package com.reactlibrary;

import android.content.Context;
import android.content.ContextWrapper;
import android.content.pm.PackageManager;
import android.content.pm.Signature;
import android.util.Base64;
import android.util.Log;

import java.nio.charset.StandardCharsets;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.ArrayList;
import java.util.Arrays;

    /**
     * Created by Chintan on 01-11-2017.
     */

    public class SignatureHelper extends ContextWrapper {
        public static final String TAG = SignatureHelper.class.getSimpleName();

        private static final String HASH_TYPE = "SHA-256";
        public static final int NUM_HASHED_BYTES = 9;
        public static final int NUM_BASE64_CHAR = 11;

        public SignatureHelper(Context context) {
            super(context);
        }

        /**
         * Get all the app signatures for the current package
         *
         * @return
         */
        public ArrayList<String> getAppSignatures() {
            ArrayList<String> appCodes = new ArrayList<>();

            try {
                // Get all package signatures for the current package
                String packageName = getPackageName();
                PackageManager packageManager = getPackageManager();
                Signature[] signatures = packageManager.getPackageInfo(packageName,
                        PackageManager.GET_SIGNATURES).signatures;

                // For each signature create a compatible hash
                for (Signature signature : signatures) {
                    String hash = hash(packageName, signature.toCharsString());
                    if (hash != null) {
                        appCodes.add(String.format("%s", hash));
                    }
                }
            } catch (PackageManager.NameNotFoundException e) {
                Log.e(TAG, "Unable to find package to obtain hash.", e);
            }
            return appCodes;
        }

        private static String hash(String packageName, String signature) {
            String appInfo = packageName + " " + signature;
            try {
                MessageDigest messageDigest = MessageDigest.getInstance(HASH_TYPE);
                messageDigest.update(appInfo.getBytes(StandardCharsets.UTF_8));
                byte[] hashSignature = messageDigest.digest();

                // truncated into NUM_HASHED_BYTES
                hashSignature = Arrays.copyOfRange(hashSignature, 0, NUM_HASHED_BYTES);
                // encode into Base64
                String base64Hash = Base64.encodeToString(hashSignature, Base64.NO_PADDING | Base64.NO_WRAP);
                base64Hash = base64Hash.substring(0, NUM_BASE64_CHAR);

                Log.e(TAG, String.format("pkg: %s -- hash: %s", packageName, base64Hash));
                return base64Hash;
            } catch (NoSuchAlgorithmException e) {
                Log.e(TAG, "hash:NoSuchAlgorithm", e);
            }
            return null;
        }
    }