Use xxHash comparison to check for unsaved changes

Author: python-processing-unit

NOTICE.md

@@ -4046,6 +4046,35 @@ OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 ```
 
+## xxhash 3.8.1
+
+**License:** UNKNOWN
+
+```
+Copyright (c) 2014-2024, Yue Du
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without modification,
+are permitted provided that the following conditions are met:
+
+    * Redistributions of source code must retain the above copyright notice,
+      this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above copyright notice,
+      this list of conditions and the following disclaimer in the documentation
+      and/or other materials provided with the distribution.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+```
+
 ## zstandard 0.25.0
 
 **License:** UNKNOWN

pyproject.toml

@@ -29,6 +29,8 @@ dependencies = [
     "zxcvbn>=4.5.0",
     # Zstandard compression inside MORGUL payloads (BSD).
     "zstandard>=0.22.0",
+    # Fast non-cryptographic hash for dirty-tracking (MIT).
+    "xxhash>=3.0.0",
 ]
 
 [project.scripts]

src/morgul/app.py

@@ -7,6 +7,7 @@
 from pathlib import Path
 from typing import TYPE_CHECKING
 
+import xxhash
 from PySide6.QtCore import (
     QEvent,
     QObject,
@@ -983,6 +984,7 @@ def __init__(self, parent: QWidget | None = None) -> None:
         self.path: Path | None = None
         self.password: str | None = None  # session key; None = plaintext file
         self.dirty = False
+        self._baseline_hash: int = 0
         self.wrap_on = True
         self.preview_on = True
         self.session_id = new_tab_id()
@@ -1031,6 +1033,38 @@ def dispose(self) -> None:
         self._editor_caret.dispose()
         self._preview_caret.dispose()
 
+    def _hash_state(self, text: str) -> int:
+        """Hash covering content and encryption state.
+
+        Returns:
+            64-bit xxHash integer.
+        """
+        marker = "\x00P" if self.password else "\x00-"
+        return xxhash.xxh3_64((text + marker).encode("utf-8")).intdigest()
+
+    def _current_hash(self) -> int:
+        """Hash of the current editor content + encryption state.
+
+        Returns:
+            64-bit xxHash integer for the live editor state.
+        """
+        return self._hash_state(self.editor.toPlainText())
+
+    def _set_baseline(self, text: str) -> None:
+        """Record the hash representing the last saved/loaded state."""
+        self._baseline_hash = self._hash_state(text)
+
+    def _sync_dirty_to_hash(self) -> None:
+        """Recompute dirty from hash comparison; emit meta_changed on change."""
+        current = self._current_hash()
+        if current != self._baseline_hash:
+            if not self.dirty:
+                self.dirty = True
+                self.meta_changed.emit()
+        elif self.dirty:
+            self.dirty = False
+            self.meta_changed.emit()
+
     def tab_label(self) -> str:
         """Short name for the tab bar (with dirty star).
 
@@ -1098,10 +1132,9 @@ def _on_text_changed(self) -> None:
                 self.editor.toPlainText(),
                 self.editor.textCursor().position(),
             )
-        if not self.dirty:
-            self.dirty = True
-            self.meta_changed.emit()
-        elif self.path is None and not self.locked:
+        if not self._applying_history and not self.locked:
+            self._sync_dirty_to_hash()
+        if self.path is None and not self.locked:
             # Untitled tab: title reflects the first line, so refresh live.
             self.meta_changed.emit()
         if self._sync_preview_from_source:
@@ -1117,8 +1150,7 @@ def apply_history_frame(self, frame: EditFrame) -> None:
             self.editor.setTextCursor(cursor)
         finally:
             self._applying_history = False
-        self.dirty = True
-        self.meta_changed.emit()
+        self._sync_dirty_to_hash()
         self.refresh_preview()
 
     def apply_source_edit(self, start: int, end: int, text: str) -> None:
@@ -1202,13 +1234,14 @@ def load_text(
         self.locked_blob = None
         self.editor.setReadOnly(False)
         self.editor.setPlaceholderText("")
+        self.path = path
+        self.password = password
+        self._set_baseline(text)
         self._applying_history = True
         try:
             self.editor.setPlainText(text)
         finally:
             self._applying_history = False
-        self.path = path
-        self.password = password
         self.dirty = False
         self.history.seed(text, self.editor.textCursor().position())
         self.refresh_preview()
@@ -1223,6 +1256,7 @@ def apply_payload(self, payload: TabPayload, *, password: str | None) -> None:
         self.path = Path(payload.path) if payload.path else None
         self.password = password
         self.dirty = payload.dirty
+        self._set_baseline(self.history.current.text)
         self.set_wrap(on=payload.wrap_on)
         self.set_preview(on=payload.preview_on)
         self._restore_scroll = payload.scroll
@@ -1254,6 +1288,7 @@ def set_locked(self, blob: bytes, *, path: Path | None, dirty: bool) -> None:
             self.editor.setPlainText("")
         finally:
             self._applying_history = False
+        self._baseline_hash = self._hash_state("")
         self.editor.setReadOnly(True)
         self.editor.setPlaceholderText("Password required — switch here to unlock.")
         self.preview.setHtml("")
@@ -2215,6 +2250,7 @@ def _save(self) -> None:
             QMessageBox.warning(self, "Morgul", f"Could not save file:\n{exc}")
             return
         self._add_recent(tab.path)
+        tab._set_baseline(tab.editor.toPlainText())  # ruff: ignore[private-member-access]
         tab.dirty = False
         self.tab_meta_changed()
 
@@ -2252,6 +2288,7 @@ def _save_as(self) -> None:
             return
         tab.path = path
         self._add_recent(path)
+        tab._set_baseline(tab.editor.toPlainText())  # ruff: ignore[private-member-access]
         tab.dirty = False
         self.tab_meta_changed()