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Component Overview

MegaDownloader consists of several core components, each with specific responsibilities in the application architecture.

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Main Window Manager

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Main.java

Location: Main.java:29 Responsibilities:
  • Application window management
  • Panel navigation using CardLayout
  • Media polling service coordination
  • Custom window dragging for undecorated frame
  • FlatLaf Darcula theme setup
  • Panel Management: Manages all application panels (Login, Main, Preferences, Media)
  • Navigation State: Tracks current and previous panel for back button functionality
  • Dependency Injection: Connects panels with shared services
  • Auto-login: Checks for saved credentials on startup
  • Configuration Check: Validates yt-dlp configuration on launch
Navigation Methods: 
public void showMainPanel() {
    previousPanel = currentPanel;
    currentPanel = "MAIN";
    cardLayout.show(cardPanel, "MAIN");
}

public void showPreferencesPanel() {
    previousPanel = currentPanel;
    currentPanel = "PREFERENCES";
    cardLayout.show(cardPanel, "PREFERENCES");
}

public void goBack() {
    cardLayout.show(cardPanel, previousPanel);
    currentPanel = previousPanel;
}

public void logout() {
    loginForm.clearToken();
    showLoginForm();
}
Window Dragging Implementation (Main.java:139): 
private void enableDragging(Component component) {
    component.addMouseListener(new MouseAdapter() {
        @Override
        public void mousePressed(MouseEvent e) {
            initialClick = e.getPoint();
        }
    });

    component.addMouseMotionListener(new MouseMotionAdapter() {
        @Override
        public void mouseDragged(MouseEvent e) {
            int thisX = Main.this.getLocation().x;
            int thisY = Main.this.getLocation().y;
            int xMoved = e.getX() - initialClick.x;
            int yMoved = e.getY() - initialClick.y;
            Main.this.setLocation(thisX + xMoved, thisY + yMoved);
        }
    });
}
The enableDragging() method is applied to the content pane, menu bar, and media polling component to allow window movement.

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Download Interface

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MainPanel.java

Location: MainPanel.java:30 Responsibilities:
  • URL input and validation
  • yt-dlp process execution
  • Download progress monitoring
  • Audio/video format selection
  • Custom arguments support
  • M3U playlist generation
  • Integration with FFmpeg for audio extraction
  • Process Execution: Spawns yt-dlp subprocess with ProcessBuilder
  • Progress Parsing: Real-time progress bar updates from yt-dlp output
  • FFmpeg Integration: Auto-detects FFmpeg in yt-dlp directory
  • Speed Limiting: Applies download speed limits from preferences
  • Playlist Support: Creates M3U playlists for downloaded media
  • File Tracking: Opens downloaded files with system default player
Download Process (MainPanel.java:481): 
SwingWorker<Integer, Integer> worker = new SwingWorker<Integer, Integer>() {
    @Override
    protected Integer doInBackground() throws Exception {
        List<String> command = new ArrayList<>();
        command.add(ytdlpPath);
        
        if (ffmpegLocation != null) {
            command.add("--ffmpeg-location");
            command.add(ffmpegLocation);
        }
        
        if (limiterEnabled) {
            command.add("--limit-rate");
            command.add(speedLimitKBps + "K");
        }
        
        if (audioOnly) {
            command.add("-x");
            command.add("--audio-format");
            command.add("mp3");
        }
        
        command.add(url);
        
        ProcessBuilder pb = new ProcessBuilder(command);
        Process process = pb.start();
        
        // Parse output for progress updates
        return process.waitFor();
    }
};
Configuration Loading (MainPanel.java:174): 
private String getYtDlpPath() {
    File configFile = new File("config.txt");
    try (BufferedReader reader = new BufferedReader(new FileReader(configFile))) {
        String line;
        while ((line = reader.readLine()) != null) {
            if (line.startsWith("path:\"") && line.endsWith("\"")) {
                return line.substring(6, line.length() - 1);
            }
        }
    }
    return null;
}

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Authentication

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LoginForm.java

Location: LoginForm.java:44 Responsibilities:
  • User authentication via API
  • Credential validation (email format, password)
  • Session persistence with Java Preferences API
  • Auto-login on startup
  • Token management
  • Email Validation: Real-time regex-based email validation
  • Visual Feedback: Red border on invalid input
  • Remember Me: Stores credentials using Preferences API
  • Auto-login: Validates saved tokens on startup
  • API Integration: Uses MediaPollingComponent for authentication
Email Validation (LoginForm.java:176): 
private boolean validateEmail() {
    String email = txtEmail.getText();
    Pattern pattern = Pattern.compile("^[\\w.-]+@[\\w.-]+\\.[a-zA-Z]{2,}$");
    if (!pattern.matcher(email).matches()) {
        txtEmail.setBorder(BorderFactory.createLineBorder(new Color(220, 53, 69)));
        return false;
    }
    txtEmail.setBorder(defaultBorder);
    return true;
}
Token Persistence (LoginForm.java:247): 
private void saveToken(String email, String token) {
    prefs.put("auth_token", token);
    prefs.put("user_email", email);
}

public boolean checkAutoLogin() {
    String savedToken = prefs.get("auth_token", null);
    String savedEmail = prefs.get("user_email", null);
    
    if (savedToken != null && savedEmail != null) {
        if (mediaPollingComponent.checkToken(savedToken)) {
            this.token = savedToken;
            mediaPollingComponent.setToken(savedToken);
            return true;
        } else {
            clearToken();
        }
    }
    return false;
}

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Media Management

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ManageMediaPanel.java

Location: ManageMediaPanel.java:39 Responsibilities:
  • Display local and server media files
  • Search and filter functionality
  • File operations (play, delete, download)
  • Server synchronization
  • Quick actions context menu
  • Dual Source Display: Shows both local and server files in one table
  • Real-time Filtering: Text search and type filtering (Video/Audio/All)
  • Quick Actions: Context menu and action list for common operations
  • Download Indicator: Shows download status with symbols (✓, ⬇, ✗)
  • Live Updates: Listens for new media from MediaPollingComponent
Media Loading (ManageMediaPanel.java:76): 
private void loadMediaFiles() {
    File directory = new File(currentDirectory);
    List<File> mediaFiles = getMediaFiles(directory);
    List<Media> serverMedia = getMediaFromNetwork();
    
    DefaultTableModel model = (DefaultTableModel) tblFiles.getModel();
    model.setRowCount(0);
    
    // Add local files with server sync status
    for (File file : mediaFiles) {
        DownloadedMedia media = new DownloadedMedia(file.getAbsolutePath());
        
        boolean existsOnServer = serverMedia.stream()
            .anyMatch(serverItem -> media.matchesServerMedia(serverItem));
        
        String status = existsOnServer ? "✓" : "";
        String source = existsOnServer ? "Both" : "Local";
        
        model.addRow(new Object[]{
            status, media.getFileName(), media.getMediaType(),
            formatFileSize(media.getFileSize()), media.getDate(), source
        });
    }
    
    // Add server-only files
    for (Media serverItem : serverMedia) {
        boolean existsLocally = mediaList.stream()
            .anyMatch(localMedia -> localMedia.matchesServerMedia(serverItem));
        
        if (!existsLocally) {
            model.addRow(new Object[]{
                "", serverItem.mediaFileName,
                getMediaTypeFromMime(serverItem.mediaMimeType),
                "", "", "Server"
            });
        }
    }
}
Live Media Updates (ManageMediaPanel.java:771): 
mediaPollingComponent.addMediaPollingListener(newMedia -> {
    SwingUtilities.invokeLater(() -> {
        mediaFromServer.addAll(newMedia);
        addNewMediaToTable(newMedia);
    });
});

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Settings Configuration

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PreferencesPanel.java

Location: PreferencesPanel.java:33 Responsibilities:
  • yt-dlp path configuration
  • Download directory selection
  • FFmpeg path configuration
  • Speed limiter settings
  • M3U playlist generation toggle
  • Configuration persistence
  • File Choosers: JFileChooser for selecting executables and directories
  • Speed Limiter: Slider and text field synchronized controls (1-100000 KB/s)
  • Config Persistence: Saves settings to config.txt
  • Validation: Ensures paths are configured before saving
Configuration Saving (PreferencesPanel.java:345): 
private void btnSaveActionPerformed(java.awt.event.ActionEvent evt) {
    String path = lblYtdlpCurrentPath.getText();
    String downloadDirectoryPath = lblDownloadDirectoryPath.getText();
    
    if (path.equals("Not configured")) {
        JOptionPane.showMessageDialog(this, 
            "Please select a yt-dlp location first");
        return;
    }
    
    try (BufferedWriter writer = new BufferedWriter(
            new FileWriter("config.txt"))) {
        writer.write("path:\"" + path + "\"");
        writer.newLine();
        if (!downloadDirectoryPath.equals("Default (where project is stored)")) {
            writer.write("downloadDir:\"" + downloadDirectoryPath + "\"");
        }
        JOptionPane.showMessageDialog(this, 
            "Configuration saved successfully!");
    }
}

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About Dialog

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AboutDialog.java

Location: AboutDialog.java:14 Responsibilities:
  • Display application information
  • Show version and author details
  • Display application logo and banner
  • Modal dialog with ESC key to close
Image Loading (AboutDialog.java:47): 
private void loadBannerImage() {
    java.net.URL imageURL = getClass().getResource("/images/YTDLPBanner.png");
    ImageIcon originalIcon = new ImageIcon(imageURL);
    
    // Scale image to fit label while maintaining aspect ratio
    double scaleX = (double) labelWidth / originalWidth;
    double scaleY = (double) labelHeight / originalHeight;
    double scale = Math.min(scaleX, scaleY);
    
    Image scaledImage = originalIcon.getImage()
        .getScaledInstance(scaledWidth, scaledHeight, Image.SCALE_SMOOTH);
    lblPhoto.setIcon(new ImageIcon(scaledImage));
}

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Data Model

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DownloadedMedia.java

Location: DownloadedMedia.java:21 Responsibilities:
  • Represent downloaded media files
  • Extract file metadata (size, date, MIME type)
  • Match local files with server media
  • File deletion operations
  • MIME Detection: Uses Files.probeContentType() to detect file type
  • Server Matching: Compares local files with server media by ID, GUID, or filename
  • Metadata Extraction: Reads file size, modification date, and type
  • File Operations: Delete functionality with validation
Server Media Matching (DownloadedMedia.java:114): 
public boolean matchesServerMedia(Media serverMedia) {
    // Match by server ID if known
    if (this.serverId != null && this.serverId == serverMedia.id) {
        return true;
    }
    
    // Match by blob GUID
    if (this.serverBlobGuid != null && 
        this.serverBlobGuid.equals(serverMedia.blobNameGuid)) {
        return true;
    }
    
    // Match by filename and MIME type
    return this.fileName.equals(serverMedia.mediaFileName) &&
           this.mimeType.equals(serverMedia.mediaMimeType);
}
MIME Type Detection (DownloadedMedia.java:66): 
private String detectMimeType(File file) {
    try {
        String mimeType = Files.probeContentType(file.toPath());
        if (mimeType != null) {
            return mimeType;
        }
    } catch (IOException ex) {
        // Log error
    }
    return "unknown";
}

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Component Relationships

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Dependency Graph

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Data Flow

  1. Authentication Flow: LoginForm → MediaPollingComponent → API → Token Storage
  2. Download Flow: MainPanel → Config → yt-dlp Process → File System
  3. Media Management Flow: ManageMediaPanel → Local Files + Server API → Table Display
  4. Configuration Flow: PreferencesPanel → config.txt → All Panels
All long-running operations (authentication, downloads, API calls) use SwingWorker to prevent UI freezing.

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