import android.support.v4.app.ActivityCompat;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.os.Build;
import android.widget.Button;
import android.support.v4.content.ContextCompat;
import android.widget.EditText;
import android.util.Log;
import android.Manifest;
import android.content.pm.PackageManager;
import android.telephony.SmsManager;
import android.text.TextUtils;
import android.widget.Toast;
import android.view.View;

public class SMSActivity extends AppCompatActivity
{
	private static final int PERMISSION_REQUEST_CODE = 1;
	private Button sendSMS;

	@Override
	protected void onCreate(Bundle savedInstanceState)
	{
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_sms);
		final EditText phoneNumber = (EditText) findViewById(R.id.phoneNumber);
		if (Build.VERSION.SDK_INT >= 23)
		{
			if (checkPermission())
			{
				Log.e("permission", "Permission already granted.");
			}
			else
			{
				requestPermission();
			}
		}
		final EditText smsText = (EditText) findViewById(R.id.message);
		sendSMS = (Button) findViewById(R.id.sendSMS);
		sendSMS.setOnClickListener(new View.OnClickListener() {
			@Override
			public void onClick(View view) {
				String sms = smsText.getText().toString();
				String phoneNum = phoneNumber.getText().toString();
				if(!TextUtils.isEmpty(sms) && !TextUtils.isEmpty(phoneNum))
				{
					if(checkPermission()) {
						SmsManager smsManager = SmsManager.getDefault();
						smsManager.sendTextMessage(phoneNum, null, sms, null, null);
					}
					else
					{
						Toast.makeText(SMSActivity.this, "Permission denied", Toast.LENGTH_SHORT).show();
					}
				}
			}
		});
	}

	private boolean checkPermission()
	{
		int result = ContextCompat.checkSelfPermission(SMSActivity.this, Manifest.permission.SEND_SMS);
		if (result == PackageManager.PERMISSION_GRANTED)
		{
			return true;
		}
		else
		{
			return false;
		}
	}

	private void requestPermission()
	{
		ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.SEND_SMS}, PERMISSION_REQUEST_CODE);
	}

	@Override
	public void onRequestPermissionsResult(int requestCode, String permissions[], int[] grantResults)
	{
		switch (requestCode)
		{
			case PERMISSION_REQUEST_CODE:
			if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED)
			{
				Toast.makeText(SMSActivity.this,"Permission accepted", Toast.LENGTH_LONG).show();
			}
			else
			{
				Toast.makeText(SMSActivity.this,"Permission denied", Toast.LENGTH_LONG).show();
				Button sendSMS = (Button) findViewById(R.id.sendSMS);
				sendSMS.setEnabled(false);
			}
		}
	}
}