#include <stdio.h>

/*
Copyright (c) 2021 Devine Lu Linvega

Permission to use, copy, modify, and distribute this software for any
purpose with or without fee is hereby granted, provided that the above
copyright notice and this permission notice appear in all copies.

THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
WITH REGARD TO THIS SOFTWARE.
*/

typedef unsigned char Uint8;
typedef unsigned short Uint16;

typedef struct {
	int ptr;
	Uint8 data[65536];
} Program;

typedef struct {
	Uint16 addr;
	char name[64];
} Label;

int labelslen;
Label labels[256];
Program p;

/* clang-format off */

char ops[][4] = {
	"BRK", "LIT", "---", "---", "PEK", "POK", "LDR", "STR",
	"JMP", "JSR", "RTI", "RTS", "---", "---", "---", "---",
	"POP", "DUP", "SWP", "OVR", "ROT", "AND", "ORA", "ROL",
	"ADD", "SUB", "MUL", "DIV", "EQU", "NEQ", "GTH", "LTH"
};

int scmp(char *a, char *b) { int i = 0; while(a[i] == b[i]) if(!a[i++]) return 1; return 0; } /* string compare */
int slen(char *s) { int i = 0; while(s[i] && s[++i]) ; return i; } /* string length */
int sihx(char *s) { int i = 0; char c; while((c = s[i++])) if(!(c >= '0' && c <= '9') && !(c >= 'a' && c <= 'f') && !(c >= 'A' && c <= 'F')) return 0; return 1; } /* string is hexadecimal */
int shex(char *s) { int n = 0, i = 0; char c; while((c = s[i++])) if(c >= '0' && c <= '9') n = n * 16 + (c - '0'); else if(c >= 'A' && c <= 'F') n = n * 16 + 10 + (c - 'A'); else if(c >= 'a' && c <= 'f') n = n * 16 + 10 + (c - 'a'); return n; } /* string to num */
int cmnt(char *w, int *skip) { if(w[0] == ')') { *skip = 0; return 1; } if(w[0] == '(') *skip = 1; if(*skip) return 1; return 0; } /* comment helper */
char *scpy(char *src, char *dst, int len) { int i = 0; while((dst[i] = src[i]) && i < len - 2) i++; dst[i + 1] = '\0'; return dst; } /* string copy */

#pragma mark - Helpers

/* clang-format on */

#pragma mark - I/O

void
pushbyte(Uint8 b, int lit)
{
	if(lit) {
		pushbyte(0x01, 0);
		pushbyte(0x01, 0);
	}
	p.data[p.ptr++] = b;
}

void
pushshort(Uint16 s, int lit)
{
	if(lit) {
		pushbyte(0x01, 0);
		pushbyte(0x02, 0);
	}
	pushbyte((s >> 8) & 0xff, 0);
	pushbyte(s & 0xff, 0);
}

void
pushtext(char *w)
{
	int i = slen(w);
	pushbyte(0x01, 0);
	pushbyte(slen(w), 0);
	while(i > 0)
		pushbyte(w[--i], 0);
}

Label *
findlabel(char *s)
{
	int i;
	for(i = 0; i < labelslen; ++i)
		if(scmp(labels[i].name, s))
			return &labels[i];
	return NULL;
}

Uint8
findoperator(char *s)
{
	int i;
	for(i = 0; i < 0x20; ++i) {
		int m = 0;
		char *o = ops[i];
		if(o[0] != s[0] || o[1] != s[1] || o[2] != s[2])
			continue;
		while(s[3 + m]) {
			if(s[3 + m] == '^') i |= (1 << 5); /* mode: 16 bits */
			if(s[3 + m] == '~') i |= (1 << 6); /* mode: signed */
			if(s[3 + m] == '?') i |= (1 << 7); /* mode: conditional */
			m++;
		}
		return i;
	}
	return 0;
}

#pragma mark - Parser

int
error(char *name, char *id)
{
	printf("Error: %s[%s]\n", name, id);
	return 0;
}

int
makelabel(char *name, Uint16 addr)
{
	Label *l;
	if(findlabel(name))
		return error("Label duplicate", name);
	l = &labels[labelslen++];
	l->addr = addr;
	scpy(name, l->name, 64);
	printf("New label: %s[0x%02x]\n", l->name, l->addr);
	return 1;
}

int
makeconst(char *id, FILE *f)
{
	char wv[64];
	fscanf(f, "%s", wv);
	return makelabel(id, shex(wv));
}

int
pass1(FILE *f)
{
	int skip = 0, vars = 0;
	Uint16 addr = 0;
	char w[64];
	while(fscanf(f, "%s", w) == 1) {
		if(cmnt(w, &skip))
			continue;
		if(w[0] == '@' && !makelabel(w + 1, addr))
			return error("Pass1 failed", w);
		if(w[0] == ';' && !makelabel(w + 1, vars++))
			return error("Pass1 failed", w);
		if(w[0] == ':') {
			if(!makeconst(w + 1, f))
				return error("Pass1 failed", w);
			else
				continue;
		}
		if(findoperator(w) || scmp(w, "BRK"))
			addr += 1;
		else {
			switch(w[0]) {
			case '|': addr = shex(w + 1); break;
			case '@':
			case ';': break;
			case '.': addr += 2; break;
			case '#': addr += 4; break;
			case '"': addr += slen(w + 1) + 2; break;
			case ',': addr += 2 + (sihx(w + 1) && slen(w + 1) == 2 ? 1 : 2); break;
			default: return error("Unknown label", w);
			}
		}
	}
	rewind(f);
	return 1;
}

int
pass2(FILE *f)
{
	int skip = 0;
	char w[64];
	while(fscanf(f, "%s", w) == 1) {
		Uint8 op = 0;
		Label *l;
		if(w[0] == '@') continue;
		if(w[0] == ';') continue;
		if(cmnt(w, &skip)) continue;
		if(w[0] == '|')
			p.ptr = shex(w + 1);
		else if(w[0] == ':')
			fscanf(f, "%s", w);
		else if(w[0] == '"')
			pushtext(w + 1);
		else if(w[0] == '#') {
			pushshort(shex(w + 1) & 0xff, 1);
		} else if((l = findlabel(w + 1)))
			pushshort(l->addr, w[0] == ',');
		else if((op = findoperator(w)) || scmp(w, "BRK"))
			pushbyte(op, 0);
		else if(sihx(w + 1) && slen(w + 1) == 2)
			pushbyte(shex(w + 1), w[0] == ',');
		else if(sihx(w + 1) && slen(w + 1) == 4)
			pushshort(shex(w + 1), w[0] == ',');
		else
			return error("Unknown label", w);
	}
	return 1;
}

int
main(int argc, char *argv[])
{
	FILE *f;
	if(argc < 3)
		return error("Input", "Missing");
	if(!(f = fopen(argv[1], "r")))
		return error("Open", "Failed");
	if(!pass1(f) || !pass2(f))
		return error("Assembly", "Failed");
	fwrite(p.data, sizeof(p.data), 1, fopen(argv[2], "wb"));
	fclose(f);
	printf("Assembled %s.\n\n", argv[2]);
	return 0;
}