Adaptive tags suggestion

app/src/main/kotlin/org/koitharu/kotatsu/core/db/dao/TagsDao.kt

@@ -51,6 +51,28 @@ abstract class TagsDao {
 	)
 	abstract suspend fun findTags(query: String, limit: Int): List<TagEntity>
 
+	@Query(
+		"""
+		SELECT tags.* FROM manga_tags 
+		LEFT JOIN tags ON tags.tag_id = manga_tags.tag_id 
+		WHERE manga_tags.manga_id IN (SELECT manga_id FROM manga_tags WHERE tag_id = :tagId)
+		GROUP BY tags.tag_id 
+		ORDER BY COUNT(manga_id) DESC;
+	""",
+	)
+	abstract suspend fun findRelatedTags(tagId: Long): List<TagEntity>
+
+	@Query(
+		"""
+		SELECT tags.* FROM manga_tags 
+		LEFT JOIN tags ON tags.tag_id = manga_tags.tag_id 
+		WHERE manga_tags.manga_id IN (SELECT manga_id FROM manga_tags WHERE tag_id IN (:ids))
+		GROUP BY tags.tag_id 
+		ORDER BY COUNT(manga_id) DESC;
+	""",
+	)
+	abstract suspend fun findRelatedTags(ids: Set<Long>): List<TagEntity>
+
 	@Upsert
 	abstract suspend fun upsert(tags: Iterable<TagEntity>)
 }

app/src/main/kotlin/org/koitharu/kotatsu/core/db/entity/EntityMapping.kt

@@ -19,6 +19,8 @@ fun TagEntity.toMangaTag() = MangaTag(
 
 fun Collection<TagEntity>.toMangaTags() = mapToSet(TagEntity::toMangaTag)
 
+fun Collection<TagEntity>.toMangaTagsList() = map(TagEntity::toMangaTag)
+
 fun MangaEntity.toManga(tags: Set<MangaTag>) = Manga(
 	id = this.id,
 	title = this.title,

app/src/main/kotlin/org/koitharu/kotatsu/filter/ui/FilterCoordinator.kt

@@ -131,7 +131,7 @@ class FilterCoordinator @Inject constructor(
 		observeState(),
 		observeAvailableTags(),
 	) { state, available ->
-		val chips = createChipsList(state, available.orEmpty())
+		val chips = createChipsList(state, available.orEmpty(), 8)
 		FilterHeaderModel(chips, state.sortOrder, state.tags.isNotEmpty())
 	}
 
@@ -157,11 +157,16 @@ class FilterCoordinator @Inject constructor(
 	private suspend fun createChipsList(
 		filterState: FilterState,
 		availableTags: Set<MangaTag>,
+		limit: Int,
 	): List<ChipsView.ChipModel> {
 		val selectedTags = filterState.tags.toMutableSet()
-		var tags = searchRepository.getTagsSuggestion("", 6, repository.source)
-		if (tags.isEmpty()) {
-			tags = availableTags.take(6)
+		var tags = if (selectedTags.isEmpty()) {
+			searchRepository.getTagsSuggestion("", limit, repository.source)
+		} else {
+			searchRepository.getTagsSuggestion(selectedTags).take(limit)
+		}
+		if (tags.size < limit) {
+			tags = tags + availableTags.take(limit - tags.size)
 		}
 		if (tags.isEmpty() && selectedTags.isEmpty()) {
 			return emptyList()

app/src/main/kotlin/org/koitharu/kotatsu/search/domain/MangaSearchRepository.kt

@@ -10,8 +10,10 @@ import kotlinx.coroutines.currentCoroutineContext
 import kotlinx.coroutines.isActive
 import kotlinx.coroutines.withContext
 import org.koitharu.kotatsu.core.db.MangaDatabase
+import org.koitharu.kotatsu.core.db.entity.toEntity
 import org.koitharu.kotatsu.core.db.entity.toManga
 import org.koitharu.kotatsu.core.db.entity.toMangaTag
+import org.koitharu.kotatsu.core.db.entity.toMangaTagsList
 import org.koitharu.kotatsu.core.prefs.AppSettings
 import org.koitharu.kotatsu.explore.data.MangaSourcesRepository
 import org.koitharu.kotatsu.parsers.model.ContentType
@@ -19,6 +21,7 @@ import org.koitharu.kotatsu.parsers.model.Manga
 import org.koitharu.kotatsu.parsers.model.MangaSource
 import org.koitharu.kotatsu.parsers.model.MangaTag
 import org.koitharu.kotatsu.parsers.util.levenshteinDistance
+import org.koitharu.kotatsu.parsers.util.mapToSet
 import org.koitharu.kotatsu.search.ui.MangaSuggestionsProvider
 import javax.inject.Inject
 
@@ -93,8 +96,17 @@ class MangaSearchRepository @Inject constructor(
 			query.isNotEmpty() -> db.tagsDao.findTags("%$query%", limit)
 			source != null -> db.tagsDao.findPopularTags(source.name, limit)
 			else -> db.tagsDao.findPopularTags(limit)
-		}.map {
-			it.toMangaTag()
+		}.toMangaTagsList()
+	}
+
+	suspend fun getTagsSuggestion(tags: Set<MangaTag>): List<MangaTag> {
+		val ids = tags.mapToSet { it.toEntity().id }
+		return if (ids.size == 1) {
+			db.tagsDao.findRelatedTags(ids.first())
+		} else {
+			db.tagsDao.findRelatedTags(ids)
+		}.mapNotNull { x ->
+			if (x.id in ids) null else x.toMangaTag()
 		}
 	}