CloudMessagingService.kt

package com.anie.anie

import android.app.NotificationChannel
import android.app.NotificationManager
import android.app.PendingIntent
import android.content.Intent
import android.os.Build
import android.support.v4.app.NotificationCompat
import android.support.v4.app.NotificationCompat.DEFAULT_ALL
import com.anie.anie.studentHome.StudentHomeActivity
import com.google.firebase.messaging.FirebaseMessagingService
import com.google.firebase.messaging.RemoteMessage

class CloudMessagingService : FirebaseMessagingService() {

    override fun onMessageReceived(message: RemoteMessage?) {
        super.onMessageReceived(message)

        val title = message?.data!!["title"]
        val body = message.data["message"]
        val fromUserId = message.data["from_user_id"]

        val intent = Intent(applicationContext, StudentHomeActivity::class.java)
        val pendingIntent = PendingIntent.getActivity(this, 0, intent, 0)

        val bigText = NotificationCompat.BigTextStyle()
        bigText.bigText(body)
        bigText.setBigContentTitle(title)
        bigText.setSummaryText(getString(R.string.new_message))

        val builder = NotificationCompat.Builder(applicationContext, getString(R.string.default_notification_channel_id))
                .setContentIntent(pendingIntent)
                .setSmallIcon(R.drawable.ic_notification)
                .setContentTitle(title)
                .setContentText(body)
                .setPriority(NotificationCompat.PRIORITY_MAX)
                .setDefaults(DEFAULT_ALL)
                .setAutoCancel(true)
                .setStyle(bigText)

        val manager = getSystemService(NOTIFICATION_SERVICE) as NotificationManager

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            val channel = NotificationChannel(getString(R.string.default_notification_channel_id),
                    getString(R.string.default_notification_channel_name),
                    NotificationManager.IMPORTANCE_HIGH)
            manager.createNotificationChannel(channel)
        }

        val chars = charArrayOf(*fromUserId?.substring(0, 3)!!.toCharArray()).map { it.toInt() }.joinToString("")

        if (message.data["remove"] != null)
            manager.cancel(chars.toInt())
        else
            manager.notify(chars.toInt(), builder.build())
    }

}