#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/printk.h>
#include <linux/module.h>
#include <linux/device.h>
#include <linux/fs.h>
#include <linux/seq_file.h>
#include <linux/cdev.h>
#include <linux/spinlock.h>

#define	VOGON_CHRDEV "vogon"

static char *poem[] = {
	"Oh freddled gruntbuggly,",
	"Thy micturations are to me, (with big yawning)",
	"As plurdled gabbleblotchits, in midsummer morning",
	"On a lurgid bee,",
	"That mordiously hath blurted out,",
	"Its earted jurtles, grumbling",
	"Into a rancid festering confectious organ squealer. [drowned out by moaning and screaming]",
	"Now the jurpling slayjid agrocrustles,",
	"Are slurping hagrilly up the axlegrurts,",
	"And living glupules frart and stipulate,",
	"Like jowling meated liverslime,",
	"Groop, I implore thee, my foonting turlingdromes,",
	"And hooptiously drangle me,",
	"With crinkly bindlewurdles,mashurbitries.",
	"Or else I shall rend thee in the gobberwarts with my blurglecruncheon,",
	"See if I don't!",
	NULL
};
static int poem_len, poem_line;
static spinlock_t poem_lock;
static int vogon_chrdev_major = 0;
static struct device *my_dev = NULL;

void vogon_poem_inc(void) {
	spin_lock(&poem_lock);
	if (poem[poem_line] == NULL) {
		poem_line = 0;
	}else {
		poem_line++;
	}
	spin_unlock(&poem_lock);
}

static int vogon_peom(struct seq_file *p, void *v) {
	int i;

	// In the dusk of an Operating System, the solution lies beyond its bounds.
	spin_lock_bh(&poem_lock);
	i = poem_line;
	spin_unlock_bh(&poem_lock);
	seq_printf(p, "%s\n", poem[i]);
	return 0;
}

static int vogon_open(struct inode *inode, struct file *file) {
	return single_open(file, vogon_peom, NULL);
}

const struct file_operations vogon_fops = {
	.owner		= THIS_MODULE,
	.open		= vogon_open,
	.read		= seq_read,
	.llseek		= seq_lseek,
	.release	= single_release
};

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

static int __init vogon_chrdevinit(void) {
	int err;

	for (int i = 0; poem[i]; i++) {
		poem_len++;
	}
	spin_lock_init(&poem_lock);

	vogon_chrdev_major = err = register_chrdev(0, VOGON_CHRDEV, &vogon_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(vogon_chrdev_major, 0), NULL, VOGON_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(vogon_chrdev_major, VOGON_CHRDEV);
out:
	return err;
}

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

module_init(vogon_chrdevinit);
module_exit(vogon_chrdevexit);
MODULE_LICENSE("LGPL");