#!/bin/bash
max_x=40
max_y=40
hx=20 hy=20
tx=20 ty=20
len=1
cur_len=0
need_food=1
level0=0.1
level1=0.05
level2=0.025

direct=u
input(){
  echo -ne "\033[?25l"
  local aKey=(0 0 0 0)
  local cESC=`echo -ne "\033"`
  local index
  while :
  do
    read -s -n 1 key
    aKey=( "${aKey[@]:1}" "$key")
    if [[ $key${aKey[2]} = $cESC$cESC ]] ; then kill -29 $1; break
    elif [[ "${aKey[@]:1:2}$key" = "${cESC} [A" ]] ; then kill -25 $1 ## direct=u
    elif [[ "${aKey[@]:1:2}$key" = "${cESC} [B" ]] ; then kill -26 $1 ## direct=d
    elif [[ "${aKey[@]:1:2}$key" = "${cESC} [C" ]] ; then kill -27 $1 ## direct=r
    elif [[ "${aKey[@]:1:2}$key" = "${cESC} [D" ]] ; then kill -28 $1 ## direct=l
    else continue
    fi
  done
  echo -ne "\033[?25h"
}
draw_head(){
   tput cup $2 $(( $1<<1 ))
   echo -ne "\033[1;47m  \033[m"
}
draw_tail(){
   tput cup $2 $(( $1<<1 ))
   echo -ne "\033[1;40m  \033[m"
}
run(){
  trap '[[ $direct != d ]] && direct=u' 25
  trap '[[ $direct != u ]] && direct=d' 26
  trap '[[ $direct != l ]] && direct=r' 27
  trap '[[ $direct != r ]] && direct=l' 28
  trap 'exit' 29

  while :
  do
    eval "[[ \"\$m${hx}_${hy}\" = f ]] && (( ++len )) && need_food=1"
    draw_head $hx $hy
    eval m${hx}_${hy}=$direct
    case $direct in
      u) (( --hy )); (( hy < 0 )) && break ;;
      d) (( ++hy )); (( hy > max_y )) && break  ;;
      r) (( ++hx )); (( hx > max_x )) && break ;;
      l) (( --hx )); (( hx < 0 )) && break ;;
    esac
    eval "[ -n \"\${m${hx}_${hy}}\" -a ! \"\${m${hx}_${hy}}\" = f ] && break"
    (( ++cur_len ))
    if (( len < cur_len )) ; then
      (( --cur_len ))
      eval local d=\$m${tx}_${ty}
      draw_tail $tx $ty
      unset m${tx}_${ty}
      case $d in
        u) (( --ty ));;
        d) (( ++ty ));;
        r) (( ++tx ));;
        l) (( --tx ));;
      esac
    fi
    if [ $need_food = 1 ] ; then
      draw_food && need_food=0
    fi
    sleep $level1
  done
  kill $1
}
draw_food(){
 local fx=$(( $RANDOM % max_x + 1 ))
 local fy=$(( $RANDOM % max_y + 1 ))
 eval local f=\$m${fx}_${fy}
 if [[ -z $f ]] ; then
    tput cup $fy $(( $fx<<1 ))
    eval m${fx}_${fy}=f
    echo -ne "\033[1;45m  \033[m"
    return 0
 fi
 return 1
}
draw_wall(){
  for (( i=0; i<=max_x; i++ ))
  do
    tput cup 0 $(( $i<<1 ))
    eval m${i}_0=w
    echo -ne "\033[1;46m  \033[m"
  done

  for (( i=0; i<=max_x; i++ ))
  do
    eval m${i}_$max_y=w
    tput cup $max_y $(( $i<<1 ))
    echo -ne "\033[1;46m  \033[m"
  done

  for (( j=0; j<=max_y; j++ ))
  do
    tput cup $j 0
    echo -ne "\033[1;46m  \033[m"
    tput cup $j $(( max_x<<1 ))
    echo -ne "\033[1;46m  \033[m"
    eval m0_$j=w m${max_x}_$j=w
  done
}
clear
draw_wall
run $$&
input $!