WordPress Plugin Development Essentials

1. Why plugin?
1. Plugin is portable and independent for specific functionality.
2. The plugin has no issue after theme update.
2. Fundamentals
1. Customize wp-config.php [Not mandatory if required]
   1. define('WP_DEBUG', false); -> define('WP_DEBUG', true);
2. index.php file isn't mandatory.  
3. Folder Structure
1. Plugin folder name should be unique. Like iftekhar.
2. Inside iftekhar (plugin folder) folder create folder_name.php(iftekhar.php).
3. Create index.php empty with single comment.
4. Class
1. Unique name for class.
3. Plugin has three basic behavioral options
1. Activation
1. generate a CPT
2. Flush rewrite rules
3. register_activation_hook( __FILE__, array( $excellentPT, 'activate' ) );
2. Deactivation
1. Flush rewrite rules
2. register_deactivation_hook( __FILE__, array( $excellentPT, 'deactivate' ) );
3. Uninstall
1. Delete CPT
2. Delete all the plugin data form the db
3. Limitation of uninstall hook -> Only a static method or function can be used in an uninstall hook.
4. uninstall.php [Predefined file inside plugin folder]
4. Path
1. __FILE__ Global predefined location that PHP uses. 
2. plugins_url( '/assets/p_script.js', __FILE__ );
3. require_once plugin_dir_path(__FILE__).'inc/abc.php';
4. plugin_basename( __FILE__ );
5. Shortcode
1. Initialization isn't required inside functions.php
2. Except functions.php initialization is required.  
6. Check Everything ok or prevent direct page access (required).
1. if ( ! defined( 'ABSPATH' ) ) { die;} or defined( 'ABSPATH' ) or die('text');
7. Plugin enqueue
1. function enqueue() {
     wp_enqueue_style( 'pluginstyle', plugins_url( '/assets/p_style.css', __FILE__ ) );
     wp_enqueue_script( 'pluginscript', plugins_url( '/assets/p_script.js', __FILE__ ) );
    }
8. Add Menu //Inside the class
1. function register(){add_action, array($this, 'add_admin_menus');}
2. public function add_admin_menus(){ add_menu_page( 'Iftekhar Plugin', 'Menu Title', 'manage_options', 'my_plugin', array($this, 'admin_index'), 'dashicons-nametag', 110 );}
3. public function admin_index(){require_once plugin_dir_path( __FILE__ ) . 'templates/admin.php';}
9. Add Link on installed plugin
1. public $plugin;
2. function __construct(){
      $this->plugin = plugin_basename( __FILE__ );
     }
3. function myFun(){add_filter( "plugin_action_links_$this->plugin", array( $this, 'settings_link' ) );}
4. public function settings_link( $links ) {
      $settings_link = '<a href="admin.php?page=my_plugin">Settings</a>';
      array_push( $links, $settings_link );
      return $links;
     }