Implement verification checkmark

backend/similarity.py

@@ -0,0 +1,147 @@
+"""
+Similarity detection utilities for username and display name comparison.
+Implements both edit distance and visual similarity detection.
+"""
+
+def levenshtein_distance(s1: str, s2: str) -> int:
+    """Calculate Levenshtein distance between two strings."""
+    if len(s1) < len(s2):
+        return levenshtein_distance(s2, s1)
+
+    if len(s2) == 0:
+        return len(s1)
+
+    previous_row = list(range(len(s2) + 1))
+    for i, c1 in enumerate(s1):
+        current_row = [i + 1]
+        for j, c2 in enumerate(s2):
+            insertions = previous_row[j + 1] + 1
+            deletions = current_row[j] + 1
+            substitutions = previous_row[j] + (c1 != c2)
+            current_row.append(min(insertions, deletions, substitutions))
+        previous_row = current_row
+    
+    return previous_row[-1]
+
+
+def check_visual_similarity(s1: str, s2: str) -> bool:
+    """
+    Check if two strings are visually similar using common homoglyphs.
+    Returns True if strings are visually similar.
+    """
+    if len(s1) != len(s2):
+        return False
+    
+    # Common homoglyph mappings
+    homoglyphs = {
+        '0': ['O', 'o', 'Q'],
+        'O': ['0', 'o', 'Q'],
+        'o': ['0', 'O', 'Q'],
+        '1': ['l', 'I', '|'],
+        'l': ['1', 'I', '|'],
+        'I': ['1', 'l', '|'],
+        '5': ['S', 's'],
+        'S': ['5', 's'],
+        's': ['5', 'S'],
+        '6': ['G', 'g'],
+        'G': ['6', 'g'],
+        'g': ['6', 'G'],
+        '8': ['B', 'b'],
+        'B': ['8', 'b'],
+        'b': ['8', 'B'],
+        '9': ['g', 'q'],
+        'g': ['9', 'q'],
+        'q': ['9', 'g'],
+        '2': ['Z', 'z'],
+        'Z': ['2', 'z'],
+        'z': ['2', 'Z'],
+        '3': ['E'],
+        'E': ['3'],
+        '4': ['A'],
+        'A': ['4'],
+        '7': ['T', 't'],
+        'T': ['7', 't'],
+        't': ['7', 'T'],
+    }
+    
+    for i in range(len(s1)):
+        c1, c2 = s1[i], s2[i]
+        if c1 == c2:
+            continue
+        
+        # Check if characters are homoglyphs
+        if (c1 in homoglyphs and c2 in homoglyphs[c1]) or \
+           (c2 in homoglyphs and c1 in homoglyphs[c2]):
+            continue
+        
+        return False
+    
+    return True
+
+
+def check_username_similarity(username1: str, username2: str) -> bool:
+    """
+    Check if two usernames are similar using both edit distance and visual similarity.
+    Returns True if usernames are considered similar.
+    """
+    if username1 == username2:
+        return False
+    
+    # Check edit distance (Levenshtein distance <= 2)
+    edit_distance = levenshtein_distance(username1.lower(), username2.lower())
+    if edit_distance <= 2:
+        return True
+    
+    # Check visual similarity
+    if check_visual_similarity(username1, username2):
+        return True
+    
+    return False
+
+
+def check_display_name_similarity(display_name1: str, display_name2: str) -> bool:
+    """
+    Check if two display names are similar using both edit distance and visual similarity.
+    Returns True if display names are considered similar.
+    """
+    if display_name1 == display_name2:
+        return False
+    
+    # Check edit distance (Levenshtein distance <= 2)
+    edit_distance = levenshtein_distance(display_name1.lower(), display_name2.lower())
+    if edit_distance <= 2:
+        return True
+    
+    # Check visual similarity
+    if check_visual_similarity(display_name1, display_name2):
+        return True
+    
+    return False
+
+
+def is_user_similar_to_verified(user_username: str, user_display_name: str, 
+                               verified_users: list[dict]) -> tuple[bool, str]:
+    """
+    Check if a user is similar to any verified user.
+    
+    Args:
+        user_username: Username to check
+        user_display_name: Display name to check
+        verified_users: List of verified user dictionaries with 'username' and 'display_name' keys
+    
+    Returns:
+        Tuple of (is_similar, similar_to_username)
+    """
+    for verified_user in verified_users:
+        verified_username = verified_user.get('username', '')
+        verified_display_name = verified_user.get('display_name', '')
+        
+        # Check username similarity
+        if check_username_similarity(user_username, verified_username):
+            return True, verified_username
+        
+        # Check display name similarity
+        if check_display_name_similarity(user_display_name, verified_display_name):
+            return True, verified_username
+    
+    return False, ""