path: root/calendar/pcs/query.c

/* Evolution calendar - Live search query implementation
 *
 * Copyright (C) 2001 Ximian, Inc.
 *
 * Author: Federico Mena-Quintero <federico@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.
 */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <string.h>
#include <glib.h>
#include <libgnome/gnome-defs.h>
#include <libgnome/gnome-i18n.h>
#include <gtk/gtksignal.h>
#include <gal/widgets/e-unicode.h>
#include <e-util/e-sexp.h>
#include <cal-util/cal-recur.h>
#include <cal-util/timeutil.h>
#include "query.h"



/* Private part of the Query structure */
struct _QueryPrivate {
    /* The backend we are monitoring */
    CalBackend *backend;

    /* Listener to which we report changes in the live query */
    GNOME_Evolution_Calendar_QueryListener ql;

    /* Sexp that defines the query */
    char *sexp;
    ESExp *esexp;

    /* Idle handler ID for asynchronous queries */
    guint idle_id;

    /* List of UIDs that we still have to process */
    GList *pending_uids;
    int n_pending;
    int pending_total;

    /* Table of the UIDs we know do match the query */
    GHashTable *uids;

    /* The next component that will be handled in e_sexp_eval(); put here
     * just because the query object itself is the esexp context.
     */
    CalComponent *next_comp;
};



static void query_class_init (QueryClass *class);
static void query_init (Query *query);
static void query_destroy (GtkObject *object);

static BonoboXObjectClass *parent_class;



BONOBO_X_TYPE_FUNC_FULL (Query,
             GNOME_Evolution_Calendar_Query,
             BONOBO_X_OBJECT_TYPE,
             query);

/* Class initialization function for the live search query */
static void
query_class_init (QueryClass *class)
{
    GtkObjectClass *object_class;

    object_class = (GtkObjectClass *) class;

    parent_class = gtk_type_class (BONOBO_X_OBJECT_TYPE);

    object_class->destroy = query_destroy;

    /* The Query interface (ha ha! query interface!) has no methods, so we
     * don't need to fiddle with the epv.
     */
}

/* Object initialization function for the live search query */
static void
query_init (Query *query)
{
    QueryPrivate *priv;

    priv = g_new0 (QueryPrivate, 1);
    query->priv = priv;

    priv->backend = NULL;
    priv->ql = CORBA_OBJECT_NIL;
    priv->sexp = NULL;

    priv->pending_uids = NULL;
    priv->uids = g_hash_table_new (g_str_hash, g_str_equal);

    priv->next_comp = NULL;
}

/* Used from g_hash_table_foreach(); frees a UID */
static void
free_uid_cb (gpointer key, gpointer value, gpointer data)
{
    char *uid;

    uid = key;
    g_free (uid);
}

/* Destroy handler for the live search query */
static void
query_destroy (GtkObject *object)
{
    Query *query;
    QueryPrivate *priv;

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

    query = QUERY (object);
    priv = query->priv;

    if (priv->backend) {
        gtk_signal_disconnect_by_data (GTK_OBJECT (priv->backend), query);
        gtk_object_unref (GTK_OBJECT (priv->backend));
        priv->backend = NULL;
    }

    if (priv->ql != CORBA_OBJECT_NIL) {
        CORBA_Environment ev;

        CORBA_exception_init (&ev);
        bonobo_object_release_unref (priv->ql, &ev);

        if (ev._major != CORBA_NO_EXCEPTION)
            g_message ("query_destroy(): Could not unref the listener\n");

        CORBA_exception_free (&ev);

        priv->ql = CORBA_OBJECT_NIL;
    }

    if (priv->sexp) {
        g_free (priv->sexp);
        priv->sexp = NULL;
    }

    if (priv->esexp) {
        e_sexp_unref (priv->esexp);
        priv->esexp = NULL;
    }

    if (priv->idle_id) {
        g_source_remove (priv->idle_id);
        priv->idle_id = 0;
    }

    if (priv->pending_uids) {
        GList *l;

        for (l = priv->pending_uids; l; l = l->next) {
            char *uid;

            uid = l->data;
            g_assert (uid != NULL);
            g_free (uid);
        }

        g_list_free (priv->pending_uids);
        priv->pending_uids = NULL;
        priv->n_pending = 0;
    }

    g_hash_table_foreach (priv->uids, free_uid_cb, NULL);
    g_hash_table_destroy (priv->uids);
    priv->uids = NULL;

    g_free (priv);
    query->priv = NULL;

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



/* E-Sexp functions */

/* (time-now)
 *
 * Returns a time_t of time (NULL).
 */
static ESExpResult *
func_time_now (ESExp *esexp, int argc, ESExpResult **argv, void *data)
{
    ESExpResult *result;

    if (argc != 0) {
        e_sexp_fatal_error (esexp, _("time-now expects 0 arguments"));
        return NULL;
    }

    result = e_sexp_result_new (esexp, ESEXP_RES_TIME);
    result->value.time = time (NULL);

    return result;
}

/* (make-time ISODATE)
 *
 * ISODATE - string, ISO 8601 date/time representation
 *
 * Constructs a time_t value for the specified date.
 */
static ESExpResult *
func_make_time (ESExp *esexp, int argc, ESExpResult **argv, void *data)
{
    const char *str;
    time_t t;
    ESExpResult *result;

    if (argc != 1) {
        e_sexp_fatal_error (esexp, _("make-time expects 1 argument"));
        return NULL;
    }

    if (argv[0]->type != ESEXP_RES_STRING) {
        e_sexp_fatal_error (esexp, _("make-time expects argument 1 "
                         "to be a string"));
        return NULL;
    }
    str = argv[0]->value.string;

    t = time_from_isodate (str);
    if (t == -1) {
        e_sexp_fatal_error (esexp, _("make-time argument 1 must be an "
                         "ISO 8601 date/time string"));
        return NULL;
    }

    result = e_sexp_result_new (esexp, ESEXP_RES_TIME);
    result->value.time = t;

    return result;
}

/* (time-add-day TIME N)
 *
 * TIME - time_t, base time
 * N - int, number of days to add
 *
 * Adds the specified number of days to a time value.
 *
 * FIXME: TIMEZONES - need to use a timezone or daylight saving changes will
 * make the result incorrect.
 */
static ESExpResult *
func_time_add_day (ESExp *esexp, int argc, ESExpResult **argv, void *data)
{
    ESExpResult *result;
    time_t t;
    int n;

    if (argc != 2) {
        e_sexp_fatal_error (esexp, _("time-add-day expects 2 arguments"));
        return NULL;
    }

    if (argv[0]->type != ESEXP_RES_TIME) {
        e_sexp_fatal_error (esexp, _("time-add-day expects argument 1 "
                         "to be a time_t"));
        return NULL;
    }
    t = argv[0]->value.time;

    if (argv[1]->type != ESEXP_RES_INT) {
        e_sexp_fatal_error (esexp, _("time-add-day expects argument 2 "
                         "to be an integer"));
        return NULL;
    }
    n = argv[1]->value.number;
    
    result = e_sexp_result_new (esexp, ESEXP_RES_TIME);
    result->value.time = time_add_day (t, n);

    return result;
}

/* (time-day-begin TIME)
 *
 * TIME - time_t, base time
 *
 * Returns the start of the day, according to the local time.
 *
 * FIXME: TIMEZONES - this uses the current Unix timezone.
 */
static ESExpResult *
func_time_day_begin (ESExp *esexp, int argc, ESExpResult **argv, void *data)
{
    time_t t;
    ESExpResult *result;

    if (argc != 1) {
        e_sexp_fatal_error (esexp, _("time-day-begin expects 1 argument"));
        return NULL;
    }

    if (argv[0]->type != ESEXP_RES_TIME) {
        e_sexp_fatal_error (esexp, _("time-day-begin expects argument 1 "
                         "to be a time_t"));
        return NULL;
    }
    t = argv[0]->value.time;

    result = e_sexp_result_new (esexp, ESEXP_RES_TIME);
    result->value.time = time_day_begin (t);

    return result;
}

/* (time-day-end TIME)
 *
 * TIME - time_t, base time
 *
 * Returns the end of the day, according to the local time.
 *
 * FIXME: TIMEZONES - this uses the current Unix timezone.
 */
static ESExpResult *
func_time_day_end (ESExp *esexp, int argc, ESExpResult **argv, void *data)
{
    time_t t;
    ESExpResult *result;

    if (argc != 1) {
        e_sexp_fatal_error (esexp, _("time-day-end expects 1 argument"));
        return NULL;
    }

    if (argv[0]->type != ESEXP_RES_TIME) {
        e_sexp_fatal_error (esexp, _("time-day-end expects argument 1 "
                         "to be a time_t"));
        return NULL;
    }
    t = argv[0]->value.time;

    result = e_sexp_result_new (esexp, ESEXP_RES_TIME);
    result->value.time = time_day_end (t);

    return result;
}

/* (get-vtype)
 *
 * Returns a string indicating the type of component (VEVENT, VTODO, VJOURNAL,
 * VFREEBUSY, VTIMEZONE, UNKNOWN).
 */
static ESExpResult *
func_get_vtype (ESExp *esexp, int argc, ESExpResult **argv, void *data)
{
    Query *query;
    QueryPrivate *priv;
    CalComponent *comp;
    CalComponentVType vtype;
    char *str;
    ESExpResult *result;

    query = QUERY (data);
    priv = query->priv;

    g_assert (priv->next_comp != NULL);
    comp = priv->next_comp;

    /* Check argument types */

    if (argc != 0) {
        e_sexp_fatal_error (esexp, _("get-vtype expects 0 arguments"));
        return NULL;
    }

    /* Get the type */

    vtype = cal_component_get_vtype (comp);

    switch (vtype) {
    case CAL_COMPONENT_EVENT:
        str = g_strdup ("VEVENT");
        break;

    case CAL_COMPONENT_TODO:
        str = g_strdup ("VTODO");
        break;

    case CAL_COMPONENT_JOURNAL:
        str = g_strdup ("VJOURNAL");
        break;

    case CAL_COMPONENT_FREEBUSY:
        str = g_strdup ("VFREEBUSY");
        break;

    case CAL_COMPONENT_TIMEZONE:
        str = g_strdup ("VTIMEZONE");
        break;

    default:
        str = g_strdup ("UNKNOWN");
        break;
    }

    result = e_sexp_result_new (esexp, ESEXP_RES_STRING);
    result->value.string = str;

    return result;
}

/* Sets a boolean value in the data to TRUE; called from
 * cal_recur_generate_instances() to indicate that at least one instance occurs
 * in the sought time range.  We always return FALSE because we want the
 * recurrence engine to finish as soon as possible.
 */
static gboolean
instance_occur_cb (CalComponent *comp, time_t start, time_t end, gpointer data)
{
    gboolean *occurs;

    occurs = data;
    *occurs = TRUE;

    return FALSE;
}

/* Call the backend function to get a timezone from a TZID. */
static icaltimezone*
resolve_tzid (const char *tzid, gpointer data)
{
    Query *query = data;

    if (!tzid || !tzid[0])
        return NULL;
    else
        return cal_backend_get_timezone (query->priv->backend, tzid);
}


/* (occur-in-time-range? START END)
 *
 * START - time_t, start of the time range
 * END - time_t, end of the time range
 *
 * Returns a boolean indicating whether the component has any occurrences in the
 * specified time range.
 */
static ESExpResult *
func_occur_in_time_range (ESExp *esexp, int argc, ESExpResult **argv, void *data)
{
    Query *query;
    QueryPrivate *priv;
    CalComponent *comp;
    time_t start, end;
    gboolean occurs;
    ESExpResult *result;

    query = QUERY (data);
    priv = query->priv;

    g_assert (priv->next_comp != NULL);
    comp = priv->next_comp;

    /* Check argument types */

    if (argc != 2) {
        e_sexp_fatal_error (esexp, _("occur-in-time-range? expects 2 arguments"));
        return NULL;
    }

    if (argv[0]->type != ESEXP_RES_TIME) {
        e_sexp_fatal_error (esexp, _("occur-in-time-range? expects argument 1 "
                         "to be a time_t"));
        return NULL;
    }
    start = argv[0]->value.time;

    if (argv[1]->type != ESEXP_RES_TIME) {
        e_sexp_fatal_error (esexp, _("occur-in-time-range? expects argument 2 "
                         "to be a time_t"));
        return NULL;
    }
    end = argv[1]->value.time;

    /* See if there is at least one instance in that range */

    occurs = FALSE;

    cal_recur_generate_instances (comp, start, end,
                      instance_occur_cb, &occurs,
                      resolve_tzid, query);

    result = e_sexp_result_new (esexp, ESEXP_RES_BOOL);
    result->value.bool = occurs;

    return result;
}

/* Returns whether a list of CalComponentText items matches the specified string */
static gboolean
matches_text_list (GSList *text_list, const char *str)
{
    GSList *l;
    gboolean matches;

    matches = FALSE;

    for (l = text_list; l; l = l->next) {
        CalComponentText *text;

        text = l->data;
        g_assert (text->value != NULL);

        if (e_utf8_strstrcasedecomp (text->value, str) != NULL) {
            matches = TRUE;
            break;
        }
    }

    return matches;
}

/* Returns whether the comments in a component matches the specified string */
static gboolean
matches_comment (CalComponent *comp, const char *str)
{
    GSList *list;
    gboolean matches;

    cal_component_get_comment_list (comp, &list);
    matches = matches_text_list (list, str);
    cal_component_free_text_list (list);

    return matches;
}

/* Returns whether the description in a component matches the specified string */
static gboolean
matches_description (CalComponent *comp, const char *str)
{
    GSList *list;
    gboolean matches;

    cal_component_get_description_list (comp, &list);
    matches = matches_text_list (list, str);
    cal_component_free_text_list (list);

    return matches;
}

/* Returns whether the summary in a component matches the specified string */
static gboolean
matches_summary (CalComponent *comp, const char *str)
{
    CalComponentText text;

    cal_component_get_summary (comp, &text);

    if (!text.value)
        return FALSE;

    return e_utf8_strstrcasedecomp (text.value, str) != NULL;
}

/* Returns whether any text field in a component matches the specified string */
static gboolean
matches_any (CalComponent *comp, const char *str)
{
    /* As an optimization, and to make life easier for the individual
     * predicate functions, see if we are looking for the empty string right
     * away.
     */
    if (strlen (str) == 0)
        return TRUE;

    return (matches_comment (comp, str)
        || matches_description (comp, str)
        || matches_summary (comp, str));
}

/* (contains? FIELD STR)
 *
 * FIELD - string, name of field to match (any, comment, description, summary)
 * STR - string, match string
 *
 * Returns a boolean indicating whether the specified field contains the
 * specified string.
 */
static ESExpResult *
func_contains (ESExp *esexp, int argc, ESExpResult **argv, void *data)
{
    Query *query;
    QueryPrivate *priv;
    CalComponent *comp;
    const char *field;
    const char *str;
    gboolean matches;
    ESExpResult *result;

    query = QUERY (data);
    priv = query->priv;

    g_assert (priv->next_comp != NULL);
    comp = priv->next_comp;

    /* Check argument types */

    if (argc != 2) {
        e_sexp_fatal_error (esexp, _("contains? expects 2 arguments"));
        return NULL;
    }

    if (argv[0]->type != ESEXP_RES_STRING) {
        e_sexp_fatal_error (esexp, _("contains? expects argument 1 "
                         "to be a string"));
        return NULL;
    }
    field = argv[0]->value.string;

    if (argv[1]->type != ESEXP_RES_STRING) {
        e_sexp_fatal_error (esexp, _("contains? expects argument 2 "
                         "to be a string"));
        return NULL;
    }
    str = argv[1]->value.string;

    /* See if it matches */

    if (strcmp (field, "any") == 0)
        matches = matches_any (comp, str);
    else if (strcmp (field, "comment") == 0)
        matches = matches_comment (comp, str);
    else if (strcmp (field, "description") == 0)
        matches = matches_description (comp, str);
    else if (strcmp (field, "summary") == 0)
        matches = matches_summary (comp, str);
    else {
        e_sexp_fatal_error (esexp, _("contains? expects argument 1 to "
                         "be one of \"any\", \"summary\", \"description\""));
        return NULL;
    }

    result = e_sexp_result_new (esexp, ESEXP_RES_BOOL);
    result->value.bool = matches;

    return result;
}

/* (has-categories? STR+)
 * (has-categories? #f)
 *
 * STR - At least one string specifying a category
 * Or you can specify a single #f (boolean false) value for components
 * that have no categories assigned to them ("unfiled").
 *
 * Returns a boolean indicating whether the component has all the specified
 * categories.
 */
static ESExpResult *
func_has_categories (ESExp *esexp, int argc, ESExpResult **argv, void *data)
{
    Query *query;
    QueryPrivate *priv;
    CalComponent *comp;
    gboolean unfiled;
    int i;
    GSList *categories;
    gboolean matches;
    ESExpResult *result;

    query = QUERY (data);
    priv = query->priv;

    g_assert (priv->next_comp != NULL);
    comp = priv->next_comp;

    /* Check argument types */

    if (argc < 1) {
        e_sexp_fatal_error (esexp, _("has-categories? expects at least 1 argument"));
        return NULL;
    }

    if (argc == 1 && argv[0]->type == ESEXP_RES_BOOL)
        unfiled = TRUE;
    else
        unfiled = FALSE;

    if (!unfiled)
        for (i = 0; i < argc; i++)
            if (argv[i]->type != ESEXP_RES_STRING) {
                e_sexp_fatal_error (esexp, _("has-categories? expects all arguments "
                                 "to be strings or one and only one "
                                 "argument to be a boolean false (#f)"));
                return NULL;
            }

    /* Search categories.  First, if there are no categories we return
     * whether unfiled components are supposed to match.
     */

    cal_component_get_categories_list (comp, &categories);
    if (!categories) {
        result = e_sexp_result_new (esexp, ESEXP_RES_BOOL);
        result->value.bool = unfiled;

        return result;
    }

    /* Otherwise, we *do* have categories but unfiled components were
     * requested, so this component does not match.
     */
    if (unfiled) {
        result = e_sexp_result_new (esexp, ESEXP_RES_BOOL);
        result->value.bool = FALSE;

        return result;
    }

    matches = TRUE;

    for (i = 0; i < argc; i++) {
        const char *sought;
        GSList *l;
        gboolean has_category;

        sought = argv[i]->value.string;

        has_category = FALSE;

        for (l = categories; l; l = l->next) {
            const char *category;

            category = l->data;

            if (strcmp (category, sought) == 0) {
                has_category = TRUE;
                break;
            }
        }

        if (!has_category) {
            matches = FALSE;
            break;
        }
    }

    cal_component_free_categories_list (categories);

    result = e_sexp_result_new (esexp, ESEXP_RES_BOOL);
    result->value.bool = matches;

    return result;
}

/* (is-completed?)
 *
 * Returns a boolean indicating whether the component is completed (i.e. has
 * a COMPLETED property. This is really only useful for TODO components.
 */
static ESExpResult *
func_is_completed (ESExp *esexp, int argc, ESExpResult **argv, void *data)
{
    Query *query;
    QueryPrivate *priv;
    CalComponent *comp;
    ESExpResult *result;
    struct icaltimetype *t;
    gboolean complete = FALSE;

    query = QUERY (data);
    priv = query->priv;

    g_assert (priv->next_comp != NULL);
    comp = priv->next_comp;

    /* Check argument types */

    if (argc != 0) {
        e_sexp_fatal_error (esexp, _("is-completed? expects 0 arguments"));
        return NULL;
    }

    cal_component_get_completed (comp, &t);
    if (t) {
        complete = TRUE;
        cal_component_free_icaltimetype (t);
    }

    result = e_sexp_result_new (esexp, ESEXP_RES_BOOL);
    result->value.bool = complete;

    return result;
}



/* Adds a component to our the UIDs hash table and notifies the client */
static void
add_component (Query *query, const char *uid, gboolean query_in_progress, int n_scanned, int total)
{
    QueryPrivate *priv;
    char *old_uid;
    CORBA_Environment ev;

    if (query_in_progress)
        g_assert (n_scanned > 0 || n_scanned <= total);

    priv = query->priv;

    if (g_hash_table_lookup_extended (priv->uids, uid, (gpointer *) &old_uid, NULL)) {
        g_hash_table_remove (priv->uids, old_uid);
        g_free (old_uid);
    }

    g_hash_table_insert (priv->uids, g_strdup (uid), NULL);

    CORBA_exception_init (&ev);
    GNOME_Evolution_Calendar_QueryListener_notifyObjUpdated (
        priv->ql,
        (char *) uid,
        query_in_progress,
        n_scanned,
        total,
        &ev);

    if (ev._major != CORBA_NO_EXCEPTION)
        g_message ("add_component(): Could not notify the listener of an "
               "updated component");

    CORBA_exception_free (&ev);
}

/* Removes a component from our the UIDs hash table and notifies the client */
static void
remove_component (Query *query, const char *uid)
{
    QueryPrivate *priv;
    char *old_uid;
    CORBA_Environment ev;

    priv = query->priv;

    if (!g_hash_table_lookup_extended (priv->uids, uid, (gpointer *) &old_uid, NULL))
        return;

    /* The component did match the query before but it no longer does, so we
     * have to notify the client.
     */

    g_hash_table_remove (priv->uids, old_uid);
    g_free (old_uid);

    CORBA_exception_init (&ev);
    GNOME_Evolution_Calendar_QueryListener_notifyObjRemoved (
        priv->ql,
        (char *) uid,
        &ev);

    if (ev._major != CORBA_NO_EXCEPTION)
        g_message ("remove_component(): Could not notify the listener of a "
               "removed component");

    CORBA_exception_free (&ev);
}

/* Removes a component from the list of pending UIDs */
static void
remove_from_pending (Query *query, const char *remove_uid)
{
    QueryPrivate *priv;
    GList *l;

    priv = query->priv;

    for (l = priv->pending_uids; l; l = l->next) {
        char *uid;

        g_assert (priv->n_pending > 0);

        uid = l->data;
        if (strcmp (remove_uid, uid))
            continue;

        g_free (uid);

        priv->pending_uids = g_list_remove_link (priv->pending_uids, l);
        g_list_free_1 (l);
        priv->n_pending--;

        g_assert ((priv->pending_uids && priv->n_pending != 0)
              || (!priv->pending_uids && priv->n_pending == 0));

        break;
    }
}

static struct {
    char *name;
    ESExpFunc *func;
} functions[] = {
    /* Time-related functions */
    { "time-now", func_time_now },
    { "make-time", func_make_time },
    { "time-add-day", func_time_add_day },
    { "time-day-begin", func_time_day_begin },
    { "time-day-end", func_time_day_end },

    /* Component-related functions */
    { "get-vtype", func_get_vtype },
    { "occur-in-time-range?", func_occur_in_time_range },
    { "contains?", func_contains },
    { "has-categories?", func_has_categories },
    { "is-completed?", func_is_completed }
};

/* Initializes a sexp by interning our own symbols */
static ESExp *
create_sexp (Query *query)
{
    ESExp *esexp;
    int i;

    esexp = e_sexp_new ();

    for (i = 0; i < (sizeof (functions) / sizeof (functions[0])); i++)
        e_sexp_add_function (esexp, 0, functions[i].name, functions[i].func, query);

    return esexp;
}

/* Evaluates the query sexp on the specified component and notifies the listener
 * as appropriate.
 */
static void
match_component (Query *query, const char *uid,
         gboolean query_in_progress, int n_scanned, int total)
{
    QueryPrivate *priv;
    CalComponent *comp;
    ESExpResult *result;

    priv = query->priv;

    comp = cal_backend_get_object_component (priv->backend, uid);
    g_assert (comp != NULL);
    gtk_object_ref (GTK_OBJECT (comp));

    /* Eval the sexp */

    g_assert (priv->next_comp == NULL);

    priv->next_comp = comp;
    result = e_sexp_eval (priv->esexp);
    gtk_object_unref (GTK_OBJECT (comp));
    priv->next_comp = NULL;

    if (!result) {
        const char *error_str;
        CORBA_Environment ev;

        error_str = e_sexp_error (priv->esexp);
        g_assert (error_str != NULL);

        CORBA_exception_init (&ev);
        GNOME_Evolution_Calendar_QueryListener_notifyEvalError (
            priv->ql,
            error_str,
            &ev);

        if (ev._major != CORBA_NO_EXCEPTION)
            g_message ("match_component(): Could not notify the listener of "
                   "an evaluation error");

        CORBA_exception_free (&ev);
        return;
    } else if (result->type != ESEXP_RES_BOOL) {
        CORBA_Environment ev;

        CORBA_exception_init (&ev);
        GNOME_Evolution_Calendar_QueryListener_notifyEvalError (
            priv->ql,
            _("Evaluation of the search expression did not yield a boolean value"),
            &ev);

        if (ev._major != CORBA_NO_EXCEPTION)
            g_message ("match_component(): Could not notify the listener of "
                   "an unexpected result value type when evaluating the "
                   "search expression");

        CORBA_exception_free (&ev);
    } else {
        /* Success; process the component accordingly */

        if (result->value.bool)
            add_component (query, uid, query_in_progress, n_scanned, total);
        else
            remove_component (query, uid);
    }

    e_sexp_result_free (priv->esexp, result);
}

/* Processes a single component that is queued in the list */
static gboolean
process_component_cb (gpointer data)
{
    Query *query;
    QueryPrivate *priv;
    char *uid;
    GList *l;

    query = QUERY (data);
    priv = query->priv;

    /* No more components? */

    if (!priv->pending_uids) {
        g_assert (priv->n_pending == 0);

        priv->idle_id = 0;
        return FALSE;
    }

    g_assert (priv->n_pending > 0);

    /* Fetch the component */

    l = priv->pending_uids;
    priv->pending_uids = g_list_remove_link (priv->pending_uids, l);
    priv->n_pending--;

    g_assert ((priv->pending_uids && priv->n_pending != 0)
          || (!priv->pending_uids && priv->n_pending == 0));

    uid = l->data;
    g_assert (uid != NULL);

    g_list_free_1 (l);

    bonobo_object_ref (BONOBO_OBJECT (query));

    match_component (query, uid,
             TRUE,
             priv->pending_total - priv->n_pending,
             priv->pending_total);

    bonobo_object_unref (BONOBO_OBJECT (query));

    g_free (uid);

    return TRUE;
}

/* Populates the query with pending UIDs so that they can be processed
 * asynchronously.
 */
static void
populate_query (Query *query)
{
    QueryPrivate *priv;

    priv = query->priv;
    g_assert (priv->idle_id == 0);

    priv->pending_uids = cal_backend_get_uids (priv->backend, CALOBJ_TYPE_ANY);
    priv->pending_total = g_list_length (priv->pending_uids);
    priv->n_pending = priv->pending_total;

    priv->idle_id = g_idle_add (process_component_cb, query);
}

/* Idle handler for starting a query */
static gboolean
start_query_cb (gpointer data)
{
    Query *query;
    QueryPrivate *priv;
    CORBA_Environment ev;

    query = QUERY (data);
    priv = query->priv;

    priv->idle_id = 0;

    priv->esexp = create_sexp (query);

    /* Compile the query string */

    g_assert (priv->sexp != NULL);
    e_sexp_input_text (priv->esexp, priv->sexp, strlen (priv->sexp));

    if (e_sexp_parse (priv->esexp) == -1) {
        const char *error_str;

        error_str = e_sexp_error (priv->esexp);
        g_assert (error_str != NULL);

        CORBA_exception_init (&ev);
        GNOME_Evolution_Calendar_QueryListener_notifyQueryDone (
            priv->ql,
            GNOME_Evolution_Calendar_QueryListener_PARSE_ERROR,
            error_str,
            &ev);

        if (ev._major != CORBA_NO_EXCEPTION)
            g_message ("start_query_cb(): Could not notify the listener of "
                   "a parse error");

        CORBA_exception_free (&ev);
        return FALSE;
    }

    /* Populate the query with UIDs so that we can process them asynchronously */

    populate_query (query);

    return FALSE;
}

/* Callback used when the backend gets loaded; we just queue the query to be
 * started later.
 */
static void
backend_opened_cb (CalBackend *backend, CalBackendOpenStatus status, gpointer data)
{
    Query *query;
    QueryPrivate *priv;

    query = QUERY (data);
    priv = query->priv;

    if (status == CAL_BACKEND_OPEN_SUCCESS) {
        g_assert (cal_backend_is_loaded (backend));
        g_assert (priv->idle_id == 0);

        priv->idle_id = g_idle_add (start_query_cb, query);
    }
}

/* Callback used when a component changes in the backend */
static void
backend_obj_updated_cb (CalBackend *backend, const char *uid, gpointer data)
{
    Query *query;

    query = QUERY (data);

    bonobo_object_ref (BONOBO_OBJECT (query));

    match_component (query, uid, FALSE, 0, 0);
    remove_from_pending (query, uid);

    bonobo_object_unref (BONOBO_OBJECT (query));
}

/* Callback used when a component is removed from the backend */
static void
backend_obj_removed_cb (CalBackend *backend, const char *uid, gpointer data)
{
    Query *query;
    QueryPrivate *priv;

    query = QUERY (data);
    priv = query->priv;

    bonobo_object_ref (BONOBO_OBJECT (query));

    remove_component (query, uid);
    remove_from_pending (query, uid);

    bonobo_object_unref (BONOBO_OBJECT (query));
}

/**
 * query_construct:
 * @query: A live search query.
 * @backend: Calendar backend that the query object will monitor.
 * @ql: Listener for query results.
 * @sexp: Sexp that defines the query.
 * 
 * Constructs a #Query object by binding it to a calendar backend and a query
 * listener.  The @query object will start to populate itself asynchronously and
 * call the listener as appropriate.
 * 
 * Return value: The same value as @query, or NULL if the query could not
 * be constructed.
 **/
Query *
query_construct (Query *query,
         CalBackend *backend,
         GNOME_Evolution_Calendar_QueryListener ql,
         const char *sexp)
{
    QueryPrivate *priv;
    CORBA_Environment ev;

    g_return_val_if_fail (query != NULL, NULL);
    g_return_val_if_fail (IS_QUERY (query), NULL);
    g_return_val_if_fail (backend != NULL, NULL);
    g_return_val_if_fail (IS_CAL_BACKEND (backend), NULL);
    g_return_val_if_fail (ql != CORBA_OBJECT_NIL, NULL);
    g_return_val_if_fail (sexp != NULL, NULL);

    priv = query->priv;

    CORBA_exception_init (&ev);
    priv->ql = CORBA_Object_duplicate (ql, &ev);
    if (ev._major != CORBA_NO_EXCEPTION) {
        g_message ("query_construct(): Could not duplicate the listener");
        priv->ql = CORBA_OBJECT_NIL;
        CORBA_exception_free (&ev);
        return NULL;
    }
    CORBA_exception_free (&ev);

    priv->backend = backend;
    gtk_object_ref (GTK_OBJECT (priv->backend));

    gtk_signal_connect (GTK_OBJECT (priv->backend), "obj_updated",
                GTK_SIGNAL_FUNC (backend_obj_updated_cb),
                query);
    gtk_signal_connect (GTK_OBJECT (priv->backend), "obj_removed",
                GTK_SIGNAL_FUNC (backend_obj_removed_cb),
                query);

    priv->sexp = g_strdup (sexp);

    /* Queue the query to be started asynchronously */

    if (cal_backend_is_loaded (priv->backend)) {
        g_assert (priv->idle_id == 0);
        priv->idle_id = g_idle_add (start_query_cb, query);
    } else
        gtk_signal_connect (GTK_OBJECT (priv->backend), "opened",
                    GTK_SIGNAL_FUNC (backend_opened_cb),
                    query);

    return query;
}

/**
 * query_new:
 * @backend: Calendar backend that the query object will monitor.
 * @ql: Listener for query results.
 * @sexp: Sexp that defines the query.
 * 
 * Creates a new query engine object that monitors a calendar backend.
 * 
 * Return value: A newly-created query object, or NULL on failure.
 **/
Query *
query_new (CalBackend *backend,
       GNOME_Evolution_Calendar_QueryListener ql,
       const char *sexp)
{
    Query *query;

    query = QUERY (gtk_type_new (QUERY_TYPE));
    if (!query_construct (query, backend, ql, sexp)) {
        bonobo_object_unref (BONOBO_OBJECT (query));
        return NULL;
    }

    return query;
}