/*
 * $Id: fscache.c,v 1.27 2003/01/19 19:29:04 tal197 Exp $
 *
 * FSCache - a glib-style object for caching files
 * Copyright (C) 2003, the ROX-Filer team.
 *
 * A cache object holds stat details about files in a hash table, along
 * with user-specified data. When you want to read in a file try to
 * get the data via the cache - if the file is cached AND has not been
 * modified since it was last loaded the cached copy is returned, else the
 * file is reloaded.
 *
 * The actual data need not be the raw file contents - a user specified
 * function loads the file and associates data with the file in the cache.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the Free
 * Software Foundation; either version 2 of the License, or (at your option)
 * any later version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program; if not, write to the Free Software Foundation, Inc., 59 Temple
 * Place, Suite 330, Boston, MA  02111-1307  USA
 */

#include "config.h"

#include "global.h"

#include "fscache.h"

typedef struct _GFSCacheKey GFSCacheKey;
typedef struct _GFSCacheData GFSCacheData;

struct _GFSCache
{
	GHashTable	*inode_to_stats;
	GFSLoadFunc	load;
	GFSUpdateFunc	update;
	gpointer	user_data;
};

struct _GFSCacheKey
{
	dev_t		device;
	ino_t		inode;
};

struct _GFSCacheData
{
	GObject		*data;		/* The object from the file */
	time_t		last_lookup;

	/* Details of the file last time we checked it */
	time_t		m_time;
	off_t		length;
	mode_t		mode;
};

#define UPTODATE(data, info)				\
		(data->m_time == info.st_mtime		\
		 && data->length == info.st_size	\
		 && data->mode == info.st_mode)		\


/* Static prototypes */

static guint hash_key(gconstpointer key);
static gint cmp_stats(gconstpointer a, gconstpointer b);
static void destroy_hash_entry(gpointer key, gpointer data, gpointer user_data);
static gboolean purge_hash_entry(gpointer key, gpointer data,
				 gpointer user_data);
static GFSCacheData *lookup_internal(GFSCache *cache, const char *pathname,
					FSCacheLookup lookup_type);


struct PurgeInfo
{
	GFSCache *cache;
	gint	 age;
	time_t	 now;
};

/****************************************************************
 *			EXTERNAL INTERFACE			*
 ****************************************************************/


/* Create a new GFSCache object and return a pointer to it.
 *
 * When someone tries to lookup a file which is not in the cache,
 * load() is called.
 * It should load the file and return a pointer to an object for the file.
 * The object should have a ref count of 1.
 *
 * ref() and unref() should modify the reference counter of the object.
 * When the counter reaches zero, destroy the object.
 * 
 * getref() returns the current value. This can be used to stop objects
 * being purged from the cache while they are being used elsewhere, which
 * is rather wasteful. If NULL then this check isn't done.
 *
 * update() will be called to update an object which is cached, but
 * out of date. If NULL, the object will be unref'd and load() used
 * to make a new one.
 * 
 * 'user_data' will be passed to all of the above functions.
 */
GFSCache *g_fscache_new(GFSLoadFunc load,
			GFSUpdateFunc update,
			gpointer user_data)
{
	GFSCache *cache;

	cache = g_new(GFSCache, 1);
	cache->inode_to_stats = g_hash_table_new(hash_key, cmp_stats);
	cache->load = load;
	cache->update = update;
	cache->user_data = user_data;

	return cache;
}

void g_fscache_destroy(GFSCache *cache)
{
	g_return_if_fail(cache != NULL);

	g_hash_table_foreach(cache->inode_to_stats, destroy_hash_entry, NULL);
	g_hash_table_destroy(cache->inode_to_stats);

	g_free(cache);
}

/* Find the data for this file in the cache, loading it into
 * the cache if it isn't there already.
 *
 * Remember to g_object_unref() the returned value when
 * you're done with it.
 *
 * Returns NULL on failure.
 */
gpointer g_fscache_lookup(GFSCache *cache, const char *pathname)
{
	return g_fscache_lookup_full(cache, pathname,
			FSCACHE_LOOKUP_CREATE, NULL);
}

/* Force this already-loaded item into the cache. The cache will
 * ref the object if it wants to keep it.
 * If update_details is FALSE then the timestamp and size aren't recorded.
 * Generally, you call this function with update_details = TRUE when you
 * start loading some data and then with update_details = FALSE when you
 * put in the loaded object.
 */
void g_fscache_insert(GFSCache *cache, const char *pathname, gpointer obj,
		      gboolean update_details)
{
	GFSCacheData	*data;

	data = lookup_internal(cache, pathname,
			update_details ? FSCACHE_LOOKUP_INIT
				       : FSCACHE_LOOKUP_INSERT);

	if (!data)
		return;

	if (obj)
		g_object_ref(obj);
	if (data->data)
		g_object_unref(data->data);
	data->data = obj;
}

/* As g_fscache_lookup, but 'lookup_type' controls what happens if the data
 * is out-of-date.
 * If found is not NULL, use it to indicate whether something is being
 * returned (a NULL return could indicate that the data is cached, but
 * the data is NULL).
 * If returned value is not NULL, value is refd.
 */
gpointer g_fscache_lookup_full(GFSCache *cache, const char *pathname,
				FSCacheLookup lookup_type,
				gboolean *found)
{
	GFSCacheData *data;

	g_return_val_if_fail(lookup_type != FSCACHE_LOOKUP_INIT, NULL);
	
	data = lookup_internal(cache, pathname, lookup_type);

	if (!data)
	{
		if (found)
			*found = FALSE;
		return NULL;
	}

	if (found)
		*found = TRUE;

	if (data->data)
		g_object_ref(data->data);

	return data->data;
}

/* Call the update() function on this item if it's in the cache
 * AND it's out-of-date.
 */
void g_fscache_may_update(GFSCache *cache, const char *pathname)
{
	GFSCacheKey	key;
	GFSCacheData	*data;
	struct stat 	info;

	g_return_if_fail(cache != NULL);
	g_return_if_fail(pathname != NULL);
	g_return_if_fail(cache->update != NULL);

	if (mc_stat(pathname, &info))
		return;

	key.device = info.st_dev;
	key.inode = info.st_ino;

	data = g_hash_table_lookup(cache->inode_to_stats, &key);

	if (data && !UPTODATE(data, info))
	{
		cache->update(data->data, pathname, cache->user_data);
		data->m_time = info.st_mtime;
		data->length = info.st_size;
		data->mode = info.st_mode;
	}
}

/* Call the update() function on this item iff it's in the cache. */
void g_fscache_update(GFSCache *cache, const char *pathname)
{
	GFSCacheKey	key;
	GFSCacheData	*data;
	struct stat 	info;

	g_return_if_fail(cache != NULL);
	g_return_if_fail(pathname != NULL);
	g_return_if_fail(cache->update != NULL);

	if (mc_stat(pathname, &info))
		return;

	key.device = info.st_dev;
	key.inode = info.st_ino;

	data = g_hash_table_lookup(cache->inode_to_stats, &key);

	if (data)
	{
		cache->update(data->data, pathname, cache->user_data);
		data->m_time = info.st_mtime;
		data->length = info.st_size;
		data->mode = info.st_mode;
	}
}

/* Remove all cache entries last accessed more than 'age' seconds
 * ago.
 */
void g_fscache_purge(GFSCache *cache, gint age)
{
	struct PurgeInfo info;
	
	g_return_if_fail(cache != NULL);

	info.age = age;
	info.cache = cache;
	info.now = time(NULL);

	g_hash_table_foreach_remove(cache->inode_to_stats, purge_hash_entry,
			(gpointer) &info);
}


/****************************************************************
 *			INTERNAL FUNCTIONS			*
 ****************************************************************/


/* Generate a hash number for some stats */
static guint hash_key(gconstpointer key)
{
	GFSCacheKey *stats = (GFSCacheKey *) key;
	
	return stats->inode;
}

/* See if two stats blocks represent the same file */
static gint cmp_stats(gconstpointer a, gconstpointer b)
{
	GFSCacheKey *c = (GFSCacheKey *) a;
	GFSCacheKey *d = (GFSCacheKey *) b;

	return c->device == d->device && c->inode == d->inode;
}

static void destroy_hash_entry(gpointer key, gpointer data, gpointer user_data)
{
	GFSCacheData *cache_data = (GFSCacheData *) data;
	
	if (cache_data->data)
		g_object_unref(cache_data->data);

	g_free(key);
	g_free(data);
}

static gboolean purge_hash_entry(gpointer key, gpointer data,
				 gpointer user_data)
{
	struct PurgeInfo *info = (struct PurgeInfo *) user_data;
	GFSCacheData *cache_data = (GFSCacheData *) data;

	/* It's wasteful to remove an entry if someone else is using it */
	if (cache_data->data && cache_data->data->ref_count > 1)
		return FALSE;

	if (cache_data->last_lookup <= info->now
		&& cache_data->last_lookup >= info->now - info->age)
		return FALSE;

	if (cache_data->data)
		g_object_unref(cache_data->data);

	g_free(key);
	g_free(data);

	return TRUE;
}

/* As for g_fscache_lookup_full, but return the GFSCacheData rather than
 * the data it contains. Doesn't increment the refcount.
 */
static GFSCacheData *lookup_internal(GFSCache *cache, const char *pathname,
					FSCacheLookup lookup_type)
{
	struct stat 	info;
	GFSCacheKey	key;
	GFSCacheData	*data;

	g_return_val_if_fail(cache != NULL, NULL);
	g_return_val_if_fail(pathname != NULL, NULL);

	if (mc_stat(pathname, &info))
		return NULL;

	key.device = info.st_dev;
	key.inode = info.st_ino;

	data = g_hash_table_lookup(cache->inode_to_stats, &key);

	if (data)
	{
		/* We've cached this file already */

		if (lookup_type == FSCACHE_LOOKUP_PEEK ||
		    lookup_type == FSCACHE_LOOKUP_INSERT)
			goto out;	/* Never update on peeks */

		if (lookup_type == FSCACHE_LOOKUP_INIT)
			goto init;

		/* Is it up-to-date? */

		if (UPTODATE(data, info))
			goto out;
		
		if (lookup_type == FSCACHE_LOOKUP_ONLY_NEW)
			return NULL;

		/* Out-of-date */
		if (cache->update)
			cache->update(data->data, pathname, cache->user_data);
		else
		{
			if (data->data)
				g_object_unref(data->data);
			data->data = NULL;
		}
	}
	else
	{
		GFSCacheKey *new_key;

		if (lookup_type != FSCACHE_LOOKUP_CREATE &&
		    lookup_type != FSCACHE_LOOKUP_INIT)
			return NULL;
		
		new_key = g_memdup(&key, sizeof(key));

		data = g_new(GFSCacheData, 1);
		data->data = NULL;

		g_hash_table_insert(cache->inode_to_stats, new_key, data);
	}

init:
	data->m_time = info.st_mtime;
	data->length = info.st_size;
	data->mode = info.st_mode;

	if (data->data == NULL &&
		lookup_type != FSCACHE_LOOKUP_INIT &&
		lookup_type != FSCACHE_LOOKUP_INSERT)
	{
		/* Create the object for the file (ie, not an update) */
		if (cache->load)
			data->data = cache->load(pathname, cache->user_data);
	}
out:
	data->last_lookup = time(NULL);

	return data;
}

