These are a few ideas of my code. In mymodule.module:

function _mymodule_implode_date($date, $hour, $minute, $ampm) {
if (variable_get('event_ampm', '0') && $ampm == 'p') {
$hour += 12;
}
$datetime= $date . ' ' . str_pad($hour, 2, '0', STR_PAD_LEFT) . ':' . str_pad($minute, 2, '0', STR_PAD_LEFT);
return $datetime;
}

function mymodule_nodeapi(&$node, $op, $teaser = NULL, $page = NULL) {
// if event enabled node
if(variable_get('event_nodeapi_'. $node->type, 'never') != 'never') {
// remove spaces from $op
$op_override = str_replace(' ', '', $op);

switch ($op) {
case 'load':
// run override for event_nodeapi
if (variable_get('event_nodeapi_' . $op_override,'none') == 'mymodule') {
// code to override load operation
}
break;
case 'validate':
// run override for event_nodeapi
if (variable_get('event_nodeapi_' . $op_override,'none') == 'mymodule') {
$form_values = $_POST;
$node->event_start = _mymodule_implode_date($node->event_start, $node->start_time_hour, $node->start_time_minute, $form_values['start_time_ampm']);
$node->event_end = _mymodule_implode_date($node->event_end, $node->end_time_hour, $node->end_time_minute, $form_values['end_time_ampm']);
if (event_is_later($node->event_start, $node->event_end, 'string')) {
$node->event_end = $node->event_start;
}
}
break;

In mymodule.install:

function mymodule_install() {
// Drop module weight so we act after event and eventrepeat
$weight = (int)db_result(db_query("SELECT weight FROM {system} WHERE name = 'eventrepeat'"));
db_query("UPDATE {system} SET weight = %d WHERE name = 'st49events'", $weight + 1);
db_query("INSERT INTO {event_nodeapi_overriders} (module, op) VALUES ('%s', '%s')", 'st49events', 'delete');
db_query("INSERT INTO {event_nodeapi_overriders} (module, op) VALUES ('%s', '%s')", 'st49events', 'delete revision');
db_query("INSERT INTO {event_nodeapi_overriders} (module, op) VALUES ('%s', '%s')", 'st49events', 'insert');
db_query("INSERT INTO {event_nodeapi_overriders} (module, op) VALUES ('%s', '%s')", 'st49events', 'load');
db_query("INSERT INTO {event_nodeapi_overriders} (module, op) VALUES ('%s', '%s')", 'st49events', 'prepare');
db_query("INSERT INTO {event_nodeapi_overriders} (module, op) VALUES ('%s', '%s')", 'st49events', 'search result');
db_query("INSERT INTO {event_nodeapi_overriders} (module, op) VALUES ('%s', '%s')", 'st49events', 'print');
db_query("INSERT INTO {event_nodeapi_overriders} (module, op) VALUES ('%s', '%s')", 'st49events', 'update');
db_query("INSERT INTO {event_nodeapi_overriders} (module, op) VALUES ('%s', '%s')", 'st49events', 'submit');
db_query("INSERT INTO {event_nodeapi_overriders} (module, op) VALUES ('%s', '%s')", 'st49events', 'update index');
db_query("INSERT INTO {event_nodeapi_overriders} (module, op) VALUES ('%s', '%s')", 'st49events', 'validate');
db_query("INSERT INTO {event_nodeapi_overriders} (module, op) VALUES ('%s', '%s')", 'st49events', 'view');
db_query("INSERT INTO {event_nodeapi_overriders} (module, op) VALUES ('%s', '%s')", 'st49events', 'alter');
db_query("INSERT INTO {event_nodeapi_overriders} (module, op) VALUES ('%s', '%s')", 'st49events', 'rss item');
}

This is how the event_nodeapi_overriders should be created from event.install, or any other part in your code if you're using this method for other modules:

db_query("CREATE TABLE {event_nodeapi_overriders} (
module varchar(64) NOT NULL default '',
op varchar(64) NOT NULL default ''
) /*!40100 DEFAULT CHARACTER SET utf8 */;");

And the original module you want to override should use something like this, in my example the functions modified are event_admin_overview_settings and event_nodeapi. These are some of the select boxes for the settings page:

$form['event_nodeapi_overriders'] = array(
'#type' => 'fieldset',
'#title' => t('Nodeapi Overriders'),
);

$form['event_nodeapi_overriders']['event_nodeapi_delete'] = array(
'#type' => 'select',
'#title' => t('Delete'),
'#default_value' => variable_get('event_nodeapi_delete','none'),
'#options' => _event_nodeapi_overriders('delete'),
'#description' => t('Module that overrides delete case in event_nodeapi')
);

$form['event_nodeapi_overriders']['event_nodeapi_deleterevision'] = array(
'#type' => 'select',
'#title' => t('Delete Revision'),
'#default_value' => variable_get('event_nodeapi_deleterevision','none'),
'#options' => _event_nodeapi_overriders('delete revision'),
'#description' => t('Module that overrides delete revision case in event_nodeapi')
);

$form['event_nodeapi_overriders']['event_nodeapi_insert'] = array(
'#type' => 'select',
'#title' => t('Insert'),
'#default_value' => variable_get('event_nodeapi_insert','none'),
'#options' => _event_nodeapi_overriders('insert'),
'#description' => t('Module that overrides insert case in event_nodeapi')
);

$form['event_nodeapi_overriders']['event_nodeapi_load'] = array(
'#type' => 'select',
'#title' => t('Load'),
'#default_value' => variable_get('event_nodeapi_load','none'),
'#options' => _event_nodeapi_overriders('load'),
'#description' => t('Module that overrides load case in event_nodeapi')
);

This is a helper function:

function _event_nodeapi_overriders($op) {
$modules = array('none' => 'none');
$sql = "SELECT module FROM {event_nodeapi_overriders} WHERE op = '%s' ORDER BY module";
$result = db_query($sql, $op);
while ($overrider = db_fetch_object($result)) {
$modules[$overrider->module] = $overrider->module;
}
return $modules;
}

And finally code like this in event_nodeapi:

function event_nodeapi(&$node, $op, $teaser = NULL, $page = NULL) {
// make sure it's an event enabled node
if(variable_get('event_nodeapi_'. $node->type, 'never') != 'never') {
$op_override = str_replace(' ', '', $op);
switch ($op) {
case 'load':
if (variable_get('event_nodeapi_' . $op_override,'none') == 'none') {
// run code here if no nodeapi override for this operation
}
break;
}

This is not code to be copied and pasted, it requires some more thought but you may get the idea from it.

Alexis Bellido