Add a button above TinyMCE to generate a shortcode

class-nh-shortcode-generator.php

<?php
/**
 * Create a button that generates a shortcode to be added to TinyMCE.
 *
 * @todo  Add an option to change the template file path.
 *        Add the ability to specify what admin pages the button is displayed on.
 */
class NH_Shortcode_Generator {

    private $form_id = null;

    private $opts = array();

    private $defaults = array(
        'button_text' => 'Add Shortcode',
        'button_icon' => 'dashicons-plus-alt',
        'shortcode'   => false
    );
    public function __construct($args) {
        $this->opts = wp_parse_args( $args, $this->defaults );
        // Verify that shortcode is valid
        if(!$this->shortcode || !shortcode_exists($this->shortcode)) return false;

        $this->form_id = sanitize_html_class( 'shortcode_popup_' . $this->shortcode );

        add_action( 'media_buttons_context', array($this, 'add_button') );
        add_action( 'admin_footer', array($this, 'popup_content') );

    }

    /**
     * Add button above TinyMCE
     *
     * @param   string   HTML for the media buttons section.
     * @return  string   HTML containing the new button.
     */
    public function add_button($context) {

        $context .= sprintf('<a class="button thickbox" title="%s" href="#TB_inline?width=480&inlineId=%s"><span class="wp-media-buttons-icon dashicons %s" style="width:auto; margin-left:0;"></span> %s</a>',
            $this->button_text,
            $this->form_id,
            $this->button_icon,
            $this->button_text
        );
        return $context;
    }

    /**
     * Create the popup form using template parts
     */
    public function popup_content() {
        ?>
        <div id="<?php echo $this->form_id; ?>" style="display:none;">
            <h2><?php echo $this->button_text; ?></h2>
            <div class="form-body">
                <?php get_template_part( 'templates/shortcode-popup', $this->shortcode ); ?>
            </div>
            <button type="button" class="button-primary" id="button-<?php echo $this->shortcode; ?>"><?php echo $this->button_text; ?></button> &nbsp;
            <a class="button" href="#" onclick="tb_remove(); return false;" style="margin-left:10px;">Cancel</a>

            <script>
            jQuery(function($) {
                var opts    = <?php echo json_encode($this->opts); ?>;
                var btn     = '#button-'+opts.shortcode;
                var content = false;
                var s_code  = '';

                $(document).on('click', btn, function(e) {
                    e.preventDefault();
                    var atts = '';

                    $(this).parent().find('.form-body').find('input, textarea, select').each(function() {
                        var name = $(this).attr('name');
                        var val  = $(this).val().trim();

                        if(val.trim() === '') continue;
                        if(name === 'content') {
                            content = $(this).val();
                            continue;
                        }
                        if( $(this).val() !== '' ) {
                            atts += ' ' + name + '="' + $(this).val() + '"';
                        }
                    });
                    s_code = '['+opts.shortcode + atts + ']';
                    window.send_to_editor();
                });
            });
            </script>
        </div>
        <?php
    }

    /**
     * Magic Functions!!
     */
    public function __set($name, $value) {
        $this->opts[$name] = $value;
    }

    public function __get($name) {
        if (array_key_exists($name, $this->opts)) {
            return $this->opts[$name];
        }
        return null;
    }

}

Sample Popup Form

<p>
    <label for="experience-type">Experience Type:</label>
    <?php wp_dropdown_categories(array(
        'show_option_none' => 'Show All',
        'taxonomy'         => 'experience-type',
        'name'             => 'type'
    )) ?>
</p>

Save file as shortcode-popup-{SHORTCODENAME}.php within a templates folder in your theme root

Sample Usage:

new NH_Shortcode_Generator(array(
    'shortcode'   => 'experiences',
    'button_icon' => 'dashicons-nametag',
    'button_text' => 'Add Experiences'
));