/*
 * This file is part of LibNSLayout
 * Licensed under the ISC License, http://opensource.org/licenses/ISC
 * Copyright 2015 Michael Drake <tlsa@netsurf-browser.org>
 */

/** \file src/dom/watcher.c
 * Implementation of DOM mutation watching.
 *
 * TODO: LibDOM mutation event listeners are really slow.
 *       Need to find a better way to get DOM change notifications.
 *       LibDOM probably needs to gain Mutation Observer support, or
 *       gain a LibDOM-specific extension API.
 */

#include <stdio.h>
#include <assert.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>

#include "libnslayout/nslayout.h"

#include "dom/debug.h"
#include "dom/watcher.h"
#include "util/dom-str.h"
#include "util/util.h"


/**
 * A dom watcher object
 */
struct nsl_dom_watcher {
	dom_document *document;
	dom_event_listener *listener; /**< DOM event listener object */
};

/**
 * LibDOM event handler
 *
 * \param[in]  evt  The LibDOM event object
 * \param[in]  pw   Pointer to our dom watcher object
 */
static void nsl__dom_event_handler(struct dom_event *evt, void *pw)
{
	const struct nsl_dom_watcher *watcher = pw;

	UNUSED(watcher);

	nsl_dom_debug_dump_event(evt);

	/* TODO: Based on event type:
	 *         1. call to do (re)selection:
	 *              a. all nodes?
	 *              b. just this node?
	 *         2. call to update layout, if needed.
	 */
}


/**
 * Destroy a DOM document's event listener
 *
 * \param[in]  listener  The listener to destroy
 * \param[in]  document  The document that the listener was registerd for.
 * \return NSLAYOUT_OK on success, appropriate error otherwise.
 */
static nslayout_error nsl__dom_listener_destroy(
		dom_event_listener *listener,
		dom_document *document)
{
	dom_exception exc;

	/* Passing NULL as type, removes listener for all event types. */
	exc = dom_event_target_remove_event_listener(
			document, NULL, listener, false);
	if (exc != DOM_NO_ERR) {
		return NSL_DOM_ERR(exc);
	}

	dom_event_listener_unref(listener);

	return NSLAYOUT_OK;
}


/**
 * Create a dom event listener.
 *
 * \param[out]  listener_out  Returns a dom listener for watcher's document.
 * \param[in]   watcher       DOM watcher object that listener is used for.
 * \return NSLAYOUT_OK on success, appropriate error otherwise.
 */
static nslayout_error nsl__dom_listener_create(
		dom_event_listener **listener_out,
		const struct nsl_dom_watcher *watcher)
{
	dom_event_listener *listener;
	dom_exception exc;

	/* Create listener */
	exc = dom_event_listener_create(nsl__dom_event_handler,
			(void *) watcher, &listener);
	if (exc != DOM_NO_ERR) {
		goto error;
	}

	/* Set the event types it should listen to */
	exc = dom_event_target_add_event_listener(watcher->document,
			nsl_dom_str_node_inserted, listener, false);
	if (exc != DOM_NO_ERR) {
		goto error;
	}
	exc = dom_event_target_add_event_listener(watcher->document,
			nsl_dom_str_subtree_modified, listener, false);
	if (exc != DOM_NO_ERR) {
		goto error;
	}
	exc = dom_event_target_add_event_listener(watcher->document,
			nsl_dom_str_node_removed, listener, false);
	if (exc != DOM_NO_ERR) {
		goto error;
	}
	exc = dom_event_target_add_event_listener(watcher->document,
			nsl_dom_str_attr_modified, listener, false);
	if (exc != DOM_NO_ERR) {
		goto error;
	}
	exc = dom_event_target_add_event_listener(watcher->document,
			nsl_dom_str_characterdata_modified, listener, false);
	if (exc != DOM_NO_ERR) {
		goto error;
	}

	*listener_out = listener;
	return NSLAYOUT_OK;

error:
	nsl__dom_listener_destroy(listener, watcher->document);

	return NSL_DOM_ERR(exc);
}

/* Exported function, documented in src/dom/watcher.h */
nslayout_error nsl_dom_watcher_create(
		struct nsl_dom_watcher **watcher_out,
		dom_document *document)
{
	struct nsl_dom_watcher *watcher;
	nslayout_error err;

	watcher = malloc(sizeof(*watcher));
	if (watcher == NULL) {
		return NSLAYOUT_NO_MEM;
	}

	watcher->document = document;

	err = nsl__dom_listener_create(&watcher->listener, watcher);
	if (err != NSLAYOUT_OK) {
		free(watcher);
		return err;
	}

	*watcher_out = watcher;
	return NSLAYOUT_OK;
}

/* Exported function, documented in src/dom/watcher.h */
nslayout_error nsl_dom_watcher_destroy(
		struct nsl_dom_watcher *watcher)
{
	nsl__dom_listener_destroy(watcher->listener, watcher->document);
	free(watcher);

	return NSLAYOUT_OK;
}