MP4: Merge existing atoms in Ilst::insert

Now, when inserting an atom that already exists in a tag, the data is taken from the provided atom and merged with the existing value in the tag. This should ensure that the value that already exists in the tag will remain the dominant one.

CHANGELOG.md

@@ -22,6 +22,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - **MP4**:
   - `Ilst::remove` will now return all of the removed atoms
   - `Ilst::insert_picture` will now combine all pictures into a single `covr` atom
+  - `Ilst::insert` will now merge atoms with the same identifier into a single atom
 
 ## [0.15.0] - 2023-07-11
 

src/mp4/ilst/mod.rs

@@ -125,6 +125,10 @@ impl Ilst {
 
 	/// Inserts an [`Atom`]
 	///
+	/// NOTE: Do not use this to replace atoms. This will take the value from the provided atom and
+	///       merge it into an atom of the same type, keeping any existing value(s). To ensure an atom
+	///       is replaced, use [`Ilst::replace_atom`].
+	///
 	/// # Examples
 	///
 	/// ```rust
@@ -142,7 +146,8 @@ impl Ilst {
 	/// let title = ilst.get(&TITLE_IDENTIFIER);
 	/// assert!(title.is_some());
 	/// ```
-	pub fn insert(&mut self, atom: Atom<'_>) {
+	#[allow(clippy::missing_panics_doc)] // Unwrap on an infallible
+	pub fn insert(&mut self, atom: Atom<'static>) {
 		if atom.ident == COVR && atom.data.is_pictures() {
 			for data in atom.data {
 				match data {
@@ -153,7 +158,14 @@ impl Ilst {
 			return;
 		}
 
-		self.atoms.push(atom.into_owned());
+		if let Some(existing) = self.get_mut(atom.ident()) {
+			existing.merge(atom).expect(
+				"Somehow the atom merge condition failed, despite the validation beforehand.",
+			);
+			return;
+		}
+
+		self.atoms.push(atom);
 	}
 
 	/// Inserts an [`Atom`], replacing any atom with the same [`AtomIdent`]
@@ -752,6 +764,7 @@ impl From<Tag> for Ilst {
 #[cfg(test)]
 mod tests {
 	use crate::mp4::ilst::atom::AtomDataStorage;
+	use crate::mp4::ilst::TITLE;
 	use crate::mp4::read::AtomReader;
 	use crate::mp4::{AdvisoryRating, Atom, AtomData, AtomIdent, Ilst, Mp4File};
 	use crate::tag::utils::test_utils;
@@ -1156,4 +1169,20 @@ mod tests {
 
 		assert_eq!(file.ilst(), Some(&Ilst::default()));
 	}
+
+	#[test]
+	fn merge_insert() {
+		let mut ilst = Ilst::new();
+
+		// Insert two titles
+		ilst.set_title(String::from("Foo"));
+		ilst.insert(Atom::new(TITLE, AtomData::UTF8(String::from("Bar"))));
+
+		// Title should still be the first value, but there should be two total values
+		assert_eq!(ilst.title().as_deref(), Some("Foo"));
+		assert_eq!(ilst.get(&TITLE).unwrap().data().count(), 2);
+
+		// Meaning we only have 1 atom
+		assert_eq!(ilst.len(), 1);
+	}
 }