Per directory history plugin

This is a implementation of per directory history for zsh, some
   implementations of which exist in bash[1,2].  It also implements
   a per-directory-history-toggle-history function to change from using the
   directory history to using the global history.  In both cases the history is
   always saved to both the global history and the directory history, so the
   toggle state will not effect the saved histories.  Being able to switch
   between global and directory histories on the fly is a novel feature as far
   as I am aware.

   [1]: http://www.compbiome.com/2010/07/bash-per-directory-bash-history.html
   [2]: http://dieter.plaetinck.be/per_directory_bash

plugins/per-directory-history/per-directory-history.plugin.zsh

@@ -0,0 +1,149 @@
+#!/usr/bin/env zsh
+#
+# This is a implementation of per directory history for zsh, some 
+# implementations of which exist in bash[1,2].  It also implements 
+# a per-directory-history-toggle-history function to change from using the 
+# directory history to using the global history.  In both cases the history is 
+# always saved to both the global history and the directory history, so the 
+# toggle state will not effect the saved histories.  Being able to switch 
+# between global and directory histories on the fly is a novel feature as far 
+# as I am aware.
+#
+#-------------------------------------------------------------------------------
+# Configuration
+#-------------------------------------------------------------------------------
+#
+# HISTORY_BASE a global variable that defines the base directory in which the 
+# directory histories are stored
+#
+#-------------------------------------------------------------------------------
+# History
+#-------------------------------------------------------------------------------
+#
+# The idea/inspiration for a per directory history is from Stewart MacArthur[1] 
+# and Dieter[2], the implementation idea is from Bart Schaefer on the the zsh 
+# mailing list[3].  The implementation is by Jim Hester in September 2012.
+#
+# [1]: http://www.compbiome.com/2010/07/bash-per-directory-bash-history.html
+# [2]: http://dieter.plaetinck.be/per_directory_bash
+# [3]: http://www.zsh.org/mla/users/1997/msg00226.html
+#
+################################################################################
+#
+# Copyright (c) 2012 Jim Hester
+#
+# This software is provided 'as-is', without any express or implied warranty.  
+# In no event will the authors be held liable for any damages arising from the 
+# use of this software.
+#
+# Permission is granted to anyone to use this software for any purpose, 
+# including commercial applications, and to alter it and redistribute it 
+# freely, subject to the following restrictions:
+#
+# 1. The origin of this software must not be misrepresented; you must not claim 
+# that you wrote the original software. If you use this software in a product, 
+# an acknowledgment in the product documentation would be appreciated but is 
+# not required.
+#
+# 2. Altered source versions must be plainly marked as such, and must not be 
+# misrepresented as being the original software.
+#
+# 3. This notice may not be removed or altered from any source distribution..
+#
+################################################################################
+
+#-------------------------------------------------------------------------------
+# configuration, the base under which the directory histories are stored
+#-------------------------------------------------------------------------------
+
+[[ -z $HISTORY_BASE ]] && HISTORY_BASE="$HOME/.directory_history"
+
+#-------------------------------------------------------------------------------
+# toggle global/directory history used for searching - ctrl-G by default
+#-------------------------------------------------------------------------------
+
+function per-directory-history-toggle-history() {
+  if [[ $_per_directory_history_is_global == true ]]; then
+    _per-directory-history-set-directory-history
+    echo "using local history\n"
+  else
+    _per-directory-history-set-global-history
+    echo "using global history\n"
+  fi
+  zle reset-prompt
+}
+
+autoload per-directory-history-toggle-history
+zle -N per-directory-history-toggle-history
+bindkey '^G' per-directory-history-toggle-history
+
+#-------------------------------------------------------------------------------
+# implementation details
+#-------------------------------------------------------------------------------
+
+_per_directory_history_global=$HISTFILE
+_per_directory_history_directory="$HISTORY_BASE${PWD:A}/history"
+
+function _per-directory-history-change-directory() {
+  _per_directory_history_directory="$HISTORY_BASE${PWD:A}/history"
+  mkdir -p ${_per_directory_history_directory:h}
+  if [[ $_per_directory_history_is_global == false ]]; then
+    #save to the global history
+    fc -AI $_per_directory_history_global
+    #save history to previous file
+    local prev="$HISTORY_BASE${OLDPWD:A}/history"
+    mkdir -p ${prev:h}
+    fc -AI $prev
+
+    #discard previous directory's history
+    local original_histsize=$HISTSIZE
+    HISTSIZE=0
+    HISTSIZE=$original_histsize
+    
+    #read history in new file
+    if [[ -e $_per_directory_history_directory ]]; then
+      fc -R $_per_directory_history_directory
+    fi
+  fi
+}
+
+function _per-directory-history-addhistory() {
+  print -sr -- ${1%%$'\n'}
+  fc -p $_per_directory_history_directory
+}
+
+
+function _per-directory-history-set-directory-history() {
+  if [[ $_per_directory_history_is_global == true ]]; then
+    fc -AI $_per_directory_history_global
+    local original_histsize=$HISTSIZE
+    HISTSIZE=0
+    HISTSIZE=$original_histsize
+    if [[ -e "$_per_directory_history_directory" ]]; then
+      fc -R "$_per_directory_history_directory"
+    fi
+  fi
+  _per_directory_history_is_global=false
+}
+function _per-directory-history-set-global-history() {
+  if [[ $_per_directory_history_is_global == false ]]; then
+    fc -AI $_per_directory_history_directory
+    local original_histsize=$HISTSIZE
+    HISTSIZE=0
+    HISTSIZE=$original_histsize
+    if [[ -e "$_per_directory_history_global" ]]; then
+      fc -R "$_per_directory_history_global"
+    fi
+  fi
+  _per_directory_history_is_global=true
+}
+
+
+#add functions to the exec list for chpwd and zshaddhistory
+chpwd_functions=(${chpwd_functions[@]} "_per-directory-history-change-directory")
+zshaddhistory_functions=(${zshaddhistory_functions[@]} "_per-directory-history-addhistory")
+
+#start in directory mode
+mkdir -p ${_per_directory_history_directory:h}
+_per_directory_history_is_global=true
+_per-directory-history-set-directory-history