.createElement("img");
				attachmentImg.src = `data:image/jpeg;base64,${file.mini_preview}`;
				attachmentA.appendChild(attachmentImg);
			}

			attachmentLi.appendChild(attachmentA);
			attachmentsUl.appendChild(attachmentLi);
		}
		postDiv.appendChild(attachmentsUl);
	}

	nodes.push(postDiv);

	return {nodes, lastTime, lastAuthor};
}


async function populateChannelContents(client, channel, contents) {
	byId("channel_contents").innerHTML = "";

	let result = {lastAuthor: null, lastTime: null, postDiv: null};

	let nodes = [];
	for (let id of contents.order) {
		result = await createMessageElement(client, contents.posts[id], result.lastTime, result.lastAuthor);
		nodes.push(...result.nodes);
	}

	byId("channel_contents").dataset["server"] = client.endpoint;
	byId("channel_contents").dataset["id"] = channel.id;
	byId("channel_contents").dataset["lastTime"] = result.lastTime.getTime();
	byId("channel_contents").dataset["lastAuthor"] = result.lastAuthor;
	byId("channel_contents").append(...nodes);
	scrollToBottom();
}


async function addMessage(client, post) {
	const shouldScroll = isScrolledToBottom();

	const result = await createMessageElement(
		client, post,
		new Date(1 * (byId("channel_contents").dataset["lastTime"])),
		byId("channel_contents").dataset["lastAuthor"]
	);
	byId("channel_contents").dataset["lastTime"] = result.lastTime.getTime();
	byId("channel_contents").dataset["lastAuthor"] = result.lastAuthor;
	byId("channel_contents").append(...result.nodes);

	if (shouldScroll) {
		scrollToBottom();
	}
}


function scrollToBottom() {
	const el = byId("channel_contents_wrapper");
	el.scrollTop = el.scrollHeight;
	el.className = "";
}


function updateComposeHeight() {
	byId("compose").style.height = "";
	byId("compose").style.height = (byId("compose").scrollHeight + 1) + "px";
}
byId("compose").addEventListener("input", updateComposeHeight);

function isScrolledToBottom() {
	const el = byId("channel_contents_wrapper");

	const scrolledTo = el.clientHeight + el.scrollTop;
	return scrolledTo + 1 >= el.scrollHeight;
}
function checkScrolledToBottom() {
	if (isScrolledToBottom()) {
		removeClass(byId("channel_contents_wrapper"), "not-at-bottom");
	} else {
		addClass(byId("channel_contents_wrapper"), "not-at-bottom");
	}
}
byId("channel_contents_wrapper").addEventListener("scroll", checkScrolledToBottom);


function currentChannel() {
	return {
		endpoint: byId("channel_contents").dataset["server"],
		channel_id: byId("channel_contents").dataset["id"]
	};
}


pubsub.subscribe("MESSAGES_NEW", post => {
	const chan = currentChannel();
	if (post.endpoint === chan.endpoint && post.channel_id === chan.channel_id) {
		addMessage(mm_client.getOrCreate(post.endpoint), post);
	}
});