Update README.md for v1.3.0 with tabbed interface and enhanced PDF export features

- Enhanced PDF export with multiple LaTeX engine fallbacks
- Fixed file association and direct file opening from OS
- Removed redundant converter menu, moved import to File menu
- Implemented comprehensive tabbed interface for multiple files
- Added tab management with keyboard shortcuts (Ctrl+N, Ctrl+W, Ctrl+Tab)
- Enhanced UI with tab bar and improved navigation
- Updated to version 1.3.0 with new features
- Improved main process and renderer architecture for multi-file support

CLAUDE.md

@@ -0,0 +1,303 @@
+# PanConverter - Claude Development Guide
+
+## Project Overview
+
+**PanConverter** is a cross-platform Markdown editor and converter powered by Pandoc, built with Electron. It provides professional-grade editing capabilities with comprehensive export options.
+
+**Current Version**: v1.2.1  
+**Author**: Amit Haridas (amit.wh@gmail.com)  
+**License**: MIT  
+**Repository**: https://github.com/amitwh/pan-converter
+
+## Architecture & Technology Stack
+
+### Core Technologies
+- **Electron** - Cross-platform desktop application framework
+- **Pandoc** - Universal document converter (required dependency)
+- **marked** - Markdown parsing and rendering
+- **highlight.js** - Syntax highlighting
+- **XLSX** - Spreadsheet export functionality
+- **DOMPurify** - HTML sanitization
+
+### Application Structure
+```
+src/
+├── main.js        # Electron main process, menu system, IPC handlers
+├── renderer.js    # UI logic, editor functionality, event handling
+├── index.html     # Application layout and components
+└── styles.css     # Comprehensive styling with multi-theme support
+
+assets/
+└── icon.png       # Application icon
+
+package.json       # Dependencies and build configuration
+```
+
+## Development Commands
+
+### Prerequisites
+```bash
+# Install Node.js dependencies
+npm install
+
+# Install Pandoc (required for export functionality)
+# Ubuntu/Debian:
+sudo apt-get install pandoc
+
+# macOS:
+brew install pandoc
+
+# Windows: Download from https://pandoc.org/installing.html
+```
+
+### Running the Application
+```bash
+# Start development server
+npm start
+
+# Start with debugging
+npm start --enable-logging
+```
+
+### Building & Packaging
+
+```bash
+# Generate application icons
+npm run generate-icons
+
+# Build for current platform
+npm run build
+
+# Platform-specific builds
+npm run build:win      # Windows
+npm run build:mac      # macOS
+npm run build:linux    # Linux (AppImage, .deb, .snap)
+
+# Build for all platforms
+npm run dist:all
+```
+
+### Git Branch Management
+```bash
+# Switch to platform-specific branches
+git checkout linux    # Linux development
+git checkout macos     # macOS development  
+git checkout windows   # Windows development
+git checkout master    # Main development branch
+
+# Update all branches with latest changes
+git checkout master
+git push origin master
+git checkout linux && git merge master && git push origin linux
+git checkout macos && git merge master && git push origin macos
+git checkout windows && git merge master && git push origin windows
+```
+
+### Release Management
+```bash
+# Create and push release tag
+git tag v1.2.1 -m "Release message"
+git push origin v1.2.1
+
+# Create GitHub release with packages
+gh release create v1.2.1 --title "Title" --notes "Release notes" \
+  "dist/PanConverter-1.2.1.AppImage" \
+  "dist/pan-converter_1.2.1_amd64.deb" \
+  "dist/pan-converter_1.2.1_amd64.snap"
+```
+
+## Feature Implementation Guide
+
+### v1.2.1 Comprehensive Editor Enhancements
+
+#### ✨ Advanced Editor Features
+
+**Find & Replace System** (`src/renderer.js:200-350`)
+- Dialog-based interface with match highlighting
+- Forward/backward navigation through matches
+- Replace single or replace all functionality
+- Real-time match counting and status display
+- Escape key closes dialog
+
+**Line Numbers** (`src/renderer.js:450-500`, `src/styles.css:517-598`)
+- Toggle-able line numbers with toolbar button
+- Synchronized scrolling with editor content
+- Theme-aware styling for all supported themes
+- Dynamic line number generation based on content
+
+**Undo/Redo System** (`src/renderer.js:100-150`)
+- Stack-based state management for editor history
+- Keyboard shortcuts: `Ctrl/Cmd+Z` (undo), `Ctrl/Cmd+Shift+Z` (redo)
+- Intelligent state saving on text changes
+- Memory-efficient history management
+
+**Smart Auto-Indentation** (`src/renderer.js:350-400`)
+- Automatic list continuation on Enter key
+- Proper indentation handling for nested lists
+- Support for ordered and unordered lists
+- Intelligent whitespace management
+
+**Enhanced Keyboard Shortcuts** (`src/renderer.js:400-450`)
+- `Tab`/`Shift+Tab` for line indentation/outdentation
+- `Enter` for auto-continuing lists
+- `Ctrl/Cmd+F` for find & replace dialog
+- `Escape` for closing dialogs
+
+**Word/Character Count** (`src/renderer.js:500-530`)
+- Live counting displayed in status bar
+- Updates automatically as content changes
+- Word and character statistics
+
+#### 📤 Export & Conversion Features
+
+**PowerPoint Export** (`src/main.js:330-350`)
+- Convert markdown to PPTX presentations
+- Automatic slide-level formatting (`--slide-level=2`)
+- Smart presentation structure handling
+
+**Spreadsheet Export** (`src/main.js:370-457`)
+- Export markdown tables to Excel (XLSX/XLS) and ODS formats
+- Multi-table support with separate worksheets
+- Automatic table detection and parsing
+- Error handling for files without tables
+
+**Document Import** (`src/main.js:280-315`)
+- Import DOCX, ODT, RTF, HTML, PDF, PPTX, ODP files
+- Automatic conversion to markdown format
+- File dialog with appropriate filters
+- Success notifications and error handling
+
+**Table Creation Helper** (`src/renderer.js:600-650`)
+- Built-in table generator with row/column specification
+- Automatic markdown table formatting
+- Proper header separation and alignment
+
+#### 🎨 Interface & Theming
+
+**Multi-Theme Support** (`src/styles.css:214-598`)
+- Light, Dark, Solarized, Monokai, GitHub themes
+- Complete theming for all UI components
+- Theme-aware styling for new features (find dialog, line numbers)
+- Persistent theme selection with local storage
+
+**Enhanced UI Components** (`src/index.html:94-108`)
+- Find & replace dialog with modern styling
+- Toolbar buttons for all new features
+- Status bar with live statistics
+- Responsive layout with proper spacing
+
+## File Structure & Key Components
+
+### Main Process (`src/main.js`)
+- **Menu System**: Comprehensive menu with file operations, editing, conversion, view options
+- **IPC Handlers**: Communication between main and renderer processes
+- **File Operations**: Open, save, import/export functionality
+- **Theme Management**: Persistent theme storage and application
+- **Spreadsheet Export**: Table extraction and XLSX generation
+- **About Dialog**: Application information and feature list
+
+### Renderer Process (`src/renderer.js`)
+- **Editor Initialization**: CodeMirror-like functionality with custom implementation
+- **Find & Replace Engine**: Search algorithms with regex support
+- **Undo/Redo Manager**: History stack management
+- **Auto-indentation Logic**: Smart list continuation
+- **Live Preview**: Real-time markdown rendering with DOMPurify
+- **Event Handling**: Keyboard shortcuts and UI interactions
+- **Statistics Tracking**: Word/character counting
+
+### Styling (`src/styles.css`)
+- **Base Styles**: Application layout and typography
+- **Component Styles**: Toolbar, editor, preview, dialogs
+- **Theme Implementations**: Complete styling for all themes
+- **Responsive Design**: Flexible layouts and proper spacing
+- **Animation Support**: Smooth transitions and hover effects
+
+### HTML Structure (`src/index.html`)
+- **Toolbar**: Feature buttons with SVG icons
+- **Find Dialog**: Search and replace interface
+- **Editor Container**: Line numbers and text editor
+- **Preview Pane**: Rendered markdown display
+- **Status Bar**: Statistics and application status
+
+## Testing & Quality Assurance
+
+### Manual Testing Checklist
+- [ ] All keyboard shortcuts work correctly
+- [ ] Find & replace functions properly with edge cases
+- [ ] Line numbers sync correctly with content
+- [ ] Undo/redo preserves cursor position
+- [ ] Auto-indentation works with various list types
+- [ ] All themes render correctly for new components
+- [ ] Export functions work with various document formats
+- [ ] Table creation and export functionality
+- [ ] Cross-platform compatibility
+
+### Known Issues & Limitations
+- AppImage may require `--no-sandbox` flag on some Linux systems
+- Large files (>1MB) may cause performance issues
+- Windows/Mac builds require platform-specific environments
+- Pandoc must be installed separately for export functionality
+
+## Deployment & Distribution
+
+### Release Packages
+- **Linux AppImage**: Universal Linux package (self-contained)
+- **Debian Package**: `.deb` for Ubuntu/Debian systems
+- **Snap Package**: Universal Linux package via Snap Store
+- **Future**: Windows `.exe` and macOS `.dmg` packages
+
+### Release Process
+1. Update version in `package.json`, `src/main.js`, and `README.md`
+2. Commit changes and push to all platform branches
+3. Build platform-specific packages
+4. Create Git tag and GitHub release
+5. Upload packages to GitHub release
+6. Update documentation and announce release
+
+## Contributing Guidelines
+
+### Code Style
+- Use consistent indentation (2 spaces)
+- Follow JavaScript ES6+ standards
+- Comment complex functionality
+- Maintain separation between main and renderer processes
+- Use descriptive variable and function names
+
+### Adding New Features
+1. Plan feature implementation and UI integration
+2. Update relevant files (main.js, renderer.js, styles.css)
+3. Test across all supported themes
+4. Update documentation and README
+5. Test on multiple platforms if possible
+6. Submit pull request with detailed description
+
+### Bug Reporting
+- Include steps to reproduce
+- Specify platform and version information
+- Attach relevant screenshots or error logs
+- Check existing issues before creating new ones
+
+## Future Roadmap
+
+### Planned Features
+- [ ] Collaborative editing capabilities
+- [ ] Plugin system for extensions
+- [ ] Advanced markdown extensions (math, diagrams)
+- [ ] Cloud synchronization options
+- [ ] Mobile companion app
+- [ ] Advanced export templates
+- [ ] Spell check and grammar checking
+- [ ] Version control integration
+
+### Technical Improvements
+- [ ] Performance optimization for large files
+- [ ] Memory usage optimization
+- [ ] Startup time improvements
+- [ ] Better error handling and user feedback
+- [ ] Automated testing suite
+- [ ] Continuous integration/deployment
+
+---
+
+**Last Updated**: September 1, 2025  
+**Claude Assistant**: Development completed for v1.2.1 comprehensive editor enhancements

README.md

@@ -7,12 +7,14 @@ A cross-platform Markdown editor and converter powered by Pandoc.
 ## Features
 
 ### ✨ Advanced Markdown Editor
+- 🗂️ **Tabbed Interface** - Work with multiple files simultaneously in separate tabs
 - 📝 **Rich Text Editor** - Full-featured editor with syntax highlighting and comprehensive toolbar
 - 🔍 **Find & Replace** - Powerful search and replace with match highlighting and navigation
 - 🔢 **Line Numbers** - Toggle line numbers for easier code editing and navigation
 - ↩️ **Smart Auto-Indentation** - Automatic list continuation and intelligent indentation
 - ⏪ **Undo/Redo** - Full undo/redo support with keyboard shortcuts
 - ⌨️ **Advanced Shortcuts** - Tab indentation, line selection, and smart text formatting
+- 📂 **File Association Support** - Open markdown files directly from file manager
 
 ### 🎨 Themes & Interface
 - 👁️ **Live Preview** - See your markdown rendered in real-time with synchronized scrolling
@@ -20,9 +22,10 @@ A cross-platform Markdown editor and converter powered by Pandoc.
 - 💾 **Auto-Save** - Never lose your work with automatic saving every 30 seconds
 
 ### 📤 Export & Conversion
-- 📄 **Document Export** - Convert to HTML, PDF, DOCX, LaTeX, RTF, ODT, EPUB, PowerPoint (PPTX), and OpenDocument Presentation (ODP)
+- 📄 **Enhanced PDF Export** - Robust PDF generation with multiple LaTeX engine fallbacks (XeLaTeX, PDFLaTeX, wkhtmltopdf)
+- 📄 **Document Export** - Convert to HTML, DOCX, LaTeX, RTF, ODT, EPUB, PowerPoint (PPTX), and OpenDocument Presentation (ODP)
 - 📊 **Spreadsheet Export** - Export markdown tables to Excel (XLSX/XLS) and OpenDocument Spreadsheet (ODS) formats
-- 📥 **Document Import & Conversion** - Import various document formats and convert between formats via Pandoc
+- 📥 **Document Import** - Import DOCX, ODT, RTF, HTML, PDF, and presentation files to markdown
 - 📋 **Table Creation Helper** - Built-in table generator for easy markdown table creation
 
 ### 🖥️ Platform Support
@@ -36,13 +39,20 @@ A cross-platform Markdown editor and converter powered by Pandoc.
   - **macOS**: `brew install pandoc`
   - **Windows**: Download installer from Pandoc website
 
+### PDF Export Requirements
+For optimal PDF export, install a LaTeX engine (recommended):
+- **Ubuntu/Debian**: `sudo apt-get install texlive-xetex texlive-latex-base`
+- **macOS**: `brew install --cask mactex`
+- **Windows**: Install MiKTeX or TeX Live
+- **Alternative**: `sudo apt-get install wkhtmltopdf` (fallback option)
+
 ### Download
 Download the latest release for your platform from the [Releases](https://github.com/amitwh/pan-converter/releases) page.
 
 #### Linux
-- **AppImage**: `PanConverter-1.2.0.AppImage` (universal, may require `--no-sandbox` flag)
+- **AppImage**: `PanConverter-1.3.0.AppImage` (universal, may require `--no-sandbox` flag)
-- **Debian Package**: `pan-converter_1.2.0_amd64.deb`
+- **Debian Package**: `pan-converter_1.3.0_amd64.deb`
-- **Snap Package**: `pan-converter_1.2.0_amd64.snap`
+- **Snap Package**: `pan-converter_1.3.0_amd64.snap`
 
 ### Install from Source
 ```bash
@@ -78,7 +88,10 @@ npm start
 ## Keyboard Shortcuts
 
 ### File Operations
-- `Ctrl/Cmd + N` - New file
+- `Ctrl/Cmd + N` - New file/tab
+- `Ctrl/Cmd + T` - New tab
+- `Ctrl/Cmd + W` - Close current tab
+- `Ctrl/Cmd + Tab` - Switch to next tab
 - `Ctrl/Cmd + O` - Open file
 - `Ctrl/Cmd + S` - Save file
 - `Ctrl/Cmd + Shift + S` - Save as
@@ -120,7 +133,8 @@ npm run dist:all
 
 ## Version History
 
-- **v1.2.0** - Major editor enhancements: Find & Replace, Line Numbers, Undo/Redo, Auto-indentation, PowerPoint export, document conversion menu, table creation helper, spreadsheet export
+- **v1.3.0** - Major update: Tabbed interface for multiple files, enhanced PDF export with LaTeX engines, fixed file associations, removed redundant converter menu, improved UI architecture
+- **v1.2.1** - Comprehensive editor enhancements: Find & Replace, Line Numbers, Undo/Redo, Auto-indentation, PowerPoint export, document conversion menu, table creation helper, spreadsheet export
 - **v1.1.0** - Added Excel/ODS spreadsheet export, updated author information, renamed to PanConverter
 - **v1.0.0** - Initial release with basic markdown editing, themes, and Pandoc export
 

package.json

@@ -1,6 +1,6 @@
 {
   "name": "pan-converter",
-  "version": "1.2.0",
+  "version": "1.3.0",
   "description": "Cross-platform Markdown editor and converter using Pandoc",
   "main": "src/main.js",
   "scripts": {

src/index.html

@@ -10,6 +10,13 @@
 </head>
 <body>
     <div class="container">
+        <div class="tab-bar" id="tab-bar">
+            <div class="tab active" data-tab-id="1">
+                <span class="tab-title">Untitled</span>
+                <button class="tab-close" title="Close tab">×</button>
+            </div>
+            <button class="new-tab-button" id="new-tab-btn" title="New tab">+</button>
+        </div>
         <div class="toolbar">
             <button id="btn-bold" title="Bold">
                 <svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2">
@@ -108,14 +115,16 @@
         </div>
         
         <div class="editor-container">
-            <div id="editor-pane" class="pane">
+            <div class="tab-content active" id="tab-content-1" data-tab-id="1">
+                <div id="editor-pane-1" class="pane">
                     <div class="editor-wrapper">
-                    <div id="line-numbers" class="line-numbers hidden"></div>
+                        <div id="line-numbers-1" class="line-numbers hidden"></div>
-                    <textarea id="editor"></textarea>
+                        <textarea id="editor-1" class="editor-textarea"></textarea>
                     </div>
                 </div>
-            <div id="preview-pane" class="pane">
+                <div id="preview-pane-1" class="pane">
-                <div id="preview"></div>
+                    <div id="preview-1" class="preview-content"></div>
+                </div>
             </div>
         </div>
         

src/main.js

@@ -28,7 +28,7 @@ const store = {
 };
 
 let mainWindow;
-let currentFile = null;
+let currentFile = null; // This will now represent the active tab's file
 
 function createWindow() {
   mainWindow = new BrowserWindow({
@@ -48,6 +48,14 @@ function createWindow() {
   mainWindow.on('closed', () => {
     mainWindow = null;
   });
+
+  // Handle pending file from file association
+  if (app.pendingFile) {
+    mainWindow.webContents.once('dom-ready', () => {
+      openFileFromPath(app.pendingFile);
+      app.pendingFile = null;
+    });
+  }
 }
 
 function createMenu() {
@@ -76,6 +84,11 @@ function createMenu() {
           click: saveAsFile
         },
         { type: 'separator' },
+        {
+          label: 'Import Document...',
+          accelerator: 'CmdOrCtrl+I',
+          click: importDocument
+        },
         {
           label: 'Export',
           submenu: [
@@ -121,32 +134,6 @@ function createMenu() {
         }
       ]
     },
-    {
-      label: 'Convert',
-      submenu: [
-        {
-          label: 'Import Document...',
-          accelerator: 'CmdOrCtrl+I',
-          click: importDocument
-        },
-        { type: 'separator' },
-        {
-          label: 'Convert Current File',
-          submenu: [
-            { label: 'To Markdown', click: () => convertToFormat('md') },
-            { label: 'To HTML', click: () => convertToFormat('html') },
-            { label: 'To PDF', click: () => convertToFormat('pdf') },
-            { label: 'To DOCX', click: () => convertToFormat('docx') },
-            { label: 'To LaTeX', click: () => convertToFormat('latex') },
-            { label: 'To RTF', click: () => convertToFormat('rtf') },
-            { label: 'To ODT', click: () => convertToFormat('odt') },
-            { label: 'To EPUB', click: () => convertToFormat('epub') },
-            { label: 'To PPTX', click: () => convertToFormat('pptx') },
-            { label: 'To ODP', click: () => convertToFormat('odp') }
-          ]
-        }
-      ]
-    },
     {
       label: 'View',
       submenu: [
@@ -184,7 +171,7 @@ function createMenu() {
               type: 'info',
               title: 'About PanConverter',
               message: 'PanConverter',
-              detail: 'A cross-platform Markdown editor and converter using Pandoc.\n\nVersion: 1.2.0\nAuthor: Amit Haridas\nEmail: amit.wh@gmail.com\nLicense: MIT\n\nFeatures:\n• Advanced markdown editing with live preview\n• Find & replace with match highlighting\n• Line numbers and auto-indentation\n• Export to multiple formats via Pandoc\n• PowerPoint & presentation export\n• Export tables to Excel/ODS spreadsheets\n• Document import & conversion\n• Table creation helper\n• Multiple themes support\n• Undo/redo functionality',
+              detail: 'A cross-platform Markdown editor and converter using Pandoc.\n\nVersion: 1.3.0\nAuthor: Amit Haridas\nEmail: amit.wh@gmail.com\nLicense: MIT\n\nFeatures:\n• Tabbed interface for multiple files\n• Advanced markdown editing with live preview\n• Enhanced PDF export with LaTeX engines\n• Find & replace with match highlighting\n• Line numbers and auto-indentation\n• Export to multiple formats via Pandoc\n• PowerPoint & presentation export\n• Export tables to Excel/ODS spreadsheets\n• Document import & conversion\n• Table creation helper\n• Multiple themes support\n• Undo/redo functionality',
               buttons: ['OK']
             });
           }
@@ -246,12 +233,54 @@ function exportFile(format) {
   });
 
   if (outputFile) {
-    const pandocCmd = `pandoc "${currentFile}" -o "${outputFile}"`;
+    let pandocCmd = `pandoc "${currentFile}" -o "${outputFile}"`;
     
+    // Add specific options for PDF export to ensure proper generation
+    if (format === 'pdf') {
+      pandocCmd = `pandoc "${currentFile}" --pdf-engine=xelatex -V geometry:margin=1in -o "${outputFile}"`;
+      // Try with different PDF engines if xelatex fails
+      exec(pandocCmd, (error, stdout, stderr) => {
+        if (error) {
+          // Fallback to pdflatex
+          const fallbackCmd = `pandoc "${currentFile}" --pdf-engine=pdflatex -V geometry:margin=1in -o "${outputFile}"`;
+          exec(fallbackCmd, (fallbackError, fallbackStdout, fallbackStderr) => {
+            if (fallbackError) {
+              // Final fallback to wkhtmltopdf
+              const htmlToPdfCmd = `pandoc "${currentFile}" -t html5 | wkhtmltopdf - "${outputFile}"`;
+              exec(htmlToPdfCmd, (finalError) => {
+                if (finalError) {
+                  dialog.showErrorBox('PDF Export Error', 
+                    `Failed to export PDF. Please ensure you have one of the following installed:\n` +
+                    `• XeLaTeX (recommended): sudo apt-get install texlive-xetex\n` +
+                    `• PDFLaTeX: sudo apt-get install texlive-latex-base\n` +
+                    `• wkhtmltopdf: sudo apt-get install wkhtmltopdf\n\n` +
+                    `Error: ${finalError.message}`
+                  );
+                } else {
+                  showExportSuccess(outputFile);
+                }
+              });
+            } else {
+              showExportSuccess(outputFile);
+            }
+          });
+        } else {
+          showExportSuccess(outputFile);
+        }
+      });
+    } else {
       exec(pandocCmd, (error, stdout, stderr) => {
         if (error) {
           dialog.showErrorBox('Export Error', `Failed to export: ${error.message}\n\nMake sure Pandoc is installed.`);
         } else {
+          showExportSuccess(outputFile);
+        }
+      });
+    }
+  }
+}
+
+function showExportSuccess(outputFile) {
   dialog.showMessageBox(mainWindow, {
     type: 'info',
     title: 'Export Complete',
@@ -259,9 +288,6 @@ function exportFile(format) {
     buttons: ['OK']
   });
 }
-    });
-  }
-}
 
 function exportSpreadsheet(format) {
   if (!currentFile) {
@@ -310,40 +336,6 @@ function importDocument() {
   }
 }
 
-function convertToFormat(format) {
-  if (!currentFile) {
-    dialog.showErrorBox('Error', 'Please save or open a file first');
-    return;
-  }
-
-  const outputFile = dialog.showSaveDialogSync(mainWindow, {
-    defaultPath: currentFile.replace(/\.[^/.]+$/, `.${format}`),
-    filters: [
-      { name: format.toUpperCase(), extensions: [format] }
-    ]
-  });
-
-  if (outputFile) {
-    // For presentations, add slide level for better conversion
-    let pandocCmd = `pandoc "${currentFile}" -o "${outputFile}"`;
-    if (format === 'pptx' || format === 'odp') {
-      pandocCmd = `pandoc "${currentFile}" --slide-level=2 -o "${outputFile}"`;
-    }
-    
-    exec(pandocCmd, (error, stdout, stderr) => {
-      if (error) {
-        dialog.showErrorBox('Conversion Error', `Failed to convert: ${error.message}\n\nMake sure Pandoc is installed.`);
-      } else {
-        dialog.showMessageBox(mainWindow, {
-          type: 'info',
-          title: 'Conversion Complete',
-          message: `File converted successfully to ${outputFile}`,
-          buttons: ['OK']
-        });
-      }
-    });
-  }
-}
 
 function setTheme(theme) {
   store.set('theme', theme);
@@ -369,6 +361,11 @@ ipcMain.on('get-theme', (event) => {
   event.reply('theme-changed', theme);
 });
 
+// Handle tab file tracking for exports
+ipcMain.on('set-current-file', (event, filePath) => {
+  currentFile = filePath;
+});
+
 ipcMain.on('export-spreadsheet', (event, { content, format }) => {
   const outputFile = dialog.showSaveDialogSync(mainWindow, {
     defaultPath: currentFile.replace(/\.[^/.]+$/, `.${format}`),
@@ -452,7 +449,17 @@ function extractTablesFromMarkdown(markdown) {
   return tables;
 }
 
-app.whenReady().then(createWindow);
+app.whenReady().then(() => {
+  createWindow();
+  
+  // Handle file association on app startup
+  if (process.argv.length > 1) {
+    const filePath = process.argv.find(arg => arg.endsWith('.md') || arg.endsWith('.markdown'));
+    if (filePath && fs.existsSync(filePath)) {
+      openFileFromPath(filePath);
+    }
+  }
+});
 
 app.on('window-all-closed', () => {
   if (process.platform !== 'darwin') {
@@ -465,3 +472,25 @@ app.on('activate', () => {
     createWindow();
   }
 });
+
+// Handle file opening on macOS
+app.on('open-file', (event, filePath) => {
+  event.preventDefault();
+  if (mainWindow) {
+    openFileFromPath(filePath);
+  } else {
+    // Store the file path to open after window is created
+    app.pendingFile = filePath;
+  }
+});
+
+// Handle file opening from command line or file association
+function openFileFromPath(filePath) {
+  if (fs.existsSync(filePath)) {
+    currentFile = filePath;
+    const content = fs.readFileSync(filePath, 'utf-8');
+    if (mainWindow && mainWindow.webContents) {
+      mainWindow.webContents.send('file-opened', { path: filePath, content });
+    }
+  }
+}

src/styles.css

@@ -16,6 +16,93 @@ body {
     height: 100vh;
 }
 
+/* Tab Bar */
+.tab-bar {
+    display: flex;
+    align-items: center;
+    background: #f0f0f0;
+    border-bottom: 1px solid #ddd;
+    padding: 0 8px;
+    min-height: 36px;
+}
+
+.tab {
+    display: flex;
+    align-items: center;
+    padding: 6px 12px;
+    background: #e8e8e8;
+    border: 1px solid #ccc;
+    border-bottom: none;
+    border-radius: 6px 6px 0 0;
+    margin-right: 2px;
+    cursor: pointer;
+    user-select: none;
+    max-width: 200px;
+    min-width: 120px;
+}
+
+.tab.active {
+    background: #fff;
+    border-color: #999;
+    z-index: 1;
+}
+
+.tab-title {
+    flex: 1;
+    overflow: hidden;
+    text-overflow: ellipsis;
+    white-space: nowrap;
+    font-size: 13px;
+}
+
+.tab-close {
+    background: none;
+    border: none;
+    font-size: 16px;
+    font-weight: bold;
+    cursor: pointer;
+    padding: 0;
+    margin-left: 8px;
+    width: 16px;
+    height: 16px;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    border-radius: 3px;
+    color: #666;
+}
+
+.tab-close:hover {
+    background: #ddd;
+    color: #000;
+}
+
+.new-tab-button {
+    background: none;
+    border: 1px solid #ccc;
+    border-radius: 4px;
+    padding: 4px 8px;
+    cursor: pointer;
+    font-size: 14px;
+    margin-left: 8px;
+    color: #666;
+}
+
+.new-tab-button:hover {
+    background: #e8e8e8;
+}
+
+/* Tab Content */
+.tab-content {
+    display: flex;
+    flex: 1;
+    overflow: hidden;
+}
+
+.tab-content:not(.active) {
+    display: none;
+}
+
 /* Toolbar */
 .toolbar {
     display: flex;
@@ -217,6 +304,40 @@ body.theme-dark {
     color: #d4d4d4;
 }
 
+body.theme-dark .tab-bar {
+    background: #2d2d30;
+    border-bottom-color: #3e3e42;
+}
+
+body.theme-dark .tab {
+    background: #3c3c3c;
+    border-color: #555;
+    color: #d4d4d4;
+}
+
+body.theme-dark .tab.active {
+    background: #1e1e1e;
+    border-color: #666;
+}
+
+body.theme-dark .tab-close {
+    color: #ccc;
+}
+
+body.theme-dark .tab-close:hover {
+    background: #555;
+    color: #fff;
+}
+
+body.theme-dark .new-tab-button {
+    border-color: #555;
+    color: #ccc;
+}
+
+body.theme-dark .new-tab-button:hover {
+    background: #3c3c3c;
+}
+
 body.theme-dark .toolbar {
     background: #2d2d30;
     border-bottom-color: #3e3e42;