%{

/* compile: leg -o calc.c calc.leg
 *			cc -o calc calc.c
 *
 * run:		echo "2+3" | ./calc
 */

#define NSYMBOLS 256

union u_t {
	int		ival;
	char	*sval;
};

typedef struct symbol_t {
	char	*ident;
	int		value;
} symbol_t;

typedef struct table_t {
	symbol_t	*array[NSYMBOLS];
	int			size;
} table_t;

#define YYSTYPE union u_t
YYSTYPE yylval;

table_t table;

// This buffer is for storing yytext identifier during assignement
char *ident_buf;

symbol_t* new_symbol(char *ident, int value)
{
	symbol_t* s = malloc(sizeof(symbol_t));

	char * ident_copy = malloc(strlen(ident) + 1);
	strcpy(ident_copy, ident);

	free(ident_buf);

	s->ident = ident_copy;
	s->value = value;
	return s;
}

symbol_t * add(char *ident, int value)
{
	symbol_t *new_s = new_symbol(ident, value);

	if (table.size >= NSYMBOLS) {
		printf("Error: too many symbols\n");
		exit(1);
	}
	int i = table.size;
	table.array[i] = new_s;
	table.size++;
	return table.array[i];
}

// Returns int value of identifier, when identifier is undefined, returns 0
int get_value(const char *ident)
{
	for(int i=0; i < table.size; i++) {
		//printf("comparaison %s, %s\n", table.array[i].ident, ident);
		if (strcmp(table.array[i]->ident, ident) == 0) {
			return table.array[i]->value;
		}
	}
	// printf("'%s' identifier not found\n", ident);
	return 0;
}

%}

start	=	e:exp					{ yylval = e }

exp		=	- (a:assign				{ $$ = a }
			| s:sum 				{ $$ = s }
			)

assign	=	l:IDENT 				{ ident_buf = strdup(l.sval) } 
			EQUAL n:sum				{ $$.ival = add(ident_buf, n.ival)->value;}

sum		=	PLUS* l:prod
			( PLUS+ r:prod			{ l.ival += r.ival }
			| MINUS r:prod			{ l.ival -= r.ival }
			)*						{ $$.ival = l.ival }

prod	=	l:neg
			( MULTI		r:neg		{ l.ival *= r.ival }
			| DIVIDE	r:neg		{ l.ival /= r.ival }
			| MODULO	r:neg		{ l.ival %= r.ival }
			)*						{ $$.ival = l.ival }

neg		=	MINUS n:neg				{ $$.ival = -n.ival }
			| n:value				{ $$.ival = n.ival }

value	=	n:NUMBER				{ $$.ival = n.ival }
			| l:IDENT				{ $$.ival = get_value(l.sval) }

-		=	[ \t]*
NUMBER	=	< [0-9]+ >	-			{ $$.ival = atoi(yytext) }
PLUS	=	'+'			-
MINUS	=	'-'			-
MULTI	=	'*'			-
DIVIDE	=	'/'			-
MODULO	=	'%'			-
EQUAL	=	'='			-
IDENT	=	< [a-zA-Z]+ >	-		{ $$.sval = yytext }

%%

int main(int argc, char **argv)
{
	while (yyparse()) {
		printf("%d\n", yylval.ival);
	}

	return 0;
}