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

/* -*- Mode: C; tab-width: 8; indent-tabs-mode: t; c-basic-offset: 8 -*- */
/* Evolution calendar backend
 *
 * Copyright (C) 2000 Helix Code, Inc.
 *
 * Author: Federico Mena-Quintero <federico@helixcode.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/gtksignal.h>
#include <cal-util/calobj.h>
#include "cal-backend.h"
#include "libversit/vcc.h"
#include "icalendar.h"




/* Private part of the CalBackend structure */
typedef struct {
    /* URI where the calendar data is stored */
    GnomeVFSURI *uri;

        /* format of this calendar (ical or vcal) */
    CalendarFormat format;

    /* List of Cal objects with their listeners */
    GList *clients;

    /* All the iCalObject structures in the calendar, hashed by UID.  The
     * hash key *is* icalobj->uid; it is not copied, so don't free it when
     * you remove an object from the hash table.
     */
    GHashTable *object_hash;

    /* All events, TODOs, and journals in the calendar */
    GList *events;
    GList *todos;
    GList *journals;

    /* Whether a calendar has been loaded */
    guint loaded : 1;

    /* Do we need to sync to permanent storage? */
    gboolean dirty : 1;
} CalBackendPrivate;



/* Signal IDs */
enum {
    LAST_CLIENT_GONE,
    LAST_SIGNAL
};

static void cal_backend_class_init (CalBackendClass *class);
static void cal_backend_init (CalBackend *backend);
static void cal_backend_destroy (GtkObject *object);

static GtkObjectClass *parent_class;

static guint cal_backend_signals[LAST_SIGNAL];



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

    if (!cal_backend_type) {
        static const GtkTypeInfo cal_backend_info = {
            "CalBackend",
            sizeof (CalBackend),
            sizeof (CalBackendClass),
            (GtkClassInitFunc) cal_backend_class_init,
            (GtkObjectInitFunc) cal_backend_init,
            NULL, /* reserved_1 */
            NULL, /* reserved_2 */
            (GtkClassInitFunc) NULL
        };

        cal_backend_type =
            gtk_type_unique (GTK_TYPE_OBJECT, &cal_backend_info);
    }

    return cal_backend_type;
}

/* Class initialization function for the calendar backend */
static void
cal_backend_class_init (CalBackendClass *class)
{
    GtkObjectClass *object_class;

    object_class = (GtkObjectClass *) class;

    parent_class = gtk_type_class (GTK_TYPE_OBJECT);

    cal_backend_signals[LAST_CLIENT_GONE] =
        gtk_signal_new ("last_client_gone",
                GTK_RUN_FIRST,
                object_class->type,
                GTK_SIGNAL_OFFSET (CalBackendClass, last_client_gone),
                gtk_marshal_NONE__NONE,
                GTK_TYPE_NONE, 0);

    gtk_object_class_add_signals (object_class, cal_backend_signals, LAST_SIGNAL);

    object_class->destroy = cal_backend_destroy;
}

/* Object initialization function for the calendar backend */
static void
cal_backend_init (CalBackend *backend)
{
    CalBackendPrivate *priv;

    priv = g_new0 (CalBackendPrivate, 1);
    backend->priv = priv;

    /* FIXME can be CAL_VCAL or CAL_ICAL */
    priv->format = CAL_VCAL;
}

static void
save_to_vcal (CalBackend *backend, char *fname)
{
    FILE *fp;
    CalBackendPrivate *priv = backend->priv;
    VObject *vcal;
    GList *l;

    if (g_file_exists (fname)){
        char *backup_name = g_strconcat (fname, "~", NULL);

        if (g_file_exists (backup_name)){
            unlink (backup_name);
        }
        rename (fname, backup_name);
        g_free (backup_name);
    }

    vcal = newVObject (VCCalProp);
    addPropValue (vcal, VCProdIdProp,
              "-//GNOME//NONSGML GnomeCalendar//EN");
    addPropValue (vcal, VCVersionProp, VERSION);

    for (l = priv->events; l; l = l->next) {
        iCalObject *ical = l->data;
        VObject *vobject = ical_object_to_vobject (ical);
        addVObjectProp (vcal, vobject);
    }
    for (l = priv->todos; l; l = l->next) {
        iCalObject *ical = l->data;
        VObject *vobject = ical_object_to_vobject (ical);
        addVObjectProp (vcal, vobject);
    }
    for (l = priv->journals; l; l = l->next) {
        iCalObject *ical = l->data;
        VObject *vobject = ical_object_to_vobject (ical);
        addVObjectProp (vcal, vobject);
    }

    fp = fopen(fname,"w");
    if (fp) {
        writeVObject(fp, vcal);
        fclose(fp);
    }
    cleanStrTbl ();
}

/* Saves a calendar */
static void
save (CalBackend *backend)
{
    char *str_uri;
    CalBackendPrivate *priv = backend->priv;

    str_uri = gnome_vfs_uri_to_string (priv->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));

    if (! priv->dirty){
        return;
    }

    switch (priv->format) {
    case CAL_VCAL:
        save_to_vcal (backend, str_uri);
        break;
    case CAL_ICAL:
        /*icalendar_calendar_save (backend, str_uri);*/
        /* FIX ME */
        break;
    default:
        /* FIX ME log */
            break;
    }

    printf ("cal-backend: '%s' saved\n", str_uri);
}


/* g_hash_table_foreach() callback to destroy an iCalObject */
static void
free_ical_object (gpointer key, gpointer value, gpointer data)
{
    iCalObject *ico;

    ico = value;
    ical_object_destroy (ico);
}

/* Destroys a backend's data */
static void
destroy (CalBackend *backend)
{
    CalBackendPrivate *priv;

    priv = backend->priv;

    if (priv->uri) {
        gnome_vfs_uri_unref (priv->uri);
        priv->uri = NULL;
    }

    g_assert (priv->clients == NULL);

    if (priv->object_hash) {
        g_hash_table_foreach (priv->object_hash, free_ical_object, NULL);
        g_hash_table_destroy (priv->object_hash);
        priv->object_hash = NULL;
    }

    g_list_free (priv->events);
    g_list_free (priv->todos);
    g_list_free (priv->journals);

    priv->events = NULL;
    priv->todos = NULL;
    priv->journals = NULL;

    priv->loaded = FALSE;
}

/* Destroy handler for the calendar backend */
static void
cal_backend_destroy (GtkObject *object)
{
    CalBackend *backend;
    CalBackendPrivate *priv;

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

    backend = CAL_BACKEND (object);
    priv = backend->priv;

    /*
    if (priv->loaded)
        save (backend);
    */

    destroy (backend);

    g_free (priv);

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



/* iCalObject manipulation functions */

/* Looks up an object by its UID in the backend's object hash table */
static iCalObject *
lookup_object (CalBackend *backend, const char *uid)
{
    CalBackendPrivate *priv;
    iCalObject *ico;

    priv = backend->priv;
    ico = g_hash_table_lookup (priv->object_hash, uid);

    return ico;
}

/* Ensures that an iCalObject has a unique identifier.  If it doesn't have one,
 * it will create one for it.  Returns whether an UID was created or not.
 */
static gboolean
ensure_uid (iCalObject *ico)
{
    char *buf;
    gulong str_time;
    static guint seqno = 0;

    if (ico->uid){
        return FALSE;
    }

    str_time = (gulong) time (NULL);

    /* Is this good enough? */

    buf = g_strdup_printf ("Evolution-Tlacuache-%d-%ld-%u",
                   (int) getpid(), str_time, seqno++);
    ico->uid = buf;
    return TRUE;
}

/* Adds an object to the calendar backend.  Does *not* perform notification to
 * calendar clients.
 */
static void
add_object (CalBackend *backend, iCalObject *ico)
{
    CalBackendPrivate *priv;

    g_assert (ico != NULL);
    priv = backend->priv;

#if 0
    /* FIXME: gnomecal old code */
    ico->new = 0;
#endif

    if (ensure_uid (ico))
        /* FIXME: mark the calendar as dirty so that we can re-save it
         * with the object's new UID.
         */
        ;

    g_hash_table_insert (priv->object_hash, ico->uid, ico);

    priv->dirty = TRUE;

    switch (ico->type) {
    case ICAL_EVENT:
        priv->events = g_list_prepend (priv->events, ico);
#if 0
        /* FIXME: gnomecal old code */
        ical_object_try_alarms (ico);
#  ifdef DEBUGGING_MAIL_ALARM
        ico->malarm.trigger = 0;
        calendar_notify (0, ico);
#  endif
#endif
        break;

    case ICAL_TODO:
        priv->todos = g_list_prepend (priv->todos, ico);
        break;

    case ICAL_JOURNAL:
        priv->journals = g_list_prepend (priv->journals, ico);
        break;

    default:
        g_assert_not_reached ();
    }

#if 0
    /* FIXME: gnomecal old code */
    ico->last_mod = time (NULL);
#endif
}

/* Removes an object from the backend's hash and lists.  Does not perform
 * notification on the clients.
 */
static void
remove_object (CalBackend *backend, iCalObject *ico)
{
    CalBackendPrivate *priv;
    GList **list, *l;

    priv = backend->priv;

    g_assert (ico->uid != NULL);
    g_hash_table_remove (priv->object_hash, ico->uid);

    priv->dirty = TRUE;

    switch (ico->type) {
    case ICAL_EVENT:
        list = &priv->events;
        break;

    case ICAL_TODO:
        list = &priv->todos;
        break;

    case ICAL_JOURNAL:
        list = &priv->journals;
        break;

    default:
        list = NULL;
    }

    if (!list){
        return;
    }

    l = g_list_find (*list, ico);
    g_assert (l != NULL);

    *list = g_list_remove_link (*list, l);
    g_list_free_1 (l);

    ical_object_destroy (ico);
}

/* Load a calendar from a VObject */
static void
load_from_vobject (CalBackend *backend, VObject *vobject)
{
    CalBackendPrivate *priv;
    VObjectIterator i;

    priv = backend->priv;

    g_assert (!priv->loaded);
    g_assert (priv->object_hash == NULL);
    priv->object_hash = g_hash_table_new (g_str_hash, g_str_equal);

    initPropIterator (&i, vobject);

    while (moreIteration (&i)) {
        VObject *this;
        iCalObject *ical;
        const char *object_name;

        this = nextVObject (&i);
        object_name = vObjectName (this);
#if 0
        /* FIXME?  What is this used for in gnomecal? */
        if (strcmp (object_name, VCDCreatedProp) == 0) {
            cal->created = time_from_isodate (str_val (this));
            continue;
        }
#endif
        if (strcmp (object_name, VCLocationProp) == 0)
            continue; /* FIXME: imlement */

        if (strcmp (object_name, VCProdIdProp) == 0)
            continue; /* FIXME: implement */

        if (strcmp (object_name, VCVersionProp) == 0)
            continue; /* FIXME: implement */

        if (strcmp (object_name, VCTimeZoneProp) == 0)
            continue; /* FIXME: implement */

        ical = ical_object_create_from_vobject (this, object_name);

        /* FIXME: some broken files may have duplicated UIDs.  This is
         * Bad(tm).  Deal with it by creating new UIDs for them and
         * spitting some messages to the console.
         */

        if (ical)
            add_object (backend, ical);
    }
}



/**
 * cal_backend_new:
 * @void:
 *
 * Creates a new empty calendar backend.  A calendar must then be loaded or
 * created before the backend can be used.
 *
 * Return value: A newly-created calendar backend.
 **/
CalBackend *
cal_backend_new (void)
{
    return CAL_BACKEND (gtk_type_new (CAL_BACKEND_TYPE));
}

/**
 * cal_backend_get_uri:
 * @backend: A calendar backend.
 *
 * Queries the URI of a calendar backend, which must already have a loaded
 * calendar.
 *
 * Return value: The URI where the calendar is stored.
 **/
GnomeVFSURI *
cal_backend_get_uri (CalBackend *backend)
{
    CalBackendPrivate *priv;

    g_return_val_if_fail (backend != NULL, NULL);
    g_return_val_if_fail (IS_CAL_BACKEND (backend), NULL);

    priv = backend->priv;
    g_return_val_if_fail (priv->loaded, NULL);
    g_assert (priv->uri != NULL);

    return priv->uri;
}

/* Callback used when a Cal is destroyed */
static void
cal_destroy_cb (GtkObject *object, gpointer data)
{
    Cal *cal;
    Cal *lcal;
    CalBackend *backend;
    CalBackendPrivate *priv;
    GList *l;

    cal = CAL (object);

    backend = CAL_BACKEND (data);
    priv = backend->priv;

    /* Find the cal in the list of clients */

    for (l = priv->clients; l; l = l->next) {
        lcal = CAL (l->data);

        if (lcal == cal)
            break;
    }

    g_assert (l != NULL);

    /* Disconnect */

    priv->clients = g_list_remove_link (priv->clients, l);
    g_list_free_1 (l);

    /* When all clients go away, notify the parent factory about it so that
     * it may decide whether to kill the backend or not.
     */
    if (!priv->clients)
        gtk_signal_emit (GTK_OBJECT (backend), cal_backend_signals[LAST_CLIENT_GONE]);
}

/**
 * cal_backend_add_cal:
 * @backend: A calendar backend.
 * @cal: A calendar client interface object.
 *
 * Adds a calendar client interface object to a calendar @backend.
 * The calendar backend must already have a loaded calendar.
 **/
void
cal_backend_add_cal (CalBackend *backend, Cal *cal)
{
    CalBackendPrivate *priv;

    g_return_if_fail (backend != NULL);
    g_return_if_fail (IS_CAL_BACKEND (backend));

    priv = backend->priv;
    g_return_if_fail (priv->loaded);

    g_return_if_fail (cal != 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 (cal_destroy_cb),
                backend);

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


static icalcomponent* 
icalendar_parse_file (char* fname)
{
    FILE* fp;
    icalcomponent* comp = NULL;
    gchar* str;
    struct stat st;
    int n;

    fp = fopen (fname, "r");
    if (!fp) {
        g_warning ("Cannot open open calendar file.");
        return NULL;
    }
    
    stat (fname, &st);
    
    str = g_malloc (st.st_size + 2);
    
    n = fread ((gchar*) str, 1, st.st_size, fp);
    if (n != st.st_size) {
        g_warning ("Read error.");
    }
    str[n] = '\0';

    fclose (fp);
    
    comp = icalparser_parse_string (str);
    g_free (str);

    return comp;
}


static void
icalendar_calendar_load (CalBackend * cal, char* fname)
{
    icalcomponent *comp;
    icalcomponent *subcomp;
    iCalObject    *ical;

    comp = icalendar_parse_file (fname);
    subcomp = icalcomponent_get_first_component (comp,
                             ICAL_ANY_COMPONENT);
    while (subcomp) {
        ical = ical_object_create_from_icalcomponent (subcomp);
        if (ical->type != ICAL_EVENT && 
            ical->type != ICAL_TODO  &&
            ical->type != ICAL_JOURNAL) {
               g_warning ("Skipping unsupported iCalendar component.");
        } else
            add_object (cal, ical);
        subcomp = icalcomponent_get_next_component (comp,
                               ICAL_ANY_COMPONENT);
    }
}


/*
ics is to be used to designate a file containing (an arbitrary set of)
calendaring and scheduling information.

ifb is to be used to designate a file containing free or busy time
information.

anything else is assumed to be a vcal file.
*/

static CalendarFormat
cal_get_type_from_filename (char *str_uri)
{
    int len;

    if (str_uri == NULL){
        return CAL_VCAL;
    }

    len = strlen (str_uri);
    if (len < 5){
        return CAL_VCAL;
    }

    if (str_uri[ len-4 ] == '.' &&
        str_uri[ len-3 ] == 'i' &&
        str_uri[ len-2 ] == 'c' &&
        str_uri[ len-1 ] == 's'){
        return CAL_ICAL;
    }

    if (str_uri[ len-4 ] == '.' &&
        str_uri[ len-3 ] == 'i' &&
        str_uri[ len-2 ] == 'f' &&
        str_uri[ len-1 ] == 'b'){
        return CAL_ICAL;
    }

    return CAL_VCAL;
}


/**
 * cal_backend_load:
 * @backend: A calendar backend.
 * @uri: URI that contains the calendar data.
 *
 * Loads a calendar backend with data from a calendar stored at the specified
 * URI.
 *
 * Return value: An operation status code.
 **/
CalBackendLoadStatus
cal_backend_load (CalBackend *backend, GnomeVFSURI *uri)
{
    CalBackendPrivate *priv;
    VObject *vobject;
    char *str_uri;

    g_return_val_if_fail (backend != NULL, CAL_BACKEND_LOAD_ERROR);
    g_return_val_if_fail (IS_CAL_BACKEND (backend),CAL_BACKEND_LOAD_ERROR);

    priv = backend->priv;
    g_return_val_if_fail (!priv->loaded, CAL_BACKEND_LOAD_ERROR);

    g_return_val_if_fail (uri != NULL, CAL_BACKEND_LOAD_ERROR);

    /* FIXME: this looks rather bad; maybe we should check for local files
     * and fail if they are remote.
     */

    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));


    /* look at the extension on the filename and decide
       if this is a ical or vcal file */

    priv->format = cal_get_type_from_filename (str_uri);

    /* load */

    switch (priv->format) {
    case CAL_VCAL:
            vobject = Parse_MIME_FromFileName (str_uri);
    
        if (!vobject){
            return CAL_BACKEND_LOAD_ERROR;
        }
    
        load_from_vobject (backend, vobject);
        cleanVObject (vobject);
        cleanStrTbl ();
        break;
    case CAL_ICAL:
        icalendar_calendar_load (backend, str_uri);
        break;
    default:
            return CAL_BACKEND_LOAD_ERROR;
    }

    g_free (str_uri);

    gnome_vfs_uri_ref (uri);

    priv->uri = uri;
    priv->loaded = TRUE;

    return CAL_BACKEND_LOAD_SUCCESS;
}

/**
 * cal_backend_create:
 * @backend: A calendar backend.
 * @uri: URI that will contain the calendar data.
 *
 * Creates a new empty calendar in a calendar backend.
 **/
void
cal_backend_create (CalBackend *backend, GnomeVFSURI *uri)
{
    CalBackendPrivate *priv;

    g_return_if_fail (backend != NULL);
    g_return_if_fail (IS_CAL_BACKEND (backend));

    priv = backend->priv;
    g_return_if_fail (!priv->loaded);

    g_return_if_fail (uri != NULL);

    /* Create the new calendar information */

    g_assert (priv->object_hash == NULL);
    priv->object_hash = g_hash_table_new (g_str_hash, g_str_equal);

    priv->dirty = TRUE;

    /* Done */

    gnome_vfs_uri_ref (uri);

    priv->uri = uri;
    priv->loaded = TRUE;

    save (backend);
}

/**
 * cal_backend_get_object:
 * @backend: A calendar backend.
 * @uid: Unique identifier for a calendar object.
 *
 * Queries a calendar backend for a calendar object based on its unique
 * identifier.
 *
 * Return value: The string representation of a complete calendar wrapping the
 * the sought object, or NULL if no object had the specified UID.  A complete
 * calendar is returned because you also need the timezone data.
 **/
char *
cal_backend_get_object (CalBackend *backend, const char *uid)
{
    CalBackendPrivate *priv;
    iCalObject *ico;
    char *buf;

    g_return_val_if_fail (backend != NULL, NULL);
    g_return_val_if_fail (IS_CAL_BACKEND (backend), NULL);

    priv = backend->priv;
    g_return_val_if_fail (priv->loaded, NULL);

    g_return_val_if_fail (uid != NULL, NULL);

    g_assert (priv->object_hash != NULL);

    ico = lookup_object (backend, uid);

    if (!ico){
        return NULL;
    }

    buf = ical_object_to_string (ico);

    return buf;
}

struct get_uids_closure {
    CalObjType type;
    GList *uid_list;
};

/* Builds a list of UIDs for objects that match the sought type.  Called from
 * g_hash_table_foreach().
 */
static void
build_uids_list (gpointer key, gpointer value, gpointer data)
{
    iCalObject *ico;
    struct get_uids_closure *c;
    gboolean store;

    ico = value;
    c = data;

    store = FALSE;

    /*
    if (c->type & CALOBJ_TYPE_ANY)
        store = TRUE;
    else */
    if (ico->type == ICAL_EVENT)
        store = (c->type & CALOBJ_TYPE_EVENT) ? TRUE : FALSE;
    else if (ico->type == ICAL_TODO)
        store = (c->type & CALOBJ_TYPE_TODO) ? TRUE : FALSE;
    else if (ico->type == ICAL_JOURNAL)
        store = (c->type & CALOBJ_TYPE_JOURNAL) ? TRUE : FALSE;
    else
        store = (c->type & CALOBJ_TYPE_OTHER) ? TRUE : FALSE;

    if (store)
        c->uid_list = g_list_prepend (c->uid_list, g_strdup (ico->uid));
}

/**
 * cal_backend_get_uids:
 * @backend: A calendar backend.
 * @type: Bitmask with types of objects to return.
 *
 * Builds a list of unique identifiers corresponding to calendar objects whose
 * type matches one of the types specified in the @type flags.
 *
 * Return value: A list of strings that are the sought UIDs.
 **/
GList *
cal_backend_get_uids (CalBackend *backend, CalObjType type)
{
    CalBackendPrivate *priv;
    struct get_uids_closure c;

    g_return_val_if_fail (backend != NULL, NULL);
    g_return_val_if_fail (IS_CAL_BACKEND (backend), NULL);

    priv = backend->priv;
    g_return_val_if_fail (priv->loaded, NULL);

    /* We go through the hash table instead of the lists of particular
     * object types so that we can pick up CALOBJ_TYPE_OTHER objects.
     */

    c.type = type;
    c.uid_list = NULL;
    g_hash_table_foreach (priv->object_hash, build_uids_list, &c);

    return c.uid_list;
}

struct build_event_list_closure {
    CalBackend *backend;
    GList *event_list;
};

/* Builds a sorted list of event object instances.  Used as a callback from
 * ical_object_generate_events().
 */
static int
build_event_list (iCalObject *ico, time_t start, time_t end, void *data)
{
    CalObjInstance *icoi;
    struct build_event_list_closure *c;

    c = data;

    icoi = g_new (CalObjInstance, 1);

    g_assert (ico->uid != NULL);
    icoi->uid = g_strdup (ico->uid);
    icoi->start = start;
    icoi->end = end;

    c->event_list = g_list_prepend (c->event_list, icoi);

    return TRUE;
}

/* Compares two CalObjInstance structures by their start times.  Called from
 * g_list_sort().
 */
static gint
compare_instance_func (gconstpointer a, gconstpointer b)
{
    const CalObjInstance *ca, *cb;
    time_t diff;

    ca = a;
    cb = b;

    diff = ca->start - cb->start;
    return (diff < 0) ? -1 : (diff > 0) ? 1 : 0;
}

/**
 * cal_backend_get_events_in_range:
 * @backend: A calendar backend.
 * @start: Start time for query.
 * @end: End time for query.
 *
 * Builds a sorted list of calendar event object instances that occur or recur
 * within the specified time range.  Each object instance contains the object
 * itself and the start/end times at which it occurs or recurs.
 *
 * Return value: A list of calendar event object instances, sorted by their
 * start times.
 **/
GList *
cal_backend_get_events_in_range (CalBackend *backend, time_t start, time_t end)
{
    CalBackendPrivate *priv;
    struct build_event_list_closure c;
    GList *l;

    g_return_val_if_fail (backend != NULL, NULL);
    g_return_val_if_fail (IS_CAL_BACKEND (backend), NULL);

    priv = backend->priv;
    g_return_val_if_fail (priv->loaded, NULL);

    g_return_val_if_fail (start != -1 && end != -1, NULL);
    g_return_val_if_fail (start <= end, NULL);

    c.backend = backend;
    c.event_list = NULL;

    for (l = priv->events; l; l = l->next) {
        iCalObject *ico;

        ico = l->data;
        ical_object_generate_events (ico, start, end,
                         build_event_list, &c);
    }

    c.event_list = g_list_sort (c.event_list, compare_instance_func);

    return c.event_list;
}

/* Notifies a backend's clients that an object was updated */
static void
notify_update (CalBackend *backend, const char *uid)
{
    CalBackendPrivate *priv;
    GList *l;

    priv = backend->priv;

    for (l = priv->clients; l; l = l->next) {
        Cal *cal;

        cal = CAL (l->data);
        cal_notify_update (cal, uid);
    }
}

/* Notifies a backend's clients that an object was removed */
static void
notify_remove (CalBackend *backend, const char *uid)
{
    CalBackendPrivate *priv;
    GList *l;

    priv = backend->priv;

    for (l = priv->clients; l; l = l->next) {
        Cal *cal;

        cal = CAL (l->data);
        cal_notify_remove (cal, uid);
    }
}

/**
 * cal_backend_update_object:
 * @backend: A calendar backend.
 * @uid: Unique identifier of the object to update.
 * @calobj: String representation of the new calendar object.
 * 
 * Updates an object in a calendar backend.  It will replace any existing
 * object that has the same UID as the specified one.  The backend will in
 * turn notify all of its clients about the change.
 * 
 * Return value: TRUE on success, FALSE on being passed an invalid object.
 **/
gboolean
cal_backend_update_object (CalBackend *backend, const char *uid,
               const char *calobj)
{
    CalBackendPrivate *priv;
    iCalObject *ico, *new_ico;
    CalObjFindStatus status;

    g_return_val_if_fail (backend != NULL, FALSE);
    g_return_val_if_fail (IS_CAL_BACKEND (backend), FALSE);

    priv = backend->priv;
    g_return_val_if_fail (priv->loaded, FALSE);
    
    g_return_val_if_fail (uid != NULL, FALSE);
    g_return_val_if_fail (calobj != NULL, FALSE);

    /* Pull the object from the string */

    status = ical_object_find_in_string (uid, calobj, &new_ico);

    if (status != CAL_OBJ_FIND_SUCCESS){
        return FALSE;
    }

    /* Update the object */

    ico = lookup_object (backend, uid);

    if (ico)
        remove_object (backend, ico);

    add_object (backend, new_ico);
    save (backend);

    /* FIXME: do the notification asynchronously */

    notify_update (backend, new_ico->uid);

    return TRUE;
}

/**
 * cal_backend_remove_object:
 * @backend: A calendar backend.
 * @uid: Unique identifier of the object to remove.
 * 
 * Removes an object in a calendar backend.  The backend will notify all of its
 * clients about the change.
 * 
 * Return value: TRUE on success, FALSE on being passed an UID for an object
 * that does not exist in the backend.
 **/
gboolean
cal_backend_remove_object (CalBackend *backend, const char *uid)
{
    CalBackendPrivate *priv;
    iCalObject *ico;

    g_return_val_if_fail (backend != NULL, FALSE);
    g_return_val_if_fail (IS_CAL_BACKEND (backend), FALSE);

    priv = backend->priv;
    g_return_val_if_fail (priv->loaded, FALSE);
    
    g_return_val_if_fail (uid != NULL, FALSE);

    ico = lookup_object (backend, uid);
    if (!ico){
        return FALSE;
    }

    remove_object (backend, ico);

    priv->dirty = TRUE;
    save (backend);

    /* FIXME: do the notification asynchronously */
    notify_remove (backend, uid);

    return TRUE;
}