m2d reactions (untested)

m2d/actions/add-reaction.js

@@ -0,0 +1,25 @@
+// @ts-check
+
+const assert = require("assert").strict
+const Ty = require("../../types")
+
+const passthrough = require("../../passthrough")
+const { discord, sync, db } = passthrough
+
+/**
+ * @param {Ty.Event.Outer<Ty.Event.M_Reaction>} event
+ */
+async function addReaction(event) {
+	const channelID = db.prepare("SELECT channel_id FROM channel_room WHERE room_id = ?").pluck().get(event.room_id)
+	if (!channelID) return // We just assume the bridge has already been created
+	const messageID = db.prepare("SELECT message_id FROM event_message WHERE event_id = ? AND part = 0").pluck().get(event.content["m.relates_to"].event_id) // 0 = primary
+	if (!messageID) return // Nothing can be done if the parent message was never bridged.
+
+	// no need to sync the matrix member to the other side. but if I did need to, this is where I'd do it
+
+	const emoji = event.content["m.relates_to"].key // TODO: handle custom text or emoji reactions
+
+	return discord.snow.channel.createReaction(channelID, messageID, emoji)
+}
+
+module.exports.addReaction = addReaction

m2d/converters/event-to-message.js

@@ -1,5 +1,6 @@
 // @ts-check
 
+const Ty = require("../../types")
 const DiscordTypes = require("discord-api-types/v10")
 const markdown = require("discord-markdown")
 
@@ -9,7 +10,7 @@ const { sync, db, discord } = passthrough
 const file = sync.require("../../matrix/file")
 
 /**
- * @param {import("../../types").Event.Outer<import("../../types").Event.M_Room_Message>} event
+ * @param {Ty.Event.Outer<Ty.Event.M_Room_Message>} event
  */
 function eventToMessage(event) {
 	/** @type {(DiscordTypes.RESTPostAPIWebhookWithTokenJSONBody & {files?: {name: string, file: Buffer}[]})[]} */

m2d/event-dispatcher.js

@@ -4,19 +4,30 @@
  * Grab Matrix events we care about, check them, and bridge them.
  */
 
+const Ty = require("../types")
 const {sync, as} = require("../passthrough")
 
 /** @type {import("./actions/send-event")} */
 const sendEvent = sync.require("./actions/send-event")
+/** @type {import("./actions/add-reaction")} */
+const addReaction = sync.require("./actions/add-reaction")
 /** @type {import("./converters/utils")} */
 const utils = sync.require("./converters/utils")
 
-
 sync.addTemporaryListener(as, "type:m.room.message",
 /**
- * @param {import("../types").Event.Outer<import("../types").Event.M_Room_Message>} event it is a m.room.message because that's what this listener is filtering for
+ * @param {Ty.Event.Outer<Ty.Event.M_Room_Message>} event it is a m.room.message because that's what this listener is filtering for
  */
 async event => {
 	if (utils.eventSenderIsFromDiscord(event.sender)) return
 	const messageResponses = await sendEvent.sendEvent(event)
 })
+
+sync.addTemporaryListener(as, "type:m.reaction",
+/**
+ * @param {Ty.Event.Outer<Ty.Event.M_Reaction>} event it is a m.reaction because that's what this listener is filtering for
+ */
+async event => {
+	if (utils.eventSenderIsFromDiscord(event.sender)) return
+	await addReaction.addReaction(event)
+})