Patch Spree to allow partial refund entry

return_item_selection.js

$(document).ready(function () {
  var formFields = $("[data-hook='admin_customer_return_form_fields'], [data-hook='admin_return_authorization_form_fields']")

  function checkAddItemBox () {
    $(this).closest('tr').find('input.add-item').attr('checked', 'checked')
    updateSuggestedAmount()
  }

  function updateSuggestedAmount (resetRefundAmount) {
    var totalPretaxRefund = 0
    var checkedItems = formFields.find('input.add-item:checked')
    $.each(checkedItems, function (i, checkbox) {
      var returnItemRow = $(checkbox).parents('tr')
      var returnQuantity = parseInt(returnItemRow.find('.refund-quantity-input').val(), 10)
      var purchasedQuantity = parseInt(returnItemRow.find('.purchased-quantity').text(), 10)
      var amount = (returnQuantity / purchasedQuantity) * parseFloat(returnItemRow.find('.charged-amount').data('chargedAmount'))
      var inputAmount = Number(returnItemRow.find('.refund-amount-input').val())
      if (!resetRefundAmount && !isNaN(inputAmount) && inputAmount < amount) {
        amount = inputAmount
      }
      returnItemRow.find('.refund-amount-input').val(amount.toFixed(2))
      totalPretaxRefund += amount
    })

    var displayTotal = isNaN(totalPretaxRefund) ? '' : totalPretaxRefund.toFixed(2)
    formFields.find('span#total_pre_tax_refund').html(displayTotal)
  }

  if (formFields.length > 0) {
    updateSuggestedAmount()

    formFields.find('input#select-all').on('change', function (ev) {
      var checkBoxes = $(ev.currentTarget).parents('table:first').find('input.add-item')
      checkBoxes.prop('checked', this.checked)
      updateSuggestedAmount()
    })

    formFields.find('input.add-item').on('change', updateSuggestedAmount.bind(null, true))
    formFields.find('.refund-amount-input').on('change', updateSuggestedAmount.bind(null, false))
    formFields.find('.refund-quantity-input').on('keyup mouseup', updateSuggestedAmount.bind(null, true))

    formFields.find('input, select').not('.add-item').on('change', checkAddItemBox)
  }
})