Fixed pagination edge cases

  Screen was emptied when `prev_page()` reached the top of the history
  buffer

pyte/screens.py

@@ -395,7 +395,8 @@ def draw(self, char):
         if mo.IRM in self.mode:
             self.insert_characters(1)
 
-        self[self.cursor.y][self.cursor.x] = self.cursor.attrs._replace(data=char)
+        self[self.cursor.y][self.cursor.x] = self.cursor.attrs \
+            ._replace(data=char)
 
         # .. note:: We can't use :meth:`cursor_forward()`, because that
         #           way, we'll never know when to linefeed.
@@ -941,7 +942,7 @@ class HistoryScreen(DiffScreen):
 
     def __init__(self, columns, lines, history=100, ratio=.5):
         self.history = History(deque(maxlen=history // 2),
-                               deque(maxlen=history - history // 2),
+                               deque(maxlen=history),
                                float(ratio),
                                history,
                                history)
@@ -970,6 +971,13 @@ def __after__(self, command):
                     self[idx] = line + take(self.columns - len(line),
                                             self.default_line)
 
+        # If we're at the bottom of the history buffer and `DECTCEM`
+        # mode is set -- show the cursor.
+        self.cursor.hidden = not (
+            abs(self.history.position - self.history.size) < self.lines and
+            mo.DECTCEM in self.mode
+        )
+
         super(HistoryScreen, self).__after__(command)
 
     def reset(self):
@@ -1007,7 +1015,7 @@ def prev_page(self):
         ``ratio = .5`` means that half the screen is restored from
         history on page switch.
         """
-        if self.history.position > self.lines:
+        if self.history.position > self.lines and self.history.top:
             mid = min(len(self.history.top),
                       int(math.ceil(self.lines * self.history.ratio)))
 
@@ -1021,9 +1029,13 @@ def prev_page(self):
 
             self.dirty = set(range(self.lines))
 
+            if len(self) is not self.lines or self.history.position > self.history.size:
+                import pdb; pdb.set_trace()
+
+
     def next_page(self):
         """Moves the screen page down through the history buffer."""
-        if self.history.position < self.history.size:
+        if self.history.position < self.history.size and self.history.bottom:
             mid = min(len(self.history.bottom),
                       int(math.ceil(self.lines * self.history.ratio)))
 
@@ -1036,3 +1048,6 @@ def next_page(self):
             ]
 
             self.dirty = set(range(self.lines))
+
+            if len(self) is not self.lines or self.history.position > self.history.size:
+                import pdb; pdb.set_trace()

tests/test_history.py

@@ -72,10 +72,10 @@ def test_reverse_index():
     assert screen.history.bottom[1] == line
 
     # c) rotation.
-    for _ in range(len(screen) * screen.lines):
+    for _ in range(len(screen) ** screen.lines):
         screen.reverse_index()
 
-    assert len(screen.history.bottom) == 25  # pages // 2 * lines
+    assert len(screen.history.bottom) == 50
 
 
 def test_prev_page():
@@ -153,8 +153,6 @@ def test_prev_page():
     # c) same with odd number of lines.
     screen = HistoryScreen(5, 5, history=50)
 
-    # Once again filling the screen with line numbers, but this time,
-    # we need them to span on multiple lines.
     for idx in range(len(screen) * 10):
         map(screen.draw, unicode(idx))
         screen.linefeed()
@@ -188,7 +186,97 @@ def test_prev_page():
         "     ",
     ]
 
+    # d) same with cursor in the middle of the screen.
+    screen = HistoryScreen(5, 5, history=50)
+
+    for idx in range(len(screen) * 10):
+        map(screen.draw, unicode(idx))
+        screen.linefeed()
+
+    assert screen.history.top
+    assert not screen.history.bottom
+    assert screen.history.position == 50
+    assert screen.display == [
+        "46   ",
+        "47   ",
+        "48   ",
+        "49   ",
+        "     "
+    ]
+
+    screen.cursor_to_line(screen.lines // 2)
+
+    while screen.history.position > screen.lines:
+        screen.prev_page()
+
+    assert screen.history.position == screen.lines
+    assert len(screen) == screen.lines
+    assert screen.display == [
+        "21   ",
+        "22   ",
+        "23   ",
+        "24   ",
+        "25   "
+    ]
+
+    while screen.history.position < screen.history.size:
+        screen.next_page()
 
+    assert screen.history.position == screen.history.size
+    assert len(screen) == screen.lines
+    assert screen.display == [
+        "46   ",
+        "47   ",
+        "48   ",
+        "49   ",
+        "     "
+    ]
+
+    # e) same with cursor near the middle of the screen.
+    screen = HistoryScreen(5, 5, history=50)
+
+    for idx in range(len(screen) * 10):
+        map(screen.draw, unicode(idx))
+        screen.linefeed()
+
+    assert screen.history.top
+    assert not screen.history.bottom
+    assert screen.history.position == 50
+    assert screen.display == [
+        "46   ",
+        "47   ",
+        "48   ",
+        "49   ",
+        "     "
+    ]
+
+    screen.cursor_to_line(screen.lines // 2 - 2)
+
+    while screen.history.position > screen.lines:
+        screen.prev_page()
+
+    assert screen.history.position == screen.lines
+    assert len(screen) == screen.lines
+    assert screen.display == [
+        "21   ",
+        "22   ",
+        "23   ",
+        "24   ",
+        "25   "
+    ]
+
+    while screen.history.position < screen.history.size:
+        screen.next_page()
+
+    assert screen.history.position == screen.history.size
+    assert len(screen) == screen.lines
+    assert screen.display == [
+        "46   ",
+        "47   ",
+        "48   ",
+        "49   ",
+        "     "
+    ]
 
 def test_next_page():
     screen = HistoryScreen(5, 5, history=50)
@@ -386,3 +474,25 @@ def test_draw():
         "24   ",
         "x    "
     ]
+
+
+def test_cursor_is_hidden():
+    screen = HistoryScreen(5, 5, history=50)
+    stream = Stream()
+    stream.attach(screen)
+    stream.escape["N"] = "next_page"
+    stream.escape["P"] = "prev_page"
+
+    for idx in range(len(screen) * 5):
+        map(stream.feed, unicode(idx) + "\n")
+
+    assert not screen.cursor.hidden
+
+    stream.feed(ctrl.ESC + "P")
+    assert screen.cursor.hidden
+    stream.feed(ctrl.ESC + "P")
+    assert screen.cursor.hidden
+    stream.feed(ctrl.ESC + "N")
+    assert screen.cursor.hidden
+    stream.feed(ctrl.ESC + "N")
+    assert not screen.cursor.hidden