/*
 * Copyright (C) 2015 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License
 */

package com.example.android.asymmetricfingerprintdialog;

import android.app.Activity;
import android.app.KeyguardManager;
import android.content.Intent;
import android.content.SharedPreferences;
import android.hardware.fingerprint.FingerprintManager;
import android.os.Bundle;
import android.security.keystore.KeyGenParameterSpec;
import android.security.keystore.KeyPermanentlyInvalidatedException;
import android.security.keystore.KeyProperties;
import android.util.Base64;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;

import java.io.IOException;
import java.security.InvalidAlgorithmParameterException;
import java.security.InvalidKeyException;
import java.security.KeyPairGenerator;
import java.security.KeyStore;
import java.security.KeyStoreException;
import java.security.NoSuchAlgorithmException;
import java.security.PrivateKey;
import java.security.Signature;
import java.security.UnrecoverableKeyException;
import java.security.cert.CertificateException;
import java.security.spec.ECGenParameterSpec;

import javax.inject.Inject;

/**
 * Main entry point for the sample, showing a backpack and "Purchase" button.
 */
public class MainActivity extends Activity {

    private static final String DIALOG_FRAGMENT_TAG = "myFragment";
    /** Alias for our key in the Android Key Store */
    public static final String KEY_NAME = "my_key";

    @Inject KeyguardManager mKeyguardManager;
    @Inject FingerprintManager mFingerprintManager;
    @Inject FingerprintAuthenticationDialogFragment mFragment;
    @Inject KeyStore mKeyStore;
    @Inject KeyPairGenerator mKeyPairGenerator;
    @Inject Signature mSignature;
    @Inject SharedPreferences mSharedPreferences;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        ((InjectedApplication) getApplication()).inject(this);

        setContentView(R.layout.activity_main);
        Button purchaseButton = (Button) findViewById(R.id.purchase_button);
        if (!mKeyguardManager.isKeyguardSecure()) {
            // Show a message that the user hasn't set up a fingerprint or lock screen.
            Toast.makeText(this,
                    "Secure lock screen hasn't set up.\n"
                            + "Go to 'Settings -> Security -> Fingerprint' to set up a fingerprint",
                    Toast.LENGTH_LONG).show();
            purchaseButton.setEnabled(false);
            return;
        }
        //noinspection ResourceType
        if (!mFingerprintManager.hasEnrolledFingerprints()) {
            purchaseButton.setEnabled(false);
            // This happens when no fingerprints are registered.
            Toast.makeText(this,
                    "Go to 'Settings -> Security -> Fingerprint' and register at least one fingerprint",
                    Toast.LENGTH_LONG).show();
            return;
        }
        createKeyPair();
        purchaseButton.setEnabled(true);
        purchaseButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                findViewById(R.id.confirmation_message).setVisibility(View.GONE);
                findViewById(R.id.encrypted_message).setVisibility(View.GONE);

                // Set up the crypto object for later. The object will be authenticated by use
                // of the fingerprint.
                if (initSignature()) {

                    // Show the fingerprint dialog. The user has the option to use the fingerprint with
                    // crypto, or you can fall back to using a server-side verified password.
                    mFragment.setCryptoObject(new FingerprintManager.CryptoObject(mSignature));
                    boolean useFingerprintPreference = mSharedPreferences
                            .getBoolean(getString(R.string.use_fingerprint_to_authenticate_key),
                                    true);
                    if (useFingerprintPreference) {
                        mFragment.setStage(
                                FingerprintAuthenticationDialogFragment.Stage.FINGERPRINT);
                    } else {
                        mFragment.setStage(
                                FingerprintAuthenticationDialogFragment.Stage.PASSWORD);
                    }
                    mFragment.show(getFragmentManager(), DIALOG_FRAGMENT_TAG);
                } else {
                    // This happens if the lock screen has been disabled or or a fingerprint got
                    // enrolled. Thus show the dialog to authenticate with their password first
                    // and ask the user if they want to authenticate with fingerprints in the
                    // future
                    mFragment.setStage(
                            FingerprintAuthenticationDialogFragment.Stage.NEW_FINGERPRINT_ENROLLED);
                    mFragment.show(getFragmentManager(), DIALOG_FRAGMENT_TAG);
                }
            }
        });
    }

    /**
     * Initialize the {@link Signature} instance with the created key in the
     * {@link #createKeyPair()} method.
     *
     * @return {@code true} if initialization is successful, {@code false} if the lock screen has
     * been disabled or reset after the key was generated, or if a fingerprint got enrolled after
     * the key was generated.
     */
    private boolean initSignature() {
        try {
            mKeyStore.load(null);
            PrivateKey key = (PrivateKey) mKeyStore.getKey(KEY_NAME, null);
            mSignature.initSign(key);
            return true;
        } catch (KeyPermanentlyInvalidatedException e) {
            return false;
        } catch (KeyStoreException | CertificateException | UnrecoverableKeyException | IOException
                | NoSuchAlgorithmException | InvalidKeyException e) {
            throw new RuntimeException("Failed to init Cipher", e);
        }
    }

    public void onPurchased(byte[] signature) {
        showConfirmation(signature);
    }

    public void onPurchaseFailed() {
        Toast.makeText(this, R.string.purchase_fail, Toast.LENGTH_SHORT).show();
    }

    // Show confirmation, if fingerprint was used show crypto information.
    private void showConfirmation(byte[] encrypted) {
        findViewById(R.id.confirmation_message).setVisibility(View.VISIBLE);
        if (encrypted != null) {
            TextView v = (TextView) findViewById(R.id.encrypted_message);
            v.setVisibility(View.VISIBLE);
            v.setText(Base64.encodeToString(encrypted, 0 /* flags */));
        }
    }

    /**
     * Generates an asymmetric key pair in the Android Keystore. Every use of the private key must
     * be authorized by the user authenticating with fingerprint. Public key use is unrestricted.
     */
    public void createKeyPair() {
        // The enrolling flow for fingerprint. This is where you ask the user to set up fingerprint
        // for your flow. Use of keys is necessary if you need to know if the set of
        // enrolled fingerprints has changed.
        try {
            // Set the alias of the entry in Android KeyStore where the key will appear
            // and the constrains (purposes) in the constructor of the Builder
            mKeyPairGenerator.initialize(
                    new KeyGenParameterSpec.Builder(KEY_NAME,
                            KeyProperties.PURPOSE_SIGN)
                            .setDigests(KeyProperties.DIGEST_SHA256)
                            .setAlgorithmParameterSpec(new ECGenParameterSpec("secp256r1"))
                            // Require the user to authenticate with a fingerprint to authorize
                            // every use of the private key
                            .setUserAuthenticationRequired(true)
                            .build());
            mKeyPairGenerator.generateKeyPair();
        } catch (InvalidAlgorithmParameterException e) {
            throw new RuntimeException(e);
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        int id = item.getItemId();

        if (id == R.id.action_settings) {
            Intent intent = new Intent(this, SettingsActivity.class);
            startActivity(intent);
            return true;
        }
        return super.onOptionsItemSelected(item);
    }
}