#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdint.h>
#include <stdbool.h>


// Standard words:
// arithmetic
// + - / * =: byte arithmetic
// ^ & |: bitwise boolean arithmetic
// p pop
// d dup
// s swap
// b push next byte
// w push next 2 bytes
// l push next 4 bytes
// $ pop N, push N bytes, push N
// ? if
// , else
// # end
// : start def/special
// ; end def/return
// if upper case, call word
// . print

#define BFORTH_PGM_SIZE  (1024)
#define BFORTH_STACK_SIZE  (64)
#define BFORTH_RSTACK_SIZE  (32)

const uint8_t * bf_prog = NULL;

const uint8_t * bfdict[26];
uint8_t bfvars[26];
uint8_t bf_stack[BFORTH_STACK_SIZE];
const uint8_t * bf_linkstack[BFORTH_RSTACK_SIZE];
uint8_t * bf_stacktop;
const uint8_t ** bf_linkstacktop;
const uint8_t * bf_pc;

static void BF_Scan(uint8_t word)
{
    while(*bf_pc != word)
        ++bf_pc;
    ++bf_pc;
}

#define DSTKPUSH(x)  (*(bf_stacktop++) = x)
#define DSTKPOP    (*(--bf_stacktop))
#define DSTKTOP    (*(bf_stacktop - 1))
#define DSTKIDX(i)   (*(bf_stacktop - 1 - i))
void BF_Step(void)
{
    if(*bf_pc == '\0')
        return;
    
    uint8_t tmp = *bf_pc++;
    if(isupper(tmp))
    {
        *bf_linkstacktop++ = bf_pc;
        bf_pc = bfdict[tmp - 'A'];
    }
    else
    {
        switch(tmp) {
            case '+': tmp = DSTKPOP; DSTKTOP += tmp; break;
            case '-': tmp = DSTKPOP; DSTKTOP -= tmp; break;
            case '*': tmp = DSTKPOP; DSTKTOP *= tmp; break;
            case '/': tmp = DSTKPOP; DSTKTOP /= tmp; break;
            case '^': tmp = DSTKPOP; DSTKTOP ^= tmp; break;
            case '&': tmp = DSTKPOP; DSTKTOP &= tmp; break;
            case '|': tmp = DSTKPOP; DSTKTOP |= tmp; break;
            
            case 'b': DSTKPUSH(*bf_pc++); break;
            case 'p': DSTKPOP; break;
            case 'd': tmp = DSTKTOP; DSTKPUSH(tmp); break;
            case 's': tmp = DSTKIDX(0); DSTKIDX(0) = DSTKIDX(1); DSTKIDX(1) = tmp; break;
            
            case '~':// Reset state
                bf_stacktop = bf_stack;
                bf_linkstacktop = bf_linkstack;
                bf_pc = bf_prog;
            break;
            
            case '?':// if
                if(!DSTKPOP)
                {
                    // Scan to first word following else (nested ifs not supported)
                    BF_Scan(',');
                }
                // else continue
            break;
            
            case ',':// else
                // Scan past else clause to end.
                BF_Scan('#');
            break;
            
            case '#':// end (do nothing)
            break;
            
            case ':':// Start definition/escape special
                tmp = *bf_pc;
                if(isupper(tmp))
                {
                    printf("defining word %c\n", tmp);
                    bfdict[tmp - 'A'] = bf_pc + 1;
                    BF_Scan(';');
                }
                // else
                // {
                //     if(tmp == 'x')
                //     
                // }
            break;
            
            case ';':// End definition/return
                bf_pc = *(--bf_linkstacktop);
            break;
            
            case '.': printf("0x%02X\n", DSTKPOP); break;
            // case '.': printf("%d\n", DSTKPOP); break;
            // case '.': printf("%c", DSTKPOP); break;
        }
    }
}


void BF_Run(const char * src)
{
    bf_prog = src;
    bf_stacktop = bf_stack;
    bf_linkstacktop = bf_linkstack;
    bf_pc = src;
    while(*bf_pc)
    {
        BF_Step();
        printf("pc: %d ", (int)(bf_pc - bf_prog));
        printf("stk: %d ", (int)(bf_stacktop - bf_stack));
        printf("lstk: %d\n", (int)(bf_linkstacktop - bf_linkstack));
    }
}


int main(int argc, const char * argv[])
{
    // strcpy(bf_prog, ":Ab\x40""b\x02+.;:Bb\x55""b\x11*.;ABA");
    // strcpy(bf_prog, "b\x42+.");
    // if(argc >= 2)
        // strcpy(bf_prog, argv[1]);
    BF_Run(":Ab\x40""b\x02+.;");
    BF_Run(":Bb\x55""b\x11*.;");
    BF_Run("ABA");
}