Handle lines longer than Android's maximum speech input length

Re: #1.

Long lines like this are now split into multiple smaller lines of
reasonable length before they are passed to the TTS engine.

This has not been implemented for Speaker.synthesizeToFile() yet.

app/src/main/java/com/danefinlay/ttsutil/Speaker.kt

@@ -68,6 +68,43 @@ class Speaker(private val context: Context,
         speak(lines)
     }
 
+    private fun splitLongLines(lines: List<String>): List<String> {
+        val maxLength = TextToSpeech.getMaxSpeechInputLength()
+        val result = mutableListOf<String>()
+        for (line in lines) {
+            if (line.length < maxLength) {
+                result.add(line)
+                continue
+            }
+
+            // Split long lines into multiple strings of reasonable length.
+            val shorterLines = mutableListOf("")
+            line.forEach {
+                val lastString = shorterLines.last()
+                if (lastString.length < maxLength) {
+                    // Separate on whitespace close to the maximum length where
+                    // possible.
+                    if (it.isWhitespace() && lastString.length > maxLength - 50)
+                        shorterLines.add(it.toString())
+
+                    // Add to the last string.
+                    else {
+                        val newLine = lastString + it.toString()
+                        shorterLines[shorterLines.lastIndex] = newLine
+                    }
+                }
+
+                // Add a new string.
+                else shorterLines.add(it.toString())
+            }
+
+            // Add the shorter lines to the result list.
+            result.addAll(shorterLines)
+        }
+
+        return result
+    }
+
     fun speak(lines: List<String?>) {
         if (!(ready && speechAllowed)) {
             return
@@ -82,26 +119,30 @@ class Speaker(private val context: Context,
             lastUtteranceWasFileSynthesis = false
         }
 
+        // Handle lines that are null, blank or too long.
+        val inputLines = splitLongLines(
+                lines.mapNotNull { it }.filter { !it.isBlank() }
+        )
+
         // Set the listener.
         val listener = SpeakingEventListener(appCtx)
         tts.setOnUtteranceProgressListener(listener)
 
-        // Get Android's TTS framework to speak each non-null line.
+        // Get Android's TTS framework to speak each line.
         // This is, quite typically, different in some versions of Android.
-        val nonEmptyLines = lines.mapNotNull { it }.filter { !it.isBlank() }
         val streamKey = TextToSpeech.Engine.KEY_PARAM_STREAM
         var utteranceId: String? = null
         if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
             val bundle = Bundle()
             bundle.putInt(streamKey, AudioManager.STREAM_MUSIC)
-            nonEmptyLines.forEach {
+            inputLines.forEach {
                 utteranceId = getUtteranceId()
                 tts.speak(it, TextToSpeech.QUEUE_ADD, bundle, utteranceId)
                 pause(100)
             }
         } else {
             val streamValue = AudioManager.STREAM_MUSIC.toString()
-            nonEmptyLines.forEach {
+            inputLines.forEach {
                 utteranceId = getUtteranceId()
                 val map = hashMapOf(streamKey to streamValue,
                         KEY_PARAM_UTTERANCE_ID to utteranceId)
@@ -149,6 +190,8 @@ class Speaker(private val context: Context,
         // Reset the stopping speech flag.
         stoppingSpeech = false
 
+        // TODO Handle lines that are null, blank or too long.
+
         // Set the listener.
         tts.setOnUtteranceProgressListener(listener)