add_action( 'rest_api_init', function () {

    // Path to meta query route e.g. localhost:3000/wp-json/reazul/v1/daily_post?for_day=10&for_month=3

    register_rest_route( 'reazul/v1', '/daily_post', array(
            'methods' => 'GET', // API request method
            'callback' => 'get_daily_post', // Call back to process request
            'args' => array( // Arguments passed on to the callback and their validations
                'for_day' => array(
                    'required' => true,
                    'validate_callback' => function($param, $request, $key) {
                        return is_numeric( $param ); // Checking for if the value is a number e.g. 1-31
                    }
                ),
                'for_month' => array(
                    'required' => true,
                    'validate_callback' => function($param, $request, $key) {
                        return is_numeric( $param ); // Checking for if the value is a number e.g. 1-12
                    }
                ),
            )
    ) );
});

// Callback function that returns API contents

function get_daily_devotional( WP_REST_Request $request ) {

    $args = array(
            'numberposts'   => 1,
            'post_type'     => 'post',
            'meta_query'    => array(
                'relation'      => 'AND', // Relationship between two variables passed onto callback
                array(
                    'key'       => 'date', // ACF field key
                    'value'     => "".$request->get_param( 'for_day' )."", // Getting query value from request. Additional Quote is used for turning it to string.
                    'compare'   => 'LIKE',
                ),
                array(
                    'key'       => 'month', // ACF field key
                    'value'     => "".$request->get_param( 'for_month' )."", // Getting query value from request. Additional Quote is used for converting it to string.
                    'compare'   => 'LIKE',
                ),
            )
        );
    $the_query = new WP_Query( $args );

    // Regular post loop
    if( $the_query->have_posts() ) {
        $data = array();

        while($the_query->have_posts()) {
            $the_query->the_post();

            // Generating custom API contents
            $data['ID'] =  get_the_ID();
            $data['title'] =  get_the_title();
            $data['permalink'] = get_the_permalink();
            $data['excerpt'] = wp_trim_words(get_the_content(), 75);
            $data['content'] =  get_the_content();
        }

        return $data;
    } else {
        return new WP_Error( 'no_post', 'No post to show.', array( 'status' => 404 ) );
    }
}