#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/printk.h>
#define st_debug(format, ...)		\
	pr_debug("(file:%s,line:%d,pid:%d): " format,		\
		   	__FILE__, __LINE__,		\
		   current->pid, ##__VA_ARGS__)

#include <linux/module.h>
#include <linux/device.h>
#include <linux/fs.h>
#include <linux/uaccess.h>
#include <linux/cdev.h>

#define	STUDENT_CHRDEV "marvin-the-robot"
#define MAX_VALUES 3

static int student_chrdev_major = 0;
static struct device *my_dev = NULL;

typedef struct student_internal {
	int values[MAX_VALUES];
	int idx;
} st_int_t;
static st_int_t *data = NULL;

#if 0
static st_int_t* get_priv_data(struct file *file) {
	return (st_int_t*)file->private_data;
}

static void set_priv_data(struct file *file, st_int_t *data) {
	file->private_data = data;
}
#endif

static int sum(int val[], int len) {
	int ret = 0;

	for (int i = 0; i < len; i++) {
		ret += val[i];
	}
	return ret + CONFIG_STUDENT_OFFSET;
}

static ssize_t student_read(struct file *file, char __user *buf, size_t count,
		       loff_t *ppos) {
	size_t len = 0;
	char tmp[10];

	if (!data) {
		st_debug("No calculation started. Doing nothing.\n");
		return 0;
	}

	len = snprintf(tmp, 10, "%d\n", sum(data->values, MAX_VALUES));
	st_debug("About to copy %lu bytes to the userspace\n", len);
	len = min(len, count);
	if (count < len) {
		pr_err("Sorry, your buffer is %lu bytes too small.\n", len - count);
	}
	if (copy_to_user(buf, tmp, len)) {
		pr_err("User copy failed!\n");
		return -EFAULT;
	}
	// Arthur Dent just likes to read the answer to the ultimate question, the Universe, and everything: 42!
	st_debug("Copied %lu bytes to the userspace\n", len);
	data = NULL;
	st_debug("Resetted internal state\n");
	*ppos += len;
	return len;
}

static ssize_t student_write(struct file *file, const char __user *buf, size_t count,
		       loff_t *ppos) {
	char *buf_copy;
	int tmp;

	buf_copy = memdup_user_nul(buf, count);
	if (IS_ERR(buf_copy)) {
		return PTR_ERR(buf_copy);
	}
	if (kstrtos32(buf_copy, 0, &tmp) != 0) {
		kfree(buf_copy);
		return -EINVAL;
	}
	kfree(buf_copy);
	st_debug("New value read: %d\n", tmp);
	if (data == NULL) {
		data = kmalloc(sizeof(*data), GFP_KERNEL);
		if (!data) {
			return -ENOMEM;
		}
		data->idx = 0;
		for (int i = 0; i < MAX_VALUES; i++) {
			data->values[i] = 0;
		}
		st_debug("Adding newly allocation st_int_t to priv_data: 0x%lx\n", (uintptr_t)data);
	}
	if (data->idx < MAX_VALUES) {
		data->values[data->idx] = tmp;
		st_debug("New value (%d) add at idx %d\n", tmp, data->idx);
		data->idx++;
	} else {
	   return -ENOMEM;
	}	   
	return count;
}

const struct file_operations student_fops = {
	.owner		= THIS_MODULE,
	.read = student_read,
	.write = student_write,
};

static struct class universe_class = {
	.name		= STUDENT_CHRDEV,
};

static int __init student_chrdevinit(void) {
	int err;

	student_chrdev_major = err = register_chrdev(0, STUDENT_CHRDEV, &student_fops);
	if (err < 0) {
		pr_err("Cannot register chrdev: %d\n", err);
		goto out;
	}
	err = class_register(&universe_class);
    if (err) {
		pr_err("Cannot register universe class: %d\n", err);
		goto out_chrdev;
	}
	my_dev = device_create(&universe_class, NULL, MKDEV(student_chrdev_major, 0), NULL, STUDENT_CHRDEV);
	if (IS_ERR(my_dev)) {
		err = PTR_ERR(my_dev);
		pr_err("Cannot create device: %d\n", err);
		goto out_class;
	}
	pr_notice("Loaded module %s\n", KBUILD_MODNAME);
	return 0;

out_class:
	class_unregister(&universe_class);
out_chrdev:
	unregister_chrdev(student_chrdev_major, STUDENT_CHRDEV);
out:
	return err;
}

static void __exit student_chrdevexit(void) {
	device_destroy(&universe_class, MKDEV(student_chrdev_major, 0));
	class_unregister(&universe_class);
	unregister_chrdev(student_chrdev_major, STUDENT_CHRDEV);
	pr_notice("Unloaded module %s\n", KBUILD_MODNAME);
}

module_init(student_chrdevinit);
module_exit(student_chrdevexit);
MODULE_LICENSE("LGPL");