feat(core): implement message tasks

includes:
- acknowledgements
- last_message_id
- embeds
- web push

crates/core/database/src/tasks/mod.rs

@@ -0,0 +1,58 @@
+//! Semi-important background task management
+
+use crate::Database;
+
+use async_std::task;
+use std::time::Instant;
+
+const WORKER_COUNT: usize = 5;
+
+pub mod ack;
+pub mod last_message_id;
+pub mod process_embeds;
+pub mod web_push;
+
+/// Spawn background workers
+pub async fn start_workers(db: Database) {
+    for _ in 0..WORKER_COUNT {
+        task::spawn(ack::worker(db.clone()));
+        task::spawn(last_message_id::worker(db.clone()));
+        task::spawn(process_embeds::worker(db.clone()));
+        task::spawn(web_push::worker(db.clone().into()));
+    }
+}
+
+/// Task with additional information on when it should run
+pub struct DelayedTask<T> {
+    pub data: T,
+    last_updated: Instant,
+    first_seen: Instant,
+}
+
+/// Commit to database every 30 seconds if the task is particularly active.
+static EXPIRE_CONSTANT: u64 = 30;
+
+/// Otherwise, commit to database after 5 seconds.
+static SAVE_CONSTANT: u64 = 5;
+
+impl<T> DelayedTask<T> {
+    /// Create a new delayed task
+    pub fn new(data: T) -> Self {
+        DelayedTask {
+            data,
+            last_updated: Instant::now(),
+            first_seen: Instant::now(),
+        }
+    }
+
+    /// Push a task further back in time
+    pub fn delay(&mut self) {
+        self.last_updated = Instant::now()
+    }
+
+    /// Check if a task should run yet
+    pub fn should_run(&self) -> bool {
+        self.first_seen.elapsed().as_secs() > EXPIRE_CONSTANT
+            || self.last_updated.elapsed().as_secs() > SAVE_CONSTANT
+    }
+}