#ifndef RESOLVE_H
#define RESOLVE_H
/* resolve.h - turn a dotted-quad OR a hostname into an IPv4 address. Hostname
   lookups go out as a DNS A query over a UDP socket to 1.1.1.1:53; the kernel
   owns UDP, this owns DNS. Header-only (one copy per program). */
#include "sock.h"

static unsigned char _dnsbuf[200];
static unsigned char _dnssrv[4];

/* parse "A.B.C.D" into out[4]; return 1 on success */
static unsigned char parse_ip(char *s, unsigned char *out) {
    unsigned char i, v;
    for (i = 0; i < 4; i++) {
        if (*s < '0' || *s > '9') return 0;
        v = 0;
        while (*s >= '0' && *s <= '9') { v = (unsigned char)(v * 10 + (*s - '0')); s++; }
        out[i] = v;
        if (i < 3) { if (*s != '.') return 0; s++; }
    }
    return 1;
}

static unsigned char _dns_query(char *host) {
    unsigned char i = 0, p = 12, lblpos, len;
    _dnsbuf[0] = 0x12; _dnsbuf[1] = 0x34; _dnsbuf[2] = 0x01; _dnsbuf[3] = 0x00;
    _dnsbuf[4] = 0; _dnsbuf[5] = 1;
    _dnsbuf[6] = 0; _dnsbuf[7] = 0; _dnsbuf[8] = 0; _dnsbuf[9] = 0; _dnsbuf[10] = 0; _dnsbuf[11] = 0;
    while (host[i]) {
        lblpos = p++; len = 0;
        while (host[i] && host[i] != '.') { _dnsbuf[p++] = host[i]; i++; len++; }
        _dnsbuf[lblpos] = len;
        if (host[i] == '.') i++;
    }
    _dnsbuf[p++] = 0; _dnsbuf[p++] = 0; _dnsbuf[p++] = 1; _dnsbuf[p++] = 0; _dnsbuf[p++] = 1;
    return p;
}
static unsigned int _dns_skip(unsigned int p) {
    for (;;) {
        if (_dnsbuf[p] == 0) return p + 1;
        if ((_dnsbuf[p] & 0xC0) == 0xC0) return p + 2;
        p += _dnsbuf[p] + 1;
    }
}
static unsigned char _dns_answer(unsigned char *ip) {
    unsigned int p, a, an, type, rdlen;
    an = ((unsigned int)_dnsbuf[6] << 8) | _dnsbuf[7];
    if (an == 0) return 0;
    p = _dns_skip(12) + 4;
    for (a = 0; a < an; a++) {
        p = _dns_skip(p);
        type = ((unsigned int)_dnsbuf[p] << 8) | _dnsbuf[p + 1];
        p += 8;
        rdlen = ((unsigned int)_dnsbuf[p] << 8) | _dnsbuf[p + 1];
        p += 2;
        if (type == 1 && rdlen == 4) {
            ip[0] = _dnsbuf[p]; ip[1] = _dnsbuf[p + 1]; ip[2] = _dnsbuf[p + 2]; ip[3] = _dnsbuf[p + 3];
            return 1;
        }
        p += rdlen;
    }
    return 0;
}

/* resolve a dotted-quad or hostname into ip[4]; return 1 on success */
static unsigned char resolve(char *host, unsigned char *ip) {
    unsigned char s, n;
    if (parse_ip(host, ip)) return 1;                 /* already an address */
    _dnssrv[0] = 1; _dnssrv[1] = 1; _dnssrv[2] = 1; _dnssrv[3] = 1;
    s = net_socket(SOCK_UDP);
    if (s == 0xFF) return 0;
    net_bind(s, 40000);
    net_connect(s, _dnssrv, 53);
    n = _dns_query(host);
    net_send(s, _dnsbuf, n);
    n = net_recv(s, _dnsbuf, 200);
    net_close(s);
    if (n == 0xFF) return 0;
    return _dns_answer(ip);
}
#endif