Syncing two local and remote db tables

DatabaseSyncer.kt

package com.test

class DatabaseSyncer() {

    // Updated thanks to @gildor
        private fun findUpdatedNotes(
        allLocalNotes: List<Note>,
        allRemoteNotes: List<Note>
    ): List<Note> {

        val newLocalNotes = allLocalNotes.minus(allRemoteNotes).associateBy(Note::id)
        val newRemoteNotes = allRemoteNotes.minus(allLocalNotes)

        val updatedNotes = newRemoteNotes.map { remoteNote ->
            val localNote = newLocalNotes[remoteNote.id]
            when {
                localNote == null -> remoteNote
                remoteNote.creationId == localNote.creationId -> newestNote(localNote, remoteNote)
                else -> remoteNote.copy(id = 0)
            }
        }.sortedByDescending {
            // we add copied notes at the end to avoid auto-incremented ID
            // from being the same as later non-conflicting notes
            it.id
        }

        return updatedNotes
    }

    private fun newestNote(note1: Note, note2: Note): Note {
        return if (note1.updatedAt.isAfter(note2.updatedAt)) {
            note1
        } else {
            note2
        }
    }
}

Note.kt

package com.test

data class Note(
    val id: Long = 0,
    val title: String,
    val creationId: String = UUID.randomUUID().toString(),
    val createdAt: OffsetDateTime = OffsetDateTime.now(),
    val updatedAt: OffsetDateTime = OffsetDateTime.now()
)

TestCases

localNotes has 1 new note, remoteDb has 2 new notes
localNotes has 2 new notes and remoteDb has 1 new note
localNotes has new notes, remoteDb has no notes at all
localNotes has no new notes, remoteDb has new notes
localNotes has no notes at all and remoteDb has new notes
localNotes and remoteDb have modified the same note, localDb modified last
localNotes has new notes, remoteDb has new notes
localNotes has new notes, remoteDb has no new notes
localNotes and remoteDb have modified the same note, remoteDb modified last