use lua script for debit

1 files changed, 35 insertions, 2 deletions

diff --git a/lib/db.js b/lib/db.js
index b22af94a..197697a0 100644
--- a/lib/db.js
+++ b/lib/db.js
@@ -1,9 +1,42 @@
 import config from "$config";
 import { sleep } from "$lib/utils";
-import { createClient } from "redis";
+import { createClient, defineScript } from "redis";
 import { warn } from "$lib/logging";
 
-export const db = createClient({ url: config.db });
+let SCRIPT = `
+local balanceKey = KEYS[1]
+local creditKey = KEYS[2]
+local amount = tonumber(ARGV[1])
+local tip = tonumber(ARGV[2])
+local fee = tonumber(ARGV[3])
+local ourfee = tonumber(ARGV[4])
+
+local balance = tonumber(redis.call('get', balanceKey) or '0')
+local credit = tonumber(redis.call('get', creditKey) or '0')
+
+local covered = math.min(credit, ourfee)
+ourfee = ourfee - covered
+
+if balance < amount + tip + fee + ourfee then
+    return {err = 'Insufficient funds'}
+end
+
+redis.call('decrby', creditKey, tostring(math.floor(covered)))
+redis.call('decrby', balanceKey, tostring(math.floor(amount + tip + fee + ourfee)))
+
+return {ok = 'ok'}
+`;
+
+let debit = defineScript({
+  NUMBER_OF_KEYS: 2,
+  SCRIPT,
+  transformArguments: (...args) => args.map(a => a.toString())
+});
+
+export const db = createClient({
+  url: config.db,
+  scripts: { debit }
+});
 await db.connect();
 export default db;