//
// Copyright 2016 Garrett D'Amore <garrett@damore.org>
//
// This software is supplied under the terms of the MIT License, a
// copy of which should be located in the distribution where this
// file was obtained (LICENSE.txt).  A copy of the license may also be
// found online at https://opensource.org/licenses/MIT.
//

#include "core/nng_impl.h"

#include <string.h>

typedef struct {
	uint32_t	ihe_key;
	uint32_t	ihe_skips;
	void *		ihe_val;
} nni_idhash_entry;

struct nni_idhash {
	uint32_t		ih_cap;
	uint32_t		ih_count;
	uint32_t		ih_load;
	uint32_t		ih_minload; // considers placeholders
	uint32_t		ih_maxload;
	uint32_t		ih_walkers;
	nni_idhash_entry *	ih_entries;
};

int
nni_idhash_create(nni_idhash **hp)
{
	nni_idhash *h;

	if ((h = NNI_ALLOC_STRUCT(h)) == NULL) {
		return (NNG_ENOMEM);
	}
	h->ih_entries = nni_alloc(8 * sizeof (nni_idhash_entry));
	if (h->ih_entries == NULL) {
		NNI_FREE_STRUCT(h);
		return (NNG_ENOMEM);
	}
	(void) memset(h->ih_entries, 0, (8 * sizeof (nni_idhash_entry)));
	h->ih_count = 0;
	h->ih_load = 0;
	h->ih_cap = 8;
	h->ih_maxload = 5;
	h->ih_minload = 0; // never shrink below this
	h->ih_walkers = 0;
	*hp = h;
	return (0);
}


void
nni_idhash_destroy(nni_idhash *h)
{
	nni_free(h->ih_entries, h->ih_cap * sizeof (nni_idhash_entry));
	NNI_FREE_STRUCT(h);
}


// Inspired by Python dict implementation.  This probe will visit every
// cell.  We always hash consecutively assigned IDs.
#define NNI_IDHASH_NEXTPROBE(h, j) \
	((((j) * 5) + 1) & (h->ih_cap - 1))

int
nni_idhash_find(nni_idhash *h, uint32_t id, void **valp)
{
	uint32_t index = id & (h->ih_cap - 1);

	for (;;) {
		if ((h->ih_entries[index].ihe_val == NULL) &&
		    (h->ih_entries[index].ihe_skips == 0)) {
			return (NNG_ENOENT);
		}
		if (h->ih_entries[index].ihe_key == id) {
			*valp = h->ih_entries[index].ihe_val;
			return (0);
		}
		index = NNI_IDHASH_NEXTPROBE(h, index);
	}
}


static int
nni_hash_resize(nni_idhash *h)
{
	uint32_t newsize;
	uint32_t oldsize;
	nni_idhash_entry *newents;
	nni_idhash_entry *oldents;
	int i;

	if ((h->ih_load < h->ih_maxload) && (h->ih_load >= h->ih_minload)) {
		// No resize needed.
		return (0);
	}
	if (h->ih_walkers && (h->ih_load < (h->ih_cap-1))) {
		// Don't resize when walkers are running.  This way
		// walk functions can remove hash nodes.
		return (0);
	}

	oldsize = h->ih_cap;
	newsize = h->ih_cap;

	newsize = 8;
	while (newsize < (h->ih_count * 2)) {
		newsize *= 2;
	}

	oldents = h->ih_entries;
	newents = nni_alloc(sizeof (nni_idhash_entry) * newsize);
	if (newents == NULL) {
		return (NNG_ENOMEM);
	}
	memset(newents, 0, sizeof (nni_idhash_entry) * newsize);

	h->ih_entries = newents;
	h->ih_cap = newsize;
	if (newsize > 8) {
		h->ih_minload = newsize / 8;
		h->ih_maxload = newsize * 2 / 3;
	} else {
		h->ih_minload = 0;
		h->ih_maxload = 5;
	}
	for (i = 0; i < oldsize; i++) {
		uint32_t index;
		if (oldents[i].ihe_val == NULL) {
			continue;
		}
		index = oldents[i].ihe_key & (newsize - 1);
		for (;;) {
			if (newents[index].ihe_val == NULL) {
				h->ih_load++;
				newents[index].ihe_val = oldents[i].ihe_val;
				newents[index].ihe_key = oldents[i].ihe_key;
				break;
			}
			newents[index].ihe_skips++;
			index = NNI_IDHASH_NEXTPROBE(h, index);
		}
	}
	nni_free(oldents, sizeof (nni_idhash_entry) * oldsize);
	return (0);
}


int
nni_idhash_remove(nni_idhash *h, uint32_t id)
{
	int rv;
	void *val;
	uint32_t index;

	// First check that it is in the table.  This may double the
	// lookup time, but it means that if we get past this then we KNOW
	// we are going to delete an element.
	if ((rv = nni_idhash_find(h, id, &val)) != 0) {
		return (rv);
	}

	index = id & (h->ih_cap - 1);

	for (;;) {
		nni_idhash_entry *ent = &h->ih_entries[index];
		if (ent->ihe_key == id) {
			ent->ihe_val = NULL;
			if (ent->ihe_skips == 0) {
				h->ih_load--;
			}
			h->ih_count--;
			break;
		}
		if (ent->ihe_skips < 1) {
			nni_panic("Skips should be nonzero!");
		}
		ent->ihe_skips--;
		if ((ent->ihe_skips == 0) && (ent->ihe_val == NULL)) {
			h->ih_load--;
		}
		index = NNI_IDHASH_NEXTPROBE(h, index);
	}

	// Shrink -- but it's ok if we can't.
	(void) nni_hash_resize(h);

	return (0);
}


int
nni_idhash_insert(nni_idhash *h, uint32_t id, void *val)
{
	uint32_t index;

	// Try to resize.  If we can't, but we still have room, go ahead
	// and store it.
	if ((nni_hash_resize(h) != 0) && (h->ih_count >= (h->ih_cap - 1))) {
		return (NNG_ENOMEM);
	}
	index = id & (h->ih_cap - 1);
	for (;;) {
		nni_idhash_entry *ent = &h->ih_entries[index];
		if ((ent->ihe_val == NULL) || (ent->ihe_key == id)) {
			if (ent->ihe_val == NULL) {
				h->ih_count++;
				h->ih_load++;
			}
			ent->ihe_key = id;
			ent->ihe_val = val;
			return (0);
		}
		ent->ihe_skips++;
		index = NNI_IDHASH_NEXTPROBE(h, index);
	}
}


int
nni_idhash_count(nni_idhash *h, uint32_t *countp)
{
	*countp = h->ih_count;
	return (0);
}


int
nni_idhash_walk(nni_idhash *h, nni_idhash_walkfn fn, void *arg)
{
	int i, rv;

	for (i = 0; i < h->ih_cap; i++) {
		nni_idhash_entry *ent = &h->ih_entries[i];

		if (ent->ihe_val == NULL) {
			continue;
		}
		rv = fn(arg, ent->ihe_key, ent->ihe_val);
		if (rv != 0) {
			return (rv);
		}
	}
	return (0);
}