improve corner cases related to resizing and mode switching

A few operations would previously fail unexpectedly:
 * Running tcvt with many columns and a small terminal width would crash
   instead of falling back to a simple screen.
 * After switching the mode, column ordering would be lost.
 * Switching the mode from simple to columns after resizing could result
   in a crash.

Instead of collecting the screen options and passing them down
individually, the Terminal class now asks for a preconfigured screen
factory. This should eliminate future potential for similar mistakes.

1 files changed, 18 insertions, 17 deletions

diff --git a/tcvt.py b/tcvt.py
index 3cdb957..c30f4e0 100755
--- a/tcvt.py
+++ b/tcvt.py
@@ -305,35 +305,34 @@ simple_characters = bytearray(
         b'\xb4\xb6\xb7\xc3\xc4\xd6\xdc\xe4\xe9\xfc\xf6')
 
 class Terminal:
-    def __init__(self, acsc, columns, reverse=False):
+    def __init__(self, acsc, screenfactory):
         self.mode = (self.feed_simple,)
         self.realscreen = None
         self.screen = None
         self.fg = self.bg = 0
         self.graphics_font = False
-        self.graphics_chars = acsc # really initialized after
+        self.graphics_chars = acsc # really initialized in __enter__
         self.lastchar = ord(b' ')
-        self.columns = columns
-        self.reverse = reverse
+        self.screenfactory = screenfactory
         self.need_refresh = None
 
-    def switchmode(self):
-        if isinstance(self.screen, Columns):
+    def makescreen(self, switch=False):
+        try:
+            if isinstance(self.screen, Simple) ^ switch:
+                raise BadWidth("use simple screen")
+            self.screen = self.screenfactory(self.realscreen)
+        except BadWidth:
             self.screen = Simple(self.realscreen)
-        else:
-            self.screen = Columns(self.realscreen, self.columns)
         self.request_refresh()
 
+    def switchmode(self):
+        self.makescreen(True)
+
     def resized(self):
         # The refresh call causes curses to notice the new dimensions.
         self.realscreen.refresh()
         self.realscreen.clear()
-        try:
-            self.screen = Columns(self.realscreen, self.columns,
-                                  reverse=self.reverse)
-        except BadWidth:
-            self.screen = Simple(self.realscreen)
-        self.request_refresh()
+        self.makescreen()
 
     def resizepty(self, ptyfd):
         ym, xm = self.screen.getmaxyx()
@@ -366,8 +365,7 @@ class Terminal:
         self.realscreen.keypad(1)
         curses.start_color()
         init_color_pairs()
-        self.screen = Columns(self.realscreen, self.columns,
-                              reverse=self.reverse)
+        self.makescreen()
         curses.noecho()
         curses.raw()
         self.graphics_chars = compose_dicts(self.graphics_chars, acs_map())
@@ -804,10 +802,13 @@ def main():
     options, args = parser.parse_args()
     keymapping, acsc = compute_keymap(symbolic_keymapping)
 
+    def screenfactory(realscreen):
+        return Columns(realscreen, options.columns, reverse=options.reverse)
+
     process = ForkPty(args or [os.environ["SHELL"]], dict(TERM="ansi"))
     try:
         with process as masterfd:
-            with Terminal(acsc, options.columns, reverse=options.reverse) as t:
+            with Terminal(acsc, screenfactory) as t:
                 t.resizepty(masterfd)
                 process.start()
                 while True: