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

typedef struct
{
    const char *name;
    int address;
    double value;
    int valid;
} sensor_t;

static int select_sensor(int fd, int address)
{
    return ioctl(fd, I2C_SLAVE, address);
}

static int request_reading(int fd, sensor_t *sensor)
{
    const char command = 'R';

    if (select_sensor(fd, sensor->address) < 0)
    {
        return -1;
    }

    if (write(fd, &command, 1) != 1)
    {
        return -1;
    }

    sensor->valid = -1;
    return 0;
}

static int receive_reading(int fd, sensor_t *sensor)
{
    unsigned char response[64] = {0};

    if (select_sensor(fd, sensor->address) < 0)
    {
        return -1;
    }

    int bytes_read = read(fd, response, sizeof(response) - 1);

    for (int retry = 0;
         bytes_read > 0 && response[0] == 254 && retry < 10;
         retry++)
    {
        usleep(100000);
        memset(response, 0, sizeof(response));
        bytes_read = read(fd, response, sizeof(response) - 1);
    }

    if (bytes_read < 2 || response[0] != 1)
    {
        return -1;
    }

    response[bytes_read] = '\0';
    char *end = NULL;
    errno = 0;
    double value = strtod((char *)&response[1], &end);

    if (errno != 0 || end == (char *)&response[1])
    {
        return -1;
    }

    sensor->value = value;
    sensor->valid = 1;
    return 0;
}

int main(int argc, char *argv[])
{
    if (argc != 2)
    {
        fprintf(stderr, "Uso: EZO_ACQUIRE /dev/i2c-1\n");
        return 2;
    }

    sensor_t sensors[] = {
        {"temperature", 0x66, 0.0, 0},
        {"ph", 0x63, 0.0, 0},
        {"do", 0x61, 0.0, 0},
        {"ec", 0x64, 0.0, 0}};
    const size_t sensor_count = sizeof(sensors) / sizeof(sensors[0]);
    int lock_fd = open(
        "/tmp/photobioreactor-i2c.lock",
        O_CREAT | O_RDWR,
        0660);

    if (lock_fd < 0 || flock(lock_fd, LOCK_EX) < 0)
    {
        fprintf(stderr, "No se pudo bloquear el bus I2C\n");
        return 3;
    }

    int fd = open(argv[1], O_RDWR);

    if (fd < 0)
    {
        fprintf(stderr, "No se pudo abrir %s\n", argv[1]);
        flock(lock_fd, LOCK_UN);
        close(lock_fd);
        return 4;
    }

    for (size_t index = 0; index < sensor_count; index++)
    {
        request_reading(fd, &sensors[index]);
    }

    usleep(1000000);

    for (size_t index = 0; index < sensor_count; index++)
    {
        if (sensors[index].valid == -1)
        {
            receive_reading(fd, &sensors[index]);
        }
    }

    printf("{");
    for (size_t index = 0; index < sensor_count; index++)
    {
        printf(
            "%s\"%s\":",
            index == 0 ? "" : ",",
            sensors[index].name);
        if (sensors[index].valid == 1)
        {
            printf("%.6f", sensors[index].value);
        }
        else
        {
            printf("null");
        }
    }
    printf("}\n");

    close(fd);
    flock(lock_fd, LOCK_UN);
    close(lock_fd);
    return 0;
}