Viewer abstracted out, cursor now detects out of bounds.

rtv/viewer.py

@@ -0,0 +1,115 @@
+import curses
+
+class Navigator(object):
+    """
+    Handles cursor movement and screen paging.
+    """
+
+    def __init__(
+            self,
+            valid_page_cb,
+            page_index=0,
+            cursor_index=0,
+            inverted=False):
+
+        self._page_cb = valid_page_cb
+
+        self.page_index = page_index
+        self.cursor_index = cursor_index
+        self.inverted = inverted
+
+    @property
+    def step(self):
+        return 1 if not self.inverted else -1
+
+    @property
+    def position(self):
+        return (self.page_index, self.cursor_index, self.inverted)
+
+    def move(self, direction, n_windows):
+        "Move the cursor down (positive direction) or up (negative direction)"
+
+        valid, redraw = True, False
+
+        # TODO: add variable movement
+        forward = ((direction*self.step) > 0)
+
+        if forward:
+            self.cursor_index += 1
+            if self.cursor_index >= n_windows - 1:
+                self.page_index += (self.step * self.cursor_index)
+                self.cursor_index = 0
+                self.inverted = not self.inverted
+                redraw = True
+        else:
+            if self.cursor_index > 0:
+                self.cursor_index -= 1
+            else:
+                if self._is_valid(self.page_index - self.step):
+                    self.page_index -= self.step
+                    redraw = True
+                else:
+                    valid = False
+
+        return valid, redraw
+
+    def _is_valid(self, page_index):
+        "Check if a page index will cause entries to fall outside valid range"
+
+        try:
+            self._page_cb(page_index)
+            self._page_cb(page_index + self.step * self.cursor_index)
+        except IndexError:
+            return False
+        else:
+            return True
+
+
+class BaseViewer(object):
+    """
+    Base terminal viewer incorperating a cursor to navigate content
+    """
+
+    def __init__(self, content):
+
+        self.content = content
+        self.nav = Navigator(self.content.get)
+
+    def draw_content(self):
+        raise NotImplementedError
+
+    @property
+    def n_subwindows(self):
+        raise NotImplementedError
+
+    def move_cursor_up(self):
+        self._move_cursor(-1)
+
+    def move_cursor_down(self):
+        self._move_cursor(1)
+
+    def add_cursor(self):
+        self._edit_cursor(curses.A_REVERSE)
+
+    def remove_cursor(self):
+        self._edit_cursor(curses.A_NORMAL)
+
+    def _move_cursor(self, direction):
+
+        self.remove_cursor()
+
+        valid, redraw = self.nav.move(direction, self.n_subwindows)
+        if not valid:
+            curses.flash()
+        if redraw:
+            self.draw_content()
+
+        self.add_cursor()
+
+    def _edit_cursor(self, attribute):
+
+        window = self._sub_windows[self.nav.cursor_index]
+        n_rows, _ = window.getmaxyx()
+        for row in xrange(n_rows):
+            window.chgat(row, 0, 1, attribute)
+        window.refresh()