#include <linux/i2c.h>
#include <linux/i2c-dev.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdint.h>
#include <errno.h>

#define check(e) ({\
		int ec = (e); \
		if(ec < 0) {\
		perror(#e); \
		exit(1);\
		}\
		ec;\
		})

enum BME280Register {
	ID = 0xd0,
	CTRL_MEAS = 0xf4,
	PRESS_MSB = 0xf5,
};

typedef struct {
	int fd;
} BME280;

int i2c_read_register(int fd, uint8_t reg) {
	if(write(fd, &reg, 1) < 0)
		return -1;
	uint8_t byte;
	if(read(fd, &byte, 1) < 0)
		return -1;
	return byte;
}

int i2c_read_registers(int fd, uint8_t start_addr, uint8_t* values, size_t n_bytes) {
	if(write(fd, &start_addr, 1) < 0)
		return -1;
	return read(fd, values, n_bytes);
}

int bme280_init(BME280* self, int fd) {
	self->fd = fd;

	if(i2c_read_register(fd, 0xd0) != 0x60)
		return -ENOTSUP;
	return 0;
}

int main() {
	int bus = check(open("/dev/i2c-1", O_RDWR));
	check(ioctl(bus, I2C_SLAVE, 0x76));

#if 0
	// Check I2C driver compatibility
	unsigned long adapter_funcs;
	check(ioctl(bus, I2C_FUNCS, &adapter_funcs));
	for(size_t i = 0; i != (sizeof(funcs)/sizeof(*funcs)); ++i) {
		if(adapter_funcs & funcs[i].bit)
			puts(funcs[i].name);
	}
#endif

	BME280 sensor;
	check(bme280_init(&sensor, bus));

	for(size_t j = 0; j != 10; ++j) {
		uint8_t ctrl_meas = (0b001u << 5) | (0b001 << 2) | 0b11;
		uint8_t bus_data[] = {CTRL_MEAS, ctrl_meas};
		check(write(bus, bus_data, 2));

		//TODO: should we sleep here? Maybe poll the busy flag?

		uint8_t sensor_data[8];
		check(i2c_read_registers(bus, PRESS_MSB, sensor_data, 8));

		for(size_t i = 0; i != sizeof(sensor_data); ++i) {
			printf("%02x ", sensor_data[i]);
		}
		puts("");

		sleep(1);
	}

	close(bus);
}