path: root/calendar/pcs/cal-backend-db.c

/* Evolution calendar - iCalendar DB backend
 *
 * Copyright (C) 2001 Ximian, Inc.
 *
 * Author: Rodrigo Moya <rodrigo@ximian.com>
 *
 * 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 <gtk/gtkobject.h>
#include "cal-util/cal-recur.h"
#include "cal-backend-db.h"
#include <db.h>
#if DB_MAJOR_VERSION < 3
#  error "You need libdb3 to compile the DB backend"
#endif

/* structure to identify an open cursor */
typedef struct {
    DBC* dbc;
    DB*  parent_db;
    /* TODO: convert into a hash table */
    GList* keys;
    GList* data;
} CalBackendDBCursor;

/* private part of the CalBackendDB structure */
struct _CalBackendDBPrivate {
    /* URI where the calendar data is stored */
    GnomeVFSURI *uri;

    /* Berkeley DB's library handles */
    DB *objects_db;
    DB *history_db;

    /* list of open cursors */
    GList *cursors;

    /* list of clients using this backend */
    GList *clients;
};

static void cal_backend_db_class_init (CalBackendDBClass *klass);
static void cal_backend_db_init (CalBackendDB *cbdb);
static void cal_backend_db_destroy (GtkObject *object);

static GnomeVFSURI *cal_backend_db_get_uri (CalBackend *backend);
static void cal_backend_db_add_cal (CalBackend *backend, Cal *cal);
static CalBackendOpenStatus cal_backend_db_open (CalBackend *backend,
                                                 GnomeVFSURI *uri,
                                                 gboolean only_if_exists);

static int cal_backend_db_get_n_objects (CalBackend *backend, CalObjType type);
static char *cal_backend_db_get_object (CalBackend *backend, const char *uid);
static CalObjType cal_backend_db_get_type_by_uid (CalBackend *backend, const char *uid);
static GList* cal_backend_db_get_uids (CalBackend *backend, CalObjType type);
static GList* cal_backend_db_get_objects_in_range (CalBackend *backend,
                                                   CalObjType type,
                                                   time_t start,
                                                   time_t end);
static GNOME_Evolution_Calendar_CalObjChangeSeq *cal_backend_db_get_changes (
    CalBackend *backend, CalObjType type, const char *change_id);

static GNOME_Evolution_Calendar_CalComponentAlarmsSeq *cal_backend_db_get_alarms_in_range (
    CalBackend *backend, time_t start, time_t end);

static GNOME_Evolution_Calendar_CalComponentAlarms *cal_backend_db_get_alarms_for_object (
    CalBackend *backend, const char *uid, time_t start, time_t end, gboolean *object_found);

static gboolean cal_backend_db_update_object (CalBackend *backend,
                                              const char *uid,
                                              const char *calobj);
static gboolean cal_backend_db_remove_object (CalBackend *backend, const char *uid);

static void close_cursor (CalBackendDB *cbdb, CalBackendDBCursor *cursor);
static CalBackendDBCursor* open_cursor (CalBackendDB *cbdb, DB *db);
static CalBackendDBCursor* find_cursor_by_db (CalBackendDB *cbdb, DB *db);
static DBT* find_record_by_id (CalBackendDBCursor *cursor, const gchar *id);

static CalBackendClass *parent_class;

/**
 * cal_backend_db_get_type:
 * @void:
 *
 * Registers the #CalBackendDB class if necessary and returns the type ID
 * associated to it.
 *
 * Return value: The type ID of the #CalBackendDB class.
 */
GtkType
cal_backend_db_get_type (void)
{
    static GtkType cal_backend_db_type = 0;

    if (!cal_backend_db_type) {
        static const GtkTypeInfo cal_backend_db_info = {
            "CalBackendDB",
            sizeof (CalBackendDB),
            sizeof (CalBackendDBClass),
            (GtkClassInitFunc) cal_backend_db_class_init,
            (GtkObjectInitFunc) cal_backend_db_init,
            NULL,
            NULL,
            (GtkClassInitFunc) NULL
        };

        cal_backend_db_type = gtk_type_unique(CAL_BACKEND_TYPE, &cal_backend_db_info);
    }

    return cal_backend_db_type;
}

/* class initialization function for the DB backend */
static void
cal_backend_db_class_init (CalBackendDBClass *klass)
{
    GtkObjectClass *object_class;
    CalBackendClass *backend_class;

    object_class = (GtkObjectClass *) klass;
    backend_class = (CalBackendClass *) klass;

    parent_class = gtk_type_class(CAL_BACKEND_TYPE);

    object_class->destroy = cal_backend_db_destroy;

    backend_class->get_uri = cal_backend_db_get_uri;
    backend_class->add_cal = cal_backend_db_add_cal;
    backend_class->open = cal_backend_db_open;
    backend_class->get_n_objects = cal_backend_db_get_n_objects;
    backend_class->get_object = cal_backend_db_get_object;
    backend_class->get_type_by_uid = cal_backend_db_get_type_by_uid;
    backend_class->get_uids = cal_backend_db_get_uids;
    backend_class->get_objects_in_range = cal_backend_db_get_objects_in_range;
    backend_class->get_changes = cal_backend_db_get_changes;
    backend_class->get_alarms_in_range = cal_backend_db_get_alarms_in_range;
    backend_class->get_alarms_for_object = cal_backend_db_get_alarms_for_object;
    backend_class->update_object = cal_backend_db_update_object;
    backend_class->remove_object = cal_backend_db_remove_object;
}

/* object initialization function for the DB backend */
static void
cal_backend_db_init (CalBackendDB *cbdb)
{
    CalBackendDBPrivate *priv;

    priv = g_new0(CalBackendDBPrivate, 1);
    cbdb->priv = priv;
}

/* Destroy handler for the DB backend */
static void
cal_backend_db_destroy (GtkObject *object)
{
    CalBackendDB *cbdb;
    CalBackendDBPrivate *priv;
    GList *node;

    g_return_if_fail(object != NULL);
    g_return_if_fail(IS_CAL_BACKEND_DB(object));

    cbdb = CAL_BACKEND_DB(object);
    priv = cbdb->priv;

    g_assert(cbdb->priv->clients == NULL);

    /* clean up */
    if (priv->uri) {
        gnome_vfs_uri_unref(priv->uri);
        priv->uri = NULL;
    }

    /* close open cursors */
    while ((node = g_list_first(cbdb->priv->cursors))) {
        close_cursor(cbdb, (CalBackendDBCursor *) node->data);
    }

    /* close open databases */
    if (cbdb->priv->objects_db)
        cbdb->priv->objects_db->close(cbdb->priv->objects_db, 0);
    if (cbdb->priv->history_db)
        cbdb->priv->history_db->close(cbdb->priv->history_db, 0);

    g_free((gpointer) priv);
    cbdb->priv = NULL;

    if (GTK_OBJECT_CLASS(parent_class)->destroy)
        (*GTK_OBJECT_CLASS(parent_class)->destroy)(object);
}

/*
 * Private functions
 */

/* close an open cursor and frees all associated memory */
static void
close_cursor (CalBackendDB *cbdb, CalBackendDBCursor *cursor)
{
    GList *node;
    DBT *dbt;

    g_return_if_fail(cursor != NULL);

    /* free all keys and data */
    while ((node = g_list_first(cursor->keys))) {
        dbt = (DBT *) node->data;
        cursor->keys = g_list_remove(cursor->keys, (gpointer) dbt);
        g_free((gpointer) dbt);
    }
    while ((node = g_list_first(cursor->data))) {
        dbt = (DBT *) node->data;
        cursor->data = g_list_remove(cursor->data, (gpointer) dbt);
        g_free((gpointer) dbt);
    }

    /* finally, close the cursor */
    cursor->dbc->c_close(cursor->dbc);

    cbdb->priv->cursors = g_list_remove(cbdb->priv->cursors, (gpointer) cursor);
    g_free((gpointer) cursor);
}

/* open a cursor for the given database */
static CalBackendDBCursor *
open_cursor (CalBackendDB *cbdb, DB *db)
{
    CalBackendDBCursor *cursor;
    gint ret;

    g_return_val_if_fail(IS_CAL_BACKEND_DB(cbdb), NULL);
    g_return_val_if_fail(db != NULL, NULL);

    /* search for the cursor in our list of cursors */
    cursor = find_cursor_by_db(cbdb, db);
    if (cursor)
        return cursor;

    /* create the cursor */
    cursor = g_new0(CalBackendDBCursor, 1);
    cursor->parent_db = db;

    ret = db->cursor(db, NULL, &cursor->dbc, 0);
    if (ret == 0) {
        DBT key;
        DBT data;

        /* read data */
        while ((ret = cursor->dbc->c_get(cursor->dbc, &key, &data, DB_NEXT)) == 0) {
            cursor->keys = g_list_append(cursor->keys, g_memdup(&key, sizeof(key)));
            cursor->data = g_list_append(cursor->data, g_memdup(&data, sizeof(data)));
        }
        if (ret == DB_NOTFOUND) {
            cbdb->priv->cursors = g_list_prepend(cbdb->priv->cursors,
                                 (gpointer) cursor);
            return cursor;
        }

        /* close cursor on error */
        close_cursor(cbdb, cursor);
    }

    return NULL;
}

/* search for a cursor in the given backend */
static CalBackendDBCursor *
find_cursor_by_db (CalBackendDB *cbdb, DB *db)
{
    GList *node;

    g_return_val_if_fail(IS_CAL_BACKEND_DB(cbdb), NULL);
    g_return_val_if_fail(cbdb->priv != NULL, NULL);
    g_return_val_if_fail(db != NULL, NULL);

    for (node = g_list_first(cbdb->priv->cursors); node != NULL; node = g_list_next(node)) {
        CalBackendDBCursor* cursor = (CalBackendDBCursor *) node->data;
        if (cursor && cursor->parent_db == db)
            return cursor;
    }

    return NULL; /* not found */
}

/* finds a record in a cursor by its ID */
static DBT *
find_record_by_id (CalBackendDBCursor *cursor, const gchar *id)
{
    GList *node;
    gint pos = 0;

    g_return_val_if_fail(cursor != NULL, NULL);
    g_return_val_if_fail(id != NULL, NULL);

    for (node = g_list_first(cursor->keys); node != NULL; node = g_list_next(node)) {
        DBT* key = (DBT *) node->data;
        if (key) {
            if (!strcmp(key->data, id)) {
                GList* tmp = g_list_nth(cursor->data, pos);
                if (tmp)
                    return (DBT *) node->data;
            }
        }
        pos++;
    }

    return NULL; /* not found */
}

/*
 * Calendar backend methods
 */

/* get_uri handler for the DB backend */
static GnomeVFSURI *
cal_backend_db_get_uri (CalBackend *backend)
{
    CalBackendDB *cbdb;

    cbdb = CAL_BACKEND_DB(backend);
    g_return_val_if_fail(IS_CAL_BACKEND_DB(cbdb), NULL);
    g_return_val_if_fail(cbdb->priv != NULL, NULL);

    return cbdb->priv->uri;
}

/* callback used when a Cal is destroyed */
static void
destroy_cal_cb (GtkObject *object, gpointer data)
{
    Cal *cal;
    Cal *tmp_cal;
    CalBackendDB *cbdb;
    GList *node;

    cal = CAL(object);
    cbdb = CAL_BACKEND_DB(data);
    
    g_return_if_fail(IS_CAL_BACKEND_DB(cbdb));
    g_return_if_fail(cbdb->priv != NULL);

    /* find the Cal in the list of clients */
    for (node = cbdb->priv->clients; node != NULL; node = g_list_next(node)) {
        tmp_cal = CAL(node->data);
        if (tmp_cal == cal)
            break;
    }

    if (node) {
        /* disconnect this Cal */
        cbdb->priv->clients = g_list_remove_link(cbdb->priv->clients, node);
        g_list_free_1(node);

        /* when all clients go away, notify the parent factory about it so that
         * it may decide to kill the backend or not.
         */
        if (!cbdb->priv->clients)
            cal_backend_last_client_gone(CAL_BACKEND(cbdb));
    }
}

/* add_cal_handler for the DB backend */
static void
cal_backend_db_add_cal (CalBackend *backend, Cal *cal)
{
    CalBackendDB *cbdb;

    cbdb = CAL_BACKEND_DB(backend);
    g_return_if_fail(IS_CAL_BACKEND_DB(cbdb));
    g_return_if_fail(cbdb->priv != NULL);
    g_return_if_fail(IS_CAL(cal));

    /* we do not keep a reference to the Cal since the calendar user agent
     * owns it
     */
    gtk_signal_connect(GTK_OBJECT(cal),
                       "destroy",
                       GTK_SIGNAL_FUNC(destroy_cal_cb),
                       backend);

    cbdb->priv->clients = g_list_prepend(cbdb->priv->clients, (gpointer) cal);
}

/* database file initialization */
static gboolean
open_database_file (CalBackendDB *cbdb, const gchar *str_uri, gboolean only_if_exists)
{
    gint ret;

    g_return_val_if_fail(IS_CAL_BACKEND_DB(cbdb), FALSE);
    g_return_val_if_fail(cbdb->priv != NULL, FALSE);
    g_return_val_if_fail(cbdb->priv->objects_db != NULL, FALSE);
    g_return_val_if_fail(cbdb->priv->history_db != NULL, FALSE);
    g_return_val_if_fail(str_uri != NULL, FALSE);

    /* open/create objects database into given file */
    if (only_if_exists) {
        ret = cbdb->priv->objects_db->open(cbdb->priv->objects_db,
                                           str_uri,
                                           "calendar_objects",
                                           DB_HASH,
                                           0,
                                           0644);
    }
    else {
        ret = cbdb->priv->objects_db->open(cbdb->priv->objects_db,
                                           str_uri,
                                           "calendar_objects",
                                           DB_HASH,
                                           DB_CREATE,
                                           0644);
    }
    if (ret == 0) {
        /* now, open the history database */
        ret = cbdb->priv->history_db->open(cbdb->priv->history_db,
                                           str_uri,
                                           "calendar_history",
                                           DB_BTREE,
                                           DB_CREATE,
                                           0644);
        if (ret == 0) return TRUE;

        /* close objects database on error */
        cbdb->priv->objects_db->close(cbdb->priv->objects_db, 0);
    }

    return FALSE;
}

/* open handler for the DB backend */
static CalBackendOpenStatus
cal_backend_db_open (CalBackend *backend, GnomeVFSURI *uri, gboolean only_if_exists)
{
    CalBackendDB *cbdb;
    gchar *str_uri;
    gint ret;

    cbdb = CAL_BACKEND_DB(backend);
    g_return_val_if_fail(IS_CAL_BACKEND_DB(cbdb), CAL_BACKEND_OPEN_ERROR);
    g_return_val_if_fail(cbdb->priv != NULL, CAL_BACKEND_OPEN_ERROR);
    g_return_val_if_fail(uri != NULL, CAL_BACKEND_OPEN_ERROR);
    g_return_val_if_fail(cbdb->priv->objects_db == NULL, CAL_BACKEND_OPEN_ERROR);

    /* open the given URI */
    if (!gnome_vfs_uri_is_local(uri))
        return CAL_BACKEND_OPEN_ERROR;
    str_uri = gnome_vfs_uri_to_string(uri,
                      (GNOME_VFS_URI_HIDE_USER_NAME
                       | GNOME_VFS_URI_HIDE_PASSWORD
                       | GNOME_VFS_URI_HIDE_HOST_NAME
                       | GNOME_VFS_URI_HIDE_HOST_PORT
                       | GNOME_VFS_URI_HIDE_TOPLEVEL_METHOD));

    /* open database file */
    if ((ret = db_create(&cbdb->priv->objects_db, NULL, 0)) != 0
        || (ret = db_create(&cbdb->priv->history_db, NULL, 0)) != 0) {
        g_free((gpointer) str_uri);
        return CAL_BACKEND_OPEN_ERROR;
    }
    if (!open_database_file(cbdb, (const gchar *) str_uri, only_if_exists)) {
        g_free((gpointer) str_uri);
        return CAL_BACKEND_OPEN_ERROR;
    }

    gnome_vfs_uri_ref(uri);
    cbdb->priv->uri = uri;
    g_free((gpointer) str_uri);

    return CAL_BACKEND_OPEN_SUCCESS;
}

/* get_n_objects handler for the DB backend */
static int
cal_backend_db_get_n_objects (CalBackend *backend, CalObjType type)
{
    CalBackendDB *cbdb;
    CalBackendDBCursor *cursor;
    int total_count = 0;

    cbdb = CAL_BACKEND_DB(backend);
    g_return_val_if_fail(IS_CAL_BACKEND_DB(cbdb), -1);
    g_return_val_if_fail(cbdb->priv != NULL, -1);

    /* open the cursor */
    cursor = open_cursor(cbdb, cbdb->priv->objects_db);
    if (cursor) {
        GList *node;

        /* we traverse all data, to check for each object's type */
        for (node = g_list_first(cursor->data); node != NULL; node = g_list_next(node)) {
            icalcomponent *icalcomp;
            DBT *data = (DBT *) node->data;

            icalcomp = icalparser_parse_string((char *) data->data);
            if (icalcomp) {
                switch (icalcomponent_isa(icalcomp)) {
                case ICAL_VEVENT_COMPONENT :
                    if (type & CALOBJ_TYPE_EVENT)
                        total_count++;
                    break;
                case ICAL_VTODO_COMPONENTS :
                    if (type & CALOBJ_TYPE_TODO)
                        total_count++;
                    break;
                case ICAL_VJOURNAL_COMPONENT :
                    if (type & CALOBJ_TYPE_JOURNAL)
                        total_count++;
                    break;
                }
                icalcomponent_free(icalcomp);
            }
        }
    }

    return total_count;
}

/* get_object handler for the DB backend */
static char *
cal_backend_db_get_object (CalBackend *backend, const char *uid)
{
    CalBackendDB *cbdb;
    CalBackendDBCursor *cursor;

    cbdb = CAL_BACKEND_DB(backend);
    g_return_val_if_fail(IS_CAL_BACKEND_DB(cbdb), NULL);
    g_return_val_if_fail(cbdb->priv != NULL, NULL);
    g_return_val_if_fail(cbdb->priv->objects_db != NULL, NULL);
    g_return_val_if_fail(uid != NULL, NULL);

    /* open cursor */
    cursor = open_cursor(cbdb, cbdb->priv->objects_db);
    if (cursor) {
        gint ret;
        DBT *data;

        data = find_record_by_id(cursor, uid);
        if (data)
            return (char *) data->data;
    }

    return NULL;
}

/* get_type_by_uid handler for the DB backend */
static CalObjType
cal_backend_db_get_type_by_uid (CalBackend *backend, const char *uid)
{
    CalBackendDB *cbdb;
    CalBackendDBCursor *cursor;

    cbdb = CAL_BACKEND_DB(backend);
    g_return_val_if_fail(IS_CAL_BACKEND_DB(cbdb), CAL_COMPONENT_NO_TYPE);
    g_return_val_if_fail(cbdb->priv != NULL, CAL_COMPONENT_NO_TYPE);
    g_return_val_if_fail(cbdb->priv->objects_db != NULL, CAL_COMPONENT_NO_TYPE);
    g_return_val_if_fail(uid != NULL, CAL_COMPONENT_NO_TYPE);

    /* open the cursor */
    cursor = open_cursor(cbdb, cbdb->priv->objects_db);
    if (cursor) {
        DBT *data = find_record_by_id(cursor, uid);
        if (data) {
            icalcomponent icalcomp = icalparser_parse_string((char *) data->data);
            if (icalcomp) {
                CalObjType type;

                switch (icalcomponent_isa(icalcomp)) {
                case ICAL_VEVENT_COMPONENT :
                    type = CALOBJ_TYPE_EVENT;
                    break;
                case ICAL_VTODO_COMPONENT :
                    type = CALOBJ_TYPE_TODO;
                    break;
                case ICAL_VJOURNAL_COMPONENT :
                    type = CALOBJ_TYPE_JOURNAL;
                    break;
                default :
                    type CAL_COMPONENT_NO_TYPE;
                }

                icalcomponent_free(icalcomp);
                return type;
            }
        }
    }

    return CAL_COMPONENT_NO_TYPE;
}

static GList *
add_uid_if_match (GList *list, CalBackendDBCursor *cursor, GList *data_node, CalObjType type)
{
    DBT *data;

    g_return_val_if_fail(cursor != NULL, list);
    g_return_val_if_fail(data_node != NULL, list);
    
    data = (DBT *) data_node->data;
    if (data) {
        icalcomponent *icalcomp;
        gchar *uid;

        icalcomp = icalparser_parse_string(data->data);
        if (!icalcomp) return list;
        switch (icalcomponent_isa(icalcomp)) {
        case ICAL_VEVENT_COMPONENT :
            if (type & CALOBJ_TYPE_EVENT)
                uid = icalcomponent_get_uid(icalcomp);
            break;
        case ICAL_VTODO_COMPONENT :
            if (type & CALOBJ_TYPE_TODO)
                uid = icalcomponent_get_uid(icalcomp);
            break;
        case ICAL_VJOURNAL_COMPONENT :
            if (type & CALOBJ_TYPE_JOURNAL)
                uid = icalcomponent_get_uid(icalcomp);
            break;
        default :
            uid = NULL;
        }

        if (uid)
            list = g_list_prepend(list, g_strdup(uid));
        icalcomponent_free(icalcomp);
    }

    return list;
}

/* get_uids handler for the DB backend */
static GList *
cal_backend_db_get_uids (CalBackend *backend, CalObjType type)
{
    CalBackendDB *cbdb;
    GList *list = NULL;
    CalBackendDBCursor *cursor;

    cbdb = CAL_BACKEND_DB(backend);
    g_return_val_if_fail(IS_CAL_BACKEND_DB(cbdb), NULL);
    g_return_val_if_fail(cbdb->priv != NULL, NULL);
    g_return_val_if_fail(cbdb->priv->objects_db != NULL, NULL);

    /* open cursor */
    cursor = open_cursor(cbdb, cbdb->priv->objects_db);
    if (cursor) {
        GList *node;

        /* we traverse all data, to check for each object's type */
        for (node = g_list_first(cursor->data); node != NULL; node = g_list_next(node)) {
            list = add_uid_if_match(list, cursor, node, type);
        }
    }

    return list;
}

/* callback used from cal_recur_generate_instances(): adds the component's UID to
 * our hash table
 */
static gboolean
add_instance (CalComponent *comp, time_t start, time_t end, gpointer data)
{
    GHashTable *uid_hash;
    const char *uid;
    const char *old_uid;

    uid_hash = data;

    cal_component_get_uid(comp, &uid);

    old_uid = g_hash_table_lookup(uid_hash, uid);
    if (old_uid)
        return FALSE;

    g_hash_table_insert(uid_hash, (char *) uid, NULL);
    return FALSE;
}

/* creates the list of UIDs in the given range */
static void
get_instances_in_range (GHashTable *uid_hash,
                        CalBackendDBCursor *cursor,
                        CalObjType type,
                        time_t start,
                        time_t end)
{
    GList *node;

    g_return_if_fail(uid_hash != NULL);
    g_return_if_fail(cursor != NULL);

    for (node = g_list_first(cursor->data); node != NULL; node = g_list_next(node)) {
        DBT *data;
        icalcomponent *icalcomp;

        data = (DBT *) node->data;
        if (data) {
            icalcomp = icalparser_parse_string((char *) data->data);
            if (icalcomp) {
                CalComponent *comp = cal_component_new();
                cal_component_set_icalcomponent(comp, icalcomp);

                switch (icalcomponent_isa(icalcomp)) {
                case ICAL_VEVENT_COMPONENT :
                    if (type & CALOBJ_TYPE_EVENT)
                        cal_recur_generate_instances(comp,
                                                     start,
                                                     end,
                                                     add_instance,
                                                     uid_hash);
                    break;
                case ICAL_VTODO_COMPONENT :
                    if (type & CALOBJ_TYPE_TODO)
                        cal_recur_generate_instances(comp,
                                                     start,
                                                     end,
                                                     add_instance,
                                                     uid_hash);
                    break;
                case ICAL_VJOURNAL_COMPONENT :
                    if (type & CALOBJ_TYPE_JOURNAL)
                        cal_recur_generate_instances(comp,
                                                     start,
                                                     end,
                                                     add_instance,
                                                     uid_hash);
                    break;
                }

                gtk_object_unref(comp);
                icalcomponent_free(icalcomp);
            }
        }
    }
}

/* callback used from g_hash_table_foreach: adds a UID from the hash table to our list */
static void
add_uid_to_list (gpointer key, gpointer value, gpointer data)
{
    GList **list;
    const char *uid;

    list = (GList **) data;

    uid = (const char *) key;
    *list = g_list_prepend(*list, (gpointer) g_strdup(uid));
}

/* get_objects_in_range handler for the DB backend */
static GList *
cal_backend_db_get_objects_in_range (CalBackend *backend,
                                     CalObjType type,
                                     time_t start,
                                     time_t end)
{
    CalBackendDB *cbdb;
    GList *list = NULL;
    CalBackendDBCursor *cursor;

    cbdb = CAL_BACKEND_DB(backend);
    g_return_val_if_fail(IS_CAL_BACKEND_DB(cbdb), NULL);
    g_return_val_if_fail(cbdb->priv != NULL, NULL);

    /* open cursor */
    cursor = open_cursor(cbdb, cbdb->priv->objects_db);
    if (cursor) {
        GHashTable *uid_hash;

        /* build the hash table */
        uid_hash = g_hash_table_new(g_str_hash, g_str_equal);
        get_instances_in_range(uid_hash, cursor, type, start, end);

        /* build the list to be returned from the hash table */
        g_hash_table_foreach(uid_hash, add_uid_to_list, &list);
        g_hash_table_destroy(uid_hash);
    }
    
    return list;
}

/* get_changes handler for the DB backend */
static GNOME_Evolution_Calendar_CalObjChangeSeq *
cal_backend_db_get_changes (CalBackend *backend, CalObjType type, const char *change_id)
{
    CalBackendDB *cbdb;

    cbdb = CAL_BACKEND_DB(backend);
    g_return_val_if_fail(IS_CAL_BACKEND_DB(cbdb), NULL);
    g_return_val_if_fail(cbdb->priv != NULL, NULL);

    return NULL;
}

/* get_alarms_in_range handler for the DB backend */
static GNOME_Evolution_Calendar_CalComponentAlarmsSeq *
cal_backend_db_get_alarms_in_range (CalBackend *backend, time_t start, time_t end)
{
    CalBackendDB *cbdb;
    CalBackendDBCursor *cursor;
    gint number_of_alarms;
    GList *alarm_list;
    GList *node;
    gint i;
    GNOME_Evolution_Calendar_CalComponentAlarmsSeq *seq = NULL;

    cbdb = CAL_BACKEND_DB(backend);
    g_return_val_if_fail(IS_CAL_BACKEND_DB(cbdb), NULL);
    g_return_val_if_fail(cbdb->priv != NULL, NULL);
    g_return_val_if_fail (start != -1 && end != -1, NULL);
    g_return_val_if_fail (start <= end, NULL);

    /* open cursor */
    cursor = open_cursor(cbdb, cbdb->priv->objects_db);
    if (cursor) {
        /* TODO: get list of alarms */
        
        /* create the CORBA sequence */
        seq = GNOME_Evolution_Calendar_CalComponentAlarmsSeq__alloc();
        CORBA_sequence_set_release(seq, TRUE);
        seq->_length = number_of_alarms;
        seq->_buffer = CORBA_sequence_GNOME_Evolution_Calendar_CalComponentAlarms_allocbuf(number_of_alarms);
        
        /* TODO: populate CORBA sequence */
    }
    
    g_list_free(alarm_list);

    return seq;
}

/* get_alarms_for_object handler for the DB backend */
static GNOME_Evolution_Calendar_CalComponentAlarms *
cal_backend_db_get_alarms_for_object (CalBackend *backend,
                                      const char *uid,
                                      time_t start,
                                      time_t end,
                                      gboolean *object_found)
{
    CalBackendDB *cbdb;
    CalBackendDBCursor *cursor;
    GNOME_Evolution_Calendar_CalComponentAlarms *corba_alarms = NULL;

    cbdb = CAL_BACKEND_DB(backend);
    g_return_val_if_fail(IS_CAL_BACKEND_DB(cbdb), NULL);
    g_return_val_if_fail(cbdb->priv != NULL, NULL);
    g_return_val_if_fail(uid != NULL, NULL);
    g_return_val_if_fail(start != -1 && end != -1, NULL);
    g_return_val_if_fail(start <= end, NULL);
    g_return_val_if_fail(object_found != NULL, NULL);

    /* open the cursor */
    cursor = open_cursor(cbdb, cbdb->priv->object_db);
    if (cursor) {
        /* TODO: retrieve list of alarms for this object */
        
        /* create the CORBA alarms */
        corba_alarms = GNOME_Evolution_Calendar_CalComponentAlarms__alloc();
        
        /* TODO: populate the CORBA alarms */
    }

    return corba_alarms;
}

/* update_object handler for the DB backend */
static gboolean
cal_backend_db_update_object (CalBackend *backend, const char *uid, const char *calobj)
{
    CalBackendDB *cbdb;
    CalBackendDBCursor *cursor;

    cbdb = CAL_BACKEND_DB(backend);
    g_return_val_if_fail(IS_CAL_BACKEND_DB(cbdb), FALSE);
    g_return_val_if_fail(cbdb->priv != NULL, FALSE);
    g_return_val_if_fail(uid != NULL, FALSE);
    g_return_val_if_fail(calobj != NULL, FALSE);

    /* open the cursor */
    cursor = open_cursor(cbdb, cbdb->priv->objects_db);
    if (cursor) {
        DBT *data;
        
        data = find_record_by_id(cursor, uid);
        if (data) {
            DBT key;
            DBT new_data;
            int ret;
            
            /* try to change the value in the cursor */
            memset(&key, 0, sizeof(key));
            key.data = (void *) uid;
            key.size = strlen(uid); // + 1
            
            memset(&new_data, 0, sizeof(new_data));
            new_data.data = (void *) calobj;
            new_data.size = strlen(calobj); // + 1
            
            /* move the cursor to the given key */
            if ((ret = cursor->dbc->c_get(cursor->dbc, &key, NULL, DB_FIRST)) != 0) {
                return FALSE;
            }
            
            /* TODO: start transaction */
            
            if ((ret = cursor->dbc->c_put(cursor->dbc, &key, &new_data, DB_CURRENT)) != 0) {
                /* TODO: rollback transaction */
                return FALSE;
            }
            
            /* TODO: update history database */
            /* TODO: commit transaction */
            
            memcpy(data, &new_data, sizeof(new_data));
            
            return TRUE;
        }
    }
    
    return FALSE;
}

/* remove_object handler for the DB backend */
static gboolean
cal_backend_db_remove_object (CalBackend *backend, const char *uid)
{
    CalBackendDB *cbdb;
    CalBackendDBCursor *cursor;

    cbdb = CAL_BACKEND_DB(backend);
    g_return_val_if_fail(IS_CAL_BACKEND_DB(cbdb), FALSE);
    g_return_val_if_fail(cbdb->priv != NULL, FALSE);
    g_return_val_if_fail(uid != NULL, FALSE);
    
    /* open cursor */
    cursor = open_cursor(cbdb, cbdb->priv->objects_db);
    if (cursor) {
        DBT *data = find_record_by_id(cursor, uid);
        if (data) {
            GList *l;
            int ret;
            DBT key;
            
            memset(&key, 0, sizeof(key);
            key.data = (void *) uid;
            key.size = strlen(uid); // + 1
            
            if ((ret = cursor->dbc->c_get(cursor->dbc, &key, NULL, DB_FIRST)) != 0) {
                return FALSE;
            }
            
            /* TODO: begin transaction */
            
            /* remove record from cursor */
            if ((ret = cursor->dbc->c_del(cursor->dbc, 0)) != 0) {
                /* TODO: rollback transaction */
                return FALSE;
            }
            
            /* TODO: update history database */
            /* TODO: commit transaction */
            
            /* remove record from in-memory lists */
            l = g_list_nth(cursor->keys,
                           g_list_index(cursor->data, (gpointer) data));
            if (l) {
                DBT *key_to_free = (DBT *) l->data;
                
                cursor->keys = g_list_remove(cursor->keys, (gpointer) key_to_free);
                g_free((gpointer) key_to_free);
                
                cursor->data = g_list_remove(cursor->data, (gpointer) data);
                g_free((gpointer) data);
            }
            
            return TRUE;
        }
    }
    
    return FALSE;
}