Add plugins page & API (#123)

Squashed

* Initial feature commit

* Remember last tab

* Refactor some logic

* Use the data attr

* Use getter to expose plugin instances

* Document feature

* PHPCBF autofix

* Fix rest of the lint

* Document usage with spaces

* Introduce way to force user to a page, once

* Make lists filterable and hide lists if empty

* Text changes

* I love you WPCS

Author: k1sul1

README.md

@@ -198,6 +198,29 @@ add_filter('wplf_dynamic_values', function($values) {
 // <input type="text" placeholder="%SOMETHING%" name="something">
 ```
 
+## Plugins
+1.5 exposes a new function, `wplf()`. It simply returns the class instance of WP Libre Form.
+
+It allows you to register your plugin as a WP Libre Form plugin, which in turn allows you to expose an API and a settings page for your plugin, should you want to.
+
+```php
+$wplf = wplf();
+$plugin = new YourPlugin();
+
+$wplf->plugins->register([
+  "name" => "YourPlugin", // The name you wish to show on the WPLF plugin page. Willl also be used to access public methods in your plugin
+  "description" => "What your plugin does in a sentence or two",
+  "link" => "https://toyourplugin.com", // Plugin URL. Can be wordpress.org or pretty much any URL where you can download the plugin
+  "version" => YOUR_PLUGIN_VERSION, // Define a constant containing your plugin version
+  "instance" => $plugin, // Your plugin, instantiated. Users can access your public methods
+  "settings_page" => [$plugin, "render_settings_page"], // Function that renders your settings page, or a string that contains the link to it. Leave empty to disable.
+]);
+```
+
+If you use spaces in the name, you can access the plugin instance like this:
+
+`wplf()->plugins->{"Your plugin"}->somePublicMethod()`
+
 ## Javascript API
 
 ### Client side callbacks

assets/scripts/wplf-plugins.js

@@ -0,0 +1,32 @@
+(function($) {
+  var menu = $('.wplf-plugins-menu');
+  var pages = $('.wplf-plugins-page');
+  var previousItem = localStorage.getItem('wplf-plugins-page-last-active-tab') || 'General';
+
+  menu.on('click', '.nav-tab', function(e) {
+    var item = $(e.target);
+    var page = item.attr('data-page');
+    var target = $('.wplf-plugins-page[data-page="' + page + '"]');
+
+    item.siblings().removeClass('nav-tab-active');
+    item.addClass('nav-tab-active');
+
+    pages.hide();
+    target.show();
+
+    try {
+      localStorage.setItem('wplf-plugins-page-last-active-tab', page);
+    } catch (e) {
+      // No one cares. Safari just throws in PB.
+      // The tab remember feature just won't work.
+      console.error(e);
+    }
+    e.preventDefault();
+  });
+
+  if (previousItem) {
+    var target = $('.wplf-plugins-menu [data-page="' + previousItem + '"]');
+
+    target.click();
+  }
+})(jQuery);

assets/styles/wplf-plugins.css

@@ -0,0 +1,46 @@
+.wplf-plugins {
+  box-sizing: border-box;
+}
+
+.wplf-plugins *, .wplf-plugins *:before, .wplf-plugins *:after {
+  box-sizing: border-box;
+}
+
+.wplf-plugins-page {
+  display: none;
+  overflow: hidden;
+}
+
+.wplf-plugin-list {
+  overflow: hidden;
+}
+
+.wplf-plugin-box {
+  padding: 1rem;
+  border: 1px solid #222;
+  width: 48%;
+  margin-right: 2%;
+  float: left;
+  background: #fff;
+}
+
+.wplf-plugin-box__meta {
+  overflow: hidden;
+  line-height: 30px; /* Poor man centering */
+}
+
+.wplf-plugin-box__meta--version {
+  color: #ccc;
+}
+
+.wplf-plugin-box__meta--links {
+  float: right;
+}
+
+@media (max-width: 768px) {
+  .wplf-plugin-box {
+    width: 100%;
+    margin-right: 0;
+    margin-bottom: 1rem;
+  }
+}