#!/bin/bash

stty -echo
trap 'end 130' EXIT INT; trap init_term WINCH

skip(){ if (( ${n:=1} > ${1:-1} )); then :; else ((n++)); false; fi; }

init_term(){
  IFS='[;' read -sp $'\e[999;999H\e[6n' -d R -rs _ LINES COLS
  ((ROWS=LINES-1)); ((snakeX=COLS/2)); ((snakeY=ROWS/2)); CENTER="$snakeY;$snakeX"

  printf '\e[?1049h\e[2J\e[?25l\e[?7l'
  rand_block
}

end(){ stty echo; printf '\e[?1049l\e[?25h\e[?7h'; exit "${1:-0}"; }

game_over(){
  local i
  until (( i > $1 )); do
    for _ in 1 7; do
      printf '\e[%sH\e[3D\e[3%dmGAME OVER\e[m' "$CENTER" "$_"
      sleep .1
    done; ((++i))
  done; end "$2"
}

read_keys(){
  local i
  case $1 in
    20) i=.7;; 19) i=.6;; 18) i=.5;; 17) i=.4;; 16) i=.3;; 15) i=.2;; 14) i=.1;;
    13) i=.09;; 12) i=.08;; 11) i=.075;; 10) i=.07;; 9) i=.065;; 8) i=.06;; 7) i=.055;;
    6) i=.05;; 5) i=.045;; 4) i=.04;; 3) i=.035;; 2) i=.03;; 1) i=.025;;
  esac

  while read -rsn1 -t "$i"; do
    [[ $REPLY == $'\e' ]]&& read -rsn2 -t "$i"; KEY="${REPLY^^}"
  done
}

status_bar(){
  printf '\e[999H\e[2K\e[1;32mSNAKE\e[m x:%d y:%d len:%d spe:%d' "$1" "$2" "$3" "$4"
}

rand_block(){
  ((blockX=SRANDOM%COLS+1)); ((blockY=SRANDOM%ROWS+1)); block="$blockY;$blockX"
  printf '\e[%sH\e[41m \e[m' "$block"
}

snake_direction(){
  case ${KEY:-$1} in
    Q) game_over 2;;
    H|A|\[D) (( dirX == 1 ))||{ dirX=-1 dirY=0; };;
    J|S|\[B) (( dirY == -1 ))||{ dirX=0 dirY=1; };;
    K|W|\[A) (( dirY == 1 ))||{ dirX=0 dirY=-1; };;
    L|D|\[C) (( dirX == -1 ))||{ dirX=1 dirY=0; };;
  esac; ((snakeX+=dirX)); ((snakeY+=dirY))
}

draw_snake(){ snake+=("$2;$1"); printf '\e[%sH\e[42m \e[m' "${snake[-1]}"; }

erase_snake(){ printf '\e[%sH \e[m' "${snake[0]}"; snake=("${snake[@]:1}"); }

consume_block(){ [[ $1 == "$block" ]]&&{ ((delay--)); ((len++)); rand_block; }; }

self_collision(){ [[ $1 == "${snake[-1]}" ]]&& game_over 4 1; }

wall_collision(){ (( $1 < 1|| $1 > COLS|| $2 < 1|| $2 > ROWS ))&& game_over 4 1; }

len=3 delay=20
init_term
for((;;)){
  status_bar "$snakeX" "$snakeY" "$len" "$delay"
  read_keys "$delay"
  snake_direction L; draw_snake "$snakeX" "$snakeY"
  wall_collision "$snakeX" "$snakeY"

  skip "$len"&&{
    erase_snake

    ((snakeBodyCount=${#snake[@]}-1))
    for _ in "${snake[@]::$snakeBodyCount}"; do
      consume_block "$_"
      self_collision "$_"
    done
  }
}