<?php
/*
 * Name: Language Filter
 * Version: 0.1
 * Description: Filters out postings in languages not spoken by the users
 * Author: Tobias Diekershoff <https://f.diekershoff.de/u/tobias>
 * License: MIT
 */

use Friendica\App;
use Friendica\Content\Text\BBCode;
use Friendica\Core\Hook;
use Friendica\Core\L10n;
use Friendica\Core\PConfig;
use Friendica\Core\Renderer;
use Friendica\DI;

/* Define the hooks we want to use
 * that is, we have settings, we need to save the settings and we want
 * to modify the content of a posting when friendica prepares it.
 */

function langfilter_install()
{
	Hook::register('prepare_body_content_filter', 'addon/langfilter/langfilter.php', 'langfilter_prepare_body_content_filter', 10);
	Hook::register('addon_settings', 'addon/langfilter/langfilter.php', 'langfilter_addon_settings');
	Hook::register('addon_settings_post', 'addon/langfilter/langfilter.php', 'langfilter_addon_settings_post');
}

function langfilter_uninstall()
{
	Hook::unregister('prepare_body_content_filter', 'addon/langfilter/langfilter.php', 'langfilter_prepare_body_content_filter');
	Hook::unregister('prepare_body', 'addon/langfilter/langfilter.php', 'langfilter_prepare_body');
	Hook::unregister('addon_settings', 'addon/langfilter/langfilter.php', 'langfilter_addon_settings');
	Hook::unregister('addon_settings_post', 'addon/langfilter/langfilter.php', 'langfilter_addon_settings_post');
}

/* The settings
 * 1st check if somebody logged in is calling
 * 2nd get the current settings
 * 3rd parse a SMARTY3 template, replacing some translateable strings for the form
 */

function langfilter_addon_settings(App $a, &$s)
{
	if (!local_user()) {
		return;
	}

	$enable_checked = (intval(DI::pConfig()->get(local_user(), 'langfilter', 'disable')) ? '' : ' checked="checked" ');
	$languages      = DI::pConfig()->get(local_user(), 'langfilter', 'languages');
	$minconfidence  = DI::pConfig()->get(local_user(), 'langfilter', 'minconfidence') * 100;
	$minlength      = DI::pConfig()->get(local_user(), 'langfilter', 'minlength');

	$t = Renderer::getMarkupTemplate("settings.tpl", "addon/langfilter/");
	$s .= Renderer::replaceMacros($t, [
		'$title'         => L10n::t("Language Filter"),
		'$intro'         => L10n::t('This addon tries to identify the language posts are writen in. If it does not match any language specifed below, posts will be hidden by collapsing them.'),
		'$enabled'       => ['langfilter_enable', L10n::t('Use the language filter'), $enable_checked, ''],
		'$languages'     => ['langfilter_languages', L10n::t('Able to read'), $languages, L10n::t('List of abbreviations (iso2 codes) for languages you speak, comma separated. For example "de,it".')],
		'$minconfidence' => ['langfilter_minconfidence', L10n::t('Minimum confidence in language detection'), $minconfidence, L10n::t('Minimum confidence in language detection being correct, from 0 to 100. Posts will not be filtered when the confidence of language detection is below this percent value.')],
		'$minlength'     => ['langfilter_minlength', L10n::t('Minimum length of message body'), $minlength, L10n::t('Minimum number of characters in message body for filter to be used. Posts shorter than this will not be filtered. Note: Language detection is unreliable for short content (<200 characters).')],
		'$submit'        => L10n::t('Save Settings'),
	]);

	return;
}

/* Save the settings
 * 1st check it's a logged in user calling
 * 2nd check the langfilter form is to be saved
 * 3rd save the settings to the DB for later usage
 */

function langfilter_addon_settings_post(App $a, &$b)
{
	if (!local_user()) {
		return;
	}

	if (!empty($_POST['langfilter-settings-submit'])) {
		PConfig::set(local_user(), 'langfilter', 'languages', trim($_POST['langfilter_languages']));
		$enable = (!empty($_POST['langfilter_enable']) ? intval($_POST['langfilter_enable']) : 0);
		$disable = 1 - $enable;
		PConfig::set(local_user(), 'langfilter', 'disable', $disable);
		$minconfidence = 0 + $_POST['langfilter_minconfidence'];
		if (!$minconfidence) {
			$minconfidence = 0;
		} elseif ($minconfidence < 0) {
			$minconfidence = 0;
		} elseif ($minconfidence > 100) {
			$minconfidence = 100;
		}
		PConfig::set(local_user(), 'langfilter', 'minconfidence', $minconfidence / 100.0);

		$minlength = 0 + $_POST['langfilter_minlength'];
		if (!$minlength) {
			$minlength = 32;
		} elseif ($minlength < 0) {
			$minlength = 32;
		}
		PConfig::set(local_user(), 'langfilter', 'minlength', $minlength);

		info(L10n::t('Language Filter Settings saved.') . EOL);
	}
}

/* Actually filter postings by their language
 * 1st check if the user wants to filter postings
 * 2nd get the user settings which languages shall be not filtered out
 * 3rd extract the language of a posting
 * 4th if the determined language does not fit to the spoken languages
 *     of the user, then collapse the posting, but provide a link to
 *     expand it again.
 */

function langfilter_prepare_body_content_filter(App $a, &$hook_data)
{
	$logged_user = local_user();
	if (!$logged_user) {
		return;
	}

	// Never filter own messages
	// TODO: find a better way to extract this
	$logged_user_profile = DI::baseUrl()->get() . '/profile/' . $a->user['nickname'];
	if ($logged_user_profile == $hook_data['item']['author-link']) {
		return;
	}

	// Don't filter if language filter is disabled
	if (DI::pConfig()->get($logged_user, 'langfilter', 'disable')) {
		return;
	}

	$naked_body = BBCode::toPlaintext($hook_data['item']['body'], false);

	// Don't filter if body lenght is below minimum
	$minlen = DI::pConfig()->get(local_user(), 'langfilter', 'minlength', 32);
	if (!$minlen) {
		$minlen = 32;
	}

	if (strlen($naked_body) < $minlen) {
		return;
	}

	$read_languages_string = DI::pConfig()->get(local_user(), 'langfilter', 'languages');
	$minconfidence = DI::pConfig()->get(local_user(), 'langfilter', 'minconfidence');

	// Don't filter if no spoken languages are configured
	if (!$read_languages_string) {
		return;
	}
	$read_languages_array = explode(',', $read_languages_string);

	// Extract the language of the post
	if (!empty($hook_data['item']['language'])) {
		$languages = json_decode($hook_data['item']['language'], true);
		if (!is_array($languages)) {
			return;
		}

		foreach ($languages as $iso2 => $confidence) {
			break;
		}

		if (empty($iso2)) {
			return;
		}

		$lang = Text_LanguageDetect_ISO639::code2ToName($iso2);
	} else {
		$opts = $hook_data['item']['postopts'];
		if (!$opts) {
			// no options associated to post
			return;
		}

		if (!preg_match('/\blang=([^;]*);([^:]*)/', $opts, $matches)) {
			// no lang options associated to post
			return;
		}

		$lang = $matches[1];
		$confidence = $matches[2];

		$iso2 = Text_LanguageDetect_ISO639::nameToCode2($lang);
	}

	// Do not filter if language detection confidence is too low
	if ($minconfidence && $confidence < $minconfidence) {
		return;
	}

	if (!$iso2) {
		return;
	}

	if (!in_array($iso2, $read_languages_array)) {
		$hook_data['filter_reasons'][] = L10n::t('Filtered language: %s', ucfirst($lang));
	}
}