package link.roadio.riff.shared.config

import android.os.Bundle
import android.os.ParcelFileDescriptor
import android.util.Log
import java.io.ByteArrayOutputStream
import java.io.IOException
import java.nio.ByteBuffer
import java.util.concurrent.Executors

/** Only small metadata crosses Binder; aggregate UTF-8 travels through a read-only descriptor.
 * Authority: https://wiki.271.pics/Riff/1-1-0/configuration#one-coherent-startup
 * Binder's shared transaction buffer cannot carry every otherwise valid configuration document.
 * https://developer.android.com/reference/android/os/TransactionTooLargeException
 */
object ConfigurationHandoff {
    private const val MAX_BYTES = 64 * 1024 * 1024
    private val writer = Executors.newSingleThreadExecutor()

    fun validate(text: String?) {
        if (text != null && text.toByteArray(Charsets.UTF_8).size > MAX_BYTES) throw IOException("Configuration aggregate exceeds bound")
    }

    fun put(
        bundle: Bundle,
        text: String?,
    ) {
        bundle.putInt("overlayLength", -1)
        if (text == null) return
        val bytes = text.toByteArray(Charsets.UTF_8)
        if (bytes.size > MAX_BYTES) throw IOException("Configuration aggregate exceeds bound")
        val pipe = ParcelFileDescriptor.createPipe()
        try {
            writer.execute {
                runCatching { ParcelFileDescriptor.AutoCloseOutputStream(pipe[1]).use { it.write(bytes) } }
                    .onFailure { Log.w("RiffConfig", "configuration_handoff_failed", it) }
            }
        } catch (error: Exception) {
            pipe.forEach { it.close() }
            throw error
        }
        bundle.putInt("overlayLength", bytes.size)
        bundle.putParcelable("overlayFd", pipe[0])
    }

    fun read(bundle: Bundle): String? {
        @Suppress("DEPRECATION")
        val descriptor = bundle.getParcelable<ParcelFileDescriptor>("overlayFd")
        val length = bundle.getInt("overlayLength", -2)
        if (length == -1 && descriptor == null) return null
        if (length !in 0..MAX_BYTES || descriptor == null) {
            descriptor?.close()
            throw IOException("Invalid configuration handoff")
        }
        return ParcelFileDescriptor.AutoCloseInputStream(descriptor).use { input ->
            val output = ByteArrayOutputStream()
            val block = ByteArray(8192)
            while (true) {
                val count = input.read(block)
                if (count < 0) break
                if (count == 0 || output.size() > length - count) throw IOException("Invalid configuration handoff length")
                output.write(block, 0, count)
            }
            if (output.size() != length) throw IOException("Truncated configuration handoff")
            Charsets.UTF_8
                .newDecoder()
                .decode(ByteBuffer.wrap(output.toByteArray()))
                .toString()
        }
    }
}