/*
	Copyright (c) 2016 CurlyMo <curlymoo1@gmail.com>

  This Source Code Form is subject to the terms of the Mozilla Public
  License, v. 2.0. If a copy of the MPL was not distributed with this
  file, You can obtain one at http://mozilla.org/MPL/2.0/.
*/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <unistd.h>
#include <time.h>

#include "wiringx.h"

void drop_privileges();

int main() {

	if(wiringXSetup("raspberrypi3", NULL) == -1) {
		wiringXGC();
		return -1;
	}

	pinMode(9, PINMODE_OUTPUT);
	digitalWrite(9, HIGH);
	pinMode(9, PINMODE_INPUT);
	pinMode(8, PINMODE_OUTPUT);

	drop_privileges();

	// start bit
	digitalWrite(8, HIGH);
	usleep(18000);
	digitalWrite(8, LOW);
	int bit = -3;
	char data[5];
	memset(&data[0], 0, 5);
	int trials = 3;
	while ((bit != 40) || ((data[0]+data[1]+data[2]+data[3]-data[4]) % 255 != 0) || ((data[0]|data[1]|data[2]|data[3]|data[4]) == 0)) {
		trials--;
		if (trials <= 0) {
			fprintf(stderr, "Failed to obtain valid reading within 3 trials.\n");
			return -1;
		}
		sleep(2);
		if (bit > -3)
			fprintf(stderr, ".");
		// start bit
		digitalWrite(8, HIGH);
		usleep(18000);
		digitalWrite(8, LOW);
		long int cycles = 0;
		int last_state = digitalRead(9);
		// ignore 2 bits: reaction on command + "official" start bit
		bit = -2;
		memset(&data[0], 0, 5);
		while (cycles < 100000) {
			cycles++;
			if (last_state == digitalRead(9))
				continue;
			if (last_state == 1) {
				if ((bit >= 0) && (cycles>150))
					data[bit / 8] |= 1 << 7 - (bit % 8);
				bit++;
			}
			cycles = 0;
			last_state = 1-last_state;
		}
	}
	FILE *of;
	of = fopen("/srv/http/tmp/sensor", "w");
	if (of == NULL) {
		fprintf(stderr, "Failed to open '%s' for writing.\n", "/srv/http/tmp/sensor");
		return -1;
	}
	time_t now = time(NULL);
	char time_str[20];
	strftime(time_str, 20, "%Y-%m-%d %H:%M:%S", gmtime(&now));
	fprintf(of, "RH: %f %%\n", data[0] + data[1]/256.);
	fprintf(of, "T: %f °C\n", data[2] + data[3]/256.);
	fprintf(of, "t: %s\n", time_str);
	fclose(of);
} // main

//
// Drop (root) privileges
//
void drop_privileges() {
	/*  Drop superuser privileges in correct order */

	int is_already_unprivileged = 0;

	if (setgid(65534) == -1) { // nobody
		perror("can't drop group privileges");
		if (! (is_already_unprivileged = (errno == 1)))
			exit(-1);
	}
	if (setuid(65534) == -1) { // nobody
		perror("can't drop user privileges");
		if (is_already_unprivileged != (errno == 1))
		exit(-1);
	}
} // drop_privileges