#include <stdlib.h>
#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include <unistd.h>
#include <sys/file.h>
#include <err.h>

#define MAX_QUERY_LEN 255
#define IP_LEN 16
#define IP_FILE "ip.txt"
#define TOKEN "<empty>"

char *form_value(const char *args, const char *field) {
        char *s;
        char *token;
        char *value;
        char *ret = NULL;
        size_t len;
        len = strlen(field);
        s = strdup(args);
        while((token = strsep(&s, "&")) != NULL) {
                if(strlen(token) < len)
                        continue;
                if(strncmp(field, token, len) == 0) {
                        value = strchr(token, '=');
                        ret = strdup(value);
                        break;
                }
        }
        free(s);
        return(ret);
}

void header() {
        puts("Status: 200 OK\r");
        puts("Content-Type: text/html\r");
        puts("\r");
}

int ctb(unsigned char a, unsigned char b) {
        unsigned char c = ~(a ^ b);
        c &= c >> 4;
        c &= c >> 2;
        c &= c >> 1;
        return((int)c);
}

int ctc(const char *a, const char *b) {
        if(!a || !b)
                return(0);
        if(strlen(a) != strlen(b))
                return(0);
        const char *x = a, *y = b;
        char v = 0;
        while(*x)
                v |= *x++ ^ *y++;
        return(ctb(v, 0));
}

int set_ip(char *env, int wfd) {
        char *ip = NULL, *token = NULL;
        int ret = 1;
        size_t len;
        ip = form_value(env, "ip");
        if(!ip)
                return(ret);
        token = form_value(env, "token");
        if(!token)
                free(ip);
                return(ret);
        if(ctc(token, TOKEN) == 1) {
                len = strlen(ip);
                if(len >= IP_LEN-1)
                        len = IP_LEN-1;
                write(wfd, ip, len);
                close(wfd);
                ret = 0;
        } else
                ret = 2;
        free(ip);
        free(token);
        return(ret);
}

char *err_msg[2] = {"invalid arguments", "wrong token"};

int main(void) {
        char *env = NULL;
        char ip[IP_LEN];
        int errn = 0, len = 0;
        int rfd, wfd;
        if((rfd = open(IP_FILE, O_RDONLY|O_SHLOCK)) == -1)
                err(EXIT_FAILURE, "read open failed");
        if(read(rfd, &ip, IP_LEN) <= 0)
                ip[0] = '\0';
        close(rfd);
        ip[IP_LEN] = '\0';
        if((wfd = open(IP_FILE, O_WRONLY|O_CREAT|O_TRUNC|O_EXLOCK)) == -1)
                err(EXIT_FAILURE, "rw open failed");
        if(pledge("stdio", NULL) == -1) 
                err(EXIT_FAILURE, "pledge");
        env = getenv("QUERY_STRING");
        header();
        if(env != NULL) {
                if(strlen(env) > MAX_QUERY_LEN) {
                        puts("query longer than 255 bytes");
                        return(EXIT_SUCCESS);
                }
                if((errn = set_ip(env, wfd)) > 0)
                        puts(err_msg[errn-1]);
                else
                        puts("ok");
        } else {
                len = strlen(ip);
                write(wfd, ip, len);
                close(wfd);
                if(len > 1)
                        puts(ip);
                else
                        puts("empty");
        }
        return(EXIT_SUCCESS);
}