package com.example.networking;

import com.jcraft.jsch.ChannelSftp;
import com.jcraft.jsch.JSch;
import com.jcraft.jsch.Session;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.ByteArrayOutputStream;
import java.nio.charset.StandardCharsets;
import java.util.Properties;

public class RemoteSshFileRetriever {
    private static final Logger logger = LoggerFactory.getLogger(RemoteSshFileRetriever.class);
    private static final int CONNECTION_TIMEOUT_MS = 20000;

    /**
     * Fetches a plain text file from a remote path and applies HTML escaping for display.
     */
    public static String pullFormattedFile(String targetHost, int servicePort, String loginAccount, String accessKey, String directoryPath, String documentName) throws Exception {
        Session connection = null;
        ChannelSftp transport = null;

        try {
            connection = initializeProtocolSession(targetHost, servicePort, loginAccount, accessKey);
            transport = activateSftpLayer(connection);

            ByteArrayOutputStream dataBuffer = new ByteArrayOutputStream();
            String fullRoute = String.join("/", directoryPath, documentName);
            transport.get(fullRoute, dataBuffer);

            String rawPayload = new String(dataBuffer.toByteArray(), StandardCharsets.UTF_8);
            return sanitizeHtmlOutput(rawPayload);
        } catch (Exception failure) {
            logger.warn("SFTP operation aborted: {}", failure.getMessage());
            throw new IllegalStateException("Failed to extract remote payload", failure);
        } finally {
            terminateResources(transport, connection);
        }
    }

    private static Session initializeProtocolSession(String endpoint, int port, String user, String secret) {
        JSch client = new JSch();
        Session active = client.getSession(user, endpoint, port);
        active.setPassword(secret);
        active.setTimeout(CONNECTION_TIMEOUT_MS);

        Properties securitySettings = new Properties();
        securitySettings.put("StrictHostKeyChecking", "no");
        active.setConfig(securitySettings);
        active.connect();
        return active;
    }

    private static ChannelSftp activateSftpLayer(Session session) {
        try {
            ChannelSftp layer = (ChannelSftp) session.openChannel("sftp");
            layer.connect();
            return layer;
        } catch (Exception setupError) {
            throw new RuntimeException("SFTP initialization failed", setupError);
        }
    }

    private static void terminateResources(ChannelSftp channel, Session session) {
        if (channel != null && channel.isConnected()) channel.disconnect();
        if (session != null && session.isConnected()) session.disconnect();
    }

    private static String sanitizeHtmlOutput(String text) {
        return text.replace("\t", "    ")
                   .replaceAll("(\\r\\n|\\n|\\r)", "<br>");
    }
}

Operational Characteristics

• Lifecycle Management: Utilizes explicit finally blocks to guarantee socket release, preventing connection pool exhaustion.
• Encoding Standardization: Forces UTF-8 parsing to bypass platform-dependent default charset behavior.
• Presentation Normalization: Converts whitespace control codes into semantic HTML entities optimized for browser viewing.