###  cdhist.sh
###
###  Copyright (c) 2001 Yusuke Shinyama <yusuke at cs . nyu . edu>
###
###  Permission to use, copy, modify, distribute this software and
###  its documentation for any purpose is hereby granted, provided
###  that existing copyright notices are retained in all copies and
###  that this notice is included verbatim in any distributions. 
###  This software is provided ``AS IS'' without any express or implied
###  warranty.
###

###  WARNING: THIS SCRIPT IS FOR GNU BASH ONLY!

###  What is this?
###
###  Cdhist adds 'web-browser like history' to your bash shell.
###  Every time you change the current directory it records the directory
###  you can go back by simply typing a short command such as '-' or '+',
###  just like clicking web-browsers's 'back' button.
###  It's more convenient than using directory stacks when
###  you walk around two or three directories.
###

###  Usage
###
###  Just call this file from your .bashrc script.
###  The following commands are added.
###
###  cd [pathname]
###	Go to the given directory, or your home directory if 
###	pathname is omitted. This overrides the original command.
###	You can use it by typing '\cd'.
###
###  + [n]
###	'Forward' button. Go to the n'th posterior directory in the history.
###	Go to the next directory if the number is omitted.
###
###  - [n]
###	'Back' button. Go to the n'th prior directory in the history.
###	Go to the previous directory if the number is omitted.
###
###  = [n]
###	Show histories with directory numbers.
###
###	A directory number shows the index to the current directory 
###	in the history. The current directory always has directory number 0.
###	For prior directories, a negative number is given.
###	For posterior directories, a positive number is given.
###
###  cdhist_reset
###	Clear the cd history.
###

###  Example
###
###	/home/yusuke:$ . cdhist.sh
###	/home/yusuke:$ cd /tmp
###	/tmp:$ cd /usr/bin
###	/usr/bin:$ cd /etc
###	/etc:$ -
###	/usr/bin:$ -
###	/tmp:$ +
###	/usr/bin:$ =
###	-2 ~
###	-1 /tmp
###	 0:/usr/bin
###	 1 /etc
###	/usr/bin:$ - 2
###     /home/yusuke:$
###


CDHIST_CDQMAX=10
declare -a CDHIST_CDQ

function cdhist_reset {
  CDHIST_CDQ=("$PWD")
}

function cdhist_disp {
  echo "$*" | sed "s $HOME ~ g"
}

function cdhist_add {
  CDHIST_CDQ=("$1" "${CDHIST_CDQ[@]}")
}

function cdhist_del {
  local i=${1-0}
  if [ ${#CDHIST_CDQ[@]} -le 1 ]; then return; fi
  for ((; i<${#CDHIST_CDQ[@]}-1; i++)); do
    CDHIST_CDQ[$i]="${CDHIST_CDQ[$((i+1))]}"
  done
  unset CDHIST_CDQ[$i]
}

function cdhist_rot {
  local i q
  for ((i=0; i<$1; i++)); do
    q[$i]="${CDHIST_CDQ[$(((i+$1+$2)%$1))]}"
  done
  for ((i=0; i<$1; i++)); do
    CDHIST_CDQ[$i]="${q[$i]}"
  done
}

function cdhist_cd {
  local i f=0
  builtin cd "$@" || return 1
  for ((i=0; i<${#CDHIST_CDQ[@]}; i++)); do
    if [ "${CDHIST_CDQ[$i]}" = "$PWD" ]; then f=1; break; fi
  done
  if [ $f -eq 1 ]; then
    cdhist_rot $((i+1)) -1
  elif [ ${#CDHIST_CDQ[@]} -lt $CDHIST_CDQMAX ]; then 
    cdhist_add "$PWD"
  else
    cdhist_rot ${#CDHIST_CDQ[@]} -1
    CDHIST_CDQ[0]="$PWD"
  fi
}

function cdhist_history {
  local i d
  if [ $# -eq 0 ]; then
    for ((i=${#CDHIST_CDQ[@]}-1; 0<=i; i--)); do
      cdhist_disp " $i ${CDHIST_CDQ[$i]}"
    done
  elif [ "$1" -lt ${#CDHIST_CDQ[@]} ]; then
    d=${CDHIST_CDQ[$1]}
    if builtin cd "$d"; then
      cdhist_rot $(($1+1)) -1
    else
      cdhist_del $1
    fi
    cdhist_disp "${CDHIST_CDQ[@]}"
  fi
}

function cdhist_forward {
  cdhist_rot ${#CDHIST_CDQ[@]} -${1-1}
  if ! builtin cd "${CDHIST_CDQ[0]}"; then
    cdhist_del 0
  fi
  cdhist_disp "${CDHIST_CDQ[@]}"
}

function cdhist_back {
  cdhist_rot ${#CDHIST_CDQ[@]} ${1-1}
  if ! builtin cd "${CDHIST_CDQ[0]}"; then
    cdhist_del 0
  fi
  cdhist_disp "${CDHIST_CDQ[@]}"
}


if [ ${#CDHIST_CDQ[@]} = 0 ]; then cdhist_reset; fi


###  Aliases
###

function cd { cdhist_cd "$@"; }
function + { cdhist_forward "$@"; }
function - { cdhist_back "$@"; }
function = { cdhist_history "$@"; }