#include "fitz.h"

/*
Simple hashtable with open addressing linear probe.
Unlike text book examples, removing entries works
correctly in this implementation, so it wont start
exhibiting bad behaviour if entries are inserted
and removed frequently.
*/

enum { MAX_KEY_LEN = 48 };
typedef struct fz_hash_entry_s fz_hash_entry;

struct fz_hash_entry_s
{
	unsigned char key[MAX_KEY_LEN];
	void *val;
};

struct fz_hash_table_s
{
	int keylen;
	int size;
	int load;
	fz_hash_entry *ents;
};

static unsigned hash(unsigned char *s, int len)
{
	unsigned val = 0;
	int i;
	for (i = 0; i < len; i++)
	{
		val += s[i];
		val += (val << 10);
		val ^= (val >> 6);
	}
	val += (val << 3);
	val ^= (val >> 11);
	val += (val << 15);
	return val;
}

fz_hash_table *
fz_new_hash_table(fz_context *ctx, int initialsize, int keylen)
{
	fz_hash_table *table;

	assert(keylen <= MAX_KEY_LEN);

	table = fz_malloc_struct(ctx, fz_hash_table);
	table->keylen = keylen;
	table->size = initialsize;
	table->load = 0;
	fz_try(ctx)
	{
		table->ents = fz_malloc_array(ctx, table->size, sizeof(fz_hash_entry));
		memset(table->ents, 0, sizeof(fz_hash_entry) * table->size);
	}
	fz_catch(ctx)
	{
		fz_free(ctx, table);
		fz_rethrow(ctx);
	}

	return table;
}

void
fz_empty_hash(fz_context *ctx, fz_hash_table *table)
{
	table->load = 0;
	memset(table->ents, 0, sizeof(fz_hash_entry) * table->size);
}

int
fz_hash_len(fz_context *ctx, fz_hash_table *table)
{
	return table->size;
}

void *
fz_hash_get_key(fz_context *ctx, fz_hash_table *table, int idx)
{
	return table->ents[idx].key;
}

void *
fz_hash_get_val(fz_context *ctx, fz_hash_table *table, int idx)
{
	return table->ents[idx].val;
}

void
fz_free_hash(fz_context *ctx, fz_hash_table *table)
{
	fz_free(ctx, table->ents);
	fz_free(ctx, table);
}

static void
fz_resize_hash(fz_context *ctx, fz_hash_table *table, int newsize)
{
	fz_hash_entry *oldents = table->ents;
	int oldsize = table->size;
	int oldload = table->load;
	int i;

	if (newsize < oldload * 8 / 10)
	{
		fz_warn(ctx, "assert: resize hash too small");
		return;
	}

	table->ents = fz_malloc_array(ctx, newsize, sizeof(fz_hash_entry));
	memset(table->ents, 0, sizeof(fz_hash_entry) * newsize);
	table->size = newsize;
	table->load = 0;

	for (i = 0; i < oldsize; i++)
	{
		if (oldents[i].val)
		{
			fz_hash_insert(ctx, table, oldents[i].key, oldents[i].val);
		}
	}

	fz_free(ctx, oldents);
}

void *
fz_hash_find(fz_context *ctx, fz_hash_table *table, void *key)
{
	fz_hash_entry *ents = table->ents;
	unsigned size = table->size;
	unsigned pos = hash(key, table->keylen) % size;

	while (1)
	{
		if (!ents[pos].val)
			return NULL;

		if (memcmp(key, ents[pos].key, table->keylen) == 0)
			return ents[pos].val;

		pos = (pos + 1) % size;
	}
}

void
fz_hash_insert(fz_context *ctx, fz_hash_table *table, void *key, void *val)
{
	fz_hash_entry *ents;
	unsigned size;
	unsigned pos;

	if (table->load > table->size * 8 / 10)
	{
		fz_resize_hash(ctx, table, table->size * 2);
	}

	ents = table->ents;
	size = table->size;
	pos = hash(key, table->keylen) % size;

	while (1)
	{
		if (!ents[pos].val)
		{
			memcpy(ents[pos].key, key, table->keylen);
			ents[pos].val = val;
			table->load ++;
			return;
		}

		if (memcmp(key, ents[pos].key, table->keylen) == 0)
			fz_warn(ctx, "assert: overwrite hash slot");

		pos = (pos + 1) % size;
	}
}

void
fz_hash_remove(fz_context *ctx, fz_hash_table *table, void *key)
{
	fz_hash_entry *ents = table->ents;
	unsigned size = table->size;
	unsigned pos = hash(key, table->keylen) % size;
	unsigned hole, look, code;

	while (1)
	{
		if (!ents[pos].val)
		{
			fz_warn(ctx, "assert: remove inexistent hash entry");
			return;
		}

		if (memcmp(key, ents[pos].key, table->keylen) == 0)
		{
			ents[pos].val = NULL;

			hole = pos;
			look = (hole + 1) % size;

			while (ents[look].val)
			{
				code = hash(ents[look].key, table->keylen) % size;
				if ((code <= hole && hole < look) ||
					(look < code && code <= hole) ||
					(hole < look && look < code))
				{
					ents[hole] = ents[look];
					ents[look].val = NULL;
					hole = look;
				}

				look = (look + 1) % size;
			}

			table->load --;

			return;
		}

		pos = (pos + 1) % size;
	}
}

void
fz_debug_hash(fz_context *ctx, fz_hash_table *table)
{
	int i, k;

	printf("cache load %d / %d\n", table->load, table->size);

	for (i = 0; i < table->size; i++)
	{
		if (!table->ents[i].val)
			printf("table % 4d: empty\n", i);
		else
		{
			printf("table % 4d: key=", i);
			for (k = 0; k < MAX_KEY_LEN; k++)
				printf("%02x", ((char*)table->ents[i].key)[k]);
			printf(" val=$%p\n", table->ents[i].val);
		}
	}
}