wip on autotagging

frontend/src/utils/disc-grouping.ts

@@ -0,0 +1,48 @@
+// Shared helpers for grouping a tracklist by disc number — used by
+// both the explore album view and the autotag review UI so the
+// rendering rules stay consistent (single-disc albums skip the
+// "Disc 1" separator, multi-disc albums show one per disc).
+
+export interface Disced {
+    discNumber?: number;
+    position?: number;
+}
+
+/**
+ * Returns true when any track has a discNumber > 1.  A list with
+ * only disc 1 (or no discNumber set) renders without "Disc N"
+ * headers.
+ */
+export function isMultiDisc<T extends Disced>(tracks: T[]): boolean {
+    return tracks.some((t) => (t.discNumber ?? 1) > 1);
+}
+
+/**
+ * Group tracks by disc number, sorting tracks within each disc
+ * by position.  Discs with no number default to disc 1, which
+ * matches MusicBrainz behaviour for releases that omit the field.
+ */
+export function groupByDisc<T extends Disced>(tracks: T[]): Map<number, T[]> {
+    const discMap = new Map<number, T[]>();
+
+    for (const track of tracks) {
+        const disc = track.discNumber ?? 1;
+        const bucket = discMap.get(disc);
+        if (bucket) {
+            bucket.push(track);
+        } else {
+            discMap.set(disc, [track]);
+        }
+    }
+
+    for (const bucket of discMap.values()) {
+        bucket.sort((a, b) => (a.position ?? 0) - (b.position ?? 0));
+    }
+
+    return discMap;
+}
+
+/** Returns disc numbers in ascending order from a grouped map. */
+export function discNumbers<T>(discMap: Map<number, T[]>): number[] {
+    return [...discMap.keys()].sort((a, b) => a - b);
+}