feat: Undo Accept (#7980)

* allow breaking of follow

* send undo

* delete by using reject follow

packages/backend/src/server/api/endpoints/following/invalidate.ts

@@ -0,0 +1,82 @@
+import $ from 'cafy';
+import { ID } from '@/misc/cafy-id';
+import * as ms from 'ms';
+import deleteFollowing from '@/services/following/delete';
+import define from '../../define';
+import { ApiError } from '../../error';
+import { getUser } from '../../common/getters';
+import { Followings, Users } from '@/models/index';
+
+export const meta = {
+	tags: ['following', 'users'],
+
+	limit: {
+		duration: ms('1hour'),
+		max: 100
+	},
+
+	requireCredential: true as const,
+
+	kind: 'write:following',
+
+	params: {
+		userId: {
+			validator: $.type(ID),
+		}
+	},
+
+	errors: {
+		noSuchUser: {
+			message: 'No such user.',
+			code: 'NO_SUCH_USER',
+			id: '5b12c78d-2b28-4dca-99d2-f56139b42ff8'
+		},
+
+		followerIsYourself: {
+			message: 'Follower is yourself.',
+			code: 'FOLLOWER_IS_YOURSELF',
+			id: '07dc03b9-03da-422d-885b-438313707662'
+		},
+
+		notFollowing: {
+			message: 'The other use is not following you.',
+			code: 'NOT_FOLLOWING',
+			id: '5dbf82f5-c92b-40b1-87d1-6c8c0741fd09'
+		},
+	},
+
+	res: {
+		type: 'object' as const,
+		optional: false as const, nullable: false as const,
+		ref: 'User'
+	}
+};
+
+export default define(meta, async (ps, user) => {
+	const followee = user;
+
+	// Check if the follower is yourself
+	if (user.id === ps.userId) {
+		throw new ApiError(meta.errors.followerIsYourself);
+	}
+
+	// Get follower
+	const follower = await getUser(ps.userId).catch(e => {
+		if (e.id === '15348ddd-432d-49c2-8a5a-8069753becff') throw new ApiError(meta.errors.noSuchUser);
+		throw e;
+	});
+
+	// Check not following
+	const exist = await Followings.findOne({
+		followerId: follower.id,
+		followeeId: followee.id
+	});
+
+	if (exist == null) {
+		throw new ApiError(meta.errors.notFollowing);
+	}
+
+	await deleteFollowing(follower, followee);
+
+	return await Users.pack(followee.id, user);
+});