fix(search): use implicit AND in FTS queries, not the AND keyword

app/src/androidTest/java/com/theveloper/pixelplay/data/database/MusicDaoTest.kt

@@ -204,4 +204,31 @@ class MusicDaoTest {
         val titles = results.map { it.title }.sorted()
         assertEquals(listOf("Cool Song", "Coolest Song Ever"), titles)
     }
+
+    /**
+     * Regression test for a real bug found on-device: FTS4 MATCH queries built with the
+     * literal "AND" keyword only behave as a boolean operator on SQLite builds compiled
+     * with SQLITE_ENABLE_FTS3_PARENTHESIS. Without it "AND" is parsed as an ordinary
+     * search term, so a two-word query would only match rows that literally contained
+     * the word "and" - silently breaking multi-word search. This runs against the real
+     * on-device/emulator SQLite engine (unlike a plain string-building unit test), which
+     * is what actually caught the bug.
+     */
+    @Test
+    @Throws(Exception::class)
+    fun searchSongs_multiWordQuery_matchesSongWithoutLiteralAndKeyword() = runTest {
+        // Insert the referenced artist/album first: songs has a foreign key to both.
+        musicDao.insertArtists(listOf(createArtistEntity(101L, "Some Artist")))
+        musicDao.insertAlbums(listOf(createAlbumEntity(201L, "Album X")))
+        val songs = listOf(
+            createSongEntity(1L, "Qué ganas de comerte", "Some Artist", "Album X", "/p1/s1.mp3"),
+            createSongEntity(2L, "Completely unrelated title", "Other Artist", "Album Y", "/p2/s2.mp3")
+        )
+        musicDao.insertSongs(songs)
+
+        val results = musicDao.searchSongs("que ganas", emptyList(), false).first()
+
+        assertEquals(1, results.size)
+        assertEquals("Qué ganas de comerte", results[0].title)
+    }
 }

app/src/main/java/com/theveloper/pixelplay/data/database/MusicDao.kt

@@ -14,32 +14,40 @@ import kotlinx.coroutines.flow.combine
 
 private val SONG_SEARCH_QUERY_TOKEN_REGEX = Regex("""[\p{L}\p{N}]+""")
 private const val EMPTY_SONG_SEARCH_MATCH_QUERY = "pixelplayemptyquery*"
+private const val MAX_SONG_SEARCH_QUERY_TOKENS = 6
 
-private fun buildSongTitleSearchMatchQuery(query: String): String {
-    val tokens = SONG_SEARCH_QUERY_TOKEN_REGEX
+private fun tokenizeSongSearchQuery(query: String): List<String> =
+    SONG_SEARCH_QUERY_TOKEN_REGEX
         .findAll(query)
         .map { it.value.trim() }
         .filter { it.isNotEmpty() }
-        .take(6)
+        .take(MAX_SONG_SEARCH_QUERY_TOKENS)
         .toList()
 
+/**
+ * Builds an FTS4 MATCH expression requiring every token to match as a prefix
+ * within [column] (or anywhere, if [column] is null).
+ *
+ * Tokens are joined with a plain space, i.e. FTS's *implicit* AND, rather than
+ * the literal "AND" keyword: that keyword requires SQLite to be compiled with
+ * SQLITE_ENABLE_FTS3_PARENTHESIS, which not every Android build has. Without
+ * it, "AND" is parsed as an ordinary search term instead of a boolean
+ * operator, so a query like "que* AND ganas*" would only match rows that
+ * literally contain the word "and" - silently breaking every multi-word
+ * search on devices without that extension.
+ */
+private fun buildFtsMatchQuery(tokens: List<String>, column: String? = null): String {
     if (tokens.isEmpty()) return EMPTY_SONG_SEARCH_MATCH_QUERY
-
-    return tokens.joinToString(separator = " AND ") { "title:${it}*" }
+    return tokens.joinToString(separator = " ") { token ->
+        if (column != null) "$column:$token*" else "$token*"
+    }
 }
 
-private fun buildSongSearchMatchQuery(query: String): String {
-    val tokens = SONG_SEARCH_QUERY_TOKEN_REGEX
-        .findAll(query)
-        .map { it.value.trim() }
-        .filter { it.isNotEmpty() }
-        .take(6)
-        .toList()
+internal fun buildSongTitleSearchMatchQuery(query: String): String =
+    buildFtsMatchQuery(tokenizeSongSearchQuery(query), column = "title")
 
-    if (tokens.isEmpty()) return EMPTY_SONG_SEARCH_MATCH_QUERY
-
-    return tokens.joinToString(separator = " AND ") { "${it}*" }
-}
+internal fun buildSongSearchMatchQuery(query: String): String =
+    buildFtsMatchQuery(tokenizeSongSearchQuery(query))
 
 private const val SONG_DETAIL_PROJECTION = """
     songs.id AS id,

app/src/test/java/com/theveloper/pixelplay/data/database/MusicDaoQueryBuilderTest.kt

@@ -0,0 +1,58 @@
+package com.theveloper.pixelplay.data.database
+
+import org.junit.Assert.assertEquals
+import org.junit.Test
+
+/**
+ * Regression coverage for the FTS4 MATCH query builders. These must use
+ * implicit AND (plain spaces) rather than the literal "AND" keyword, which
+ * only behaves as a boolean operator on SQLite builds compiled with
+ * SQLITE_ENABLE_FTS3_PARENTHESIS - not guaranteed on every Android device
+ * (confirmed absent on at least one real device during manual testing).
+ */
+class MusicDaoQueryBuilderTest {
+
+    @Test
+    fun buildSongSearchMatchQuery_singleWord_returnsSinglePrefixTerm() {
+        assertEquals("que*", buildSongSearchMatchQuery("que"))
+    }
+
+    @Test
+    fun buildSongSearchMatchQuery_multipleWords_joinsWithImplicitAndNotLiteralKeyword() {
+        val result = buildSongSearchMatchQuery("que ganas")
+
+        assertEquals("que* ganas*", result)
+        assertEquals(false, result.contains("AND", ignoreCase = true))
+    }
+
+    @Test
+    fun buildSongSearchMatchQuery_blankQuery_returnsEmptyQuerySentinel() {
+        assertEquals("pixelplayemptyquery*", buildSongSearchMatchQuery(""))
+        assertEquals("pixelplayemptyquery*", buildSongSearchMatchQuery("   "))
+    }
+
+    @Test
+    fun buildSongSearchMatchQuery_capsAtSixTokens() {
+        val result = buildSongSearchMatchQuery("one two three four five six seven eight")
+
+        assertEquals("one* two* three* four* five* six*", result)
+    }
+
+    @Test
+    fun buildSongTitleSearchMatchQuery_singleWord_scopesToTitleColumn() {
+        assertEquals("title:que*", buildSongTitleSearchMatchQuery("que"))
+    }
+
+    @Test
+    fun buildSongTitleSearchMatchQuery_multipleWords_joinsWithImplicitAnd() {
+        val result = buildSongTitleSearchMatchQuery("que ganas")
+
+        assertEquals("title:que* title:ganas*", result)
+        assertEquals(false, result.contains("AND", ignoreCase = true))
+    }
+
+    @Test
+    fun buildSongTitleSearchMatchQuery_blankQuery_returnsEmptyQuerySentinel() {
+        assertEquals("pixelplayemptyquery*", buildSongTitleSearchMatchQuery(""))
+    }
+}