Refactor: Remove obsolete Alembic migration script and add input validation utilities

- Deleted the migration script `7fc823789534_remove_extra_line.py` as it was no longer needed.
- Introduced a new file `validation.py` containing input validation utilities to ensure data integrity and security across various fields, including username, email, contest name, project name, and more.

Author: Aditya0545

backend/alembic/versions/7fc823789534_remove_extra_line.py

@@ -0,0 +1,178 @@
+"""Input validation utilities for security and data integrity."""
+
+MAX_USERNAME_LENGTH = 50
+MAX_EMAIL_LENGTH = 255
+MAX_CONTEST_NAME_LENGTH = 200
+MAX_PROJECT_NAME_LENGTH = 100
+MAX_DESCRIPTION_LENGTH = 5000
+MAX_URL_LENGTH = 2048
+MAX_COMMENT_LENGTH = 2000
+MAX_CATEGORY_COUNT = 50
+
+
+def validate_string_length(value, field_name, max_length, min_length=0):
+    """
+    Validate that a string is within allowed length limits.
+    
+    Args:
+        value: String value to validate
+        field_name: Name of the field (for error messages)
+        max_length: Maximum allowed length
+        min_length: Minimum allowed length (default: 0)
+    
+    Returns:
+        tuple: (is_valid: bool, error_message: str or None)
+    """
+    if not isinstance(value, str):
+        return False, f'{field_name} must be a string'
+
+    if len(value) < min_length:
+        return False, f'{field_name} must be at least {min_length} characters'
+
+    if len(value) > max_length:
+        return False, f'{field_name} must be at most {max_length} characters'
+
+    return True, None
+
+
+def validate_username_length(username):
+    """
+    Validate username length.
+    
+    Args:
+        username: Username string to validate
+    
+    Returns:
+        tuple: (is_valid: bool, error_message: str or None)
+    """
+    return validate_string_length(
+        username, 'Username', MAX_USERNAME_LENGTH, min_length=3
+    )
+
+
+def validate_email_length(email):
+    """
+    Validate email length.
+    
+    Args:
+        email: Email string to validate
+    
+    Returns:
+        tuple: (is_valid: bool, error_message: str or None)
+    """
+    return validate_string_length(
+        email, 'Email', MAX_EMAIL_LENGTH, min_length=5
+    )
+
+
+# REMOVED: validate_password_length - password-based authentication removed
+# Authentication is now exclusively via MediaWiki OAuth
+
+
+def validate_contest_name_length(name):
+    """
+    Validate contest name length.
+    
+    Args:
+        name: Contest name string to validate
+    
+    Returns:
+        tuple: (is_valid: bool, error_message: str or None)
+    """
+    return validate_string_length(
+        name, 'Contest name', MAX_CONTEST_NAME_LENGTH, min_length=1
+    )
+
+
+def validate_project_name_length(project_name):
+    """
+    Validate project name length.
+    
+    Args:
+        project_name: Project name string to validate
+    
+    Returns:
+        tuple: (is_valid: bool, error_message: str or None)
+    """
+    return validate_string_length(
+        project_name, 'Project name', MAX_PROJECT_NAME_LENGTH, min_length=1
+    )
+
+
+def validate_description_length(description):
+    """
+    Validate description length.
+    
+    Args:
+        description: Description string to validate
+    
+    Returns:
+        tuple: (is_valid: bool, error_message: str or None)
+    """
+    if description is None:
+        return True, None
+
+    return validate_string_length(
+        description, 'Description', MAX_DESCRIPTION_LENGTH, min_length=0
+    )
+
+
+def validate_url_length(url):
+    """
+    Validate URL length.
+    
+    Args:
+        url: URL string to validate
+    
+    Returns:
+        tuple: (is_valid: bool, error_message: str or None)
+    """
+    return validate_string_length(
+        url, 'URL', MAX_URL_LENGTH, min_length=1
+    )
+
+
+def validate_comment_length(comment):
+    """
+    Validate comment/review comment length.
+    
+    Args:
+        comment: Comment string to validate
+    
+    Returns:
+        tuple: (is_valid: bool, error_message: str or None)
+    """
+    if comment is None:
+        return True, None
+
+    return validate_string_length(
+        comment, 'Comment', MAX_COMMENT_LENGTH, min_length=0
+    )
+
+
+def validate_category_list(categories):
+    """
+    Validate category list length and individual URLs.
+    
+    Args:
+        categories: List of category URLs
+    
+    Returns:
+        tuple: (is_valid: bool, error_message: str or None)
+    """
+    if not isinstance(categories, list):
+        return False, 'Categories must be a list'
+
+    if len(categories) > MAX_CATEGORY_COUNT:
+        return False, f'Maximum {MAX_CATEGORY_COUNT} categories allowed'
+
+    # Validate each category URL length
+    for i, category in enumerate(categories):
+        if not isinstance(category, str):
+            return False, f'Category {i+1} must be a string'
+
+        is_valid, error = validate_url_length(category)
+        if not is_valid:
+            return False, f'Category {i+1}: {error}'
+
+    return True, None