meta_tags.install

<?php

/**
* Implements hook_install()
*/

function meta_tags_install() {
  // Check to see if the annotation field exists.
  $field = field_info_field('meta_title');
  // If the annotation field does not exist then create it.
  if (empty($field)) {
    $field = array(
      'field_name' => 'meta_title',
      'entity_types' => array('node'),
      'translatable' => TRUE,
	  'type' => 'text',

    );
    $field = field_create_field($field);
  }
  
  // Check to see if the annotation field exists.
  $field = field_info_field('meta_desc');
  // If the annotation field does not exist then create it.
  if (empty($field)) {
    $field = array(
      'field_name' => 'meta_desc',
      'type' => 'text',
      'entity_types' => array('node'),
      'translatable' => TRUE,
	  'widget' => array(
		'type' => 'text_textarea_with_summary',
		'settings' => array(
		  'rows' => 10,
		  'summary_rows' => 3,
		),

	  ),
    );
    $field = field_create_field($field);
  }
  
  // Check to see if the annotation field exists.
  $field = field_info_field('meta_keywords');
  // If the annotation field does not exist then create it.
  if (empty($field)) {
    $field = array(
      'field_name' => 'meta_keywords',
      'type' => 'text',
      'entity_types' => array('node'),
      'translatable' => TRUE,
	  'widget' => array(
		'type' => 'text_textarea_with_summary',
		'settings' => array(
		  'rows' => 10,
		  'summary_rows' => 3,
		),
	  ),	  
    );
    $field = field_create_field($field);
  }
  
  drupal_set_message('Module installed');
}

/**
* Implements hook_uninstall()
*/
function meta_tags_uninstall() {
  watchdog("Meta tags Module", "Uninstalling module and deleting fields");
  $types = node_type_get_types();
  foreach($types as $type) {
    meta_tags_delete_meta_tags($type);
  }
  $field = field_info_field('meta_title');
  if ($field) {
    field_delete_field('meta_title');
  }
  
  $field = field_info_field('meta_desc');
  if ($field) {
    field_delete_field('meta_desc');
  }
  
  $field = field_info_field('meta_keywords');
  if ($field) {
    field_delete_field('meta_keywords');
  }

  	variable_del('meta_tags_default_keywords');
	variable_del('meta_tags_default_desc');
	variable_del('meta_tags_default_title');
	variable_del('meta_tags_node_types');

	cache_clear_all('variables', 'cache');
}

function meta_tags_delete_meta_tags($type) {
  $instance = field_info_instance('node', 'meta_title', $type->type);
  if ($instance) {
    field_delete_instance($instance, false);
  }
  
  $instance = field_info_instance('node', 'meta_desc', $type->type);
  if ($instance) {
    field_delete_instance($instance, false);
  }
  
  $instance = field_info_instance('node', 'meta_keywords', $type->type);
  if ($instance) {
    field_delete_instance($instance, false);
  }
}