fix: incorrect disc number handling in ape tag writer

CHANGELOG.md

@@ -26,6 +26,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   - Some encoders will only write a BOM to the frame's description, rather than to every string in the frame.
     This was previously only supported in `SYLT` frames, and has been extended to `COMM` and `USLT`.
 - **Vorbis Comments**: Parse `TRACKNUMBER` with respect to `ParseOptions::implicit_conversions` ([issue](https://github.com/Serial-ATA/lofty-rs/issues/540)) ([PR](https://github.com/Serial-ATA/lofty-rs/issues/542))
+- **APE**: Fix disc number removal/writing ([issue](https://github.com/Serial-ATA/lofty-rs/issues/545)) ([PR](https://github.com/Serial-ATA/lofty-rs/pull/546))
 
 ### Removed
 

lofty/src/ape/tag/mod.rs

@@ -285,11 +285,11 @@ impl Accessor for ApeTag {
 	}
 
 	fn remove_disk_total(&mut self) {
-		let existing_track_number = self.track();
+		let existing_disk_number = self.disk();
 		self.remove("Disc");
 
-		if let Some(track) = existing_track_number {
-			self.insert(ApeItem::text("Disc", track.to_string()));
+		if let Some(disk) = existing_disk_number {
+			self.insert(ApeItem::text("Disc", disk.to_string()));
 		}
 	}
 
@@ -564,7 +564,7 @@ pub(crate) fn tagitems_into_ape(tag: &Tag) -> impl Iterator<Item = ApeItemRef<'_
 		.chain(create_apeitemref_for_number_pair(
 			tag.get_string(ItemKey::DiscNumber),
 			tag.get_string(ItemKey::DiscTotal),
-			"Disk",
+			"Disc",
 		))
 }
 
@@ -947,4 +947,18 @@ mod tests {
 
 		assert_eq!(ape.len(), 1);
 	}
+
+	#[test_log::test]
+	fn remove_disk_total_preserves_disk_number() {
+		let mut ape = ApeTag::new();
+		ape.set_track(2);
+		ape.set_disk(3);
+		ape.set_disk_total(5);
+
+		ape.remove_disk_total();
+
+		assert_eq!(ape.disk(), Some(3));
+		assert!(ape.disk_total().is_none());
+		assert_eq!(ape.track(), Some(2));
+	}
 }

lofty/tests/files/wavpack.rs

@@ -1,9 +1,10 @@
 use crate::{set_artist, temp_file, verify_artist};
-use lofty::config::ParseOptions;
+use lofty::ape::ApeTag;
+use lofty::config::{ParseOptions, WriteOptions};
 use lofty::file::FileType;
 use lofty::prelude::*;
 use lofty::probe::Probe;
-use lofty::tag::TagType;
+use lofty::tag::{Tag, TagType};
 
 use std::io::Seek;
 
@@ -77,3 +78,42 @@ fn read_no_properties() {
 fn read_no_tags() {
 	crate::no_tag_test!("tests/files/assets/minimal/full_test.wv");
 }
+
+#[test_log::test]
+fn write_ape_disc_key() {
+	let mut file = crate::temp_file!("tests/files/assets/minimal/full_test.wv");
+	let mut tagged_file = Probe::new(&mut file)
+		.options(ParseOptions::new())
+		.guess_file_type()
+		.unwrap()
+		.read()
+		.unwrap();
+
+	// Create and insert a new Tag and set disk information
+	let mut tag = Tag::new(TagType::Ape);
+	tag.set_disk(3);
+	tag.set_disk_total(5);
+	tagged_file.insert_tag(tag);
+	file.rewind().unwrap();
+	tagged_file
+		.save_to(&mut file, WriteOptions::default())
+		.unwrap();
+
+	// Reread the file to get the actual APE tag
+	file.rewind().unwrap();
+	let reread_tagged_file = Probe::new(&mut file)
+		.options(ParseOptions::new())
+		.guess_file_type()
+		.unwrap()
+		.read()
+		.unwrap();
+	let tag_ref = reread_tagged_file.tag(TagType::Ape).unwrap();
+	let ape_tag: ApeTag = tag_ref.clone().into();
+
+	assert!(
+		ape_tag.get("Disc").is_some(),
+		"APE tag should contain `Disc` key with disk information"
+	);
+	assert_eq!(ape_tag.disk(), Some(3));
+	assert_eq!(ape_tag.disk_total(), Some(5));
+}