CallActivity.kt

package com.github.arekolek.phone

import android.annotation.SuppressLint
import android.content.Context
import android.content.Intent
import android.os.Bundle
import android.telecom.Call
import androidx.appcompat.app.AppCompatActivity
import androidx.core.view.isVisible
import io.reactivex.disposables.CompositeDisposable
import io.reactivex.rxkotlin.addTo
import kotlinx.android.synthetic.main.activity_call.*
import java.util.concurrent.TimeUnit

class CallActivity : AppCompatActivity() {

    private val disposables = CompositeDisposable()

    private lateinit var number: String

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_call)
        number = intent.data.schemeSpecificPart
    }

    override fun onStart() {
        super.onStart()

        answer.setOnClickListener {
            OngoingCall.answer()
        }

        hangup.setOnClickListener {
            OngoingCall.hangup()
        }

        OngoingCall.state
            .subscribe(::updateUi)
            .addTo(disposables)

        OngoingCall.state
            .filter { it == Call.STATE_DISCONNECTED }
            .delay(1, TimeUnit.SECONDS)
            .firstElement()
            .subscribe { finish() }
            .addTo(disposables)
    }

    @SuppressLint("SetTextI18n")
    private fun updateUi(state: Int) {
        callInfo.text = "${state.asString().toLowerCase().capitalize()}\n$number"

        answer.isVisible = state == Call.STATE_RINGING
        hangup.isVisible = state in listOf(
            Call.STATE_DIALING,
            Call.STATE_RINGING,
            Call.STATE_ACTIVE
        )
    }

    override fun onStop() {
        super.onStop()
        disposables.clear()
    }

    companion object {
        fun start(context: Context, call: Call) {
            Intent(context, CallActivity::class.java)
                .setFlags(Intent.FLAG_ACTIVITY_NEW_TASK)
                .setData(call.details.handle)
                .let(context::startActivity)
        }
    }
}