GST, HST, PST, and QST for Canada eh? Event Espresso 4.

canada_taxes.php

<?php
//* Please do NOT include the opening php tag, except of course if you're starting with a blank file

/**
 * PLEASE READ AND FOLLOW ALL INSTRUCTIONS IN CAPS
 *
 * IN ORDER FOR THIS TO WORK YOU NEED TO ACTIVATE THE "ADDRESS QUESTION GROUP"
 * THEN SET THE STATE/PROVINCE QUESTION TO BE REQUIRED
 *
 * BECAUSE THIS QUESTION SHOULD ONLY BE ASKED ONCE PER TRANSACTION
 * THE ADDRESS QUESTION GROUP SHOULD NOT BE SET FOR ADDITIONAL REGISTRANTS
 * IN OTHER WORDS, 
 * CHECK THE BOX NEXT TO ADDRESS IN THE "Questions for Primary Registrant" 
 * SIDEBAR METABOX ONLY
 *
 *
 * @return void
 */
 
 
function bc_ee_determine_whether_to_apply_surcharge() {
  if ( isset( $_REQUEST[ 'ee_reg_qstn' ] ) ) {
    foreach ( $_REQUEST[ 'ee_reg_qstn' ] as $registrations ) {
      if ( ! empty( $registrations ) ) {
        foreach ( $registrations as $QST_ID => $response ) {
          if ( $QST_ID === 'state' ) {
            switch ( $response ) {
              case '60' :
              case '70' :
              case '71' :
              case '72' :
                // apply 5% surcharge Alberta, NWT, Nunavet, Yukon
                add_filter( 'FHEE__bc_ee_apply_transaction_surcharge__apply_surcharge', '__return_true' );
                add_filter( 'FHEE__bc_ee_apply_transaction_surcharge__surcharge_details', 'ee_al_north_surcharge_details' );
                break;
              case '61' :
              case '62' :
                // apply 12% surcharge BC, Manitoba
                add_filter( 'FHEE__bc_ee_apply_transaction_surcharge__apply_surcharge', '__return_true' );
                add_filter( 'FHEE__bc_ee_apply_transaction_surcharge__surcharge_details', 'ee_bc_mb_surcharge_details' );
                break;
              case '63' :
              case '64' :
              case '65' :
              case '67' :
                // apply 15% surcharge NB, NL, NS, PE
                add_filter( 'FHEE__bc_ee_apply_transaction_surcharge__apply_surcharge', '__return_true' );
                add_filter( 'FHEE__bc_ee_apply_transaction_surcharge__surcharge_details', 'ee_nb_nl_ns_pe_surcharge_details' );
                break;
              case '66' :
                // apply 13% surcharge Ontario
                add_filter( 'FHEE__bc_ee_apply_transaction_surcharge__apply_surcharge', '__return_true' );
                add_filter( 'FHEE__bc_ee_apply_transaction_surcharge__surcharge_details', 'ee_on_surcharge_details' );
                break;
              case '68' :
                // apply 14.975% surcharge Quebec
                add_filter( 'FHEE__bc_ee_apply_transaction_surcharge__apply_surcharge', '__return_true' );
                add_filter( 'FHEE__bc_ee_apply_transaction_surcharge__surcharge_details', 'ee_qc_surcharge_details' );
                break;
              case '69' :
                // apply 11% surcharge SK
                add_filter( 'FHEE__bc_ee_apply_transaction_surcharge__apply_surcharge', '__return_true' );
                add_filter( 'FHEE__bc_ee_apply_transaction_surcharge__surcharge_details', 'ee_sk_surcharge_details' );
                break;
              default :
              add_filter( 'FHEE__bc_ee_apply_transaction_surcharge__apply_surcharge', '__return_false' );
            }
          }
        }
      }
    }
  }
}
add_action( 'AHEE__EE_System__core_loaded_and_ready', 'bc_ee_determine_whether_to_apply_surcharge', 1 );

function ee_al_north_surcharge_details() {
  return array(
    'name'          => 'gst',
    'code'          => 'gst',
    'description'   => 'gst 5%',
    'percent'       => 5,
    'taxable'       => false,
  );
}

function ee_bc_mb_surcharge_details() {
  return array(
    'name'          => 'gst + pst',
    'code'          => 'gst-pst',
    'description'   => 'gst 5% + pst 7%',
    'percent'       => 12,
    'taxable'       => false,
  );
}

function ee_nb_nl_ns_pe_surcharge_details() {
  return array(
    'name'          => 'hst',
    'code'          => 'hst',
    'description'   => 'hst 15%',
    'percent'       => 15,
    'taxable'       => false,
  );
}

function ee_on_surcharge_details() {
  return array(
    'name'          => 'ontario hst',
    'code'          => 'ontario-hst',
    'description'   => 'ontario hst 13%',
    'percent'       => 13,
    'taxable'       => false,
  );
}

function ee_qc_surcharge_details() {
  return array(
    'name'          => 'quebec gst + qst',
    'code'          => 'quebec-gst-qst',
    'description'   => 'quebec gst + qst 14.975%',
    'percent'       => 14.975,
    'taxable'       => false,
  );
}

function ee_sk_surcharge_details() {
  return array(
    'name'          => 'sk gst + pst',
    'code'          => 'sk-gst-pst',
    'description'   => 'gst 5% + pst 6%',
    'percent'       => 11,
    'taxable'       => false,
  );
}

/**
 * DO NOT EDIT ANYTHING EXCEPT DEFAULT SURCHARGE DETAILS
 *
 * bc_ee_apply_transaction_surcharge
 *
 * @param \EE_Checkout $checkout
 * @return \EE_Checkout
 */
function bc_ee_apply_transaction_surcharge( EE_Checkout $checkout ) {
  // DEFAULT SURCHARGE DETAILS - EDIT THIS
  $surcharge_details = apply_filters(
    'FHEE__bc_ee_apply_transaction_surcharge__surcharge_details',
    array(
      //  name for surcharge that will be displayed
      'name'        => 'gst',
      // unique code used to identify surcharge in the db
      'code'        => 'province-gst',
      // description for line item
      'description' => 'province gst',
      // percentage amount
      'percent'     => 5,
      // whether or not tax is applied on top of the surcharge
      'taxable'     => false,
    )
  );
  // STOP EDITING
  // apply the surcharge ?
  if ( ! apply_filters( 'FHEE__bc_ee_apply_transaction_surcharge__apply_surcharge', false ) ) {
    return $checkout;
  }
  // verify checkout
  if ( ! $checkout instanceof EE_Checkout ) {
    return $checkout;
  }
  // verify cart
  $cart = $checkout->cart;
  if ( ! $cart instanceof EE_Cart ) {
    return $checkout;
  }
  // verify grand total line item
  $grand_total = $cart->get_grand_total();
  if ( ! $grand_total instanceof EE_Line_Item ) {
    return $checkout;
  }
  // has surcharge already been applied ?
  $existing_surcharge = $grand_total->get_child_line_item( $surcharge_details[ 'code' ] );
  if ( $existing_surcharge instanceof EE_Line_Item ) {
    return $checkout;
  }
  EE_Registry::instance()->load_helper( 'Line_Item' );
  $pre_tax_subtotal = EEH_Line_Item::get_pre_tax_subtotal( $grand_total );
  $pre_tax_subtotal->add_child_line_item(
    EE_Line_Item::new_instance( array(
      'LIN_name'       => $surcharge_details[ 'name' ],
      'LIN_desc'       => $surcharge_details[ 'description' ],
      'LIN_unit_price' => 0,
      'LIN_percent'    => $surcharge_details[ 'percent' ],
      'LIN_quantity'   => NULL,
      'LIN_is_taxable' => $surcharge_details[ 'taxable' ],
      'LIN_order'      => 0,
      'LIN_total'      => (float) ( $surcharge_details[ 'percent' ] * ( $pre_tax_subtotal->total() / 100 ) ),
      'LIN_type'       => EEM_Line_Item::type_line_item,
      'LIN_code'       => $surcharge_details[ 'code' ],
    ) )
  );
  $grand_total->recalculate_total_including_taxes();
  return $checkout;
}
add_filter( 'FHEE__EED_Single_Page_Checkout___initialize_checkout__checkout', 'bc_ee_apply_transaction_surcharge' );

not calculated.
plus, the discounts are applied after the taxes calculated using the script - so it doesn't make much sense. See this example

I removed the HTML section from the UI in the INVOICE and RECEIPT.
I just figure it out.

@joshfeck I found a bug possibly related to this code. When a student registers to an event and then updates their province, the code adds the new tax code to the invoice and does not remove the other one. It results in 2 tax codes on the invoice. Any idea how to fix this?
Many thanks in advance.