feat(api): Message Accessories API (#131)

src/api/MessageAccessories.ts

@@ -0,0 +1,41 @@
+export type AccessoryCallback = (props: Record<string, any>) => JSX.Element;
+export type Accessory = {
+    callback: AccessoryCallback;
+    position?: number;
+};
+
+export const accessories = new Map<String, Accessory>();
+
+export function addAccessory(
+    identifier: string,
+    callback: AccessoryCallback,
+    position?: number
+) {
+    accessories.set(identifier, {
+        callback,
+        position,
+    });
+}
+
+export function removeAccessory(identifier: string) {
+    accessories.delete(identifier);
+}
+
+export function _modifyAccessories(
+    elements: JSX.Element[],
+    props: Record<string, any>
+) {
+    for (const accessory of accessories.values()) {
+        elements.splice(
+            accessory.position != null
+                ? accessory.position < 0
+                    ? elements.length + accessory.position
+                    : accessory.position
+                : elements.length,
+            0,
+            accessory.callback(props)
+        );
+    }
+
+    return elements;
+}