#!/bin/bash
# Snowflake - Draw falling snowflakes on the screen
# Copyright (C) 2007 Lars Stoltenow <penma@penma.de>
# 
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
# 
# 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.
# 
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

nomodechg=0

function usage()
{
	# Show the help text.
	cat << EOT
Usage: $0 [ options ] <freq1> <char1> [ <freq2> <char2> [ ... ] ]

freq1, freq2, ... freqn are the frequencies of which the given char1, char2, ... charn fall down the screen.

	--help      or -h  Show this help message.
	--nomodechg or -n  Don't change the screen mode.
EOT
}

# Show the welcome message
echo "Snowflakes, Copyright (C) 2007 Lars Stoltenow"
echo "This is free software, and you are welcome to redistribute it under certain conditions; for details, see the GNU General Public License."

while [ "$(cut -b 1 <<<$1)" = "-" ]
do
	case "$1" in
	--help | -h ) usage; exit;;
	--nomodechg | -n ) nomodechg=1;;
	* ) echo "$0: unknown option '$1'."; echo "'$0 --help' gives more options."; exit 1;;
	esac
	
	shift
done

# The main program, depending on the fact that all additional parameters are already passed.
# Make sure there are enough arguments...
if [ $# -eq 0 ]
then
	echo "$0: missing operands"
	echo "'$0 --help' gives more options."
	exit 1
fi

f=()
c=()
s=0
t=
while [ "$1" != "" ]
do
	f[${#f[*]}]="$1"
	c[${#c[*]}]="$2"
	shift 2
done

while [ $s -lt ${#f[*]} ]
do
	t="$t ${f[$s]}"
	s=$[$s+1]
done

function low_begin()
{
	# Initialize our screen, and such stuff.
	if [ $nomodechg -ne 1 ]
	then
		echo -ne '\e[?1049h\e[?25l'
	fi
}

function low_end()
{
	# Reset our screen and do some really needed cleanup.
	if [ $nomodechg -ne 1 ]
	then
		echo -ne '\e[?1049l\e[?25h'
	fi
	exit
}

function update_termsize()
{
	export w=$(stty size | cut -d' ' -f 2)
	export h=$(stty size | cut -d' ' -f 1)
}

function throw_flakes()
{
	# Throw one line of snowflakes. The frequency can be given as arguments.
	# The numbers are in x of 100 flakes.
	local ctr r s t _f
	_f=()
	while [ "$1" != "" ]
	do
		_f[${#_f[*]}]="$1"
		shift
	done
	
	echo -ne '\e[H\e[L'
	
	ctr=1
	while [ $ctr -lt $w ]
	do
		r=$RANDOM
		s=0
		t=0
		while [ $s -lt ${#_f[*]} ]
		do
			t=$[$t+${_f[$s]}]
			if [ $r -le $[(32768/100)*$t] ]
			then
				echo -n "${c[$s]}"
				t=0
				break
			fi
			
			s=$[$s+1]
		done
		if [ $t -ne 0 ]
		then
			echo -n " "
		fi
		
		ctr=$[$ctr+1]
	done
	
	sleep 0.01
}

function begin()
{
	# Called to slightly fade the snowflakes in.
	local ctr s t
	
	ctr=0
	while [ $ctr -lt $h ]
	do
		s=0
		t=
		while [ $s -lt ${#f[*]} ]
		do
			t="$t $[($ctr*${f[$s]})/$h]"
			s=$[$s+1]
		done
		throw_flakes $t
		ctr=$[$ctr+1]
	done
}

function end()
{
	# Called to slightly fade the snowflakes out.
	local ctr s t
	
	echo -ne '\e[M'
	
	ctr=$h
	while [ $ctr -gt 0 ]
	do
		s=0
		t=
		while [ $s -lt ${#f[*]} ]
		do
			t="$t $[($ctr*${f[$s]})/$h]"
			s=$[$s+1]
		done
		throw_flakes $t
		ctr=$[$ctr-1]
	done
	
	ctr=$h
	while [ $ctr -gt 0 ]
	do
		echo -ne '\e[L'
		sleep 0.1
		ctr=$[$ctr-1]
	done
	low_end
	exit
}

trap end 2
trap low_end 9
trap low_end 15

update_termsize
low_begin
begin
while true
do
	throw_flakes $t
	if [ $RANDOM -lt $[(32768/100)*10] ]
	then
		update_termsize
	fi
done