From 2388255803a9188b6e69a76ca30a751449070ce2 Mon Sep 17 00:00:00 2001
From: 728 <septem.duo.octo@outlook.com>
Date: Sat, 20 May 2023 13:58:55 +0800
Subject: [PATCH] rel #43

---
 ismism.ts/src/eid/is.ts  |  4 +---
 ismism.ts/src/eid/rel.ts | 28 ++++++++++++++++++++++++++++
 2 files changed, 29 insertions(+), 3 deletions(-)
 create mode 100644 ismism.ts/src/eid/rel.ts

diff --git a/ismism.ts/src/eid/is.ts b/ismism.ts/src/eid/is.ts
index 8af24a3..9746ef1 100644
--- a/ismism.ts/src/eid/is.ts
+++ b/ismism.ts/src/eid/is.ts
@@ -11,9 +11,7 @@ export const lim_code = 10 ** len_code
 export const lst_re = 2
 export const lim_re = 64
 
-export const lim_sec = 8
-export const lim_uid = 128
-export const lim_res = 64
+export const lim_rel = { sec: 8, uid: 128, res: 64 }
 
 export const lim_itm = 16
 export const lim_loc = 16
diff --git a/ismism.ts/src/eid/rel.ts b/ismism.ts/src/eid/rel.ts
new file mode 100644
index 0000000..ef312eb
--- /dev/null
+++ b/ismism.ts/src/eid/rel.ts
@@ -0,0 +1,28 @@
+import type { Rel, Usr } from "./typ.ts"
+import { Update } from "./db.ts";
+import { is_id, is_lim, lim_rel } from "./is.ts";
+
+export type UpdateRel = {
+	rel: keyof Rel,
+	op: "add" | "pull",
+	uid?: Usr["_id"]
+}
+
+export function rel_u(
+	rel: Rel,
+	u: UpdateRel
+): Update<Rel> | null {
+	if (u.uid !== undefined && !is_id(u.uid)) return null
+	const r = rel[u.rel]
+	switch (u.op) {
+		case "add": {
+			if (!u.uid) return r ? null : { $set: { [u.rel]: [] } }
+			if (!r || !is_lim(r.length + 1, lim_rel[u.rel])) return null
+			return { $addToSet: { [u.rel]: u.uid } }
+		} case "pull": {
+			if (!u.uid) return r ? { $unset: { [u.rel]: "" } } : null
+			if (!r || !r.includes(u.uid)) return null
+			return { $pull: { [u.rel]: u.uid } }
+		}
+	}
+}