#!/usr/bin/perl
#
# Matthew Reeves
#
# This is a perl program to act as a scanner/interpreter for an imaginary language
#

use Modern::Perl;

my $filename = $ARGV[0];
my $filestring;
my $string;
my $position = 0;
my %table;

open (FILE, $filename) or die "\nUnable to open file: $filename: $!\n";

while (<FILE>)
{
	$filestring = $_;

	if ($filestring =~ /\/\/.+/)
	{
		$filestring = "";	
	}
	
	if ($filestring =~ /func.+/)
	{
		$filestring = "";	
	}
	
	if ($filestring =~ /endfunc/)
	{
		$filestring = "";	
	}
	
	if ($filestring ~~ "\n")
	{
		$filestring = "";	
	}
	
	if ($filestring =~ /^\s*\w+:/)
	{
		$filestring =~ s/:/:;/g;
	}
	
	if ($filestring =~ /^\s+.+/)
	{
		$filestring =~ s/^\s+//g;
	}
	
	if ($filestring =~ /\s+$/)
	{
		$filestring =~ s/\s+$/\n/g;
	}

	if ($filestring =~ /^if/i)
	{
		$filestring .= ";"; 
	}

	$string .= $filestring;	
}

close (FILE);

$string =~ s/\n//g;

my @stack = split(/;/, $string);

my $len = @stack;

while ($position < $len)
{
        if ($stack[$position] ~~ /^write/i)
        {
                &write();
        }
        elsif ($stack[$position] ~~ /^read/i)
        {
                &read();
        }
        elsif ($stack[$position] ~~ /^\w+:/i)
        {
		$position++;
        }
	elsif ($stack[$position] ~~ /^to/i)
	{
		&goto();
	}
	elsif ($stack[$position] ~~ /^if/i)
	{
		&if();
	}
	elsif ($stack[$position] ~~ /^\w+/i)
	{
		&assign();
	}
	else
	{
		$position++;
	}
}

sub write
{
	my $tmp;

	if ($stack[$position] =~ /^write\s*\(\s*"(.*)?"\s*\)/i)
	{
		say "$1";
	}
	elsif ($stack[$position] =~ /^write\s*\(\s*(\w*)?\s*\)/i)
	{
		say "$table{$1}";
	}
	$position++;
}

sub read
{
	my $tmp;

	if ($stack[$position] =~ /^read\s*\(\s*(\w*)?\s*\)/i)
	{
		$tmp = <STDIN>;
		chomp $tmp;
		$table{$1} = $tmp;
	}

	$position++;
}

sub goto
{
	my $tmp;
	my $count = 0;

	if ($stack[$position] =~ /^to\s+(.+)/i)
	{
		$tmp = $1.":";
		
		while ($count < $len)
		{
			if ($stack[$count] ~~ $tmp)
			{
				$position = $count;
				$count = $len;
			}
			else
			{
				$count++;
			}
		}
	}
	else
	{
		$position++;
	}
}

sub if
{
	my $compare;
	my $test1;
	my $test2;

	if ($stack[$position] =~ 
		/^if\s*\(\s*(\w\w)\s*\(\s*(\w+|\d+)?\s*,\s*(\w+|\d+)?\s*\)/i)
	{
		if ($2 ~~ /^\d+$/)
		{
			$test1 = $2;
		}
		else
		{
			$test1 = $table{$2};
		}

		###########################################

		if ($3 ~~ /^\d+$/)
		{
			$test2 = $3;
		}
		else
		{
			$test2 = $table{$3};
		}

		###########################################

		if ($1 ~~ /gt/i)
		{
			if ($test1 > $test2)
			{
				$position++;
			}
			else
			{
				$position+=2;
			}	
		}
		elsif ($1 ~~ /lt/i)
		{
			if ($test1 < $test2)
			{
				$position++;
			}
			else
			{
				$position+=2;
			}	
		}
		elsif ($1 ~~ /eq/i)
		{
			if ($test1 == $test2)
			{
				$position++;
			}
			else
			{
				$position+=2;
			}	
		}
		elsif ($1 ~~ /ge/i)
		{
			if ($test1 >= $test2)
			{
				$position++;
			}
			else
			{
				$position+=2;
			}	
		}
		elsif ($1 ~~ /le/i)
		{
			if ($test1 <= $test2)
			{
				$position++;
			}
			else
			{
				$position+=2;
			}	
		}
		elsif ($1 ~~ /ne/i)
		{
			if ($test1 != $test2)
			{
				$position++;
			}
			else
			{
				$position+=2;
			}	
		}
	}
	elsif ($stack[$position] =~ /^if\s*\(\s*true\s*\)/i)
	{
		$position++;
	}
	else
	{	
		$position+=2;
	}
}

sub assign
{
	my $expr = $stack[$position];

	$expr =~ s/\s*=\s*/ = /g;
	$expr =~ s/\s*\+\s*/ \+ /g;
	$expr =~ s/\s*-\s*/ - /g;
	$expr =~ s/\s*\*\s*/ \* /g;
	$expr =~ s/\s*\/\s*/ \/ /g;
	$expr =~ s/\s*%\s*/ % /g;
	$expr =~ s/\s*\(\s*/ \( /g;
	$expr =~ s/\s*\)\s*/ \) /g;
	$expr =~ s/\s+/ /g;
	$expr =~ s/;//g;
	$expr =~ s/\n//g;

	my @arr = split(/ /, $expr);
	my $count = 0;
	my $eva = "";

	if ($expr =~ /\w+\s*=\s*\d+$/)
	{
		$table{$arr[0]} = $arr[2];
	}
	else
	{
		foreach (@arr)
		{
			if ($count > 1)
			{
				if ($_ ~~ /(\d+|\+|\/|-|%|\*|\(|\))/)
				{
					$eva .= $_;
				}
				else
				{
					$eva .= $table{$_};
				}
			}
			$count++;		
		}
		$table{$arr[0]} = eval "$eva";
	}

	$position++;
}