/*
 *  Copyright (c) 2021, WSO2 Inc. (http://www.wso2.org) All Rights Reserved.
 *
 *  WSO2 Inc. licenses this file to you 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 org.wso2.micro.integrator.initializer.utils;

import com.google.gson.Gson;
import com.google.gson.JsonArray;
import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.JsonParser;
import com.google.gson.stream.MalformedJsonException;
import org.apache.axiom.om.OMElement;
import org.apache.commons.io.FileUtils;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.synapse.commons.resolvers.ResolverException;
import org.apache.synapse.commons.resolvers.SystemResolver;
import org.apache.synapse.config.SynapseConfigUtils;
import org.wso2.carbon.securevault.SecretCallbackHandlerService;
import org.wso2.config.mapper.ConfigParser;
import org.wso2.micro.application.deployer.AppDeployerUtils;
import org.wso2.micro.application.deployer.CarbonApplication;
import org.wso2.micro.core.util.CarbonException;
import org.wso2.micro.core.util.StringUtils;
import org.wso2.micro.integrator.initializer.deployment.application.deployer.CappDeployer;
import org.wso2.securevault.SecretResolver;
import org.wso2.securevault.SecretResolverFactory;
import org.wso2.securevault.commons.MiscellaneousUtil;
import org.yaml.snakeyaml.DumperOptions;
import org.yaml.snakeyaml.Yaml;

import javax.net.ssl.HostnameVerifier;
import javax.net.ssl.HttpsURLConnection;
import java.io.*;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.ProtocolException;
import java.net.URL;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.ArrayList;
import java.util.Base64;
import java.util.Collection;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.zip.ZipEntry;
import java.util.zip.ZipOutputStream;

import static org.wso2.micro.integrator.initializer.utils.Constants.*;

/**
 * Util class for service catalog feature.
 */
public class ServiceCatalogUtils {

    private static final Log log = LogFactory.getLog(ServiceCatalogUtils.class);
    private static SecretResolver secretResolver;
    private static List<Map<String, String>> md5List = new ArrayList<>();
    private static Boolean alreadyUploaded = false;

    /**
     * Update the service url by injecting env variables.
     *
     * @param currentUrl current url.
     * @return updated url.
     * @throws ResolverException environment variables are not set correctly.
     */
    private static String updateServiceUrl(String currentUrl) throws ResolverException {
        /*
            Supported formats
            https://{host}:{port}/api1
            https://{url}/api1
        */
        SystemResolver resolver = new SystemResolver();
        if (currentUrl.contains(HOST) && currentUrl.contains(PORT)) {
            resolver.setVariable(MI_HOST);
            String host = resolver.resolve();
            resolver.setVariable(MI_PORT);
            String port = resolver.resolve();
            currentUrl = currentUrl.replace(HOST, host).replace(PORT, port);
        } else if (currentUrl.contains(URL)) {
            resolver.setVariable(MI_URL);
            String url = resolver.resolve();
            currentUrl = currentUrl.replace(MI_URL, url);
        }
        return currentUrl;
    }

    /**
     * Update the serviceUrl of the given metadata file (if required) and return its key value.
     *
     * @param yamlFile metadata yaml file.
     * @return key value of the metadata file.
     * @throws IOException       Error occurred while updating the metadata file.
     * @throws ResolverException Error occurred while reading env variables.
     */
    public static String updateMetadataWithServiceUrl(File yamlFile) throws IOException, ResolverException {
        Yaml yaml = new Yaml();
        InputStream yamlStream = new FileInputStream(yamlFile);
        Map<String, Object> obj = (Map<String, Object>) yaml.load(yamlStream);
        String currentServiceUrl = (String) obj.get(SERVICE_URL);
        obj.put(SERVICE_URL, updateServiceUrl(currentServiceUrl));

        // Additional configurations
        DumperOptions options = new DumperOptions();
        options.setIndent(2);
        options.setPrettyFlow(true);
        options.setDefaultFlowStyle(DumperOptions.FlowStyle.BLOCK);

        Yaml output = new Yaml(options);
        String updatedYaml = output.dump(obj);

        DataOutputStream outputStream = new DataOutputStream(new FileOutputStream(yamlFile, false));
        outputStream.write(updatedYaml.getBytes());
        outputStream.close();
        yamlStream.close();
        return (String) obj.get(METADATA_KEY);
    }

    /**
     * Publish a given ZIP file to APIM service catalog endpoint. Retry if failed.
     *
     * @param apimConfigs        Map containing deployment.toml configuration
     * @param attachmentFilePath path of the ZIP file to be updated.
     */
    public static void publishToAPIM(Map<String, String> apimConfigs, String attachmentFilePath) {
        int responseCode = uploadZip(apimConfigs, attachmentFilePath);
        if (responseCode == -1) return; // error occurred while uploading to service catalog
        switch (responseCode) {
            case HttpURLConnection.HTTP_OK:
                log.info("Successfully updated the service catalog");
                break;
            case HttpURLConnection.HTTP_GATEWAY_TIMEOUT:
            case HttpURLConnection.HTTP_UNAVAILABLE:
                if (log.isDebugEnabled()) {
                    log.debug("APIM responds with the status code : " + responseCode + " start " +
                            "retrying");
                }
                int retryCount = RETRY_COUNT;
                for (int i = 0; i < retryCount; i++) {
                    try {
                        log.info("Retrying to connect with APIM. Remaining retry count : " + (retryCount - i));
                        Thread.sleep(INTERVAL_BETWEEN_RETRIES);
                        responseCode = uploadZip(apimConfigs, attachmentFilePath);
                        if (responseCode == HttpURLConnection.HTTP_OK) {
                            break;
                        }
                    } catch (InterruptedException e) {
                        log.error("Service catalog thread interrupted", e);
                    }
                }
                log.error("Could not connect with APIM after " + retryCount + " retries.");
                break;
            case UNAUTHENTICATED:
                log.error("Unauthenticated, please verify the username and password provided for service catalog");
                break;
            default:
                log.error("Unknown response code received from the service catalog endpoint: " + responseCode);
                break;
        }
    }

    /**
     * Call service catalog and fetch details of all the services.
     *
     * @param apimConfigs Map containing APIM configuration.
     * @return Map of APIs and their current MD5 sum values, null if error occurred.
     */
    public static Map<String, String> getAllServices(Map<String, String> apimConfigs) {

        Map<String, String> md5Map = new HashMap<>();
        String APIMHost = apimConfigs.get(APIM_HOST);
        String credentials =
                Base64.getEncoder().encodeToString(
                        (apimConfigs.get(USER_NAME) + ":" + apimConfigs.get(PASSWORD)).getBytes());

        // create get all services url
        if (APIMHost.endsWith("/")) {
            APIMHost = APIMHost + SERVICE_CATALOG_GET_SERVICES_ENDPOINT;
        } else {
            APIMHost = APIMHost + "/" + SERVICE_CATALOG_GET_SERVICES_ENDPOINT;
        }

        try {
            HttpsURLConnection connection = (HttpsURLConnection) new URL(APIMHost).openConnection();
            connection.setDoOutput(true);
            connection.setRequestMethod("GET");
            connection.addRequestProperty("Accept", "application/json");
            connection.addRequestProperty("Authorization", "Basic " + credentials);
            connection.setHostnameVerifier(getHostnameVerifier());

            int responseCode = connection.getResponseCode();
            if (responseCode == HttpURLConnection.HTTP_OK) {
                BufferedReader in = new BufferedReader(new InputStreamReader(
                        connection.getInputStream()));
                String inputLine;
                StringBuilder response = new StringBuilder();

                while ((inputLine = in.readLine()) != null) {
                    response.append(inputLine);
                }
                in.close();

                JsonParser parser = new JsonParser();
                JsonObject rootObject = parser.parse(response.toString()).getAsJsonObject();
                JsonArray serviceList = rootObject.getAsJsonArray(LIST_STRING);
                for (JsonElement service : serviceList) {
                    String serviceKey = ((JsonObject) service).get(SERVICE_KEY).getAsString();
                    String md5 = ((JsonObject) service).get(MD5).getAsString();
                    md5Map.put(serviceKey, md5);
                }
                return md5Map;
            } else {
                log.error("Error occurred while fetching services from the service catalog");
            }
        } catch (MalformedURLException e) {
            log.error("Service catalog url " + APIMHost + " is malformed. Please check the configuration", e);
        } catch (MalformedJsonException e) {
            log.error("Invalid JSON response received from service catalog", e);
        } catch (ProtocolException e) {
            log.error("Error occurred while creating the connection with APIM", e);
        } catch (IOException e) {
            log.error("Error occurred while reading the response from service catalog", e);
        }
        return null;
    }

    /**
     * Upload the given ZIP file to the APIM service catalog endpoint.
     *
     * @param apimConfigs        map containing APIM configurations.
     * @param attachmentFilePath location of the zip file that needs to be uploaded.
     * @return status code returned from APIM, -1 if error occurred.
     */
    private static int uploadZip(Map<String, String> apimConfigs, String attachmentFilePath) {
        try {
            String APIMHost = apimConfigs.get(APIM_HOST);

            // create POST URL
            if (APIMHost.endsWith("/")) {
                APIMHost = APIMHost + SERVICE_CATALOG_PUBLISH_ENDPOINT;
            } else {
                APIMHost = APIMHost + "/" + SERVICE_CATALOG_PUBLISH_ENDPOINT;
            }

            String encodeBytes =
                    Base64.getEncoder().encodeToString(
                            (apimConfigs.get(USER_NAME) + ":" + apimConfigs.get(PASSWORD)).getBytes());

            File binaryFile = new File(attachmentFilePath);
            String boundary = "------------------------" +
                    Long.toHexString(System.currentTimeMillis()); // Generate some unique random value.
            String CRLF = "\r\n"; // Line separator required by multipart/form-data.
            HttpsURLConnection connection = (HttpsURLConnection) new URL(APIMHost).openConnection();
            connection.setDoOutput(true);
            connection.setRequestProperty("Content-Type", "multipart/form-data; boundary=" + boundary);
            connection.addRequestProperty("Accept", "application/json");
            connection.addRequestProperty("Authorization", "Basic " + encodeBytes);
            connection.setHostnameVerifier(getHostnameVerifier());

            OutputStream output = connection.getOutputStream();

            // Send binary file - part
            PrintWriter writer = new PrintWriter(new OutputStreamWriter(output, StandardCharsets.UTF_8), true);
            writer.append("--").append(boundary).append(CRLF);
            writer.append("Content-Disposition: form-data; name=\"file\"; filename=\"").append(
                    binaryFile.getName()).append("\"").append(CRLF);
            writer.append("Content-Type: application/octet-stream").append(CRLF);
            writer.append(CRLF).flush();

            // File data
            Files.copy(binaryFile.toPath(), output);
            output.flush();

            // Add verifier
            String verifier = new Gson().toJson(md5List);
            writer.append("--").append(boundary).append(CRLF);
            writer.append("Content-Disposition: form-data; name=\"" + VERIFIER + "\"").append(CRLF);
            writer.append(CRLF);
            writer.append(verifier).append(CRLF);

            // End of multipart/form-data.
            writer.append(CRLF).append("--").append(boundary).append("--").flush();

            // Read the response if debug enabled.
            if (log.isDebugEnabled()) {
                StringBuilder response = new StringBuilder();
                BufferedReader br = new BufferedReader(new InputStreamReader(connection.getInputStream()));
                String strCurrentLine;
                while ((strCurrentLine = br.readLine()) != null) {
                    response.append(strCurrentLine);
                }
                br.close();
                log.debug("Response from APIM : " + response);
            }
            return connection.getResponseCode();
        } catch (MalformedURLException e) {
            log.error("Service catalog url is malformed, please check the configured APIM host", e);
        } catch (IOException e) {
            log.error("Error occurred while uploading metadata to service catalog endpoint", e);
        }
        return -1;
    }

    /**
     * Read APIM host configurations from deployment.toml file.
     *
     * @param secretCallbackHandlerService secret callback handler reference.
     * @return map of resolved values.
     */
    public static Map<String, String> readConfiguration(SecretCallbackHandlerService secretCallbackHandlerService) {
        Map<String, String> configMap = new HashMap<>();
        Map<String, String> catalogProperties =
                (Map<String, String>) ((ArrayList) ConfigParser.getParsedConfigs().get(
                        SERVICE_CATALOG_CONFIG)).get(0);

        String apimHost = catalogProperties.get(APIM_HOST);

        String userName = catalogProperties.get(USER_NAME);
        String password = catalogProperties.get(PASSWORD);
        if (secretResolver == null) {
            secretResolver = SecretResolverFactory.create((OMElement) null, false);
        }
        if (!secretResolver.isInitialized()) {
            secretResolver.init(secretCallbackHandlerService.getSecretCallbackHandler());
        }
        String alias = MiscellaneousUtil.getProtectedToken(userName);
        if (!StringUtils.isEmpty(alias)) {
            userName = secretResolver.resolve(alias);
        }
        alias = MiscellaneousUtil.getProtectedToken(password);
        if (!StringUtils.isEmpty(alias)) {
            password = secretResolver.resolve(alias);
        }

        configMap.put(APIM_HOST, apimHost);
        configMap.put(USER_NAME, userName);
        configMap.put(PASSWORD, password);
        return configMap;
    }

    /**
     * Process metadata folder and move to temporary location.
     *
     * @param tempDir            temporary directory to put metadata.
     * @param metadataFolder     metadata folder inside CAPP.
     * @param metadataYamlFolder YAML folder inside CAPP.
     * @param md5MapOfAllService map containing md5 values of all services.
     * @return metadata processed successfully
     * @throws IOException              error occurred while moving files.
     * @throws ResolverException        error occurred while updating the metadata file.
     * @throws NoSuchAlgorithmException could not find the MD% algorithm.
     */
    private static boolean processMetadata(File tempDir, File metadataFolder, File metadataYamlFolder,
                                           Map<String, String> md5MapOfAllService) throws IOException
            , ResolverException, NoSuchAlgorithmException {
        String metaFileName = metadataYamlFolder.getName();
        String APIName = metaFileName.substring(0, metaFileName.indexOf(METADATA_FOLDER_STRING));
        String APIVersion =
                metaFileName.substring(metaFileName.lastIndexOf(METADATA_FOLDER_STRING) +
                        METADATA_FOLDER_STRING.length());
        // Create new folder in temp directory for this API
        File newMetaFile = new File(tempDir, APIName + "_v" + APIVersion);

        File newYamlFile = new File(newMetaFile, METADATA_FILE_NAME);
        File metadataYamlFile =
                new File(metadataYamlFolder, APIName + METADATA_FILE_STRING + APIVersion + YAML_FILE_EXTENSION);

        File swaggerFolder = new File(metadataFolder, APIName + SWAGGER_FOLDER_STRING + APIVersion);
        File swaggerFile =
                new File(swaggerFolder, APIName + SWAGGER_FILE_STRING + APIVersion + YAML_FILE_EXTENSION);
        File newSwaggerFile = new File(newMetaFile, SWAGGER_FILE_NAME);


        // Edit metadata yaml and add host details
        String key = updateMetadataWithServiceUrl(metadataYamlFile);
        String md5FromServer = md5MapOfAllService.get(key);

        // generate md5 values for verifier
        String md5SumOfMetadata = getFileChecksum(metadataYamlFile);
        String md5SumOfSwagger = getFileChecksum(swaggerFile);
        String newMD5String = md5SumOfSwagger + md5SumOfMetadata;

        // if API is not registered yet or, API is modified (md5 changed), add metadata files to temp folder
        if (StringUtils.isEmpty(md5FromServer) || !newMD5String.equals(md5FromServer)) {
            if (!newMetaFile.mkdir()) {
                log.error("Could not create temporary files");
                return false;
            }
            // Copy metadata yaml file to the temp location.
            FileUtils.copyFile(metadataYamlFile, newYamlFile);
            // Copy swagger yaml file to the temp location.
            FileUtils.copyFile(swaggerFile, newSwaggerFile);

            // Add to map to be included in filter formdata field.
            Map<String, String> md5Map = new HashMap<>();
            md5Map.put(METADATA_KEY, key);
            // if API is changed add the previous MD5 sum, if new API add the new MD5 sum.
            md5Map.put(MD5, StringUtils.isEmpty(md5FromServer) ? newMD5String : md5FromServer);
            md5List.add(md5Map);
        } else {
            alreadyUploaded = true;
            if (log.isDebugEnabled()) {
                log.debug(APIName + " is already updated in the service catalog");
            }
        }
        return true;
    }

    /**
     * Create the final ZIP file wrapping all the metadata files.
     *
     * @param destArchiveName location of the ZIP file.
     * @param sourceDir       location of the metadata folder.
     * @return result of zip creation process. ( successful / failed ).
     */
    public static boolean archiveDir(String destArchiveName, String sourceDir) {
        File zipDir = new File(sourceDir);
        if (zipDir.exists() && zipDir.list().length == 0) {
            if (alreadyUploaded) {
                log.info("Service catalog already contains the latest configs, aborting the service-catalog uploader");
            } else {
                log.info("Could not find metadata to upload, aborting the service-catalog uploader");
            }
            return false;
        }

        try (ZipOutputStream zos = new ZipOutputStream(new FileOutputStream(destArchiveName))) {
            zipDir(zipDir, zos, sourceDir);

        } catch (Exception ex) {
            log.error("Error occurred while creating the archive", ex);
            return false;
        }
        return true;
    }

    private static void zipDir(File zipDir, ZipOutputStream zos, String archiveSourceDir) throws IOException {
        //get a listing of the directory content
        String[] dirList = zipDir.list();
        byte[] readBuffer = new byte[40960];
        int bytesIn;
        //loop through dirList, and zip the files
        for (String s : dirList) {
            File f = new File(zipDir, s);
            //place the zip entry in the ZipOutputStream object
            zos.putNextEntry(new ZipEntry(getZipEntryPath(f, archiveSourceDir)));
            if (f.isDirectory()) {
                //if the File object is a directory, call this
                //function again to add its content recursively
                zipDir(f, zos, archiveSourceDir);
                //loop again
                continue;
            }
            //if we reached here, the File object f was not a directory
            //create a FileInputStream on top of f
            FileInputStream fis = new FileInputStream(f);

            //now write the content of the file to the ZipOutputStream
            while ((bytesIn = fis.read(readBuffer)) != -1) {
                zos.write(readBuffer, 0, bytesIn);
            }
            //close the Stream
            fis.close();
        }
    }

    private static String getZipEntryPath(File f, String archiveSourceDir) {
        String entryPath = f.getPath();
        entryPath = entryPath.substring(archiveSourceDir.length() + 1);
        if (File.separatorChar == '\\') {
            entryPath = entryPath.replace(File.separatorChar, '/');
        }
        if (f.isDirectory()) {
            entryPath += "/";
        }
        return entryPath;
    }

    /**
     * Disabling the hostname verification.
     *
     * @return true for all the host names.
     */
    private static HostnameVerifier getHostnameVerifier() {
        return (s, sslSession) -> true;
    }

    /**
     * Check pre-conditions before stating the service-catalog uploading process.
     *
     * @return pre-condition are matched / not matched.
     */
    public static boolean checkPreConditions() {
        if (log.isDebugEnabled()) {
            log.debug("Start service-catalog uploading process");
        }
        // Check for faulty CAPPs. If atleast one CAPP is fault MI is not ready - readiness probe.
        ArrayList<String> faultyCapps = new ArrayList<>(CappDeployer.getFaultyCapps());
        if (!faultyCapps.isEmpty()) {
            log.info("Faulty CAPPs detected - aborting the service-catalog uploader");
            return false;
        }
        // Skip if no CAPPs are deployed
        ArrayList<CarbonApplication> deployedCapps = new ArrayList<>(CappDeployer.getCarbonApps());
        if (deployedCapps.isEmpty()) {
            log.info("Cannot find carbon applications - aborting the service-catalog uploader");
            return false;
        }
        // Skip if no APIs are deployed
        Collection APITable =
                SynapseConfigUtils.getSynapseConfiguration(
                        org.wso2.micro.core.Constants.SUPER_TENANT_DOMAIN_NAME).getAPIs();
        if (APITable.isEmpty()) {
            log.info("Cannot find APIs - aborting the service-catalog uploader");
            return false;
        }
        return true;
    }

    /**
     * Extract CAPPs and put metadata files in the temporary folder.
     *
     * @param targetDir          temporary folder location.
     * @param repoLocation       location of the deployment folder of MI.
     * @param md5MapOfAllService map containing md5 values of all services.
     * @return extracted successfully.
     */
    public static boolean extractMetadataFromCAPPs(File targetDir, String repoLocation,
                                                   Map<String, String> md5MapOfAllService) {
        FilenameFilter cappFilter = (f, name) -> name.endsWith(".car");
        FilenameFilter metaFilter = (f, name) -> name.contains(METADATA_FOLDER_STRING);

        /*
         * Sample folder structure of metadata inside the new Carbon Application
         * metadata
         *  - testApi_metadata_1.0.0
         *    - testApi_metadata-1.0.0.yaml
         *    - artifact.xml
         *  - testApi_swagger_1.0.0
         *    - testApi_swagger-1.0.0.yaml
         *    - artifact.xml
         */

        File cappFolder = new File(repoLocation, CAPP_FOLDER_NAME);
        File[] files = cappFolder.listFiles(cappFilter);
        if (files == null) return false; // should not reach here. Checked in checkPreConditions() method
        for (File file : files) {
            try {
                // Extract the CAPP and get extracted location.
                String tempExtractedDirPath = AppDeployerUtils.extractCarbonApp(file.getPath());
                File metadataFolder = new File(tempExtractedDirPath, METADATA_FOLDER_NAME);
                // does not have a metadata folder -> old CAPP format.
                if (metadataFolder.exists()) {
                    File[] metadataFolders = metadataFolder.listFiles(metaFilter);
                    if (metadataFolders != null) {
                        for (File metadataYamlFolder : metadataFolders) {
                            if (!processMetadata(targetDir, metadataFolder, metadataYamlFolder, md5MapOfAllService)) {
                                return false;
                            }
                        }
                    }
                }
            } catch (IOException e) {
                log.error("Error occurred while processing the metadata files", e);
                return false;
            } catch (CarbonException e) {
                log.error("Error occurred when extracting the carbon application", e);
                return false;
            } catch (ResolverException e) {
                log.error("Environment variables are not configured correctly", e);
                return false;
            } catch (NoSuchAlgorithmException e) {
                log.error("Could not generate the MD5 sum", e);
                return false;
            }
        }
        return true;
    }

    /**
     * Create temporary folder structure.
     *
     * @param folderPath path to the temp directory.
     * @return folder creation result.
     */
    public static boolean createTemporaryFolders(String folderPath) {
        File serviceCatalogFolder = new File(folderPath);
        if (serviceCatalogFolder.exists()) {
            try {
                FileUtils.forceDelete(serviceCatalogFolder);
            } catch (IOException e) {
                log.error("Error occurred while removing temporary directories", e);
            }
        }
        boolean created = serviceCatalogFolder.mkdir();
        if (!created) {
            log.error("Could not create temporary directories required for service catalog");
            return false;
        }

        File tempDir = new File(folderPath, TEMP_FOLDER_NAME);
        if (tempDir.exists()) {
            tempDir.delete();
        }
        created = tempDir.mkdir();
        if (!created) {
            log.error("Could not create temporary directories required for service catalog");
        }
        return created;
    }

    /**
     * Generate MD5 sum of a given file.
     *
     * @param file input file.
     * @return MD5 sum of the given file.
     * @throws IOException              error occurred while processing the file.
     * @throws NoSuchAlgorithmException Could not find the MD5 sum algo.
     */
    private static String getFileChecksum(File file) throws NoSuchAlgorithmException, IOException {
        MessageDigest md5Digest = MessageDigest.getInstance("MD5");
        FileInputStream fis = new FileInputStream(file);

        byte[] byteArray = new byte[1024];
        int bytesCount;

        while ((bytesCount = fis.read(byteArray)) != -1) {
            md5Digest.update(byteArray, 0, bytesCount);
        }
        fis.close();

        byte[] bytes = md5Digest.digest();

        StringBuilder sb = new StringBuilder();
        for (byte aByte : bytes) {
            sb.append(Integer.toString((aByte & 0xff) + 0x100, 16).substring(1));
        }
        return sb.toString();
    }
}
