# Copyright 2009, Chris F.A. Johnson
# Released under the terms of the GNU General Public License
# http://www.gnu.org/licenses/gpl.html

#@ These bash functions store a grid as a single string.
#@ They work only on square grids, NxN
#@ Most require the size of the grid to be stored in $gridsize

#@ DESCRIPTION: Fill N x N grid with a character
#@ USAGE: initgrid gridname size character
initgrid()
{
  [ $# -lt 2 ] && return 1
  local grid
  size=$(( $2 * $2 ))
  printf -v grid "%$size.${size}s" ' '
  eval "$1=\${grid// /${3:-.}}"
}

#@ DESCRIPTION: Store row/column's index into string in $_GRIDPOS
#@ USAGE: _gridpos row column [gridsize]
_gridpos()
{
  [ $# -lt 2 ] && return 1
  local gridsize=${3:-$gridsize}
  _GRIDPOS=$(( ($1 - 1) * $gridsize + $2 ))
}

#@ DESCRIPTION: Get character from grid in row Y, column X
#@ USAGE: getgrid gridname row column var
getgrid()
{
  [ $# -lt 4 ] && return 1
  _gridpos $2 $3
  eval "$4=\${$1:_GRIDPOS-1:1}"
}

#@ DESCRIPTION: Insert character int grid at row and column
#@ USAGE: putgrid gridname row column char
putgrid()
{
  local left right _GRIDPOS _GRID gridname=$1
  _gridpos $2 $3
  eval "left=\${$1:0:_GRIDPOS-1}
  eval "right=\${$1:_GRIDPOS}
  _GRID=$left$4$right
  eval "$gridname=\$_GRID"
}

#@ DESCRIPTION: print grid to stdout
#@ USAGE: showgrid gridname
showgrid()
{
  local _grid
  eval "_grid=\${$1}"
  while [ -n "$_grid" ]
  do
    row=${_grid:0:gridsize}
    printf "%s\n" "$row"
   _grid=${_grid#"$row"}
  done
}