#include <stdio.h>
#include <stdlib.h>
#include <cstring>

#include "grammar.h"
#include "grammar.tab.h"

#define	NSTACK	256
#define	NPROG	2000

namespace Private {

typedef struct Setting {

    Datum	stack[NSTACK];	/* the stack */
    Datum	*stackp;	/* next free spot on stack */

    Inst	prog[NPROG];	/* the machine */
    Inst	*progp;		/* next free spot for code generation */
    Inst	*pc;		/* program counter during execution */

} Setting;

Datum	*stack       = NULL;	/* the stack */
Datum	*stackp      = NULL;	/* next free spot on stack */

Inst	*prog        = NULL;	/* the machine */
Inst	*progp       = NULL;	/* next free spot for code generation */
Inst	*pc          = NULL;	/* program counter during execution */

void initcode(char *name)	/* initialize for code generation */
{
        printf("setting %s\n", name);
        Setting *s = (Setting*) malloc(sizeof(Setting));
        memset((void *) s, 0, sizeof(Setting));

        prog = (Inst *) &s->prog;
        stack = (Datum *) &s->stack;

	stackp = stack;
	progp = prog;
}

int push(Datum d)		/* push d onto stack */
{
	if (stackp >= &stack[NSTACK])
		abort();
 	//	execerror("stack overflow", (char *) 0);
	*stackp++ = d;
	return 0;
}

Datum pop()	/* pop and return top elem from stack */
{
	if (stackp <= stack)
	       abort();
	//	execerror("stack underflow", (char *) 0);
	return *--stackp;
}

int constpush()	/* push constant onto stack */
{
	Datum d;
	d.val = ((Symbol *)*pc++)->u.val;
	printf("pushing %d\n", d.val);
	push(d);
	return 0;
}

int strpush()	/* push constant onto stack */
{
	Datum d;
	d.str = ((Symbol *)*pc++)->u.str;
	printf("pushing %s\n", d.str);
	push(d);
	return 0;
}


int varpush()	/* push variable onto stack */
{
	Datum d;
	d.sym = (Symbol *)(*pc++);
	printf("var pushing %s", d.sym->name);
	push(d);
	return 0;
}


int eval()		/* evaluate variable on stack */
{
	Datum d;
	d = pop();
	//if (d.sym->type == UNDEF)
	//	execerror("undefined variable", d.sym->name);
	d.val = d.sym->u.val;
	push(d);
	return 0;
}

int add()		/* add top two elems on stack */
{
	Datum d1, d2;
	d2 = pop();
	d1 = pop();
	printf("adding %d %d\n",d1.val, d2.val);
	d1.val += d2.val;
	push(d1);
	return 0;
}

int negate()
{
	Datum d;
	d = pop();
	d.val = !d.val;
	push(d);
	return 0;
}

int assign()	/* assign top value to next value */
{
	Datum d1, d2;
	d1 = pop();
	d2 = pop();
	/*if (d1.sym->type != VAR && d1.sym->type != UNDEF)
		execerror("assignment to non-variable",
			d1.sym->name);*/
	d1.sym->u.val = d2.val;
	d1.sym->type = NAME;
	push(d2);
	return 0;
}

int print()		/* pop top value from stack, print it */
{
	Datum d;
	d = pop();
	printf("\t%d\n", d.val);
	return 0;
}

Inst *code(Inst f)	/* install one instruction or operand */
{
 	Inst *oprogp = progp;
	if (progp >= &prog[NPROG])
		abort();
	*progp++ = f;
	return oprogp;
}

void execute(Inst *p)	/* run the machine */
{
	for (pc = p; *pc != STOP; )
		(*(*pc++))();
}

}