Add AI-Powered Text Summarization to an Android App

class CloudSummarizer {
    private val model = Firebase.ai(backend = GenerativeBackend.googleAI()).generativeModel(
        modelName = "gemini-3.8-flash",             // check current model names
        generationConfig = generationConfig { temperature = 0.2f; maxOutputTokens = 600 },
        systemInstruction = content {
            text(
                "Summarize the provided document faithfully. Use only information in the document. " +
                "If something is unclear, say so. Output 3-5 bullet points, then one line 'Action items:' if any."
            )
        },
    )

    fun summarizeStream(document: String): Flow<String> =
        model.generateContentStream("<document>\n$document\n</document>").mapNotNull { it.text }

    suspend fun summarize(text: String): String = model.generateContent("<document>\n$text\n</document>").text.orEmpty()
}

class MapReduceSummarizer(private val summarizer: CloudSummarizer) {

    /** Split at paragraph boundaries into chunks of at most [maxChars]. */
    fun chunk(text: String, maxChars: Int = 12_000): List<String> {
        val chunks = mutableListOf<String>()
        val current = StringBuilder()
        text.split("\n\n").forEach { paragraph ->
            if (current.length + paragraph.length > maxChars && current.isNotEmpty()) {
                chunks += current.toString(); current.clear()
            }
            current.append(paragraph).append("\n\n")
        }
        if (current.isNotBlank()) chunks += current.toString()
        return chunks
    }

    suspend fun summarize(text: String): String = coroutineScope {
        val parts = chunk(text)
        if (parts.size == 1) return@coroutineScope summarizer.summarize(parts.single())
        val partials = parts
            .chunked(4)                                          // limit parallelism (rate limits)
            .flatMap { batch -> batch.map { async { summarizer.summarize(it) } }.awaitAll() }
        summarizer.summarize(partials.joinToString("\n\n"))      // reduce step
    }
}

@Composable
fun SummaryPanel(summary: String, isStreaming: Boolean, onViewSource: () -> Unit) {
    Card(Modifier.fillMaxWidth()) {
        Column(Modifier.padding(16.dp)) {
            Text("AI summary", style = MaterialTheme.typography.titleSmall)
            Text(summary, Modifier.padding(vertical = 8.dp))
            if (isStreaming) LinearProgressIndicator(Modifier.fillMaxWidth())
            Text("Summaries can miss or misstate details.", style = MaterialTheme.typography.labelSmall)
            TextButton(onClick = onViewSource) { Text("Read the full text") }
        }
    }
}