Use xclip directly if available

This gives better ergonomics because we can terminate xclip ourselves

.. instead of using paste to check whether the copy buffer is the same
as our previous TOTP code

src/ttotp/__main__.py

@@ -6,6 +6,7 @@
 
 from dataclasses import dataclass, field
 
+import signal
 import time
 import hashlib
 import pathlib
@@ -35,6 +36,13 @@ from typing import TypeGuard  # use `typing_extensions` for Python 3.9 and below
 # workaround for pyperclip being un-typed
 if TYPE_CHECKING:
 
+    class CopyProcessor:
+        def do_copy(self, data: str) -> None:
+            ...
+
+        def do_clear_copy(self) -> bool:
+            ...
+
     def pyperclip_paste() -> str:
         ...
 
@@ -45,6 +53,63 @@ else:
     from pyperclip import copy as pyperclip_copy
 
 
+def command_exists(s: str) -> bool:
+    status = subprocess.run(
+        ["which", s],
+        stdout=subprocess.DEVNULL,
+        stderr=subprocess.DEVNULL,
+        stdin=subprocess.DEVNULL,
+    )
+    return status.returncode == 0
+
+
+@dataclass
+class PyperclipCopyProcessor:
+    copied: str = ""
+
+    def do_copy(self, data: str) -> None:
+        self.copied = data
+
+    def do_clear_copy(self) -> bool:
+        if self.copied and pyperclip_paste() == self.copied:
+            pyperclip_copy("")
+            return True
+        return False
+
+
+@dataclass
+class XClipCopyProcessor:
+    process: subprocess.Popen[bytes] | None = None
+
+    def do_copy(self, data: str) -> None:
+        self.do_clear_copy()
+        self.process = subprocess.Popen(
+            ["xclip", "-verbose", "-sel", "c"],
+            stdout=subprocess.DEVNULL,
+            stderr=subprocess.DEVNULL,
+            stdin=subprocess.PIPE,
+        )
+        assert self.process.stdin is not None  # mypy worries about this at night
+        self.process.stdin.write(data.encode("utf-8"))
+        self.process.stdin.close()
+
+    def do_clear_copy(self) -> bool:
+        if self.process is None:
+            return False
+        self.process.send_signal(signal.SIGINT)
+        returncode = self.process.wait(0.1)
+        if returncode is None:
+            self.process.send_signal(signal.SIGKILL)
+            returncode = self.process.wait(0.1)
+        self.process = None
+        return True
+
+
+copy_processor = (
+    XClipCopyProcessor() if command_exists("xclip") else PyperclipCopyProcessor()
+)
+
+
 def is_str_list(val: Any) -> TypeGuard[list[str]]:
     """Determines whether all objects in the list are strings"""
     if not isinstance(val, list):
@@ -319,9 +384,8 @@ class TTOTP(App[None]):
         self.notify("Will exit soon due to inactivity", title="Auto-exit")
 
     def clear_clipboard_func(self) -> None:
-        if pyperclip_paste() == self.copied:
+        if copy_processor.do_clear_copy():
             self.notify("Clipboard cleared", title="")
-            pyperclip_copy("")
 
     def timer_func(self) -> None:
         now = time.time()
@@ -350,8 +414,7 @@ class TTOTP(App[None]):
         if widget is not None:
             otp = cast(TOTPLabel, widget).otp
             code = otp.totp.now()
-            pyperclip_copy(code)
-            self.copied = code
+            copy_processor.do_copy(code)
             if self.clear_clipboard_timer is not None:
                 self.clear_clipboard_timer.pause()