Add synchronized lyrics (#126)

app/src/main/kotlin/it/vfsfitvnm/vimusic/utils/SynchronizedLyrics.kt

@@ -0,0 +1,33 @@
+package it.vfsfitvnm.vimusic.utils
+
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.setValue
+import it.vfsfitvnm.synchronizedlyrics.parseSentences
+
+class SynchronizedLyrics(text: String, private val positionProvider: () -> Long) {
+    val sentences = parseSentences(text)
+
+    var index by mutableStateOf(currentIndex)
+        private set
+
+    private val currentIndex: Int
+        get() {
+            var index = -1
+            for (item in sentences) {
+                if (item.first >= positionProvider()) break
+                index++
+            }
+            return index
+        }
+
+    fun update(): Boolean {
+        val newIndex = currentIndex
+        return if (newIndex != index) {
+            index = newIndex
+            true
+        } else {
+            false
+        }
+    }
+}