Enhance HostsManager to prevent modification and movement of default system entries; add is_default_entry method to HostEntry and update sorting methods to prioritize default entries.

src/hosts/core/manager.py

@@ -181,6 +181,11 @@ class HostsManager:
         
         try:
             entry = hosts_file.entries[index]
+            
+            # Prevent modification of default system entries
+            if entry.is_default_entry():
+                return False, "Cannot modify default system entries"
+            
             old_state = "active" if entry.is_active else "inactive"
             entry.is_active = not entry.is_active
             new_state = "active" if entry.is_active else "inactive"
@@ -207,6 +212,13 @@ class HostsManager:
             return False, "Cannot move entry up"
         
         try:
+            entry = hosts_file.entries[index]
+            target_entry = hosts_file.entries[index - 1]
+            
+            # Prevent moving default system entries or moving entries above default entries
+            if entry.is_default_entry() or target_entry.is_default_entry():
+                return False, "Cannot move default system entries"
+            
             # Swap with previous entry
             hosts_file.entries[index], hosts_file.entries[index - 1] = \
                 hosts_file.entries[index - 1], hosts_file.entries[index]
@@ -232,6 +244,13 @@ class HostsManager:
             return False, "Cannot move entry down"
         
         try:
+            entry = hosts_file.entries[index]
+            target_entry = hosts_file.entries[index + 1]
+            
+            # Prevent moving default system entries or moving entries below default entries
+            if entry.is_default_entry() or target_entry.is_default_entry():
+                return False, "Cannot move default system entries"
+            
             # Swap with next entry
             hosts_file.entries[index], hosts_file.entries[index + 1] = \
                 hosts_file.entries[index + 1], hosts_file.entries[index]
@@ -262,6 +281,12 @@ class HostsManager:
             return False, "Invalid entry index"
         
         try:
+            entry = hosts_file.entries[index]
+            
+            # Prevent modification of default system entries
+            if entry.is_default_entry():
+                return False, "Cannot modify default system entries"
+            
             # Create new entry to validate
             new_entry = HostEntry(
                 ip_address=ip_address,

src/hosts/core/models.py

@@ -33,6 +33,28 @@ class HostEntry:
         """Validate the entry after initialization."""
         self.validate()
 
+    def is_default_entry(self) -> bool:
+        """
+        Check if this entry is a system default entry.
+        
+        Returns:
+            True if this is a default system entry (localhost, broadcasthost, ::1)
+        """
+        if not self.hostnames:
+            return False
+        
+        canonical_hostname = self.hostnames[0]
+        default_entries = [
+            {"ip": "127.0.0.1", "hostname": "localhost"},
+            {"ip": "255.255.255.255", "hostname": "broadcasthost"},
+            {"ip": "::1", "hostname": "localhost"},
+        ]
+        
+        for entry in default_entries:
+            if entry["ip"] == self.ip_address and entry["hostname"] == canonical_hostname:
+                return True
+        return False
+
     def validate(self) -> None:
         """
         Validate the host entry data.
@@ -176,13 +198,42 @@ class HostsFile:
         """Get all inactive entries."""
         return [entry for entry in self.entries if not entry.is_active]
 
-    def sort_by_ip(self) -> None:
-        """Sort entries by IP address."""
-        self.entries.sort(key=lambda entry: ipaddress.ip_address(entry.ip_address))
+    def sort_by_ip(self, ascending: bool = True) -> None:
+        """
+        Sort entries by IP address, keeping default entries on top.
+        
+        Args:
+            ascending: Sort in ascending order if True, descending if False
+        """
+        def sort_key(entry):
+            try:
+                ip_str = entry.ip_address.lstrip('# ')
+                ip_obj = ipaddress.ip_address(ip_str)
+                # Default entries always come first (priority 0), others get priority 1
+                priority = 0 if entry.is_default_entry() else 1
+                # Create a tuple for sorting: (priority, version, ip_int)
+                return (priority, ip_obj.version, int(ip_obj))
+            except ValueError:
+                # If IP parsing fails, use string comparison with high sort priority
+                priority = 0 if entry.is_default_entry() else 1
+                return (priority, 999, entry.ip_address)
+        
+        self.entries.sort(key=sort_key, reverse=not ascending)
 
-    def sort_by_hostname(self) -> None:
-        """Sort entries by first hostname."""
-        self.entries.sort(key=lambda entry: entry.hostnames[0].lower())
+    def sort_by_hostname(self, ascending: bool = True) -> None:
+        """
+        Sort entries by first hostname, keeping default entries on top.
+        
+        Args:
+            ascending: Sort in ascending order if True, descending if False
+        """
+        def sort_key(entry):
+            # Default entries always come first (priority 0), others get priority 1
+            priority = 0 if entry.is_default_entry() else 1
+            hostname = (entry.hostnames[0] if entry.hostnames else "").lower()
+            return (priority, hostname)
+        
+        self.entries.sort(key=sort_key, reverse=not ascending)
 
     def find_entries_by_hostname(self, hostname: str) -> List[int]:
         """

src/hosts/main.py

@@ -240,8 +240,17 @@ class HostsManagerApp(App):
             # Get the canonical hostname (first hostname)
             canonical_hostname = entry.hostnames[0] if entry.hostnames else ""
             
-            # Add row with styling based on active status
-            if entry.is_active:
+            # Check if this is a default system entry
+            is_default = entry.is_default_entry()
+            
+            # Add row with styling based on active status and default entry status
+            if is_default:
+                # Default entries are always shown in dim grey regardless of active status
+                active_text = Text("✓" if entry.is_active else "", style="dim white")
+                ip_text = Text(entry.ip_address, style="dim white")
+                hostname_text = Text(canonical_hostname, style="dim white")
+                table.add_row(active_text, ip_text, hostname_text)
+            elif entry.is_active:
                 # Active entries in green with checkmark
                 active_text = Text("✓", style="bold green")
                 ip_text = Text(entry.ip_address, style="bold green")
@@ -304,6 +313,12 @@ class HostsManagerApp(App):
             f"Status: {'Active' if entry.is_active else 'Inactive'}",
         ]
         
+        # Add notice for default system entries
+        if entry.is_default_entry():
+            details_lines.append("")
+            details_lines.append("⚠️  SYSTEM DEFAULT ENTRY")
+            details_lines.append("This is a default system entry and cannot be modified.")
+        
         if entry.comment:
             details_lines.append(f"Comment: {entry.comment}")
         
@@ -379,20 +394,8 @@ class HostsManagerApp(App):
             self.sort_column = "ip"
             self.sort_ascending = True
         
-        # Sort the entries
-        import ipaddress
-        def ip_sort_key(entry):
-            try:
-                ip_str = entry.ip_address.lstrip('# ')
-                ip_obj = ipaddress.ip_address(ip_str)
-                # Create a tuple for sorting: (version, ip_int)
-                # This ensures IPv4 comes before IPv6, and within each version they're sorted numerically
-                return (ip_obj.version, int(ip_obj))
-            except ValueError:
-                # If IP parsing fails, use string comparison with high sort priority
-                return (999, entry.ip_address)
-        
-        self.hosts_file.entries.sort(key=ip_sort_key, reverse=not self.sort_ascending)
+        # Sort the entries using the new method that keeps defaults on top
+        self.hosts_file.sort_by_ip(self.sort_ascending)
         self.populate_entries_table()
         
         direction = "ascending" if self.sort_ascending else "descending"
@@ -407,11 +410,8 @@ class HostsManagerApp(App):
             self.sort_column = "hostname"
             self.sort_ascending = True
         
-        # Sort the entries
-        self.hosts_file.entries.sort(
-            key=lambda entry: (entry.hostnames[0] if entry.hostnames else "").lower(),
-            reverse=not self.sort_ascending
-        )
+        # Sort the entries using the new method that keeps defaults on top
+        self.hosts_file.sort_by_hostname(self.sort_ascending)
         self.populate_entries_table()
         
         direction = "ascending" if self.sort_ascending else "descending"

tests/test_main.py

@@ -326,9 +326,9 @@ class TestHostsManagerApp:
             
             app.action_sort_by_ip()
             
-            # Check that entries are sorted
-            assert app.hosts_file.entries[0].ip_address == "10.0.0.1"
-            assert app.hosts_file.entries[1].ip_address == "127.0.0.1"
+            # Check that entries are sorted with default entries on top
+            assert app.hosts_file.entries[0].ip_address == "127.0.0.1"  # Default entry first
+            assert app.hosts_file.entries[1].ip_address == "10.0.0.1"   # Then sorted non-defaults
             assert app.hosts_file.entries[2].ip_address == "192.168.1.1"
             
             assert app.sort_column == "ip"

tests/test_manager.py

@@ -321,7 +321,7 @@ class TestHostsManager:
             manager.edit_mode = True
             
             hosts_file = HostsFile()
-            entry = HostEntry("127.0.0.1", ["localhost"], is_active=True)
+            entry = HostEntry("192.168.1.1", ["router"], is_active=True)  # Non-default entry
             hosts_file.entries.append(entry)
             
             success, message = manager.toggle_entry(hosts_file, 0)
@@ -363,7 +363,7 @@ class TestHostsManager:
             manager.edit_mode = True
             
             hosts_file = HostsFile()
-            entry1 = HostEntry("127.0.0.1", ["localhost"])
+            entry1 = HostEntry("10.0.0.1", ["test1"])  # Non-default entries
             entry2 = HostEntry("192.168.1.1", ["router"])
             hosts_file.entries.extend([entry1, entry2])
             
@@ -372,7 +372,7 @@ class TestHostsManager:
             assert success
             assert "moved up" in message
             assert hosts_file.entries[0].hostnames[0] == "router"
-            assert hosts_file.entries[1].hostnames[0] == "localhost"
+            assert hosts_file.entries[1].hostnames[0] == "test1"
     
     def test_move_entry_up_invalid_index(self):
         """Test moving entry up with invalid index."""
@@ -396,7 +396,7 @@ class TestHostsManager:
             manager.edit_mode = True
             
             hosts_file = HostsFile()
-            entry1 = HostEntry("127.0.0.1", ["localhost"])
+            entry1 = HostEntry("10.0.0.1", ["test1"])  # Non-default entries
             entry2 = HostEntry("192.168.1.1", ["router"])
             hosts_file.entries.extend([entry1, entry2])
             
@@ -405,7 +405,7 @@ class TestHostsManager:
             assert success
             assert "moved down" in message
             assert hosts_file.entries[0].hostnames[0] == "router"
-            assert hosts_file.entries[1].hostnames[0] == "localhost"
+            assert hosts_file.entries[1].hostnames[0] == "test1"
     
     def test_move_entry_down_invalid_index(self):
         """Test moving entry down with invalid index."""
@@ -429,7 +429,7 @@ class TestHostsManager:
             manager.edit_mode = True
             
             hosts_file = HostsFile()
-            entry = HostEntry("127.0.0.1", ["localhost"])
+            entry = HostEntry("10.0.0.1", ["test"])  # Non-default entry
             hosts_file.entries.append(entry)
             
             success, message = manager.update_entry(
@@ -449,7 +449,7 @@ class TestHostsManager:
             manager.edit_mode = True
             
             hosts_file = HostsFile()
-            entry = HostEntry("127.0.0.1", ["localhost"])
+            entry = HostEntry("127.0.0.1", ["localhost"])  # Default entry - cannot be modified
             hosts_file.entries.append(entry)
             
             success, message = manager.update_entry(
@@ -457,7 +457,7 @@ class TestHostsManager:
             )
             
             assert not success
-            assert "Invalid entry data" in message
+            assert "Cannot modify default system entries" in message
     
     @patch('tempfile.NamedTemporaryFile')
     @patch('subprocess.run')

tests/test_models.py

@@ -224,20 +224,21 @@ class TestHostsFile:
         assert inactive_entries[0] == inactive_entry
     
     def test_sort_by_ip(self):
-        """Test sorting entries by IP address."""
+        """Test sorting entries by IP address with default entries on top."""
         hosts_file = HostsFile()
         entry1 = HostEntry(ip_address="192.168.1.1", hostnames=["router"])
-        entry2 = HostEntry(ip_address="127.0.0.1", hostnames=["localhost"])
+        entry2 = HostEntry(ip_address="127.0.0.1", hostnames=["localhost"])  # Default entry
         entry3 = HostEntry(ip_address="10.0.0.1", hostnames=["test"])
-        
+
         hosts_file.add_entry(entry1)
         hosts_file.add_entry(entry2)
         hosts_file.add_entry(entry3)
-        
+
         hosts_file.sort_by_ip()
-        
-        assert hosts_file.entries[0].ip_address == "10.0.0.1"
-        assert hosts_file.entries[1].ip_address == "127.0.0.1"
+
+        # Default entries should come first, then sorted non-default entries
+        assert hosts_file.entries[0].ip_address == "127.0.0.1"  # Default entry first
+        assert hosts_file.entries[1].ip_address == "10.0.0.1"   # Then sorted non-defaults
         assert hosts_file.entries[2].ip_address == "192.168.1.1"
     
     def test_sort_by_hostname(self):