//
//Sensirion SHT71 (http://www.acmesystems.it/?id=89) by Douglas Gilbert

#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include "./z2-gpio.h"

// -----------------------------------------------------------------------
// SHT71 sensor define
// -----------------------------------------------------------------------

#define CLOCK_BIT         53
#define DATA_BIT          54

#define DATA_LINE_IN      gpio_dir_in(DATA_BIT)
#define DATA_LINE_OUT     gpio_dir_out(DATA_BIT)

#define DATA_LINE_LOW     set_gpio_value(DATA_BIT, 0)
#define DATA_LINE_HIGH    set_gpio_value(DATA_BIT, 1)
#define DATA_LINE_READ    get_gpio_value(DATA_BIT)

#define CLOCK_LINE_LOW    set_gpio_value(CLOCK_BIT, 0)
#define CLOCK_LINE_HIGH   set_gpio_value(CLOCK_BIT, 1)

#define CMD_RESET	  0x1e
#define CMD_READ_TEMP     0x03
#define CMD_READ_HUM      0x05

// -----------------------------------------------------------------------
// Send the start sequence
// -----------------------------------------------------------------------
static void SendStart(void)
{
	CLOCK_LINE_LOW;
    	DATA_LINE_OUT;
    	DATA_LINE_HIGH;
    	usleep(1000);
    	CLOCK_LINE_HIGH;
    	usleep(1000);
    	DATA_LINE_LOW;
    	usleep(1000);
    	CLOCK_LINE_LOW;
    	usleep(1000);
    	CLOCK_LINE_HIGH;
    	usleep(1000);
    	DATA_LINE_HIGH;
    	usleep(1000);
    	CLOCK_LINE_LOW;
}

// -----------------------------------------------------------------------
// Sensor reset
// -----------------------------------------------------------------------
static void SendReset (void)
{
    	int k;
    	DATA_LINE_OUT;
    	DATA_LINE_HIGH;
    	for (k = 0; k < 12; k++) {
        	CLOCK_LINE_HIGH;
        	usleep(1000);
        	CLOCK_LINE_LOW;
		usleep(1000);
    	}
	CLOCK_LINE_HIGH;
	usleep(1000);
	DATA_LINE_LOW;
	usleep(1000);
	CLOCK_LINE_LOW;
	usleep(1000);
	CLOCK_LINE_HIGH;
	usleep(1000);
	DATA_LINE_HIGH;
	usleep(1000);
	CLOCK_LINE_LOW;
}

// -----------------------------------------------------------------------
// Send a byte to the sensor
// -----------------------------------------------------------------------
static int SendByte(unsigned char byte)
{
    	unsigned char tempbyte;
    	int k;
    	DATA_LINE_OUT;
    	tempbyte = byte;
    	for (k = 0x80; k > 0; k /= 2) {

        	if (tempbyte & k){
            		DATA_LINE_HIGH;
        	} else {
            		DATA_LINE_LOW;
		}
		usleep(1000);
        	CLOCK_LINE_HIGH;
        	usleep(1000);
        	CLOCK_LINE_LOW;
		usleep(1000);
    		}
    	DATA_LINE_IN;
    	CLOCK_LINE_HIGH;
	usleep(10000);
    	CLOCK_LINE_LOW;
	usleep(10000);
    	return 1;
}

// -----------------------------------------------------------------------
// Read a byte from the sensor
// -----------------------------------------------------------------------
static unsigned char ReadByte(int withack)
{
    	unsigned char tempbyte;
    	int k;
    	tempbyte = 0;
    	DATA_LINE_IN;
    	for (k = 0x80; k > 0; k /= 2) {
        	CLOCK_LINE_HIGH;
		usleep(1000);
        	if (DATA_LINE_READ){
	        	tempbyte |= k;
		}
	      	CLOCK_LINE_LOW;
		usleep(1000);
    	}
    	if (withack) {
        	DATA_LINE_OUT;
		DATA_LINE_HIGH;
		usleep(1000);
        	DATA_LINE_LOW;
		usleep(1000);
        	CLOCK_LINE_HIGH;
		usleep(1000);
        	CLOCK_LINE_LOW;
		usleep(1000);
        	DATA_LINE_IN;
    	} else {
        	DATA_LINE_OUT;
        	DATA_LINE_HIGH;
		usleep(1000);
        	CLOCK_LINE_HIGH;
		usleep(1000);
        	CLOCK_LINE_LOW;
		usleep(1000);
        	DATA_LINE_IN;
    	}
    	return tempbyte;
}

// ----------------------
// Read the temperature
// ----------------------
static int ReadTemperature(void)
{
    	unsigned char Lsb, Msb, Chk;
    	SendStart();
	usleep(1000);
	SendByte(CMD_READ_TEMP);
    	usleep(500000);
    	Msb = ReadByte(1);
    	Lsb = ReadByte(1);
    	Chk = ReadByte(0);
    	return (Msb << 8) + Lsb;
}

// ------------------
// Read the humidity
// ------------------
static int ReadHumidity(void)
{
    	unsigned char Lsb, Msb, Chk;
    	SendStart();
    	if (! SendByte(CMD_READ_HUM))
        	return 0;
    	while (DATA_LINE_READ)
        	;
    	Msb = ReadByte(1);
    	Lsb = ReadByte(1);
    	Chk = ReadByte(0);
    	return (Msb << 8) + Lsb ;
}

float AirDensity(float humidity, float temperature, float barometric)
{
	barometric = 758.952;
	float kelvin = (273.15 + temperature);
	float exponent = exp(-5315.56 / kelvin);
	float pressure = (0.0004646 * (barometric - (4990221.6 * humidity * exponent)));
	return (pressure / kelvin) ;
}

// ----------
// main code
// ----------
//int main(int argc, char ** argv)
int main(int argc, char *argv[])
{
    	int opt, soh, sot;
    	int do_reset = 0;
	double dew_point_lf, denominator, numerator;
    	float rel_humidity, temperature_c, Tn = 243.12, m = 17.62;

	gpio_export(DATA_BIT);
	gpio_export(CLOCK_BIT);
	gpio_dir_out(CLOCK_BIT);

	SendReset();
	usleep(100000);
	soh = ReadHumidity();
	sot = ReadTemperature();
//	rel_humidity = -2.0468 + (0.0367 * soh) + (-1.5955E-6 * soh * soh);
    	rel_humidity = -4 + (0.0405 * soh) + -2.8E-6;
    	if (rel_humidity > 99.9)
        	rel_humidity = 100.0;
    	else if (rel_humidity < 0.1)
        	rel_humidity = 0.0;
    	temperature_c = -39.66 + (0.01 * sot);
	printf ("      Rel. Humidity : %.2f %% RH\n", rel_humidity);
    	printf ("        Temperature : %.2f °C\n", temperature_c);
	printf ("Barometric Pressure : %.3f mmHg\n", 758.952);
    	gpio_unexport(53);
    	gpio_unexport(54);

	numerator = log(rel_humidity / 100) + ((m * temperature_c) / (Tn + temperature_c));
	denominator = m - log(rel_humidity / 100) - ((m * temperature_c) / (Tn + temperature_c));
	printf ("         Dew Point  : %.2f ºC\n", Tn * (numerator / denominator));
	printf ("       Air Density  : %.7f g/cm^3\n", AirDensity(rel_humidity, temperature_c, 0.00));
    	return 0;
}