Add a deposit product to the cart based on cart total

booking-deposit.liquid

<script>
  {% assign deposit = all_products['deposit'] %}
  BookingDeposit = function() {
    var _this = this;
    
    _this.cart = {{ cart | json }};
    _this.depositProduct = {{ deposit | json }};
    _this.depositAmount = 0;
    _this.depositLine = -1;
    _this.cartDepositVariantId = -1;
    _this.lineQuantities = [];
    
    this.init = function() {
      _this.initData();
      _this.calcDepositAmount();
      
      if (_this.depositAmount == 0) {
        if (_this.depositLine > -1) {
          // remove existing deposit product
          _this.removeDeposit().done(function() {
            location.href = '/cart';
          });
        }
      } else {
        var depositVariant = _this.findDepositVariant();
        
        if (_this.depositLine > -1) { // deposit variant is already in cart
          if (_this.cartDepositVariantId != depositVariant.id) {
            // remove existing deposit product then add new one
            _this.removeDeposit().done(function() {
              _this.addDepositThenReturn(depositVariant);
            });
          }
        } else {
          _this.addDepositThenReturn(depositVariant);
        }
      }
    };
    
    this.calcDepositAmount = function() {
      for (var i = 0; i < _this.cart.items.length; i++) {
        var item = _this.cart.items[i];
        if (item.handle != 'deposit') {
        	_this.depositAmount += item.line_price;
        }
      }
    }; 
    
    this.findDepositVariant = function() {
      var amount = _this.depositAmount * 100;
      
      var index = 0,
          variant = _this.depositProduct.variants[0];
      
      while ((variant.price - amount < 0) && index < _this.depositProduct.variants.length) {
        index++
        variant = _this.depositProduct.variants[index];
      }
      
      return variant;
    };
    
    this.removeDeposit = function() {
      return $.ajax({
        type: 'POST',
        url: '/cart/change.js', 
        data: {line: _this.depositLine, quantity: 0}, 
        dataType: 'json'
      });
    }
      
    this.addDepositThenReturn = function(variant) {
      $.ajax({
        type: 'POST',
        url: '/cart/add.js', 
        data: {id:variant.id, quantity:1}, 
        dataType: 'json'
      }).done(function(cart) {
        location.href = '/cart';
      });
    }
    
    this.initData = function() {
      {% for item in cart.items %}
        {% if item.product.handle == 'deposit' %}
        _this.depositLine = {{ forloop.index }};
        _this.cartDepositVariantId = {{ item.variant_id }};
        {% endif %}
        
        _this.lineQuantities.push({{ item.quantity }});
      {% endfor %}
    }
    
    this.init();
  }
        
  document.addEventListener("DOMContentLoaded", function(event) { 
    new BookingDeposit();
  });
</script>