Timed comments on previews too

pl8list gives where a preview cuts in (previewStart, a fraction of the full
track). The server keeps it and hands previews their start in seconds; the
card moves each comment by it and keeps the ones inside the clip. Tracks
crawled before this show none until their artist comes round again.

backend/src/db.rs

@@ -133,6 +133,11 @@ CREATE TABLE IF NOT EXISTS meta (
 );
 "#;
 
+// preview_start: where a preview cuts in, as a fraction of the full track.
+const SCHEMA_V5: &str = r#"
+ALTER TABLE tracks ADD COLUMN preview_start REAL;
+"#;
+
 pub fn now() -> f64 {
     SystemTime::now().duration_since(UNIX_EPOCH).unwrap_or_default().as_secs_f64()
 }
@@ -229,6 +234,9 @@ fn migrate(conn: &Connection) -> rusqlite::Result<()> {
     if version < 4 {
         conn.execute_batch(&format!("BEGIN; {SCHEMA_V4} PRAGMA user_version = 4; COMMIT;"))?;
     }
+    if version < 5 {
+        conn.execute_batch(&format!("BEGIN; {SCHEMA_V5} PRAGMA user_version = 5; COMMIT;"))?;
+    }
     Ok(())
 }
 
@@ -379,6 +387,8 @@ pub struct Track {
     pub key: Option<String>,
     pub duration: Option<f64>,
     pub preview_duration: Option<f64>,
+    /// Where the preview cuts in, 0..1 of the full track.
+    pub preview_start: Option<f64>,
     pub price: f64,
     pub created_at: Option<String>,
     pub upload_id: Option<String>,
@@ -393,9 +403,9 @@ pub struct Track {
     pub related_of: Option<i64>,
 }
 
-const TRACK_COLS: [&str; 23] = [
+const TRACK_COLS: [&str; 24] = [
     "id", "handle", "artist_name", "artist_img", "artist_verified", "slug", "title", "description",
-    "bpm", "key", "duration", "preview_duration", "price", "created_at", "upload_id",
+    "bpm", "key", "duration", "preview_duration", "preview_start", "price", "created_at", "upload_id",
     "preview_upload_id", "waveform", "preview_waveform", "full_access", "saves", "downloads",
     "purchases", "comments",
 ];
@@ -415,6 +425,7 @@ impl Track {
             key: r.get("key")?,
             duration: r.get("duration")?,
             preview_duration: r.get("preview_duration")?,
+            preview_start: r.get("preview_start")?,
             price: r.get::<_, Option<f64>>("price")?.unwrap_or(0.0),
             created_at: r.get("created_at")?,
             upload_id: r.get("upload_id")?,
@@ -449,6 +460,7 @@ impl Track {
             opt(&self.key),
             optf(self.duration),
             optf(self.preview_duration),
+            optf(self.preview_start),
             price,
             opt(&self.created_at),
             opt(&self.upload_id),

backend/src/pl8/normalize.rs

@@ -82,6 +82,7 @@ fn track(t: &Value, extra: Extra) -> Option<Track> {
         key: text(t, "key"),
         duration: num(t, "duration"),
         preview_duration: num(t, "previewDuration"),
+        preview_start: num(t, "previewStart"),
         price: num(t, "price").unwrap_or(0.0),
         created_at: text(t, "createdAt"),
         upload_id: text(t, "uploadId"),

backend/src/ranker.rs

@@ -479,6 +479,8 @@ pub fn serialize(r: &Track, score: Option<f64>) -> Value {
         "purchases": r.purchases,
         "comments": r.comments,
         "preview": preview,
+        // Seconds into the full track where the preview cuts in.
+        "preview_start": if preview { r.preview_start.zip(r.duration).map(|(f, d)| f * d) } else { None },
         "upload_id": if preview { &r.preview_upload_id } else { &r.upload_id },
         "waveform": wave.as_deref().and_then(|w| serde_json::from_str::<Value>(w).ok()),
         "score": score.map(|s| (s * 1000.0).round() / 1000.0),

web/src/api.ts

@@ -19,6 +19,8 @@ export interface Track {
   purchases: number;
   comments: number;
   preview: boolean;
+  /// For a preview: seconds into the full track where it cuts in.
+  preview_start?: number | null;
   upload_id: string | null;
   waveform: number[] | null;
   followed?: boolean;

web/src/cards.ts

@@ -93,12 +93,16 @@ export class Card {
   private comments: WaveComments | null = null;
   private commentsAsked = false;
 
-  /// Fetch the timed comments, once. Previews have none: their moments are those
-  /// of the full track.
+  /// Fetch the timed comments, once. Their moments are those of the full track, so
+  /// a preview shows only the ones inside its clip, moved to where the clip starts.
   loadComments(): void {
-    if (this.commentsAsked || this.track.preview || !this.track.comments) return;
+    const t = this.track;
+    const start = t.preview ? t.preview_start : 0;
+    if (this.commentsAsked || start == null || !t.comments) return;
     this.commentsAsked = true;
-    comments(this.track.id).then(({ comments: list }) => {
+    comments(t.id).then(({ comments: all }) => {
+      const end = t.preview ? (t.duration ?? 0) : Infinity;
+      const list = start ? all.map((c) => ({ ...c, at: c.at - start })).filter((c) => c.at >= 0 && c.at <= end) : all;
       if (!list.length) return;
       this.comments = new WaveComments(list, () => this.actions.duration(this));
       const wrap = this.canvas?.parentElement;