reactions: support unicode custom emojis

Signed-off-by: Sumner Evans <sumner.evans@automattic.com>

pkg/connector/emojis/emojis.go

@@ -0,0 +1,41 @@
+package emojis
+
+import (
+	_ "embed"
+	"encoding/json"
+
+	"maunium.net/go/mautrix/bridgev2/networkid"
+
+	"go.mau.fi/mautrix-telegram/pkg/connector/ids"
+)
+
+//go:embed unicodemojipack.json
+var unicodemojiPackJSON []byte
+
+var unicodemojiPack = map[string]int64{}
+var reverseUnicodemojiPack = map[int64]string{}
+
+func init() {
+	if err := json.Unmarshal(unicodemojiPackJSON, &unicodemojiPack); err != nil {
+		panic("Failed to unmarshal unicodemojipack")
+	}
+
+	for k, v := range unicodemojiPack {
+		reverseUnicodemojiPack[v] = k
+	}
+}
+
+// ConvertKnownEmojis converts known document IDs from the unicode emoji pack
+// to the corresponding unicode string and returns the remaining IDs.
+func ConvertKnownEmojis(emojiIDs []int64) (result map[networkid.EmojiID]string, remaining []int64) {
+	result = map[networkid.EmojiID]string{}
+	for _, e := range emojiIDs {
+		if v, ok := reverseUnicodemojiPack[e]; ok {
+			emojiID := ids.MakeEmojiIDFromDocumentID(e)
+			result[emojiID] = v
+		} else {
+			remaining = append(remaining, e)
+		}
+	}
+	return
+}