feat: Add Excel export functionality and unit tests

Features:
- Excel export with formatted multi-sheet workbooks (Contents, Comments, Creators)
- Professional styling: blue headers, auto-width columns, borders, text wrapping
- Smart export: empty sheets automatically removed
- Support for all platforms (xhs, dy, ks, bili, wb, tieba, zhihu)

Testing:
- Added pytest framework with asyncio support
- Unit tests for Excel store functionality
- Unit tests for store factory pattern
- Shared fixtures for test data
- Test coverage for edge cases

Documentation:
- Comprehensive Excel export guide (docs/excel_export_guide.md)
- Updated README.md and README_en.md with Excel examples
- Updated config comments to include excel option

Dependencies:
- Added openpyxl>=3.1.2 for Excel support
- Added pytest>=7.4.0 and pytest-asyncio>=0.21.0 for testing

This contribution adds immediate value for users who need data analysis
capabilities and establishes a testing foundation for future development.

store/excel_store_base.py

@@ -0,0 +1,263 @@
+# -*- coding: utf-8 -*-
+# Copyright (c) 2025 relakkes@gmail.com
+#
+# This file is part of MediaCrawler project.
+# Repository: https://github.com/NanmiCoder/MediaCrawler
+# GitHub: https://github.com/NanmiCoder
+# Licensed under NON-COMMERCIAL LEARNING LICENSE 1.1
+#
+# 声明:本代码仅供学习和研究目的使用。使用者应遵守以下原则:
+# 1. 不得用于任何商业用途。
+# 2. 使用时应遵守目标平台的使用条款和robots.txt规则。
+# 3. 不得进行大规模爬取或对平台造成运营干扰。
+# 4. 应合理控制请求频率,避免给目标平台带来不必要的负担。
+# 5. 不得用于任何非法或不当的用途。
+#
+# 详细许可条款请参阅项目根目录下的LICENSE文件。
+# 使用本代码即表示您同意遵守上述原则和LICENSE中的所有条款。
+
+"""
+Excel Store Base Implementation
+Provides Excel export functionality for crawled data with formatted sheets
+"""
+
+import os
+from datetime import datetime
+from typing import Dict, List, Any
+from pathlib import Path
+
+try:
+    import openpyxl
+    from openpyxl.styles import Font, PatternFill, Alignment, Border, Side
+    from openpyxl.utils import get_column_letter
+    EXCEL_AVAILABLE = True
+except ImportError:
+    EXCEL_AVAILABLE = False
+
+from base.base_crawler import AbstractStore
+from tools import utils
+
+
+class ExcelStoreBase(AbstractStore):
+    """
+    Base class for Excel storage implementation
+    Provides formatted Excel export with multiple sheets for contents, comments, and creators
+    """
+    
+    def __init__(self, platform: str, crawler_type: str = "search"):
+        """
+        Initialize Excel store
+        
+        Args:
+            platform: Platform name (xhs, dy, ks, etc.)
+            crawler_type: Type of crawler (search, detail, creator)
+        """
+        if not EXCEL_AVAILABLE:
+            raise ImportError(
+                "openpyxl is required for Excel export. "
+                "Install it with: pip install openpyxl"
+            )
+        
+        super().__init__()
+        self.platform = platform
+        self.crawler_type = crawler_type
+        
+        # Create data directory
+        self.data_dir = Path("data") / platform
+        self.data_dir.mkdir(parents=True, exist_ok=True)
+        
+        # Initialize workbook
+        self.workbook = openpyxl.Workbook()
+        self.workbook.remove(self.workbook.active)  # Remove default sheet
+        
+        # Create sheets
+        self.contents_sheet = self.workbook.create_sheet("Contents")
+        self.comments_sheet = self.workbook.create_sheet("Comments")
+        self.creators_sheet = self.workbook.create_sheet("Creators")
+        
+        # Track if headers are written
+        self.contents_headers_written = False
+        self.comments_headers_written = False
+        self.creators_headers_written = False
+        
+        # Generate filename
+        timestamp = datetime.now().strftime("%Y%m%d_%H%M%S")
+        self.filename = self.data_dir / f"{platform}_{crawler_type}_{timestamp}.xlsx"
+        
+        utils.logger.info(f"[ExcelStoreBase] Initialized Excel export to: {self.filename}")
+    
+    def _apply_header_style(self, sheet, row_num: int = 1):
+        """
+        Apply formatting to header row
+        
+        Args:
+            sheet: Worksheet object
+            row_num: Row number for headers (default: 1)
+        """
+        header_fill = PatternFill(start_color="366092", end_color="366092", fill_type="solid")
+        header_font = Font(bold=True, color="FFFFFF", size=11)
+        header_alignment = Alignment(horizontal="center", vertical="center", wrap_text=True)
+        border = Border(
+            left=Side(style='thin'),
+            right=Side(style='thin'),
+            top=Side(style='thin'),
+            bottom=Side(style='thin')
+        )
+        
+        for cell in sheet[row_num]:
+            cell.fill = header_fill
+            cell.font = header_font
+            cell.alignment = header_alignment
+            cell.border = border
+    
+    def _auto_adjust_column_width(self, sheet):
+        """
+        Auto-adjust column widths based on content
+        
+        Args:
+            sheet: Worksheet object
+        """
+        for column in sheet.columns:
+            max_length = 0
+            column_letter = get_column_letter(column[0].column)
+            
+            for cell in column:
+                try:
+                    if cell.value:
+                        max_length = max(max_length, len(str(cell.value)))
+                except:
+                    pass
+            
+            # Set width with min/max constraints
+            adjusted_width = min(max(max_length + 2, 10), 50)
+            sheet.column_dimensions[column_letter].width = adjusted_width
+    
+    def _write_headers(self, sheet, headers: List[str]):
+        """
+        Write headers to sheet
+        
+        Args:
+            sheet: Worksheet object
+            headers: List of header names
+        """
+        for col_num, header in enumerate(headers, 1):
+            sheet.cell(row=1, column=col_num, value=header)
+        
+        self._apply_header_style(sheet)
+    
+    def _write_row(self, sheet, data: Dict[str, Any], headers: List[str]):
+        """
+        Write data row to sheet
+        
+        Args:
+            sheet: Worksheet object
+            data: Data dictionary
+            headers: List of header names (defines column order)
+        """
+        row_num = sheet.max_row + 1
+        
+        for col_num, header in enumerate(headers, 1):
+            value = data.get(header, "")
+            
+            # Handle different data types
+            if isinstance(value, (list, dict)):
+                value = str(value)
+            elif value is None:
+                value = ""
+            
+            cell = sheet.cell(row=row_num, column=col_num, value=value)
+            
+            # Apply basic formatting
+            cell.alignment = Alignment(vertical="top", wrap_text=True)
+            cell.border = Border(
+                left=Side(style='thin'),
+                right=Side(style='thin'),
+                top=Side(style='thin'),
+                bottom=Side(style='thin')
+            )
+    
+    async def store_content(self, content_item: Dict):
+        """
+        Store content data to Excel
+        
+        Args:
+            content_item: Content data dictionary
+        """
+        # Define headers (customize based on platform)
+        headers = list(content_item.keys())
+        
+        # Write headers if first time
+        if not self.contents_headers_written:
+            self._write_headers(self.contents_sheet, headers)
+            self.contents_headers_written = True
+        
+        # Write data row
+        self._write_row(self.contents_sheet, content_item, headers)
+        
+        utils.logger.info(f"[ExcelStoreBase] Stored content to Excel: {content_item.get('note_id', 'N/A')}")
+    
+    async def store_comment(self, comment_item: Dict):
+        """
+        Store comment data to Excel
+        
+        Args:
+            comment_item: Comment data dictionary
+        """
+        # Define headers
+        headers = list(comment_item.keys())
+        
+        # Write headers if first time
+        if not self.comments_headers_written:
+            self._write_headers(self.comments_sheet, headers)
+            self.comments_headers_written = True
+        
+        # Write data row
+        self._write_row(self.comments_sheet, comment_item, headers)
+        
+        utils.logger.info(f"[ExcelStoreBase] Stored comment to Excel: {comment_item.get('comment_id', 'N/A')}")
+    
+    async def store_creator(self, creator_item: Dict):
+        """
+        Store creator data to Excel
+        
+        Args:
+            creator_item: Creator data dictionary
+        """
+        # Define headers
+        headers = list(creator_item.keys())
+        
+        # Write headers if first time
+        if not self.creators_headers_written:
+            self._write_headers(self.creators_sheet, headers)
+            self.creators_headers_written = True
+        
+        # Write data row
+        self._write_row(self.creators_sheet, creator_item, headers)
+        
+        utils.logger.info(f"[ExcelStoreBase] Stored creator to Excel: {creator_item.get('user_id', 'N/A')}")
+    
+    def flush(self):
+        """
+        Save workbook to file
+        """
+        try:
+            # Auto-adjust column widths
+            self._auto_adjust_column_width(self.contents_sheet)
+            self._auto_adjust_column_width(self.comments_sheet)
+            self._auto_adjust_column_width(self.creators_sheet)
+            
+            # Remove empty sheets
+            if self.contents_sheet.max_row == 1:
+                self.workbook.remove(self.contents_sheet)
+            if self.comments_sheet.max_row == 1:
+                self.workbook.remove(self.comments_sheet)
+            if self.creators_sheet.max_row == 1:
+                self.workbook.remove(self.creators_sheet)
+            
+            # Save workbook
+            self.workbook.save(self.filename)
+            utils.logger.info(f"[ExcelStoreBase] Excel file saved successfully: {self.filename}")
+            
+        except Exception as e:
+            utils.logger.error(f"[ExcelStoreBase] Error saving Excel file: {e}")
+            raise