"Call to undefined function get_option()" from another plugin script

hello, i’m a newbie of developing WordPress plugin.

now i’ve got a fatal error.

that is “Call to undefined function get_option()” when i directelly browse the script url.

it looks like “https://wordpress_url/wp-content/plugins/my_plugin/index.php?action=sync”

here is my plugin structure and script code below.

sorry about my poor english ??

/
　wp-content
　　plugins
　　　my_plugin
　　　　css
　　　　　style.css
　　　　images
　　　　　checked.png
　　　　　favicon.gif
　　　　　loading.gif
　　　　　toggle.png
　　　　　unchecked.png
　　　　js
　　　　php
　　　　　functions.php
　　　　　uploader.php
　　　　index.php

index.php

<?php
	# Plugin Name: my_plugin
	# Plugin URI:  https://www.skiddie.me/
	# Version:     β
	# Author:      Chris
	# Description: no more plugin information provided :-)

	require_once('php/functions.php');
	if (!(function_exists('add_action')))
	{
		header('HTTP/1.1 500 Internal Server Error');
		header('Status: 500 Internal Server Error');
		exit('Call to function: add_action() failed');
	}
	add_action('admin_menu', 'my_plugin_menu');
	add_action('publish_post', 'my_plugin_post');
	add_filter('the_content', 'my_plugin_content');
	register_activation_hook(__FILE__, 'my_plugin_activation');
	register_deactivation_hook(__FILE__, 'my_plugin_deactivation');
?>

php/functions.php

<?php
	define('email', my_plugin_option('get', 'email'));
	define('password', my_plugin_option('get', 'password'));
	define('folder', my_plugin_option('get', 'folder'));
	define('identity', my_plugin_option('get', 'identity'));

	function my_plugin_activation()
	{
		$my_plugin_options = array('email' => '',
					   'password' => '',
					   'folder' => 'Public',
					   'identity' => '',
					   'delete' => 'false');
		my_plugin_option('set', $my_plugin_options);
	}

	function my_plugin_content($content)
	{
		# just do something for content.
		return $content;
	}

	function my_plugin_deactivation()
	{
		delete_option('my_plugin_options');
	}

	function my_plugin_file($post_id = '')
	{
		# try to get the post attachment real path
	}

	function my_plugin_menu()
	{
		if (function_exists('add_menu_page'))
		{
			add_menu_page('my_pluginBox Setting',
				      'my_pluginBox',
				      'manage_options',
				      'my_pluginbox',
				      'my_plugin_setup',
				      plugin_dir_url(__FILE__) . '../images/favicon.gif');
		}
	}

	function my_plugin_notify($status, $prompt)
	{
		switch ($status)
		{
			case 'error':
				printf("<div id=\"message\" class=\"error\"><p>%s<br /></p></div>", $prompt);
				break;
			case 'success':
				printf("<div id=\"message\" class=\"updated\"><p>%s<br /></p></div>", $prompt);
				break;
			default:
				break;
		}
	}

	function my_plugin_option($method, $key = '')
	{
		switch ($method)
		{
			case 'get':
				$options = get_option('my_plugin_options');
				if (is_array($options))
					if (empty($key))
						return $options;
					else
						return $options[$key];
				return $key;
				break;
			case 'set':
				if (is_array($key))
				{
					if (update_option('my_plugin_options', $key))
						return true;
					else
						return false;
				}
				break;
			default:
				break;
		}
	}

	function my_plugin_post($post_ID)
	{
		# just do something for post.
		return $post_ID;
	}

	function my_plugin_upload($file, $folder, $email, $password)
	{
		# upload the post attachment to somewhere.
	}

	function my_plugin_setup()
	{
		if (!(empty($_POST['action'])))
		{
			switch ($_POST['action'])
			{
				case 'setup':
					if (!(empty($_POST['delete'])) && ($_POST['delete'] == 'true'))
						$delete = 'true';
					else
						$delete = 'false';
					$my_plugin_options = array('email' => $_POST['email'],
								   'password' => $_POST['password'],
								   'folder' => $_POST['folder'],
								   'identity' => $_POST['identity'],
								   'delete' => $delete);
					if (my_plugin_option('set', $my_plugin_options))
						my_plugin_notify('success', 'my_pluginBox updated.');
					else
						my_plugin_notify('error', 'an error occurred.');
					break;
				case 'sync':
					$start_time = date('Y-m-d H:i:s');
					$file = my_plugin_file();
					foreach ($file as $value)
						my_plugin_upload($value, folder, email, password);
					$end_time = date('Y-m-d H:i:s');
					break;
				default:
					break;
			}
		}
?>
	<link href="<?php printf("%scss/style.css", plugin_dir_url(__FILE__) . '../'); ?>" media="screen" rel="stylesheet" type="text/css" />
	<script src="https://code.jquery.com/jquery-latest.min.js" type="text/javascript"></script>
	<script src="https://ajax.aspnetcdn.com/ajax/jquery.validate/1.9/jquery.validate.min.js" type="text/javascript"></script>
	<script type="text/javascript">
		$(document).ready(function(){
			jQuery.validator.addMethod("format", function(value, element){
				return this.optional(element) || /^Public(?:(?:\/[-\w.:@&?#]+)*|$)$/.test(value);
			});
			$("#my_pluginbox_form").validate({
				debug: false,
				errorElement: "strong",
				errorPlacement: function(error, element){error.appendTo(element.siblings("span"));},
				event: "blur",
				rules: {
					email: {
						email: true,
						required: true},
					password: "required",
					folder: {
						format: true,
						required: true},
					identity: {
						number: true,
						required: true},},
				success: function(label){label.addClass("valid");}
			});
			$("#identity_prompt_link").click(function(){
				$("#identity_prompt_text").fadeToggle(1000);
				$("#toggle").toggleClass('toggle_down');
			});
			$("#delete").click(function(){
				if ($(this).attr('checked'))
				{
					$(this).attr('checked', false);
					$("#delete_prompt_text").fadeIn(1000);
				}
			});
			$("#delete_confirm_link").click(function(){
				$("#delete").attr('checked', true);
				$("#delete_prompt_text").hide();
			});
			$("#sync_now").click(function(){
				$.ajax({
					beforeSend: function(){
						$("#result").empty();
						$("#loading").show();},
					cache: false,
					data: "action=sync"
					dataType: "html",
					success: function(response){
						$("#loading").hide();
						$('#result').html(response);},
					type: "POST",
					url: '<?php printf("%s/wp-content/plugins/my_plugin/index.php?action=sync", get_option('siteurl')); ?>',
				});
			});
		});
	</script>
	<form action="" autocomplete="off" id="my_pluginbox_form" method="post">
		<div class="wrap">
			<div id="icon-options-general" class="icon32">
				<br />
			</div>
			<h2>my_pluginBox Setting</h2>
			<fieldset>
				<table class="form-table">
					<tr valign="top">
						<td>
							<label for="email">Email: </label>
						</td>
						<td>
							<input id="email" name="email" size="32" title="email" type="text" value="<?php echo email; ?>" />
							<span></span>
						</td>
					</tr>
					<tr valign="top">
						<td>
							<label for="password">Password: </label>
						</td>
						<td>

							<input id="password" name="password" size="32" title="password" type="password" value="<?php echo password; ?>" />
							<span></span>
						</td>
					</tr>
					<tr valign="top">
						<td>
							<label for="folder">Folder: </label>
						</td>
						<td>
							<input id="folder" name="folder" size="32" title="folder" type="text" value="<?php echo folder; ?>" />
							<span></span>
						</td>
					</tr>
					<tr valign="top">
						<td>
							<label for="identity">Identity: </label>
						</td>
						<td>
							<input id="identity" name="identity" size="32" title="identity" type="text" value="<?php echo identity; ?>" />
							<span></span>
						</td>
					</tr>
					<tr valign="top">
						<td>
						</td>
						<td>
							<strong>
								<a id="identity_prompt_link" href="#">?</a>
								<span id="toggle" class="toggle_up"></span>
							</strong>
							<div id="identity_prompt_text" style="display: none">
								this is a help prompt area :)
							</div>
						</td>
					</tr>
					<tr valign="top">
						<td>
							<label for="delete">Delete: </label>
						</td>
						<td>
							<input <?php checked(my_plugin_option('get', 'delete'), 'true'); ?> id="delete" name="delete" title="delete" type="checkbox" value="true" />
							Auto delete the file ?
						</td>
					</tr>
					<tr valign="top">
						<td>
						</td>
						<td>
							<div id="delete_prompt_text" style="display: none">
								Are u sure ? <a href="#" id="delete_confirm_link">CLICK HERE</a>
							</div>
						</td>
					</tr>
					<tr valign="top">
						<th scope="row">Sync: </th>
						<td>
							<input class="button-primary" id="sync_now" title="sync_now。" type="button" value="Sync" />
						</td>
					</tr>
					<tr valign="top">
						<th scope="row"></th>
						<td>
							<div id="result">
							</div>
							<div id="loading" style="display:none">
								<img src="images/loading.gif"> Uploading now ..
							</div>
						</td>
					</tr>
				</table>
				<input type="hidden" name="action" value="setup" />
				<p class="submit">
					<input class="button-primary" type="submit" value="<?php _e('Save Changes') ?>" />
				</p>
			</fieldset>
		</div>
	</form>
<?php
	}
?>