#!/usr/bin/env ksh

# '_' : unclaimed
# 'O' : player
# 'X' : AI
set -A board "_ _ _" "_ _ _" "_ _ _"

# manual
function instructions {
   echo "type position to claim (x:y)"
   echo "type 'q' to quit"
}

# if check founds a connected line, this determines who won
function get_outcome {
   [ $1 = "X" ] && echo "lost" || echo "won"
}

function check {
   # rows
   for row in "${board[@]}"; do
      if [[ $row = "O O O" || $row = "X X X" ]]; then
         echo $(get_outcome $(echo row | awk '{print $1}'))
         return
      fi
   done

   # columns
   local r1
   local r2
   local r3
   set -A r1 ${board[0]}
   set -A r2 ${board[1]}
   set -A r3 ${board[2]}

   for i in `seq 0 2`; do
      local column="${r1[$i]} ${r3[$i]} ${r2[$i]}"
      if [[ $column = "O O O" || $column = "X X X" ]]; then
         echo $(get_outcome ${r1[$i]})
         return
      fi
   done

   # diagonals
   local d1="${r1[0]} ${r2[1]} ${r3[2]}"
   local d2="${r3[0]} ${r2[1]} ${r1[2]}"
      if [[ $d1 = "O O O" || $d2 = "O O O" || $d1 = "X X X" || $d2 = "X X X" ]]
      then
         echo $(get_outcome ${r2[1]})
         return
      fi
  
   # tie
   if [[ $(echo ${board[@]} | grep '_') = '' ]]; then
      echo "tie"
      return
   fi

   echo "nothing"
}

function player_turn {
   read pos?'> '

   # quit
   [ "$pos" = 'q' ] && exit 0

   # validate input
   [[ "$pos" = [012]:[012] ]] || { player_turn; return; }

   local x=$(echo $pos | awk -F ':' '{print $1}')
   local y=$(echo $pos | awk -F ':' '{print $2}')

   # claim if unclaimed
   local row
   set -A row ${board[$y]}

   if [ ${row[$x]} = '_' ]; then
      row[$x]='O'
      board[$y]=${row[@]}
   else
      player_turn
   fi
}

# determines how beneficial would some play be for AI
function ai_try { # x y
   local outcome
   local row
   set -A row ${board[$2]}

   # check if it would win the game
   row[$1]='X'
   board[$2]=${row[@]}
   outcome=$(check)

   # if not, check if it would win for the player
   if [ $outcome != 'lost' ]; then
      row[$1]='O'
      board[$2]=${row[@]}
      outcome=$(check)
   fi
  
   # change back state
   row[$1]='_'
   board[$2]=${row[@]}

   echo $outcome
}

function ai_turn {
   # possible spaces
   local possible
   # needs local to be local, but that somehow makes it persistent
   # unset clears it
   unset possible
   set -A possible
   # these would prevent player from winning
   local block
   unset block
   set -A block

   local to_play

   # gather all possible plays
   for y in `seq 0 2`; do
      local row
      set -A row ${board[$y]}

      for x in `seq 0 2`; do
         if [[ ${row[$x]} = "_" ]]; then
            case $(ai_try $x $y) in
               # if it would win, play it
               "lost") to_play="$x $y" ;;
               # this is how you append I guess
               "won") block[${#block[@]}]="$x $y" ;;
               *) possible[${#possible[@]}]="$x $y" ;;
            esac
         fi
      done
   done

   # choose which one to play
   if [[ -z $to_play ]]; then
      # prefer blocks
      if [[ ${#block[@]} != 0 ]]; then
         to_play="${block[$(( RANDOM % ${#block[@]} ))]}"
      else
         to_play="${possible[$(( RANDOM % ${#possible[@]} ))]}"
      fi
   fi

   # play
   local x=$(echo $to_play | awk '{print $1}')
   local y=$(echo $to_play | awk '{print $2}')

   local row
   set -A row ${board[$y]}
   row[$x]="X"
   board[$y]=${row[@]}
}

function display {
   local i=0

   echo "\n     0 1 2"
   for row in "${board[@]}"; do # needs to be in quotes
      echo "   $i $row"
      ((i++))
   done
}

function lost {
   display
   echo 
   echo "###############"
   echo "## YOU LOST! ##"
   echo "###############"
   exit 0
}

function won {
   display
   echo 
   echo "##############"
   echo "## YOU WON! ##"
   echo "##############"
   exit 0
}

function tie {
   display
   echo 
   echo "#################"
   echo "## IT'S A TIE! ##"
   echo "#################"
   exit 0
}

function play {
   instructions
   local turn="player"

   while true; do
      if [ $turn = "player" ]; then
         display
         player_turn
         turn="ai"
      else
         ai_turn
         turn="player"
      fi

      case "$(check)" in
         "lost") lost ;;
         "won") won ;;
         "tie") tie ;;
      esac
   done
}

play