🌦️ Weather App

A very simple weather app demonstrating clean architecture, code organisation, loose coupling, unit testing and some of the best practices used in modern iOS programming using Swift, SwiftUI and SwiftData

📱 App Goal

• Search by city name or postcode Implement a search to allow the user to enter a city name or postcode. The result of the search is to display the current weather information for the searched location.
• Recent Searches Implement a screen that lists recently searched locations. You can tap on a recent search location and see the current weather location.
• Delete recent searches Provide the ability to delete one or more recently searched locations.

💡 Weather API

OpenWeatherMap API: http://openweathermap.org/api

For simple query mechanism, I have used weather search by city name end the endpoint available here: https://api.openweathermap.org/data/2.5/weather?q={city name},{country code}&appid={API key}

✋🏼NOTE: This endpoint returns response of a single city's weather matched by the query param (q). If we don't pass any country code to the param, then it performs a global search. This ends up showing too many results while typing London for example, it searches for Lon and London successfully. Similarly, searches for Melbourne, results in Mel, Melbourn and so on which are valid global cities.

To avoid this fuzzy searching scenario which results in random city responses across the world, I have restricted search to Australia 🇦🇺 only by appending ,au in the query param, which shows predictable Australia only city names and the same endpoint support zip codes specific to Australia. Please see the technical note left inside WeatherUseCase.swift file regarding this.

This can be improved in the app if we change the UX.

• Step-1 api call: Search for a city globally across the world. We can use the https://openweathermap.org/api/geocoding-api to list the list of cities first on the UI. Each city response would have (latitude, longitude) information
• Step-2 api call: Tap on a city name from the list. Then fetch the weather for the tapped city's (lat, lon) and that would uniquely return the city's weather

👨🏽‍💻 Solution Approach

To break down the app layers and architecture as per best practice, I tried to resemble Clean-Architecture pattern which is very close to well known VIPER pattern. Actually, I adopted clean MVVM with integration to UseCase layer.

A good reference article here: clean-architecture-swiftui

Clean Architecture with MVVM

The Codebase is broken down into 4 logical layers (via Swift Packages)

• DataLayer:
  • Network fetching of raw data and JSON decoding via URL, error code mapping etc.
• DomainLayer:
  • Business logic of fetching the weather data, query processing and management, relevant transformation, potential chaining of data sources to connect multiple remote services together
  • UseCases live here (aka. Interactor in some codebases)
• PresentationLayer:
  • Domain data to SwiftUI binding logic
  • All UI specific code (SwiftUI)
• SharedUtils:
  • Common light weight utility helpers and extensions
• A mix of MVVM and VIPER design pattern is used to achieve loose coupling and unit testing via Dependency Injection patterns, spy & mocks
• Currently using Apple's Combine based Reactive Binding
• ✋🏽TODO: Migrate from Combine driven Publishers into Swift's Modern Concurrency Async Await paradigm (probably UseCase can adopt this)
• Unit Testing is covered in each core layer's functionality & logic, except SwiftUI view's local logic
• Some TODO notes left in the code deliberately for potential improvements and SwiftLint warns us about those to trace them

The package dependencies (import logic from one to another) are shown below:

  graph TD;
      A[Presentation Layer] --> B[Domain Layer];
      B-->C[Data Layer];
      A-.->C;
      A-->D[Shared Utils];
      B-->D;
      C-->D;

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Please refer from the project navigator in Xcode to see the layering.

Project	Targets	Tests

The overall summary in terms of UML

sequenceDiagram
    participant WeatherSummaryViewUI
    participant WeatherSearchUI
    participant ViewModel
    participant UseCase
    participant NetworkService
    participant URLSession

    WeatherSummaryViewUI->>ViewModel: Reactively bound to viewModel's response
    
    ViewModel->>UseCase: Get the desired CityWeather domain model for a city (reactively)
  
    UseCase->>NetworkService: Get the WeatherInfo data model for a city query
    NetworkService->>URLSession: Get the full raw JSON data as HTTP request
    URLSession->>NetworkService: HTTP response body
    loop Mapping
        NetworkService->>NetworkService: Apply custom JSON decoding into data models and error mapping
    end

    NetworkService->>UseCase: The WeatherInfo response
    UseCase->>ViewModel: Weather object returned (reactively)

    ViewModel->>WeatherSearchUI: Pass back list of WeatherPresentationItem
    loop Transformation
        ViewModel->>ViewModel: Transform & cook raw domain level data into UI friendly WeatherPresentationItem
    end

   WeatherSearchUI->>WeatherSummaryViewUI: SwiftUI binding of WeatherPresentationItem

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💻 Installation & Testing

• Xcode 15 or later (required)
• Clean the /DerivedData folder if any
• Let the Swift package Manager load and sync
• Build the project and let the Swift Package Manager pulls the remote SwiftLint plugin
• iOS 17 minimum support for the app
  • To be able to use the new SwiftData framework

🛠️ Use of Apple Frameworks

• SwiftUI
• SwiftData
• Combine
• No 3rd party libraries used

Screenshots

Scenario 1	Scenario 2	Scenario 2

Screen 1	Screen 2	Screen 3

⛈️ Error Handling UX

• Custom error UI is shown when loading error occurs
• NetworkFailure (i.e. internet disconnected) shows its custom message and animated icon
• All other server errors have a generic message and animated icon
• If 404 NotFound error returned that means city not found, which is shown slightly differently to fix the city name or post code

Generic Sever Error	Internet Lost Error
Modify the API KEY in ApiConstants.swift to something incorrect	Disconnect WiFi & connect back and test