/* g-lru-cache.c
 *
 * Copyright (C) 2009 - Christian Hergert
 *
 * This is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 * 
 * This 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
 * Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */

/* 
 * Ideally, you want to use fast_get. This is because we are using a
 * GStaticRWLock which is indeed slower than a mutex if you have lots of writer
 * acquisitions. This doesn't make it a true LRU, though, as the oldest
 * retrieval from strorage is the first item evicted.
 */

#include "g-lru-cache.h"

// #define DEBUG

#define LRU_CACHE_PRIVATE(object)          \
    (G_TYPE_INSTANCE_GET_PRIVATE((object), \
    G_TYPE_LRU_CACHE,                      \
    GLruCachePrivate))

struct _GLruCachePrivate
{
    GStaticRWLock   rw_lock;
    guint           max_size;
    gboolean        fast_get;
    
    GHashTable     *hash_table;
    GEqualFunc      key_equal_func;
    GCopyFunc       key_copy_func;
    GList          *newest;
    GList          *oldest;
    
    GLookupFunc     retrieve_func;
    
    gpointer        user_data;
    GDestroyNotify  user_destroy_func;
};

G_DEFINE_TYPE (GLruCache, g_lru_cache, G_TYPE_OBJECT);

static void
g_lru_cache_finalize (GObject *object)
{
    GLruCachePrivate *priv = LRU_CACHE_PRIVATE (object);
    
    if (priv->user_data && priv->user_destroy_func)
        priv->user_destroy_func (priv->user_data);
    
    priv->user_data = NULL;
    priv->user_destroy_func = NULL;
    
    g_hash_table_destroy (priv->hash_table);
    priv->hash_table = NULL;
    
    g_list_free (priv->newest);
    priv->newest = NULL;
    priv->oldest = NULL;
    
    G_OBJECT_CLASS (g_lru_cache_parent_class)->finalize (object);
}

static void
g_lru_cache_class_init (GLruCacheClass *klass)
{
    GObjectClass *object_class = G_OBJECT_CLASS (klass);
    
    object_class->finalize = g_lru_cache_finalize;

    g_type_class_add_private (object_class, sizeof (GLruCachePrivate));
}

static void
g_lru_cache_init (GLruCache *self)
{
    self->priv = LRU_CACHE_PRIVATE (self);
    
    self->priv->max_size = 1024;
    self->priv->fast_get = FALSE;
    g_static_rw_lock_init (&self->priv->rw_lock);
}

static void
g_lru_cache_evict_n_oldest_locked (GLruCache *self, gint n)
{
    GList *victim;
    gint   i;
    
    for (i = 0; i < n; i++)
    {
        victim = self->priv->oldest;
        
        if (victim == NULL)
            return;
        
        if (victim->prev)
            victim->prev->next = NULL;
        
        self->priv->oldest = victim->prev;
        g_hash_table_remove (self->priv->hash_table, victim->data);
        
        if (self->priv->newest == victim)
            self->priv->newest = NULL;
        
        g_list_free1 (victim); /* victim->data is owned by hashtable */
    }
    
#ifdef DEBUG
    g_assert (g_hash_table_size (self->priv->hash_table) == g_list_length (self->priv->newest));
#endif
}

GLruCache*
g_lru_cache_new (GHashFunc      hash_func,
                 GEqualFunc     key_equal_func,
                 GCopyFunc      key_copy_func,
                 GLookupFunc    retrieve_func,
                 GDestroyNotify key_destroy_func,
                 GDestroyNotify value_destroy_func,
                 gpointer       user_data,
                 GDestroyNotify user_destroy_func)
{
    GLruCache *self = g_object_new (G_TYPE_LRU_CACHE, NULL);
    
    self->priv->hash_table = g_hash_table_new_full (hash_func,
                                                    key_equal_func,
                                                    key_destroy_func,
                                                    value_destroy_func);
    
    self->priv->key_equal_func = key_equal_func;
    self->priv->key_copy_func = key_copy_func;
    self->priv->retrieve_func = retrieve_func;
    self->priv->user_data = user_data;
    self->priv->user_destroy_func = user_destroy_func;
    
    return self;
}

void
g_lru_cache_set_max_size (GLruCache *self, guint max_size)
{
    g_return_if_fail (G_IS_LRU_CACHE (self));
    
    guint old_max_size = self->priv->max_size;
    
    g_static_rw_lock_writer_lock (&(self->priv->rw_lock));
    
    self->priv->max_size = max_size;
    
    if (old_max_size > max_size)
        g_lru_cache_evict_n_oldest_locked (self, old_max_size - max_size);
    
    g_static_rw_lock_writer_unlock (&(self->priv->rw_lock));
}

guint
g_lru_cache_get_max_size (GLruCache *self)
{
    g_return_val_if_fail (G_IS_LRU_CACHE (self), -1);
    return self->priv->max_size;
}

guint
g_lru_cache_get_size (GLruCache *self)
{
    g_return_val_if_fail (G_IS_LRU_CACHE (self), -1);
    return g_hash_table_size (self->priv->hash_table);
}

gpointer
g_lru_cache_get (GLruCache *self, gpointer key)
{
    g_return_val_if_fail (G_IS_LRU_CACHE (self), NULL);
    
    gpointer value;
    
    g_static_rw_lock_reader_lock (&(self->priv->rw_lock));
    
    value = g_hash_table_lookup (self->priv->hash_table, key);
    
#ifdef DEBUG
    if (value)
        g_debug ("Cache Hit!");
    else
        g_debug ("Cache miss");
#endif
    
    g_static_rw_lock_reader_unlock (&(self->priv->rw_lock));
    
    if (!value)
    {
        g_static_rw_lock_writer_lock (&(self->priv->rw_lock));
        
        if (!g_hash_table_lookup (self->priv->hash_table, key))
        {
            if (g_hash_table_size (self->priv->hash_table) >= self->priv->max_size)
#ifdef DEBUG
            {
                g_debug ("We are at capacity, must evict oldest");
#endif
                g_lru_cache_evict_n_oldest_locked (self, 1);
#ifdef DEBUG
            }
            
            g_debug ("Retrieving value from external resource");
#endif

            value = self->priv->retrieve_func (key, self->priv->user_data);
            
            if (self->priv->key_copy_func)
                g_hash_table_insert (self->priv->hash_table,
                    self->priv->key_copy_func (key, self->priv->user_data),
                    value);
            else
                g_hash_table_insert (self->priv->hash_table, key, value);
            
            self->priv->newest = g_list_prepend (self->priv->newest, key);
            
            if (self->priv->oldest == NULL)
                self->priv->oldest = self->priv->newest;
        }
#ifdef DEBUG
        else g_debug ("Lost storage race with another thread");
#endif
        
        g_static_rw_lock_writer_unlock (&(self->priv->rw_lock));
    }

    /* fast_get means that we do not reposition the item to the head
     * of the list. it essentially makes the lru, a lru from storage,
     * not lru to user.
     */

    else if (!self->priv->fast_get &&
             !self->priv->key_equal_func (key, self->priv->newest->data))
    {
#ifdef DEBUG
        g_debug ("Making item most recent");
#endif

        g_static_rw_lock_writer_lock (&(self->priv->rw_lock));

        GList *list = self->priv->newest;
        GList *tmp;
        GEqualFunc equal = self->priv->key_equal_func;

        for (tmp = list; tmp; tmp = tmp->next)
        {
            if (equal (key, tmp->data))
            {
                GList *tmp1 = g_list_remove_link (list, tmp);
                self->priv->newest = g_list_prepend (tmp1, tmp);
                break;
            }
        }

        g_static_rw_lock_writer_unlock (&(self->priv->rw_lock));
    }
    
    return value;
}

void
g_lru_cache_evict (GLruCache *self, gpointer key)
{
    g_return_if_fail (G_IS_LRU_CACHE (self));
    
    GEqualFunc  equal = self->priv->key_equal_func;
    GList      *list  = NULL;
    
    g_static_rw_lock_writer_lock (&(self->priv->rw_lock));
    
    if (equal (key, self->priv->oldest))
    {
        g_lru_cache_evict_n_oldest_locked (self, 1);
    }
    else
    {        
        for (list = self->priv->newest; list; list = list->next)
        {
            /* key, list->data is owned by hashtable */
            if (equal (key, list->data))
            {
                self->priv->newest = g_list_remove_link (self->priv->newest, list);
                g_list_free (list);
                break;
            }
        }
        g_hash_table_remove (self->priv->hash_table, key);
    }
    
    g_static_rw_lock_writer_unlock (&(self->priv->rw_lock));
}

void
g_lru_cache_clear (GLruCache *self)
{
    g_return_if_fail (G_IS_LRU_CACHE (self));
    
    g_static_rw_lock_writer_lock (&(self->priv->rw_lock));
    
    g_hash_table_remove_all (self->priv->hash_table);
    g_list_free (self->priv->newest);
    
    self->priv->oldest = NULL;
    self->priv->newest = NULL;
    
    g_static_rw_lock_writer_unlock (&(self->priv->rw_lock));
}

void
g_lru_cache_set_fast_get (GLruCache *self, gboolean fast_get)
{
    g_return_if_fail (G_IS_LRU_CACHE (self));
    self->priv->fast_get = fast_get;
}

gboolean
g_lru_cache_get_fast_get (GLruCache *self)
{
    g_return_val_if_fail (G_IS_LRU_CACHE (self), FALSE);
    return self->priv->fast_get;
}