✨ Add a cache facility to the PEP source viewer screen

Author: davep

src/peplum/app/screens/pep_viewer.py

@@ -1,5 +1,9 @@
 """A dialog for viewing the text of a PEP."""
 
+##############################################################################
+# Python imports.
+from pathlib import Path
+
 ##############################################################################
 # Textual imports.
 from textual import on, work
@@ -11,7 +15,7 @@
 ##############################################################################
 # Local imports.
 from ...peps import API
-from ..data import PEP
+from ..data import PEP, cache_dir
 
 
 ##############################################################################
@@ -57,7 +61,7 @@ class PEPViewer(ModalScreen[None]):
     }
     """
 
-    BINDINGS = [("escape", "close")]
+    BINDINGS = [("escape", "close"), ("ctrl+r", "refresh")]
 
     def __init__(self, pep: PEP) -> None:
         """Initialise the dialog.
@@ -75,34 +79,67 @@ def compose(self) -> ComposeResult:
             dialog.border_title = f"PEP{self._pep.number}"
             yield VerticalScroll(Static(id="text"), id="viewer")
             with Horizontal(id="buttons"):
-                yield Button("Close [dim]\\[Esc][/]", variant="default")
+                yield Button("Refresh [dim]\\[^r][/]", id="refresh")
+                yield Button("Close [dim]\\[Esc][/]", id="close")
+
+    @property
+    def _cache_name(self) -> Path:
+        """The name of the file that is the cached version of the PEP source."""
+        return cache_dir() / API.pep_file(self._pep.number)
 
     @work
     async def _download_text(self) -> None:
-        """Download the text of the PEP."""
-        try:
-            self.query_one("#text", Static).update(
-                await API().get_pep(self._pep.number)
-            )
-        except API.RequestError as error:
-            self.query_one("#text", Static).update("[error]Error[/]")
-            self.notify(
-                str(error), title="Error downloading PEP source", severity="error"
-            )
-            return
-        finally:
-            self.query_one("#viewer").loading = False
+        """Download the text of the PEP.
+
+        Notes:
+            Once downloaded a local copy will be saved. Subsequently, when
+            attempting to download the PEP, this local copy will be used
+            instead.
+        """
+        pep_source = ""
+        if self._cache_name.exists():
+            try:
+                pep_source = self._cache_name.read_text(encoding="utf-8")
+            except IOError:
+                pass
+
+        if not pep_source:
+            try:
+                self._cache_name.write_text(
+                    pep_source := await API().get_pep(self._pep.number),
+                    encoding="utf-8",
+                )
+            except IOError:
+                pass
+            except API.RequestError as error:
+                pep_source = "Error downloading PEP source"
+                self.notify(
+                    str(error), title="Error downloading PEP source", severity="error"
+                )
+
+        self.query_one("#text", Static).update(pep_source)
+        self.query_one("#viewer").loading = False
         self.set_focus(self.query_one("#viewer"))
 
     def on_mount(self) -> None:
         """Populate the dialog once the"""
         self.query_one("#viewer").loading = True
         self._download_text()
 
-    @on(Button.Pressed)
+    @on(Button.Pressed, "#close")
     def action_close(self) -> None:
         """Close the dialog."""
         self.dismiss(None)
 
+    @on(Button.Pressed, "#refresh")
+    def action_refresh(self) -> None:
+        """Refresh the PEP source."""
+        try:
+            self._cache_name.unlink(missing_ok=True)
+        except IOError:
+            pass
+        self.query_one("#viewer").loading = True
+        self._download_text()
+
 
 ### pep_viewer.py ends here