feat: retain bounded preview caches across selections and views

src/main.rs

@@ -21,7 +21,11 @@
 //! Left-aligned text starts one column after the actual image width, including height-limited images.
 //! A blank row separates the bold title from the dimmed author · publication date.
 //! Text retains a two-column right gutter; overflowing excerpts end with … without splitting wide glyphs.
-//! Both previews share asynchronous full-description fetching and per-video caching.
+//! Both previews share an in-memory LRU of 64 full descriptions, keyed by video ID across views.
+//! Thumbnails retain eight recently used inactive decoded images plus the selected image.
+//! Reopening or revisiting cached videos skips extraction/download/decoding; resize work stays off-thread.
+//! Title, author, and publication metadata remain in loaded view rows; preview caches survive view/query changes.
+//! Caches last for this session without a timer. A successful r refresh clears both preview buffers.
 //! curl fetches JPEGs lazily into memory; decoding and image resizing/encoding run off-thread.
 //! Channel tags live in `$XDG_CONFIG_HOME/tubular/config.toml`, or `~/.config/tubular/config.toml`.
 //! `[categories]` stores flat, overlapping tags: one channel can appear in several arrays.
@@ -92,6 +96,18 @@ struct Options {
     query: Option<String>,
 }
 
+const DESCRIPTION_CACHE_SIZE: usize = 64;
+
+fn cached_description<'a>(
+    cache: &'a std::collections::VecDeque<(String, String)>,
+    id: &str,
+) -> Option<&'a str> {
+    cache
+        .iter()
+        .find(|(cached, _)| cached == id)
+        .map(|(_, text)| text.as_str())
+}
+
 #[derive(Debug, PartialEq, Eq)]
 enum Mode {
     Insert,
@@ -150,7 +166,7 @@ impl View {
             videos.sort_by(|a, b| b.timestamp.cmp(&a.timestamp));
         }
         if !videos.is_empty() {
-            // Borrow IDs before moving rows, retaining existing rows and their description caches.
+            // Borrow IDs before moving rows, retaining the existing row data.
             let keep: Vec<_> = {
                 let mut ids = HashSet::with_capacity(self.videos.len() + videos.len());
                 ids.extend(self.videos.iter().map(|video| video.id.as_str()));
@@ -221,6 +237,8 @@ struct App {
     description_open: bool,
     description_job: Option<(usize, Job)>,
     description_error: Option<String>,
+    // ponytail: 64-entry linear lookup; use a keyed LRU if the buffer grows.
+    descriptions: std::collections::VecDeque<(String, String)>,
     description_scroll: u16,
     description_max_scroll: u16,
     description_viewport: Option<(u16, u16)>,
@@ -251,6 +269,7 @@ impl App {
             description_open: false,
             description_job: None,
             description_error: None,
+            descriptions: std::collections::VecDeque::with_capacity(DESCRIPTION_CACHE_SIZE),
             description_scroll: 0,
             description_max_scroll: 0,
             description_viewport: None,
@@ -458,6 +477,8 @@ impl App {
         self.close_thumbnail();
         match config::load(&self.config_path) {
             Ok(config) => {
+                self.thumbnail.clear_cache();
+                self.descriptions.clear();
                 self.apply_config(config);
                 self.load_view();
             }
@@ -644,7 +665,12 @@ impl App {
             return;
         };
         let video = &view.videos[index];
-        if video.description.is_some() {
+        if let Some(index) = self.descriptions.iter().position(|(id, _)| id == &video.id) {
+            let hit = self
+                .descriptions
+                .remove(index)
+                .expect("cache position exists");
+            self.descriptions.push_back(hit);
             return;
         }
         match Job::description(&video.id) {
@@ -653,6 +679,20 @@ impl App {
         }
     }
 
+    fn remember_description(&mut self, id: String, description: String) {
+        if let Some(index) = self
+            .descriptions
+            .iter()
+            .position(|(cached, _)| cached == &id)
+        {
+            self.descriptions.remove(index);
+        }
+        if self.descriptions.len() == DESCRIPTION_CACHE_SIZE {
+            self.descriptions.pop_front();
+        }
+        self.descriptions.push_back((id, description));
+    }
+
     fn play(&mut self) {
         let view = &self.views[self.view_index];
         let Some(video) = view
@@ -689,9 +729,9 @@ impl App {
                 .description_job
                 .take()
                 .expect("completed description job exists");
-            if let Some(video) = self.views[self.view_index].videos.get_mut(index) {
+            if let Some(video) = self.views[self.view_index].videos.get(index) {
                 match result.and_then(|output| youtube::full_description(&output, &video.id)) {
-                    Ok(description) => video.description = Some(description),
+                    Ok(description) => self.remember_description(video.id.clone(), description),
                     Err(error) => self.description_error = Some(error),
                 }
             }
@@ -974,7 +1014,7 @@ impl App {
         {
             let popup = preview_area(frame.area());
             frame.render_widget(Clear, popup);
-            let text = match video.description.as_deref() {
+            let text = match cached_description(&self.descriptions, &video.id) {
                 Some("") => "This video has no description.",
                 Some(description) => description,
                 None => self
@@ -1065,7 +1105,8 @@ impl App {
             excerpt.height -= height + gap;
             details.height = height;
             frame.render_widget(metadata, details);
-            let description = match video.description.as_deref() {
+            let cached = cached_description(&self.descriptions, &video.id);
+            let description = match cached {
                 Some("") => "This video has no description.",
                 Some(description) => description,
                 None => self
@@ -1074,10 +1115,7 @@ impl App {
                     .unwrap_or("Loading full description..."),
             };
             let paragraph = Paragraph::new(description).wrap(Wrap { trim: false }).dim();
-            let overflow = video
+            let overflow = cached.is_some_and(|text| !text.is_empty())
-                .description
-                .as_deref()
-                .is_some_and(|text| !text.is_empty())
                 && !excerpt.is_empty()
                 && paragraph.line_count(excerpt.width) > usize::from(excerpt.height);
             frame.render_widget(paragraph, excerpt);
@@ -1312,6 +1350,46 @@ mod tests {
         )
     }
 
+    #[test]
+    fn descriptions_are_shared_across_views_and_evict_least_recently_used_entries() {
+        let mut app = app(&["tubular"]);
+        let output = r#"{"entries":[{"id":"jNQXAC9IVRw","title":"Shared video"}]}"#;
+        for view in &mut app.views {
+            view.videos = youtube::search_results(output).unwrap().videos;
+            view.selection.select(Some(0));
+            view.loaded = true;
+        }
+        app.remember_description("jNQXAC9IVRw".into(), "Shared full description".into());
+        for index in 1..DESCRIPTION_CACHE_SIZE {
+            app.remember_description(format!("video{index:06}"), format!("Description {index}"));
+        }
+        app.switch_view(1);
+        app.load_description(); // A hit in Feed promotes the Search video's description.
+        assert!(app.description_job.is_none());
+        app.remember_description("new00000000".into(), "New description".into());
+        assert_eq!(
+            cached_description(&app.descriptions, "jNQXAC9IVRw"),
+            Some("Shared full description")
+        );
+        assert_eq!(cached_description(&app.descriptions, "video000001"), None);
+        assert_eq!(
+            cached_description(&app.descriptions, "video000002"),
+            Some("Description 2")
+        );
+        // Updating an existing entry, including a known empty description, must not evict another.
+        app.remember_description("jNQXAC9IVRw".into(), String::new());
+        app.load_description();
+        assert!(app.description_job.is_none());
+        assert_eq!(
+            cached_description(&app.descriptions, "jNQXAC9IVRw"),
+            Some("")
+        );
+        assert_eq!(
+            cached_description(&app.descriptions, "video000002"),
+            Some("Description 2")
+        );
+    }
+
     #[test]
     fn thumbnail_ellipsis_marks_only_hidden_content_and_preserves_wide_characters() {
         use ratatui::{Terminal, backend::TestBackend};
@@ -1329,11 +1407,14 @@ mod tests {
             ("a界界界界界界界界界", true, Some(63)),
             ("", true, Some(46)),
         ] {
-            app.views[0].videos[0].description = Some(format!(
+            app.remember_description(
-                "{}{last_line}{}",
+                "jNQXAC9IVRw".into(),
-                "line\n".repeat(6),
+                format!(
-                if hidden { "\nhidden content" } else { "" },
+                    "{}{last_line}{}",
-            ));
+                    "line\n".repeat(6),
+                    if hidden { "\nhidden content" } else { "" },
+                ),
+            );
             let mut terminal = Terminal::new(TestBackend::new(80, 24)).unwrap();
             terminal
                 .draw(|frame| app.draw(frame, Duration::ZERO))
@@ -1369,8 +1450,10 @@ mod tests {
         app.views[0].videos = youtube::search_results(
             r#"{"entries":[{"id":"jNQXAC9IVRw","title":"First second third fourth fifth","channel":"Creator","upload_date":"20050423"}]}"#,
         ).unwrap().videos;
-        app.views[0].videos[0].description =
+        app.remember_description(
-            Some(format!("{}CLIPPED SENTINEL", "Excerpt line\n".repeat(30)));
+            "jNQXAC9IVRw".into(),
+            format!("{}CLIPPED SENTINEL", "Excerpt line\n".repeat(30)),
+        );
         app.views[0].selection.select(Some(0));
         app.thumbnail_open = true;
         for (width, height) in [(80, 24), (120, 40), (20, 10)] {
@@ -1464,7 +1547,7 @@ mod tests {
     }
 
     #[test]
-    fn search_pages_preserve_relevance_selection_and_cached_descriptions() {
+    fn search_pages_preserve_relevance_and_selection() {
         let mut view = View::new("Search".into());
         let mut first = youtube::search_results(
             r#"{"entries":[{"id":"jNQXAC9IVRw","title":"First","timestamp":100},{"id":"rQ_J9WH6CGk","title":"Second","timestamp":200}]}"#,
@@ -1473,7 +1556,6 @@ mod tests {
         first.has_more = true;
         view.accept_page(first, false).unwrap();
         view.selection.select(Some(1));
-        view.videos[1].description = Some("Cached full description.".into());
         let mut next = youtube::search_results(
             r#"{"entries":[{"id":"rQ_J9WH6CGk","title":"Duplicate"},{"id":"l-GaaivVJCE","title":"Relevant","timestamp":50},{"id":"l-GaaivVJCE","title":"Repeated"},{"id":"aaaaaaaaaaa","title":"Later","timestamp":300}]}"#,
         )
@@ -1488,10 +1570,6 @@ mod tests {
             ["jNQXAC9IVRw", "rQ_J9WH6CGk", "l-GaaivVJCE", "aaaaaaaaaaa"]
         );
         assert_eq!(view.videos[1].title, "Second");
-        assert_eq!(
-            view.videos[1].description.as_deref(),
-            Some("Cached full description.")
-        );
         assert_eq!(view.selection.selected(), Some(1));
         assert_eq!(view.next_start, 41);
         assert!(view.has_more);
@@ -1517,17 +1595,12 @@ mod tests {
         assert_eq!(view.videos.last().unwrap().timestamp, Some(200));
         assert_eq!(view.pending.len(), 2);
         view.selection.select(Some(PAGE_SIZE - 1));
-        view.videos[PAGE_SIZE - 1].description = Some("Keep this cache.".into());
         let second = youtube::feed_results(&format!("{}\n{short}", long_page(180))).unwrap();
         view.accept_page(second, true).unwrap();
         assert_eq!(view.videos.len(), PAGE_SIZE * 2);
         assert_eq!(view.videos.last().unwrap().timestamp, Some(180));
         assert_eq!(view.pending.len(), 2);
         assert_eq!(view.selection.selected(), Some(PAGE_SIZE - 1));
-        assert_eq!(
-            view.videos[PAGE_SIZE - 1].description.as_deref(),
-            Some("Keep this cache.")
-        );
         view.accept_page(
             youtube::feed_results(
                 r#"{"entries":[{"id":"l-GaaivVJCE","title":"Long last row","timestamp":179}]} {"entries":[]}"#,
@@ -1647,7 +1720,7 @@ mod tests {
         app.finish_page(Ok(serde_json::json!({"entries": entries}).to_string()));
         assert_eq!(app.views[0].next_start, 21);
         app.views[0].selection.select(Some(17));
-        app.views[0].videos[17].description = Some("Cached.".into());
+        app.remember_description(app.views[0].videos[17].id.clone(), "Cached.".into());
         app.switch_view(1);
         app.switch_view(0);
         assert_eq!(app.views[0].next_start, 21);
@@ -1657,7 +1730,7 @@ mod tests {
         assert!(app.job.is_none());
         assert_eq!(app.views[0].videos.len(), PAGE_SIZE);
         assert_eq!(
-            app.views[0].videos[17].description.as_deref(),
+            cached_description(&app.descriptions, &app.views[0].videos[17].id),
             Some("Cached.")
         );
         assert_eq!(app.views[0].next_start, 21);
@@ -1876,7 +1949,6 @@ mod tests {
                 uploader_id: None,
                 timestamp: None,
                 publication_date: None,
-                description: None,
             },
             Video {
                 id: "rQ_J9WH6CGk".into(),
@@ -1886,7 +1958,6 @@ mod tests {
                 uploader_id: None,
                 timestamp: None,
                 publication_date: None,
-                description: None,
             },
         ];
         app.views[0].selection.select(Some(0));
@@ -2045,7 +2116,10 @@ mod tests {
         .unwrap()
         .videos;
         app.views[1].page_error = Some("Retained page error".into());
-        app.views[1].videos[1].description = Some("Retained description".into());
+        app.remember_description(
+            app.views[1].videos[1].id.clone(),
+            "Retained description".into(),
+        );
         app.views[3].videos = youtube::feed_results(videos).unwrap().videos;
         app.views[3].selection.select(Some(0));
         app.views[3].loaded = true;
@@ -2080,7 +2154,7 @@ mod tests {
             Some("Retained page error")
         );
         assert_eq!(
-            app.views[1].videos[1].description.as_deref(),
+            cached_description(&app.descriptions, &app.views[1].videos[1].id),
             Some("Retained description")
         );
         assert!(!app.views[4].loaded);
@@ -2358,7 +2432,7 @@ mod tests {
         app.views[0].videos = youtube::search_results(
             r#"{"entries":[{"id":"jNQXAC9IVRw","title":"Me at the zoo","channel_id":"UC4QobU6STFB0P71PMvOGN5A","uploader_id":"@jawed"}]}"#,
         ).unwrap().videos;
-        app.views[0].videos[0].description = Some("A cached full description.".into());
+        app.remember_description("jNQXAC9IVRw".into(), "A cached full description.".into());
         app.views[0].selection.select(Some(0));
         app.views[0].loaded = true;
         app.thumbnail_open = true;

src/thumbnail.rs

@@ -18,6 +18,8 @@ use ratatui_image::{
 
 use crate::youtube::ThumbnailJob;
 
+const CACHE_SIZE: usize = 8;
+
 struct ThumbnailImage {
     id: String,
     protocol: ThreadProtocol,
@@ -31,8 +33,8 @@ pub struct Thumbnail {
     fetch: Option<ThumbnailJob>,
     decoder: Option<Receiver<Result<ThumbnailImage, String>>>,
     image: Option<ThumbnailImage>,
-    // ponytail: one completed thumbnail plus an in-flight replacement, not a video cache.
+    // ponytail: eight-entry linear lookup; use a keyed LRU if the buffer grows.
-    cached: Option<ThumbnailImage>,
+    cached: std::collections::VecDeque<ThumbnailImage>,
     error: Option<String>,
 }
 
@@ -44,7 +46,7 @@ impl Thumbnail {
             fetch: None,
             decoder: None,
             image: None,
-            cached: None,
+            cached: std::collections::VecDeque::with_capacity(CACHE_SIZE),
             error: None,
         }
     }
@@ -62,10 +64,16 @@ impl Thumbnail {
         if self.selected.as_deref() == Some(id) {
             return;
         }
+        // Remove a hit before storing the previous image so eviction cannot discard the target.
+        let cached = self
+            .cached
+            .iter()
+            .position(|image| image.id == id)
+            .and_then(|index| self.cached.remove(index));
         self.cancel();
         self.selected = Some(id.to_owned());
-        if self.cached.as_ref().is_some_and(|image| image.id == id) {
+        if let Some(image) = cached {
-            self.image = self.cached.take();
+            self.image = Some(image);
             return;
         }
         match ThumbnailJob::start(id) {
@@ -83,10 +91,18 @@ impl Thumbnail {
         if let Some(image) = self.image.take()
             && image.complete
         {
-            self.cached = Some(image);
+            if self.cached.len() == CACHE_SIZE {
+                self.cached.pop_front();
+            }
+            self.cached.push_back(image);
         }
     }
 
+    pub fn clear_cache(&mut self) {
+        self.cancel();
+        self.cached.clear();
+    }
+
     pub fn is_loading(&self) -> bool {
         self.selected.is_some()
             && self.error.is_none()
@@ -180,7 +196,6 @@ impl Thumbnail {
                     // area again before rendering, so rapid resizes cannot draw an old size.
                     if image.protocol.update_resized_protocol(response) {
                         image.complete = true;
-                        self.cached = None;
                     }
                 }
                 Ok(Err(error)) => {
@@ -281,6 +296,62 @@ mod tests {
         assert!(thumbnail.error.is_none());
     }
 
+    #[test]
+    fn thumbnail_hits_survive_a_full_buffer_and_promote_recent_images() {
+        let mut thumbnail = Thumbnail::new();
+        let completed = |id: String| {
+            let (requests, _receiver) = mpsc::channel();
+            let (_sender, replies) = mpsc::channel();
+            ThumbnailImage {
+                id,
+                protocol: ThreadProtocol::new(
+                    requests,
+                    Some(
+                        Picker::halfblocks()
+                            .new_resize_protocol(image::DynamicImage::new_rgb8(1, 1)),
+                    ),
+                ),
+                replies,
+                complete: true,
+            }
+        };
+        for index in 0..CACHE_SIZE {
+            thumbnail.image = Some(completed(format!("video{index:06}")));
+            thumbnail.cancel();
+        }
+        thumbnail.image = Some(completed("video000008".into()));
+        thumbnail.selected = Some("video000008".into());
+        // This is the oldest cached image: storing the outgoing image first would evict it.
+        thumbnail.select("video000000");
+        assert_eq!(thumbnail.image.as_ref().unwrap().id, "video000000");
+        assert!(thumbnail.fetch.is_none());
+        thumbnail.select("video000001");
+        assert_eq!(thumbnail.image.as_ref().unwrap().id, "video000001");
+        assert!(thumbnail.fetch.is_none());
+        thumbnail.cancel();
+        assert!(
+            !thumbnail
+                .cached
+                .iter()
+                .any(|image| image.id == "video000002")
+        );
+        assert!(
+            thumbnail
+                .cached
+                .iter()
+                .any(|image| image.id == "video000000")
+        );
+        assert!(
+            thumbnail
+                .cached
+                .iter()
+                .any(|image| image.id == "video000008")
+        );
+        thumbnail.clear_cache();
+        assert!(thumbnail.cached.is_empty());
+        assert!(thumbnail.image.is_none());
+    }
+
     #[test]
     fn small_thumbnail_fills_popup_proportionally_and_resizes() {
         use ratatui::{Terminal, backend::TestBackend, style::Color};

src/youtube.rs

@@ -27,9 +27,6 @@ pub struct Video {
     /// Cached YYYY-MM-DD label; a leading ~ marks an estimated UTC date.
     #[serde(default, rename = "upload_date")]
     pub publication_date: Option<String>,
-    // Search descriptions are truncated; only full video metadata populates this cache.
-    #[serde(skip)]
-    pub description: Option<String>,
 }
 
 #[derive(Deserialize)]