Filter data using HTTP query params (like OData)

{
    "Customers": [
        {
            "Country": "France",
            "Address": "184, chausse de Tournai",
            "City": "Lille",
            "Phone": "20.16.10.16",
            "CompanyName": "Folies gourmandes",
            "CustomerID": "FOLIG",
            "Fax": "20.16.10.17"
        },
        {
            "Country": "France",
            "Address": "59 rue de l'Abbaye",
            "City": "Reims",
            "Phone": "26.47.15.10",
            "CompanyName": "Vins et alcools Chevalier",
            "CustomerID": "VINET",
            "Fax": "26.47.15.11"
        },
        {
            "Country": "France",
            "Address": "67, avenue de l'Europe",
            "City": "Versailles",
            "Phone": "30.59.84.10",
            "CompanyName": "La corne d'abondance",
            "CustomerID": "LACOR",
            "Fax": "30.59.85.11"
        },
        {
            "Country": "France",
            "Address": "54, rue Royale",
            "City": "Nantes",
            "Phone": "40.32.21.21",
            "CompanyName": "France restauration",
            "CustomerID": "FRANR",
            "Fax": "40.32.21.20"
        },
        {
            "Country": "France",
            "Address": "67, rue des Cinquante Otages",
            "City": "Nantes",
            "Phone": "40.67.88.88",
            "CompanyName": "Du monde entier",
            "CustomerID": "DUMON",
            "Fax": "40.67.89.89"
        },
        {
            "Country": "France",
            "Address": "1 rue Alsace-Lorraine",
            "City": "Toulouse",
            "Phone": "61.77.61.10",
            "CompanyName": "La maison d'Asie",
            "CustomerID": "LAMAI",
            "Fax": "61.77.61.11"
        },
        {
            "Country": "France",
            "Address": "2, rue du Commerce",
            "City": "Lyon",
            "Phone": "78.32.54.86",
            "CompanyName": "Victuailles en stock",
            "CustomerID": "VICTE",
            "Fax": "78.32.54.87"
        },
        {
            "Country": "France",
            "Address": "24, place Klber",
            "City": "Strasbourg",
            "Phone": "88.60.15.31",
            "CompanyName": "Blondesddsl pre et fils",
            "CustomerID": "BLONP",
            "Fax": "88.60.15.32"
        },
        {
            "Country": "France",
            "Address": "12, rue des Bouchers",
            "City": "Marseille",
            "Phone": "91.24.45.40",
            "CompanyName": "Bon app'",
            "CustomerID": "BONAP",
            "Fax": "91.24.45.41"
        }
    ]
}

%dw 2.0
import * from dw::core::Arrays
output application/java
var ArrParams = attributes.queryString splitBy "&"

//This is how ArrayParams looks like.
[$format=json,$select=CustomerID,CompanyName,Address,City,
Country,Phone,Fax, $filter=Country eq 'France' , $orderby=Phone, $top=10, $skip=2]

var SQLFilter = (filter) -> 
      
     filter replace "eq null" with "is null" 
     replace "ne null" with "is not null" 
     replace " eq " with " like " 
     replace " ne " with " != " 
     replace " gt " with " > " 
     replace " lt " with " < " 
     replace " ge " with " >= " 
     replace " le " with " <= " 
     replace " and " with " AND " 
     replace " or " with " OR " 
     
var toSQLOrderBy = (orderby ) -> if(orderby != "") (" ORDER BY " ++ (orderby replace "=" with " ")) else ""

var toSQLSkipAndTop = (top, skip) -> if(top != "" and skip != "") " LIMIT $top OFFSET $skip" else if (top == "" and skip != "") " LIMIT 2147483647 OFFSET $skip" else if (top != "" and skip == "") " LIMIT $top"  else ""

var toSQLWhere = (filter) -> if(filter !=  "") " WHERE " ++ SQLFilter(filter) else ""
---

using(SelectIndex = ArrParams indexWhere (item) -> item contains "select") 
using(ArrSelect =  ArrParams[SelectIndex] splitBy "=")
using(select = ArrSelect[1])

using(FilterIndex = ArrParams indexWhere (item) -> item contains "filter") 
using(ArrFilter =  ArrParams[FilterIndex] splitBy "=")
using(filter = ArrFilter[1])

using(OrderByIndex = ArrParams indexWhere (item) -> item contains "orderby") 
using(ArrOrderBy =  ArrParams[OrderByIndex] splitBy "=")
using(orderby = ArrOrderBy[1])

using(TopIndex = ArrParams indexWhere (item) -> item contains "top") 
using(ArrTop =  ArrParams[TopIndex] splitBy "=")
using(top = ArrTop[1])

using(SkipIndex = ArrParams indexWhere (item) -> item contains "skip") 
using(ArrSkip =  ArrParams[SkipIndex] splitBy "=")
using(skip = ArrSkip[1])

"SELECT " ++ select ++ " FROM customers" ++ (toSQLWhere(filter)) ++ (toSQLOrderBy(orderby)) ++ (toSQLSkipAndTop(top,skip))