#!/bin/sh   


  # File: test.sh
  
  verbose=2; # TODO

  # for debugging purposes; TODO - delete after finishing
  if [ "$1" == "-x" ]; then
    set -x;
    shift 1
  fi
  
  expr2() { # expr without output
   
    result=$( expr "$@" )
    return $( expr $result "=" 0 )  
  }
  
  usage() {
  
    echo "Usage: "; # TODO   
  }


  process() {
    
    num_stack=0;
    op_stack=0;
    number1=0;
    number2=0;
    op="";    
    opened_with_logical_switch=$1;
    deepness=$2    
    shift 2;
    
    num_stack_in() {  # number stack
      
      num_stack=$(( $num_stack + 1 ));

      echo "Deepness: $deepness; Num_stack: $num_stack; Value: $1" >&2      

      eval "number${num_stack}=$1"            
      
      if expr2 $num_stack ">" 2; then
      
        echo "Error: Stack overflow";
        exit 1;
      
      elif expr2 $num_stack "=" 2; then      
        return 0;      
      else       
        return 1                    
      fi       
    }
    
    op_stack_in() {  # operation stack
    
      op_stack=$(( $op_stack + 1 ));
      eval "op${op_stack}=\"$1\""      
                
    }

    op_stack_out() {
    
      eval "op=\$op${op_stack};"
      op_stack=$(( $op_stack - 1 ));
    }

    do_op() {
    
      op_stack_out;
      
      case "$op" in        
        "="|">"|"<"|"!=") num_stack=0;
                          num_stack_in $(expr $number1 "$op" $number2);;        
 
                    "-a") num_stack=0;
                          echo $number1 $number2 >&2; 
                          if expr2 $number1 "=" 1 && expr2 $number2 "=" 1; then
                            num_stack_in 1;
                          else
                            num_stack_in 0;
                          fi;;            
                    "-o") num_stack=0;
                          
                          if expr2 $number1 "=" 1 || expr2 $number2 "=" 1; then
                            num_stack_in 1;
                          else
                            num_stack_in 0;
                          fi;;            
                       *) echo "Unknown operation: "'`'"$op\""; exit 1;;
      esac
    
    }

    
    while expr2 $# ">" "0"; do
    
      switch="$1"
      echo 'Deepness: '"$deepness"'; Switch: `'"$switch\"" >&2
      shift      
      
      case "$switch" in
         
          ')')  #if expr2 $opened_with_bracket "=" 0; then
                #  echo "$number1 "$(($# - 1)); # process ")" again
                #else
                  echo "$number1 $#";
                #fi   
                return 0;;
         
          '(')  partial_result=$(process 0 $(( $deepness + 1 )) "$@");
                switch=$(echo "$partial_result" | cut -d" " -f 1);
                remaining_switches=$(echo "$partial_result" | cut -d" " -f 2);                
                shift $(($# - $remaining_switches));; # shift after ")"
         
          # test if $1 is empty
          "-z") if expr2 "dd${1}dd" "=" "dddd"; then
                  switch=1;
                else
                  switch=0;
                fi
                shift;;

          "-n") if expr2 "dd${1}dd" "=" "dddd"; then
                  switch=0;
                else
                  switch=1;
                fi
                shift;;                                  
      esac
      
      case "$switch" in      
                 "-a"|"-o") if expr2 $opened_with_logical_switch "=" 1; then
                              # $# + 1 because we want to process -a or -o again. 
                              # (in this function the switch -a / -o are shifted)
                              echo "$number1 "$(($# + 1)); 
                              return 0; 
                            fi                                              

                            op_stack_in "$switch";

                            partial_result=$(process 1 $(( $deepness + 1 )) "$@");
                            
                            if echo "$partial_result" | grep -q '^[10]\{1\}$'; then
                              switch=$partial_result;
                              remaining_switches=0;
                            else                            
                              switch=$(echo "$partial_result" | cut -d" " -f 1);
                              remaining_switches=$(echo "$partial_result" | cut -d" " -f 2);
                            fi
                            
                            if num_stack_in $switch; then
                              do_op # with "$number1" "$number2"
                            fi
                            shift $(( $# - $remaining_switches ));;                            
                    [0-9]*) if num_stack_in "$switch"; then
                              do_op # with "$number1" "$number2"
                            fi;;
                       "=") op_stack_in "=";;
                      "!=") op_stack_in "!=";;
                       ')') op_stack_in ')';;
                       '(') op_stack_in '(';;
                     '-gt') op_stack_in '>';;
                     '-lt') op_stack_in '<';;
                         *) echo 'Switch `'"$switch\" - not known"; exit 2;;
      esac      
    
    done;    
    
    if expr2 $num_stack "=" 1 && expr2 $number1 "=" "1"; then      
      echo 1        
      return 0;
    else
      echo 0
      return 1;
    fi    
  
  }
  
  
  # MAIN SCRIPT STARTS HERE
  # ========================= 
  
  if expr2 "$#" "=" "0"; then  
    usage;    
  else               
    
    process 0 "1" "$@"               # verbose version
    # process "1" "$@" >/dev/null    # silent version
    exit $?   
  fi