Feat #5: choose additive or replacement import

README.md

@@ -22,7 +22,8 @@ on macOS and Linux.
 - Creates a timestamped Pre-edit Backup before Privileged Mode begins.
 - Restores the current session's Pre-edit Backup after explicit confirmation.
 - Supports undo and redo during the current Privileged Mode session.
-- Exports Host Entries as hosts, JSON, or CSV files, and imports those formats in Privileged Mode.
+- Exports Host Entries as hosts, JSON, or CSV files. In Privileged Mode,
+  imports can add Host Entries or replace the Hosts File after confirmation.
 
 The application starts in Read-only Mode. Default Entries cannot be edited,
 deleted, activated, deactivated, or moved.

src/hosts/tui/app.py

@@ -36,7 +36,14 @@ from .backup_restore_modal import BackupRestoreModal
 from .delete_confirmation_modal import DeleteConfirmationModal
 from .filter_modal import FilterModal
 from .help_modal import HelpModal
-from .import_export_modal import ExportModal, ImportModal, ExportRequest, ImportRequest
+from .import_export_modal import (
+    ExportModal,
+    ImportModal,
+    ExportRequest,
+    ImportMode,
+    ImportRequest,
+    ReplaceImportConfirmationModal,
+)
 from .custom_footer import CustomFooter
 from .styles import HOSTS_DARK_THEME, HOSTS_MANAGER_CSS
 from .keybindings import HOSTS_MANAGER_BINDINGS
@@ -955,18 +962,52 @@ class HostsManagerApp(App):
         def import_file(format: ImportFormat, path):
             return importers[format](path)
 
+        def apply_import(request: ImportRequest) -> None:
+            result = request.result
+            snapshot = self.capture_mutation_state()
+            if request.mode is ImportMode.ADD:
+                self.hosts_file = HostsFile(
+                    entries=[*self.hosts_file.entries, *result.entries],
+                    header_comments=list(self.hosts_file.header_comments),
+                    footer_comments=list(self.hosts_file.footer_comments),
+                )
+                action = "Add imported Host Entries"
+                outcome = "Added and saved"
+            else:
+                self.hosts_file = HostsFile(entries=list(result.entries))
+                action = "Replace Hosts File from import"
+                outcome = "Replaced Hosts File with"
+            self.selected_entry_index = 0
+            if self.save_mutation(snapshot, action):
+                self.table_handler.populate_entries_table()
+                self.details_handler.update_entry_details()
+                noun = (
+                    "Host Entry"
+                    if result.successfully_imported == 1
+                    else "Host Entries"
+                )
+                self.update_status(
+                    f"✓ {outcome} {result.successfully_imported} "
+                    f"{'imported ' if request.mode is ImportMode.REPLACE else ''}"
+                    f"{noun} from {request.path}"
+                )
+
         def handle_import(request: ImportRequest | None) -> None:
             if request is None:
                 return
-            result = request.result
+            if request.mode is ImportMode.ADD:
-            snapshot = self.capture_mutation_state()
+                apply_import(request)
-            self.hosts_file = HostsFile(entries=result.entries)
+                return
-            self.selected_entry_index = 0
+
-            if self.save_mutation(snapshot, "Import"):
+            def handle_replace_confirmation(confirmed: bool | None) -> None:
-                self.table_handler.populate_entries_table()
+                if confirmed:
-                self.details_handler.update_entry_details()
+                    apply_import(request)
-                self.update_status(
+
-                    f"✓ Imported and saved {result.successfully_imported} Host Entries from {request.path}"
+            self.push_screen(
+                ReplaceImportConfirmationModal(
+                    len(self.hosts_file.entries), len(request.result.entries)
+                ),
+                handle_replace_confirmation,
             )
 
         self.push_screen(

src/hosts/tui/import_export_modal.py

@@ -1,6 +1,7 @@
 """Keyboard-first import and export forms for Host Entries."""
 
 from dataclasses import dataclass
+from enum import Enum
 from pathlib import Path
 
 from rich.text import Text
@@ -21,12 +22,20 @@ class ExportRequest:
     format: ExportFormat
 
 
+class ImportMode(Enum):
+    """How imported Host Entries are applied to the current Hosts File."""
+
+    ADD = "add"
+    REPLACE = "replace"
+
+
 @dataclass(frozen=True)
 class ImportRequest:
-    """A validated request to replace the Hosts File from an import."""
+    """A validated request to apply imported Host Entries."""
 
     path: Path
     format: ImportFormat
+    mode: ImportMode
     result: ImportResult
 
 
@@ -55,6 +64,10 @@ class _FormatModal(ModalScreen):
         height: 5; margin-top: 1; padding: 0 1; border: round $primary;
     }
     #format-select { height: 3; margin: 0; padding: 0; border: none; }
+    .import-mode-section {
+        height: 4; margin-top: 1; padding: 0 1; border: round $primary;
+    }
+    #import-mode-select { height: 2; margin: 0; padding: 0; border: none; }
     .button-row { margin-top: 1; height: 3; align: center middle; }
     """
 
@@ -181,7 +194,7 @@ class ExportModal(_FormatModal):
 
 
 class ImportModal(_FormatModal):
-    """Collect an import file and format before replacing Host Entries."""
+    """Collect an import file, format, and application mode."""
 
     def __init__(self, formats: list[ImportFormat], import_file):
         super().__init__()
@@ -192,7 +205,7 @@ class ImportModal(_FormatModal):
         with Vertical(id="format-container"):
             yield Static("Import Host Entries", classes="format-title")
             yield Static(
-                "Import replaces the current Host Entries and saves the Hosts File.",
+                "Choose a file, format, and how to apply its Host Entries.",
                 classes="format-copy",
             )
             with Vertical(classes="path-section") as location:
@@ -220,6 +233,15 @@ class ImportModal(_FormatModal):
                             value=index == 0,
                             compact=True,
                         )
+            with Vertical(classes="import-mode-section") as modes:
+                modes.border_title = "Import action"
+                with RadioSet(id="import-mode-select", compact=True):
+                    yield RadioButton(
+                        "Add to Hosts File", id="mode-add", value=True, compact=True
+                    )
+                    yield RadioButton(
+                        "Replace Hosts File", id="mode-replace", compact=True
+                    )
             with Horizontal(classes="button-row"):
                 yield Button("Cancel", id="cancel-button")
                 yield Button("Import and save", id="import-button", variant="primary")
@@ -238,7 +260,12 @@ class ImportModal(_FormatModal):
                 if not result.success:
                     self._show_message("#workflow-error", "; ".join(result.errors))
                     return
-                self.dismiss(ImportRequest(path, format, result))
+                mode = (
+                    ImportMode.REPLACE
+                    if self.query_one("#mode-replace", RadioButton).value
+                    else ImportMode.ADD
+                )
+                self.dismiss(ImportRequest(path, format, mode, result))
         elif event.button.id == "browse-button":
             self.action_browse()
 
@@ -256,6 +283,59 @@ class ImportModal(_FormatModal):
         self.app.push_screen(FileBrowserModal(start, choose_directory=False), selected)
 
 
+class ReplaceImportConfirmationModal(ModalScreen[bool]):
+    """Warn before replacing every current Host Entry with imported entries."""
+
+    BINDINGS = [Binding("escape", "cancel", "Cancel")]
+    CSS = """
+    ReplaceImportConfirmationModal { align: center middle; }
+    #replace-import-confirmation-container {
+        width: 68; height: auto; max-width: 90%; background: $surface;
+        border: thick $error; padding: 1 2;
+    }
+    .replace-title {
+        text-align: center; text-style: bold; color: $error;
+    }
+    #replace-warning { height: auto; margin-top: 1; color: $warning; }
+    .replace-consequence { height: auto; margin-top: 1; }
+    .button-row { margin-top: 1; height: 3; align: center middle; }
+    """
+
+    def __init__(self, current_count: int, imported_count: int):
+        super().__init__()
+        self._current_count = current_count
+        self._imported_count = imported_count
+
+    def compose(self) -> ComposeResult:
+        with Vertical(id="replace-import-confirmation-container"):
+            yield Static("Replace Hosts File?", classes="replace-title")
+            yield Static(
+                f"This will remove all {_entry_count(self._current_count, 'current')} "
+                f"and replace the Hosts File with "
+                f"{_entry_count(self._imported_count, 'imported')}.",
+                id="replace-warning",
+            )
+            yield Static(
+                "The current Hosts File will not be changed unless you confirm.",
+                classes="replace-consequence",
+            )
+            with Horizontal(classes="button-row"):
+                yield Button("Cancel", id="cancel-button")
+                yield Button("Replace Hosts File", id="replace-button", variant="error")
+
+    def on_mount(self) -> None:
+        self.query_one("#cancel-button", Button).focus()
+
+    def on_button_pressed(self, event: Button.Pressed) -> None:
+        if event.button.id == "replace-button":
+            self.dismiss(True)
+        elif event.button.id == "cancel-button":
+            self.action_cancel()
+
+    def action_cancel(self) -> None:
+        self.dismiss(False)
+
+
 class ParentDirectoryTree(DirectoryTree):
     """Directory tree with a conventional parent entry above its root."""
 
@@ -378,6 +458,12 @@ def _format_label(format: ExportFormat | ImportFormat) -> str:
     }[format.value]
 
 
+def _entry_count(count: int, qualifier: str) -> str:
+    """Describe a qualified number of Host Entries with correct grammar."""
+    noun = "Host Entry" if count == 1 else "Host Entries"
+    return f"{count} {qualifier} {noun}"
+
+
 def _format_suffix(format: ExportFormat) -> str:
     """Provide an editable default filename after choosing an export folder."""
     return {

tests/test_import_export_workflow.py

@@ -15,7 +15,12 @@ from hosts.core.import_export import (
 )
 from hosts.core.models import HostEntry, HostsFile
 from hosts.tui.app import HostsManagerApp
-from hosts.tui.import_export_modal import ExportModal, FileBrowserModal, ImportModal
+from hosts.tui.import_export_modal import (
+    ExportModal,
+    FileBrowserModal,
+    ImportModal,
+    ReplaceImportConfirmationModal,
+)
 
 
 @pytest.mark.asyncio
@@ -236,14 +241,45 @@ async def test_import_shortcut_requires_privileged_mode_and_surfaces_service_err
 
 
 @pytest.mark.asyncio
-async def test_successful_import_replaces_entries_and_saves_through_the_manager():
+async def test_import_form_asks_how_to_apply_entries_at_minimum_supported_size():
-    """A valid import reaches the persistence seam without a real Hosts File."""
+    """Both import actions remain visible and reachable at 100 by 30."""
+    app = HostsManagerApp()
+    app.edit_mode = True
+    app.manager.edit_mode = True
+    app.import_export_service = Mock()
+    app.import_export_service.get_supported_import_formats.return_value = list(
+        ImportFormat
+    )
+
+    async with app.run_test(size=(100, 30)) as pilot:
+        app.action_import_entries()
+        await pilot.pause()
+
+        assert isinstance(app.screen, ImportModal)
+        actions = app.screen.query_one("#import-mode-select", RadioSet)
+        assert [button.label.plain for button in actions.query(RadioButton)] == [
+            "Add to Hosts File",
+            "Replace Hosts File",
+        ]
+        assert app.screen.query_one("#mode-add", RadioButton).value
+        assert not app.screen.query_one("#mode-replace", RadioButton).value
+        container = app.screen.query_one("#format-container")
+        submit = app.screen.query_one("#import-button", Button)
+        assert submit.region.bottom <= container.region.bottom
+
+
+@pytest.mark.asyncio
+async def test_successful_import_adds_entries_and_saves_through_the_manager():
+    """The safe default appends imported Host Entries to the Hosts File."""
     app = HostsManagerApp()
     app.hosts_file = HostsFile(
-        entries=[HostEntry(ip_address="192.0.2.10", hostnames=["original.test"])]
+        entries=[HostEntry(ip_address="192.0.2.10", hostnames=["original.test"])],
+        header_comments=["existing header"],
+        footer_comments=["existing footer"],
     )
     app.edit_mode = True
     app.manager.edit_mode = True
+    app.load_hosts_file = Mock()
     app.save_mutation = Mock(return_value=True)
     app.import_export_service = Mock()
     app.import_export_service.get_supported_import_formats.return_value = list(
@@ -269,9 +305,74 @@ async def test_successful_import_replaces_entries_and_saves_through_the_manager(
         await pilot.pause()
 
         assert [entry.hostnames for entry in app.hosts_file.entries] == [
-            ["imported.test"]
+            ["original.test"],
+            ["imported.test"],
         ]
+        assert app.hosts_file.header_comments == ["existing header"]
+        assert app.hosts_file.footer_comments == ["existing footer"]
         app.save_mutation.assert_called_once()
-        assert "Imported and saved 1 Host Entries" in str(
+        assert "Added and saved 1 Host Entry" in str(
+            app.query_one("#message-rail", Static).render()
+        )
+
+
+@pytest.mark.asyncio
+async def test_replace_import_requires_explicit_destructive_confirmation():
+    """Replacement cannot mutate until the warning modal is confirmed."""
+    app = HostsManagerApp()
+    original = HostEntry(ip_address="192.0.2.10", hostnames=["original.test"])
+    imported = HostEntry(ip_address="198.51.100.3", hostnames=["imported.test"])
+    app.hosts_file = HostsFile(entries=[original])
+    app.edit_mode = True
+    app.manager.edit_mode = True
+    app.load_hosts_file = Mock()
+    app.save_mutation = Mock(return_value=True)
+    app.import_export_service = Mock()
+    app.import_export_service.get_supported_import_formats.return_value = list(
+        ImportFormat
+    )
+    app.import_export_service.import_json_format.return_value = ImportResult(
+        success=True,
+        entries=[imported],
+        errors=[],
+        warnings=[],
+        total_processed=1,
+        successfully_imported=1,
+    )
+
+    async with app.run_test(size=(120, 40)) as pilot:
+
+        async def request_replacement() -> None:
+            app.action_import_entries()
+            await pilot.pause()
+            app.screen.query_one("#path-input", Input).value = "/tmp/entries.json"
+            app.screen.query_one("#format-json", RadioButton).value = True
+            app.screen.query_one("#mode-replace", RadioButton).value = True
+            await pilot.click("#import-button")
+            await pilot.pause()
+
+        await request_replacement()
+
+        assert isinstance(app.screen, ReplaceImportConfirmationModal)
+        assert app.focused is app.screen.query_one("#cancel-button", Button)
+        assert "remove all 1 current Host Entry" in str(
+            app.screen.query_one("#replace-warning", Static).render()
+        )
+        assert app.hosts_file.entries == [original]
+        app.save_mutation.assert_not_called()
+
+        await pilot.click("#cancel-button")
+        await pilot.pause()
+        assert app.hosts_file.entries == [original]
+        app.save_mutation.assert_not_called()
+
+        await request_replacement()
+        await pilot.click("#replace-button")
+        await pilot.pause()
+        await pilot.pause()
+
+        assert app.hosts_file.entries == [imported]
+        app.save_mutation.assert_called_once()
+        assert "Replaced Hosts File with 1 imported Host Entry" in str(
             app.query_one("#message-rail", Static).render()
         )