From 2fd2079330582fd30aeb074f0ff0ba4caa395119 Mon Sep 17 00:00:00 2001
From: Alex Page <alex@anpage.me>
Date: Wed, 8 Mar 2023 18:35:30 -0500
Subject: [PATCH] Implement moving to the next track

---
 src/queue.rs | 102 ++++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 89 insertions(+), 13 deletions(-)

diff --git a/src/queue.rs b/src/queue.rs
index 36dd1c1..06953f7 100644
--- a/src/queue.rs
+++ b/src/queue.rs
@@ -1,10 +1,15 @@
 //! Implements a queue for the bot to play songs in order
 
+use std::sync::Arc;
+
 use anyhow::Result;
+use parking_lot::Mutex;
+use poise::async_trait;
 use songbird::{
+    events::EventData,
     input::Input,
     tracks::{self, TrackHandle},
-    Driver,
+    Driver, Event, EventContext, EventHandler, TrackEvent,
 };
 use thiserror::Error;
 
@@ -14,19 +19,69 @@ pub enum QueueError {
     EmptyQueue,
 }
 
+/// Event handler for the queue
+struct QueueHandler {
+    remote_lock: Arc<Mutex<QueueCore>>,
+}
+
+#[async_trait]
+impl EventHandler for QueueHandler {
+    async fn act(&self, ctx: &EventContext<'_>) -> Option<Event> {
+        let mut inner = self.remote_lock.lock();
+
+        // Due to possibility that users might remove, reorder,
+        // or dequeue+stop tracks, we need to verify that the FIRST
+        // track is the one who has ended.
+        match ctx {
+            EventContext::Track(ts) => {
+                // This slice should have exactly one entry.
+                // If the ended track has same id as the queue head, then
+                // we can progress the queue.
+                if inner.tracks.first()?.uuid() != ts.first()?.1.uuid() {
+                    return None;
+                }
+            }
+            _ => return None,
+        }
+
+        let _old = inner.tracks.remove(0);
+
+        // Keep going until we find one track which works, or we run out.
+        while let Some(new) = inner.tracks.first() {
+            if new.play().is_err() {
+                // Discard files which cannot be used for whatever reason.
+                inner.tracks.remove(0);
+            } else {
+                break;
+            }
+        }
+
+        None
+    }
+}
+
+/// Inner queue data behind a Mutex to allow the event handler to access it
+struct QueueCore {
+    tracks: Vec<TrackHandle>,
+}
+
+/// A queue of tracks to play
 pub struct Queue {
-    queue: Vec<TrackHandle>,
+    inner: Arc<Mutex<QueueCore>>,
 }
 
 impl Queue {
     #[must_use]
     pub fn new() -> Self {
-        Self { queue: Vec::new() }
+        Self {
+            inner: Arc::new(Mutex::new(QueueCore { tracks: Vec::new() })),
+        }
     }
 
     /// Resumes the current track
     pub fn resume(&mut self) -> Result<()> {
-        let Some(track) = self.queue.first() else {
+        let inner = self.inner.lock();
+        let Some(track) = inner.tracks.first() else {
             return Err(QueueError::EmptyQueue.into());
         };
         track.play()?;
@@ -35,17 +90,19 @@ impl Queue {
 
     /// Stops the current track and removes it from the queue
     pub fn stop(&mut self) -> Result<()> {
-        let Some(track) = self.queue.first() else {
+        let mut inner = self.inner.lock();
+        let Some(track) = inner.tracks.first() else {
             return Err(QueueError::EmptyQueue.into());
         };
         track.stop()?;
-        self.queue.remove(0);
+        inner.tracks.remove(0);
         Ok(())
     }
 
     /// Pauses the current track
     pub fn pause(&mut self) -> Result<()> {
-        let Some(track) = self.queue.first() else {
+        let inner = self.inner.lock();
+        let Some(track) = inner.tracks.first() else {
             return Err(QueueError::EmptyQueue.into());
         };
         track.pause()?;
@@ -54,9 +111,25 @@ impl Queue {
 
     /// Adds a track to the end of the queue
     pub fn add_to_end(&mut self, source: Input, handler: &mut Driver) -> TrackHandle {
+        let mut inner = self.inner.lock();
         let (mut track, handle) = tracks::create_player(source);
         track.pause();
-        self.queue.push(handle.clone());
+        let position = track.position();
+        // Event to remove the track from the queue when it ends
+        track
+            .events
+            .as_mut()
+            .expect("Why is this even an Option?")
+            .add_event(
+                EventData::new(
+                    Event::Track(TrackEvent::End),
+                    QueueHandler {
+                        remote_lock: self.inner.clone(),
+                    },
+                ),
+                position,
+            );
+        inner.tracks.push(handle.clone());
         handler.play(track);
         handle
     }
@@ -76,12 +149,13 @@ impl Queue {
 
     /// Adds a track to play next
     pub fn add_next(&mut self, source: Input, handler: &mut Driver) -> TrackHandle {
+        let mut inner = self.inner.lock();
         let (mut track, handle) = tracks::create_player(source);
         track.pause();
-        if self.queue.is_empty() {
-            self.queue.push(handle.clone());
+        if inner.tracks.is_empty() {
+            inner.tracks.push(handle.clone());
         } else {
-            self.queue.insert(1, handle.clone());
+            inner.tracks.insert(1, handle.clone());
         }
         handler.play(track);
         handle
@@ -89,7 +163,8 @@ impl Queue {
 
     /// Clears the queue
     pub fn clear(&mut self) {
-        for track in self.queue.drain(..) {
+        let mut inner = self.inner.lock();
+        for track in inner.tracks.drain(..) {
             let _ = track.stop();
         }
     }
@@ -97,6 +172,7 @@ impl Queue {
     /// Returns whether the queue is empty
     #[must_use]
     pub fn is_empty(&self) -> bool {
-        self.queue.is_empty()
+        let inner = self.inner.lock();
+        inner.tracks.is_empty()
     }
 }