Centralize periodic checks for mutes, tempbans, vcalerts, reminders, and scheduled posts

This should result in a significant performance improvement.
The new method is also more precise than the old one, allowing
the aforementioned checks to be performed with second-precision.

backend/src/plugins/Reminders/functions/postReminder.ts

@@ -0,0 +1,41 @@
+import { GuildPluginData } from "knub";
+import { RemindersPluginType } from "../types";
+import { Reminder } from "../../../data/entities/Reminder";
+import { Snowflake, TextChannel } from "discord.js";
+import moment from "moment-timezone";
+import { disableLinkPreviews } from "knub/dist/helpers";
+import { DBDateFormat, SECONDS } from "../../../utils";
+import humanizeDuration from "humanize-duration";
+
+export async function postReminder(pluginData: GuildPluginData<RemindersPluginType>, reminder: Reminder) {
+  const channel = pluginData.guild.channels.cache.get(reminder.channel_id as Snowflake);
+  if (channel && (channel.isText() || channel.isThread())) {
+    try {
+      // Only show created at date if one exists
+      if (moment.utc(reminder.created_at).isValid()) {
+        const createdAtTS = Math.floor(moment.utc(reminder.created_at, DBDateFormat).valueOf() / 1000);
+        await channel.send({
+          content: disableLinkPreviews(
+            `Reminder for <@!${reminder.user_id}>: ${reminder.body} \nSet <t:${createdAtTS}:R>`,
+          ),
+          allowedMentions: {
+            users: [reminder.user_id as Snowflake],
+          },
+        });
+      } else {
+        await channel.send({
+          content: disableLinkPreviews(`Reminder for <@!${reminder.user_id}>: ${reminder.body}`),
+          allowedMentions: {
+            users: [reminder.user_id as Snowflake],
+          },
+        });
+      }
+    } catch (err) {
+      // If we were unable to post the reminder, we'll try again later
+      console.warn(`Error when posting reminder for ${reminder.user_id} in guild ${reminder.guild_id}: ${String(err)}`);
+      return;
+    }
+  }
+
+  await pluginData.state.reminders.delete(reminder.id);
+}