/**
 * Read FAQs section on the left for more information on how to use the editor
**/
// DO NOT CHANGE FUNCTION NAMES

// Simple utility to check if an object is empty
function isObjEmpty(obj){
  return !Object.keys(obj).length
}

function filter(collection, callback) {
  // DO NOT REMOVE
  'use strict';

  // validation checks
  if(!collection){
    throw new TypeError("An argument for collection was not provided")
  }
  if(!callback){
    throw new TypeError("An argument for callback was not provided")
  }
  if(typeof collection !== "object"){
    throw new TypeError("Collection must be of type object")
  }
  if(typeof callback !== "function"){
    throw new TypeError("Callback must be of type function")
  }
  
  function filterRecurse(obj){
    const res = {};
    Object.entries(obj).forEach(([k,v])=>{
      if(typeof v === "object"){
        // If filtered object is empty, then the key is removed from object
        const filteredValue = filterRecurse(v);
        if(!isObjEmpty(filteredValue)){
          res[k] = filteredValue
        }
      }
      else {
        if(callback(v)){
          res[k] = v;
        }
      }
    })
    
    return res
  }
  
  return filterRecurse(collection)
}