Add Windows log static tail

nomadnet/ui/textui/Log.py

@@ -1,35 +1,43 @@
+import os
+import sys
+import itertools
+import mmap
 import urwid
 import nomadnet
 
+
 class LogDisplayShortcuts():
     def __init__(self, app):
         import urwid
         self.app = app
 
         self.widget = urwid.AttrMap(urwid.Text(""), "shortcutbar")
 
+
 class LogDisplay():
     def __init__(self, app):
         self.app = app
-        self.log_term = None
 
         self.shortcuts_display = LogDisplayShortcuts(self.app)
         self.widget = None
 
+    @property
+    def log_term(self):
+        return self.widget
+
     def show(self):
-        if self.log_term == None:
-            self.log_term = LogTerminal(self.app)
-            self.widget = urwid.LineBox(self.log_term)
+        if self.widget is None:
+            self.widget = log_widget(self.app)
 
     def kill(self):
-        if self.log_term != None:
-            self.log_term.terminate()
-            self.log_term = None
+        if self.widget is not None:
+            self.widget.terminate()
             self.widget = None
 
     def shortcuts(self):
         return self.shortcuts_display
 
+
 class LogTerminal(urwid.WidgetWrap):
     def __init__(self, app):
         self.app = app
@@ -39,7 +47,8 @@ def __init__(self, app):
             escape_sequence="up",
             main_loop=self.app.ui.loop,
         )
-        super().__init__(self.log_term)
+        self.widget = urwid.LineBox(self.log_term)
+        super().__init__(self.widget)
 
     def terminate(self):
         self.log_term.terminate()
@@ -49,4 +58,73 @@ def keypress(self, size, key):
         if key == "up":
             nomadnet.NomadNetworkApp.get_shared_instance().ui.main_display.frame.focus_position = "header"
 
-        return super(LogTerminal, self).keypress(size, key)
+        return super(LogTerminal, self).keypress(size, key)
+
+
+class LogTail(urwid.WidgetWrap):
+    def __init__(self, app):
+        self.app = app
+        self.log_tail = urwid.Text(tail(self.app.logfilepath, 50))
+        self.log = urwid.Scrollable(self.log_tail)
+        self.log.set_scrollpos(-1)
+        self.log_scrollbar = urwid.ScrollBar(self.log)
+        # We have this here because ui.textui.Main depends on this field to kill it
+        self.log_term = None
+
+        super().__init__(self.log_scrollbar)
+
+    def terminate(self):
+        pass
+
+
+def log_widget(app, platform=sys.platform):
+    if platform == "linux":
+        return LogTerminal(app)
+    elif platform == "win32":
+        return LogTail(app)
+    else:
+        raise ValueError(f"Unknown platform {platform}. Expected linux/win32")
+
+
+# https://stackoverflow.com/a/34029605/3713120
+def _tail(f_name, n, offset=0):
+    def skip_back_lines(mm: mmap.mmap, numlines: int, startidx: int) -> int:
+        '''Factored out to simplify handling of n and offset'''
+        for _ in itertools.repeat(None, numlines):
+            startidx = mm.rfind(b'\n', 0, startidx)
+            if startidx < 0:
+                break
+        return startidx
+
+    # Open file in binary mode
+    with open(f_name, 'rb') as binf, mmap.mmap(binf.fileno(), 0, access=mmap.ACCESS_READ) as mm:
+        # len(mm) - 1 handles files ending w/newline by getting the prior line
+        startofline = skip_back_lines(mm, offset, len(mm) - 1)
+        if startofline < 0:
+            return []  # Offset lines consumed whole file, nothing to return
+            # If using a generator function (yield-ing, see below),
+            # this should be a plain return, no empty list
+
+        endoflines = startofline + 1  # Slice end to omit offset lines
+
+        # Find start of lines to capture (add 1 to move from newline to beginning of following line)
+        startofline = skip_back_lines(mm, n, startofline) + 1
+
+        # Passing True to splitlines makes it return the list of lines without
+        # removing the trailing newline (if any), so list mimics f.readlines()
+        # return mm[startofline:endoflines].splitlines(True)
+        # If Windows style \r\n newlines need to be normalized to \n
+        return mm[startofline:endoflines].replace(os.linesep.encode(sys.getdefaultencoding()), b'\n').splitlines(True)
+
+
+def tail(f_name, n):
+    """
+    Return the last n lines of a given file name, f_name.
+    Akin to `tail -<n> <f_name>`
+    """
+    def decode(b):
+        return b.decode(encoding)
+
+    encoding = sys.getdefaultencoding()
+    lines = map(decode, _tail(f_name=f_name, n=n))
+    return ''.join(lines)