The facade pattern allows you to provide the operations that might be desirable by a user. The pattern encapsulates the interface of each object that is considered as a low-level interface. To construct the unified interface, we might need to implement some methods that will compose the low-level interfaces:

The facade pattern is designed to hide the complexity of a system. Its interface can be entirely new. It must not conform to the existing interface. We can provide several facades to the same system depending on the end user that we have and the functionality that we want to provide to the facade:

The participants of this pattern are as follows:

Clients communicate with the system through the facade façade. Then, the façade itself invokes classes and components of the system. The facade doesn't only send requests to classes and components of the subsystem. It must also adapt its own interface to the objects and components interfaces, using a specific code to allow communication of objects.

The following sequence diagram describes this case:

Clients using the facade should not directly access the objects of the system.

We want to provide a simple interface to provide our clients with an easy way to find hotels near an input address and corresponding to some criteria (such as the number of stars.)

In our company, we have a subsystem that provides a catalog of hotels that includes their locations and number of stars for each of them.

We already have a FindPoi Webservice that can search for a hotel near a location point (latitude and longitude), which uses some criteria: the maximum distance to search and the numbers of stars we want.

As you can see, the service needs a location point, which means that we pass an object with a latitude and longitude.

As the consumer of our facade will only tell us its real address, we need services that will geocode the address to a GPS point with a latitude and longitude.

The sequence diagram shows you what we will do to provide our simplified interface:

Open the Xcode project called FacadePattern and the main.swift file. This file represents a client that will consume our facade.

Our facade is, in fact, a service that allows a client to search for a hotel near the location that is sent as an input that has two criteria: distanceMax and number of stars for the hotel.

This is how the service will be called:

var results = svcFacadeFindHotel.findHotel(myAdress, distanceMax: 2.0, stars: 4)

The complete code of the client is as follows:

import Foundation


//I am a consumer of the service
// my addess is
// 1 infinite Loop
// Cupertino, CA 95014

let svcFacadeFindHotel = ServiceFindHotelNearBy()

let myAdress = " 1 Infinite Loop Cupertino, CA 95014 USA"
var results = svcFacadeFindHotel.findHotel(myAdress, distanceMax: 2.0, stars: 4)

print("*** RESULTS ")
print("Their is (results?.count) results :")

if let results = results {
  for var h in results{
    print("Hotel latitude:(h.location.latitude) longitude:(h.location.longitude), stars: (h.stars)")
  }
}

We open a connection for our ServiceFindHotelNearBy service. We tell what our current address is and then display the results if any. Here, we have 125 results (from 1,000 generated in the HotelCatalog object):

import Foundation

class ServiceFindHotelNearBy: ServiceFindHotelNearByProtocol {
  
  //return a list of hotel that corresponds to our criteria
  func findHotel(from: String, distanceMax: Double, stars: Int) -> [Hotel]? {
      let svcGeocoding = Geocoding()
      let svcFindPoi = FindPoi()
      let systemhotelCatalog = HotelCatalog()
    
      //Geocode our adress to GPS Points
      let fromLocation = svcGeocoding.getGeocoordinates(from)
    
      //retrieve all hotels in the catalog
      let allHotels = systemhotelCatalog.getCatalog()
    
      //find POI that corresponds to our criteria
      let results = svcFindPoi.findPoiNearBy(fromLocation, distanceMax: distanceMax, stars: stars, catalog: allHotels)
    return results
  }
}