Sync pins back from Matrix to Discord

src/m2d/actions/update-pins.js

@@ -0,0 +1,25 @@
+// @ts-check
+
+const {sync, from, discord} = require("../../passthrough")
+
+/** @type {import("../converters/diff-pins")} */
+const diffPins = sync.require("../converters/diff-pins")
+
+/**
+ * @param {string[]} pins
+ * @param {string[]} prev
+ */
+async function updatePins(pins, prev) {
+	const diff = diffPins.diffPins(pins, prev)
+	for (const [event_id, added] of diff) {
+		const row = from("event_message").join("message_channel", "message_id").where({event_id}).select("channel_id", "message_id").get()
+		if (!row) continue
+		if (added) {
+			discord.snow.channel.addChannelPinnedMessage(row.channel_id, row.message_id, "Message pinned on Matrix")
+		} else {
+			discord.snow.channel.removeChannelPinnedMessage(row.channel_id, row.message_id, "Message unpinned on Matrix")
+		}
+	}
+}
+
+module.exports.updatePins = updatePins

src/m2d/converters/diff-pins.js

@@ -0,0 +1,17 @@
+// @ts-check
+
+/**
+ * @param {string[]} pins
+ * @param {string[]} prev
+ * @returns {[string, boolean][]}
+ */
+function diffPins(pins, prev) {
+	/** @type {[string, boolean][]} */
+	const result = []
+	return result.concat(
+		prev.filter(id => !pins.includes(id)).map(id => [id, false]), // removed
+		pins.filter(id => !prev.includes(id)).map(id => [id, true]) // added
+	)
+}
+
+module.exports.diffPins = diffPins

src/m2d/converters/diff-pins.test.js

@@ -0,0 +1,11 @@
+// @ts-check
+
+const {test} = require("supertape")
+const diffPins = require("./diff-pins")
+
+test("diff pins: diff is as expected", t => {
+	t.deepEqual(
+		diffPins.diffPins(["same", "new"], ["same", "old"]),
+		[["old", false], ["new", true]]
+	)
+})

src/m2d/event-dispatcher.js

@@ -14,6 +14,8 @@ const sendEvent = sync.require("./actions/send-event")
 const addReaction = sync.require("./actions/add-reaction")
 /** @type {import("./actions/redact")} */
 const redact = sync.require("./actions/redact")
+/** @type {import("./actions/update-pins")}) */
+const updatePins = sync.require("./actions/update-pins")
 /** @type {import("../matrix/matrix-command-handler")} */
 const matrixCommandHandler = sync.require("../matrix/matrix-command-handler")
 /** @type {import("./converters/utils")} */
@@ -159,6 +161,33 @@ async event => {
 	db.prepare("UPDATE channel_room SET nick = ? WHERE room_id = ?").run(name, event.room_id)
 }))
 
+sync.addTemporaryListener(as, "type:m.room.pinned_events", guard("m.room.pinned_events",
+/**
+ * @param {Ty.Event.StateOuter<Ty.Event.M_Room_PinnedEvents>} event
+ */
+async event => {
+	if (event.state_key !== "") return
+	if (utils.eventSenderIsFromDiscord(event.sender)) return
+	const pins = event.content.pinned
+	if (!Array.isArray(pins)) return
+	let prev = event.unsigned?.prev_content?.pinned
+	if (!Array.isArray(prev)) {
+		if (pins.length === 1) {
+			/*
+				In edge cases, prev_content isn't guaranteed to be provided by the server.
+				If prev_content is missing, we can't diff. Better safe than sorry: we'd like to ignore the change rather than wiping the whole channel's pins on Discord.
+				However, that would mean if the first ever pin came from Matrix-side, it would be ignored, because there would be no prev_content (it's the first pinned event!)
+				So to handle that edge case, we assume that if there's exactly 1 entry in `pinned`, this is the first ever pin and it should go through.
+			*/
+			prev = []
+		} else {
+			return
+		}
+	}
+
+	await updatePins.updatePins(pins, prev)
+}))
+
 sync.addTemporaryListener(as, "type:m.room.member", guard("m.room.member",
 /**
  * @param {Ty.Event.StateOuter<Ty.Event.M_Room_Member>} event

src/types.d.ts

@@ -241,6 +241,10 @@ export namespace Event {
 		name?: string
 	}
 
+	export type M_Room_PinnedEvents = {
+		pinned: string[]
+	}
+
 	export type M_Power_Levels = {
 		/** The level required to ban a user. Defaults to 50 if unspecified. */
 		ban?: number,

test/test.js

@@ -139,6 +139,7 @@ file._actuallyUploadDiscordFileToMxc = function(url, res) { throw new Error(`Not
 	require("../src/d2m/converters/remove-reaction.test")
 	require("../src/d2m/converters/thread-to-announcement.test")
 	require("../src/d2m/converters/user-to-mxid.test")
+	require("../src/m2d/converters/diff-pins.test")
 	require("../src/m2d/converters/event-to-message.test")
 	require("../src/m2d/converters/utils.test")
 	require("../src/m2d/converters/emoji-sheet.test")