#!/bin/bash
#This program is free software; you can redistribute it and/or modify
#it under the terms of the GNU General Public License version 2 as published by
#the Free Software Foundation.

#This program is distributed in the hope that it will be useful,
#but WITHOUT ANY WARRANTY; without even the implied warranty of
#MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#GNU General Public License for more details:
#http://www.gnu.org/copyleft/gpl.html

#Any questions at all, email me at: dave@davidstark.name


DONE=false
SINGLE=false
DEBUG=false
while ! $DONE
  do
  case "$1" in
      -1)
	  SINGLE=true
	  shift;;
      -d)
	  DEBUG=true
	  shift;;
      *)
	  DONE=true;;
  esac
done

if ! (echo "$1" | grep '^[0-9A-Fa-f]\{6,6\}$' &> /dev/null) || ! (echo "$2" | grep '^[0-9A-Fa-f]\{6,6\}$' &> /dev/null)
    then
    echo
    echo "Usage: `basename \"$0\"` [-1] [-d] <night-colour> <day-colour>"
    echo
    echo "Where <*-colour> is a 6 digit RGB hex colour (no leading # or 0x)."
    echo "The -1 flag runs the set operation once, then exits, otherwise"
    echo " the background colour is adjusted every $RATE seconds"
    echo "The -d flag prints an information message when the colour is set"
    exit 1
fi

if [ -x /usr/bin/xsri ]
    then
    SETROOTCOM="xsri --color="
elif [ -x /usr/bin/xsetroot ]
    then
    SETROOTCOM="/usr/bin/xsetroot -solid "
elif [ -x /usr/openwin/bin/xsetroot ]
    then
    SETROOTCOM="/usr/openwin/bin/xsetroot -solid "
else
    echo "Couldn't find a utility to set the root window colour"
    exit 1
fi

#Update rate in seconds
RATE=60

#Make the hex uppercase (dc gets confused otherwise)
A=`echo $1 | tr a-z A-Z`
B=`echo $2 | tr a-z A-Z`

#Split the 6 char string into 3 2 char hex values
RAHEX=${A:0:2}
GAHEX=${A:2:2}
BAHEX=${A:4:2}
RBHEX=${B:0:2}
GBHEX=${B:2:2}
BBHEX=${B:4:2}

#Convert to decimal
RA=$(echo -e "16\ni\n${RAHEX}\np" | dc)
GA=$(echo -e "16\ni\n${GAHEX}\np" | dc)
BA=$(echo -e "16\ni\n${BAHEX}\np" | dc)
RB=$(echo -e "16\ni\n${RBHEX}\np" | dc)
GB=$(echo -e "16\ni\n${GBHEX}\np" | dc)
BB=$(echo -e "16\ni\n${BBHEX}\np" | dc)

RRANGE=$(($RB - $RA))
GRANGE=$(($GB - $GA))
BRANGE=$(($BB - $BA))

while true
  do
  MINUTES=$(echo "((`date +%k` * 60) + `date +%M`)" | bc)
  MAG=$(echo "((c (($MINUTES * 0.00436332312998582394))) -1) * -0.5" | bc -l)

  RVAL=$(echo "($MAG * $RRANGE) + $RA + 0.5" | bc | awk -F'.' '{print $1}')
  GVAL=$(echo "($MAG * $GRANGE) + $GA + 0.5" | bc | awk -F'.' '{print $1}')
  BVAL=$(echo "($MAG * $BRANGE) + $BA + 0.5" | bc | awk -F'.' '{print $1}')

  # Convert back to hex
  RHEXVAL=$(echo -e "10\ni\n16\no\n${RVAL:-0}\np" | dc)
  if [ ${#RHEXVAL} -lt 2 ]
      then
      RHEXVAL=0$RHEXVAL
  fi
  GHEXVAL=$(echo -e "10\ni\n16\no\n${GVAL:-0}\np" | dc)
  if [ ${#GHEXVAL} -lt 2 ]
      then
      GHEXVAL=0$GHEXVAL
  fi
  BHEXVAL=$(echo -e "10\ni\n16\no\n${BVAL:-0}\np" | dc)
  if [ ${#BHEXVAL} -lt 2 ]
      then
      BHEXVAL=0$BHEXVAL
  fi

  $SETROOTCOM"#$RHEXVAL$GHEXVAL$BHEXVAL"
  if $DEBUG
      then
      echo -e "`date +%b" "%d" "%H:%M:%S` `hostname | awk -F'.' '{print $1}'` $0 $DISPLAY $RHEXVAL$GHEXVAL$BHEXVAL"
  fi

  if $SINGLE
      then
      exit 0
  fi
  sleep $RATE
done