# WordPress Edge Integrations: Interest

## Namespace: `Pantheon\EI\WP\Interest`

The namespace for the analytics functionality is `Pantheon\EI\WP\Interest`. When using functions that are part of this namespace, it is recommended that you `use` the namespace at the top of your file.

```php
use Pantheon\EI\WP\Interest;
```

Doing this allows you to use the functions without the full namespace prefix. 

**More information**
* [Namespaces](https://www.php.net/manual/en/language.namespaces.php) (php.net)
* [Namespace and Function Imports](https://engineering.hmn.md/standards/style/php/#namespace-and-function-imports) (engineering.hmn.md/standards)

## Function reference

### `Interest\get_interest_header_key`

Return the interest header key.

#### Return 

_(string)_ The (possibly filtered) interest header key.

#### Example

```php
use Pantheon\EI\WP\Interest;

/*
 * Check if the interest header key is one that we expect. 
 * This is defined in the application (not necessarily what's returned by the CDN).
 */
if ( Interest\get_interest_header_key() !== 'P13n-Interest' ) {
	return;
}
```

### `Interest\get_interest`

Return or alter interest data in the global header.

#### Parameters

_(array)_ Data to pass to the HeaderData class. If an empty array is passed, `get_interest` will return all Interest data.

#### Return

_(string)_ The interest data in a JSON encoded string.

#### Example

```php
use Pantheon\EI\WP\Interest;

// Returns interest data from HeaderData class.
$interest = Interest\get_interest();
```

### `Interest\set_interest`

Set the interest data in global header.

#### Parameters

`$data` _(array)_ Interest data to pass to the HeaderData class.

#### Example

```php
use Pantheon\EI\WP\Interest;

// Manually pass data to interest header.
$data = ['HTTP_INTEREST' =>'Interest One|Interest Two'];
$interest = Interest\set_interest( $data );

// Pass interest to header from query string, ei_interest
$interest_from_query_string = isset( $_GET['ei_interest'] ) ? sanitize_text_field( $_GET['ei_interest'] ) : '';
Interest\set_interest( [ 'HTTP_INTEREST' => $interest_query_string ] );
```

## Filter reference

### `pantheon.ei.interest_header_key`

Use this filter to change the interest header key to use. This filter is used anywhere that `get_interest_header_key()` is used to return the interest header key (`P13n-Interest` by default).

Note that if you update the interest header key here, you must ensure that the proper header is being returned from the CDN, otherwise the interest tracking functionality will not work.

#### Parameters

_(string)_ The interest header key.

#### Example

```php
add_filter( 'pantheon.ei.interest_header_key', 'pantheon_modify_header_key' );
function modify_header_key() : string {
	return 'Interest';
}
```

### `pantheon.ei.localized_terms`

Modify terms before they are localized.

#### Parameters

_(array)_ An array of terms to modify.

#### Example

Add term to array:
```php
add_filter( 'pantheon.ei.localized_terms', 'pantheon_ei_add_term' );
function pantheon_ei_add_term( array $terms ) : array {
	$terms[] = 'term-from-theme';

	return $terms;
}
```

Remove term(s) from array:
```php
add_filter( 'pantheon.ei.localized_terms', 'pantheon_ei_remove_term' );
function pantheon_ei_remove_term( array $terms ) : array {
	// This can be one or many terms.
	$terms_to_remove = [ 'category-1', 'category-2' ];

	foreach ( $terms_to_remove as $term ) {
		$key = array_search( $term, $terms );
		if ( $key !== false ) {
			unset( $terms[ $key ] );
		}
	}

	return array_values( $terms );
}
```

### `pantheon.ei.interest_threshold`

Modify the interest threshold. Default `3`.

#### Parameters

_(int)_ The interest threshold.

#### Example

```php
add_filter( 'pantheon.ei.interest_threshold', 'pantheon_ei_change_threshold' );
function pantheon_ei_change_threshold() : int {
	return 5;
}
```

### `pantheon.ei.cookie_expiration`

Modify the number of days until the interest cookie expires. Default `14`.

#### Parameters

_(int)_ The number of days until the cookie expires.

#### Example

```php
add_filter( 'pantheon.ei.cookie_expiration', 'pantheon_ei_change_cookie_expiration' );
function pantheon_ei_change_cookie_expiration() : int {
	return 7;
}
```

## `pantheon.ei.taxonomy`

Modify the targeted taxonomy. Default `category`.

### Parameters

_(array)_  An array of taxonomies to target for personalization.

#### Example

Replace default taxonomy:
```php
add_filter( 'pantheon.ei.taxonomy', 'pantheon_ei_replace_taxonomy' );
function pantheon_ei_replace_taxonomy( array $taxonomy ) : array {
	$taxonomy = 'my-custom-taxonomy';

	return $taxonomy;
}
```

Add interest taxonomy:
```php
add_filter( 'pantheon.ei.taxonomy', 'pantheon_ei_add_taxonomy' );
function pantheon_ei_add_taxonomy( array $taxonomy ) : array {
	$taxonomy[] = 'my-custom-taxonomy';

	return $taxonomy;
}
```

### `pantheon.ei.post_types`

Modify post type support. Default `post`.

#### Parameters

_(array)_ An array of post types to target for personalization.

#### Example

```php
add_filter( 'pantheon.ei.post_types', 'pantheon_ei_add_post_type' );
function pantheon_ei_add_post_type( array $post_types ) : array {
	$post_types[] = 'my-custom-post-type';

	return $post_types;
}
```

### `pantheon.ei.parsed_interest_data`

Get the interest data from the HeaderData class and allow it to be modified.

#### Parameters

_(array)_ The full, parsed Interest data as an array.

#### Example

```php
add_filter( 'pantheon.ei.parsed_interest_data', 'pantheon_ei_parsed_interest_data' );
function pantheon_ei_parsed_interest_data( array $data ) : array {
	// Add term to array of interests.
	$data[] = 'some-interest';

	return $data;
}
```

### `pantheon.ei.applied_interest_data`

Modify HeaderData being set by set_interest.

#### Parameters

_(array)_ Interest data as an array.

#### Example

```php
add_filter( 'pantheon.ei.set_interest_data', 'pantheon_ei_set_interest_data' );
function pantheon_ei_set_interest_data( array $data ) : array {
	// Remove last element from $data.
	return array_pop( $data );
}
```