#!/bin/bash
#
# ex1.bash: Advent2020 game, day 3/game 2.

CMD=${0##*/}

XMOVES=(1 3 5 7 1)								  # moves right
YMOVES=(1 1 1 1 2)								  # moves down
declare -i linelen=0 modpos=0 res=1 ypos=1
declare -a xpos xcount

read -r line									  # ignore 1st line

while read -r line; do
	(( ypos++ ))
	(( linelen = ${#line} ))

	for ((i=0; i<${#XMOVES[@]}; ++i)); do
		if ((ypos % YMOVES[i] == 0)); then
			(( xpos[i] += XMOVES[i] ))			  # move right
			(( modpos = (xpos[i] % linelen) ))
			[[ ${line:modpos:1} = \# ]] && ((xcount[i]++))
		fi
	done
done

for ((i=0; i<${#XMOVES[@]}; ++i)); do
	(( res *= xcount[i] ))
done
printf "%s : lines=%d res=%d\n " "$CMD" $ypos $res
exit 0