#  Copyright (c) 1997-2015
#  Ewgenij Gawrilow, Michael Joswig (Technische Universitaet Berlin, Germany)
#  http://www.polymake.org
#
#  This program is free software; you can redistribute it and/or modify it
#  under the terms of the GNU General Public License as published by the
#  Free Software Foundation; either version 2, or (at your option) any
#  later version: http://www.gnu.org/licenses/gpl.txt.
#
#  This program is distributed in the hope that it will be useful,
#  but WITHOUT ANY WARRANTY; without even the implied warranty of
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#  GNU General Public License for more details.
#-------------------------------------------------------------------------------

# TODO: introduce "tropical Monomials" interpreting "DD x" as "x ** DD"
# and get rid of this function

# This file contains methods to parse a tropical polynomial in the form
# "max(3x+4,...)" and the like.

# @category Data Conversion
# This converts a string into a tropical polynomial. The syntax for the string is as follows:
# It is of the form "min(...)" or "max(...)" or "min{...}" or "max{...}", where ...
# is a comma-separated list of sums of the form "a + bx + c + dy + ...", where a,c are 
# rational numbers, b,d are Ints and x,y are variables. 
# Such a sum can contain several such terms for the same variable and they need not be in any order. 
# Any text that starts with a letter and does not contain any of +-*,(){} or whitespace can be a variable.
# A term in a sum can be of the form "3x", "3*x", but "x3"will be interpreted as 1 * "x3".
# Coefficients should not contain letters and there is no evaluation of arithmetic, i.e. "(2+4)*x" does 
# not work (though "2x+4x" would be fine). 
# In fact, further brackets should only be used (but are not necessary!) for single coefficienst, 
# e.g. "(-3)*x".
# Warning: The parser will remove all brackets before parsing the individual sums.
# If no further arguments are given, the function will take the number of occuring variables
# as total number of variables and create a ring for the result. The variables will be sorted alphabetically.
# @param String s The string to be parsed
# @param String vars Optional. A list of variables. If this is given, all variables used in s must match one of the variables in this list. 
# @return Polynomial<TropicalNumber<Addition,Rational> >, where Addition depends on 
# whether min or max was used in the string.
user_function toTropicalPolynomial(String; @) {
	my ($string,@vars) = @_;

	#Remove any whitespace before parsing
	$string =~ s/\s+//g;

	#Check if variables have been given
	my $vars_defined = (scalar(@vars) > 0);
	my $varset = new Set<String>(\@vars);
	if($vars_defined) {
		#If there are double variables, throw an error
		if( $varset->size() < scalar(@vars)) {
			die "Error: Variable names must be unique.";
		}
	}

	#First separate min/max from the list of the functions
	# The first part will contain min or max, the second the rest
	my @minmax_separator = ($string =~ /^(max|min)[\(\{](.+)[\)\}]$/i);
	
	if(scalar(@minmax_separator) != 2) {
		die "Error: Wrong syntax. See documentation.";
	}

	#Determine whether we're using min or max
	my $uses_min = ($minmax_separator[0] =~ /^min$/i);

	#Remove any brackets from the function list and separate by commas
	$minmax_separator[1] =~ s/[\(\{\)\}]+//g;
	my @functionlist = split(/,/,$minmax_separator[1]);

	#This will store the monomials
	#The i-th element corresponds to the i-th function. It is a reference to a 
	#hash, which maps variable names to exponents.
	# (We need this, since we might not know until the end how many variables we have and
	# what order they appear in)
	my @monomial_maps=();

	#This stores the coefficients of each function.
	my $coefficients = $uses_min ? (new Vector<TropicalNumber<Min> >(scalar(@functionlist))) :
												(new Vector<TropicalNumber<Max> >(scalar(@functionlist)));
	
	#Now parse every single function by splitting at + or -
	for my $index (0 .. scalar(@functionlist)-1) {
		my %functionCoeffMap = ();

		$coefficients->[$index] = $uses_min ? (new TropicalNumber<Min>(0)) : (new TropicalNumber<Max>(0));

		#We split along any consecutive sequence of + and -, keeping the actual signs for counting
	  	my @termlist = split(/[\+\-]+/,$functionlist[$index]); #We split along any consecutive sequence of + and -
	  	my @signlist = ($functionlist[$index] =~ /[\+\-]+/g);

		#If the first terms empty that means there are signs before the actual first term
		if($termlist[0] eq "") {
			shift(@termlist);
		}
		#If not then we don't have a sign for the first term and add it
		else {
			@signlist = ("+",@signlist);
		}
		#If the last term is empty that means there is an empty term at the end. 
		if($termlist[scalar(@termlist)-1] eq "") {
			die "Error: Empy term at the end of function $functionlist[$index]";
		}

		#Now every element in signlist corresponds to an element in termlist. We count the number of -'s
		#to determine the actual sign.
		for my $termindex (0 .. scalar(@termlist)-1) {
			my $minussigns = scalar(($signlist[$termindex] =~ tr/\-//));
			if ($minussigns % 2) { #If the number of -'s is odd, set sign to -
				$termlist[$termindex] = "-" . $termlist[$termindex];
			}
		}
		
		#Now parse every single term
		for my $term (@termlist){
			#Separate into coefficient and variable
	      my @termsep = ($term =~ /^(\-?[^a-zA-Z\*]*)?\*?([a-zA-Z]+[^\+\-\(\)\{\}]*)?$/);

			#Check for basic validity
			#If both parts are empty, we have a term of the form "*", which is nonsense
			if(scalar(@termsep) != 2) {
				die "Error: $term has invalid form. See documentation for allowed syntax.";
			}
			if($termsep[0] eq "" && $termsep[1] eq "") {
				die "Error: $term has invalid form. See documentation for allowed syntax.";
			}

			#Parse the coefficient (if there is none, set it to 1, since there must be a variable)
			my $rational_termcoeff = new Rational($termsep[0] eq ""? 1: ($termsep[0] eq "-"? -1 : $termsep[0]));
			my $termcoeff = $uses_min? (new TropicalNumber<Min>($rational_termcoeff)) : (new TropicalNumber<Max>($rational_termcoeff));

			#If there's no variable, add to the coefficient, otherwise add to the correct monomial
			#(Note that we're already using tropical arithmetic here!)
			if($termsep[1] eq "") {
				$coefficients->[$index] *= $termcoeff;
			}
			else {
				#Add the variable, if none were given in the function call. 
				if(!$vars_defined) {
					$varset = $varset + (new String($termsep[1]));
				}
				#Otherwise check if it's an allowed variable
				else {
					if(!$varset->contains($termsep[1])) {
						die "Error: Variable $termsep[1] is not in the list of variables.";
					}
				}
			}

			#Save the coefficient in the hash map
			if(!defined($functionCoeffMap{$termsep[1]})) {
				$functionCoeffMap{$termsep[1]} = $termcoeff;
			}
			else {
				$functionCoeffMap{$termsep[1]} *= $termcoeff;
			}			
		}#END parse all terms
		
		$monomial_maps[$index] = \%functionCoeffMap;
	}#END for(functionlist)

	#If no variables were given, we remove double variables and sort them alphabetically
	if(!$vars_defined) {
		if($varset->size() == 0) { die "Error: There must be at least one variable.";}
		@vars = sort(@{$varset});		
	}

	#Now create exponent matrix
	my $monom_matrix = new Matrix<Int>(scalar(@functionlist), scalar(@vars));
	for my $func (0 .. scalar(@functionlist)-1) {
		my $hashref = $monomial_maps[$func];
		my %monmap = %$hashref;
		for my $v (0 .. scalar(@vars)-1) {
			$monom_matrix->elem($func,$v) = defined($monmap{$vars[$v]})? $monmap{$vars[$v]} : 0;
		}
	}

	my $min= $uses_min ? typeof Min : typeof Max;
	return new Polynomial<TropicalNumber<$min>>($coefficients, $monom_matrix);

}#END toTropicalPolynomial(String,...)
