Wrong cart and line items cost - total and subtotal

[hagsonz]

Discussed in #430

^{Originally posted by hagsonz January 23, 2024}
Using product discount. for the cart, I am getting same amount for the total and subtotal fields. in addition, tax and duty values are null.
also, if i have a coupon applied, the Input is still the exact same.

for the line items, the item which is discounted by the function is with full price which is logical as the function haven't applied the discount yet. but the one which is discounted by a coupon, is still with full price.

how can i calculate the correct amount of the cart and line items?

Input (STDIN)

{
  "presentmentCurrencyRate": "1.0",
  "cart": {
    "cost": {
      "subtotalAmount": {
        "amount": "1500.0",
        "currencyCode": "ILS"
      },
      "totalAmount": {
        "amount": "1500.0",
        "currencyCode": "ILS"
      },
      "totalTaxAmount": null,
      "totalDutyAmount": null
    },
    "lines": [
      {
        "id": "gid://shopify/CartLine/0",
        "quantity": 1,
        "cost": {
          "totalAmount": {
            "amount": "600.0",
            "currencyCode": "ILS"
          },
          "subtotalAmount": {
            "amount": "600.0",
            "currencyCode": "ILS"
          }
        },
        "merchandise": {
          "__typename": "ProductVariant",
          "id": "gid://shopify/ProductVariant/44579562455318",
          "product": {
            "id": "gid://shopify/Product/8218915930390"
          }
        },
        "attribute": null
      },
      {
        "id": "gid://shopify/CartLine/1",
        "quantity": 1,
        "cost": {
          "totalAmount": {
            "amount": "900.0",
            "currencyCode": "ILS"
          },
          "subtotalAmount": {
            "amount": "900.0",
            "currencyCode": "ILS"
          }
        },
        "merchandise": {
          "__typename": "ProductVariant",
          "id": "gid://shopify/ProductVariant/44579562881302",
          "product": {
            "id": "gid://shopify/Product/8218916258070"
          }
        },
        "attribute": {
          "key": "_order_bump_offer_id",
          "value": "7MWcCsmycOQbf4kZZStQx"
        }
      }
    ]
  },
  "discountNode": {
    "metafield": {
      "value": "{\"offers\":[{\"expanded\":true,\"enabled\":true,\"offerName\":\"Edit this offer name\",\"layout\":\"vertical\",\"cardLayout\":\"vertical\",\"minCartQuantity\":\"1\",\"maxCartQuantity\":\"601\",\"minCartValue\":0,\"maxCartValue\":\"1000\",\"products\":[\"gid://shopify/Product/8218916258070\"],\"onlyProducts\":[],\"discountAmount\":\"10\",\"discountType\":\"percentage\",\"cartMessage\":\"Edit me\",\"offerType\":\"product\",\"id\":\"7MWcCsmycOQbf4kZZStQx\"},{\"expanded\":true,\"enabled\":false,\"offerName\":\"Edit this offer name\",\"layout\":\"vertical\",\"cardLayout\":\"horizontal\",\"minCartQuantity\":0,\"maxCartQuantity\":99999,\"minCartValue\":0,\"maxCartValue\":100000,\"products\":[\"gid://shopify/Product/8218916126998\",\"gid://shopify/Product/8218916192534\",\"gid://shopify/Product/8218915963158\"],\"onlyProducts\":[],\"discountAmount\":\"5\",\"discountType\":\"percentage\",\"cartMessage\":\"Edit me\",\"offerType\":\"product\",\"id\":\"1wpsj73LB5LO_Ir9dSNzE\"}]}"
    }
  }
}
</div>