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src/calibre/utils/pyconsole/history.py

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+#!/usr/bin/env python
+# vim:fileencoding=UTF-8:ts=4:sw=4:sta:et:sts=4:ai
+
+__license__   = 'GPL v3'
+__copyright__ = '2010, Kovid Goyal <kovid@kovidgoyal.net>'
+__docformat__ = 'restructuredtext en'
+
+from collections import deque
+
+class History(object): # {{{
+
+    def __init__(self, current, entries):
+        self.entries = deque(entries, maxlen=max(2000, len(entries)))
+        self.index = len(self.entries) - 1
+        self.current = self.default = current
+        self.last_was_back = False
+
+    def back(self, amt=1):
+        if self.entries:
+            oidx = self.index
+            ans = self.entries[self.index]
+            self.index = max(0, self.index - amt)
+            self.last_was_back = self.index != oidx
+            return ans
+
+    def forward(self, amt=1):
+        if self.entries:
+            d = self.index
+            if self.last_was_back:
+                d += 1
+            if d >= len(self.entries) - 1:
+                self.index = len(self.entries) - 1
+                self.last_was_back = False
+                return self.current
+            if self.last_was_back:
+                amt += 1
+            self.index = min(len(self.entries)-1, self.index + amt)
+            self.last_was_back = False
+            return self.entries[self.index]
+
+    def enter(self, x):
+        try:
+            self.entries.remove(x)
+        except ValueError:
+            pass
+        self.entries.append(x)
+        self.index = len(self.entries) - 1
+        self.current = self.default
+        self.last_was_back = False
+
+    def serialize(self):
+        return list(self.entries)
+
+# }}}
+
+