Swift: Swift Optional Chaining and Type Casting Tutorial

if let data = json["data"] as? [String: Any] {
    if let city = data["city"] as? [String: Any] {
        if let weather = city["weather"] as? [String: Any] {
            if let temperature = weather["temperature"] as? [String: Any] {
                if let current = temperature["current"] as? Double {
                    print("Temperature: \(current)")
                }
            }
        }
    }
}

// Simplified version using optional chaining + optional binding
if let data = json["data"] as? [String: Any],
   let city = data["city"] as? [String: Any],
   let weather = city["weather"] as? [String: Any],
   let temperature = weather["temperature"] as? [String: Any],
   let current = temperature["current"] as? Double {
    print("Temperature: \(current)")
}

// ============================================
// Basic usage of optional chaining
// ============================================
class Address {
    let city: String
    let street: String?
    init(city: String, street: String?) {
        self.city = city
        self.street = street
    }
}
class Person {
    let name: String
    var address: Address?
    init(name: String, address: Address?) {
        self.name = name
        self.address = address
    }
    func greeting() -> String { "Hello, I'm \(name)" }
}
let alice = Person(name: "Alice", address: Address(city: "Tokyo", street: nil))
let bob = Person(name: "Bob", address: nil)
print(alice.address?.city ?? "Unknown city")
print(bob.address?.city ?? "Unknown city")
print(bob.address?.street ?? "No street info")
print(bob.greeting())

// ============================================
// Simulating multi-level nested optional access like JSON
// ============================================
struct Team {
    let name: String
    let leader: Person?
}
struct Company {
    let name: String
    let team: Team?
}
let company = Company(
    name: "TechCorp",
    team: Team(
        name: "iOS Team",
        leader: Person(name: "Charlie", address: nil)
    )
)
let leaderCity = company.team?.leader?.address?.city ?? "None"
print("Leader city: \(leaderCity)")
let noTeamCompany = Company(name: "Startup", team: nil)
let result = noTeamCompany.team?.leader?.address?.city ?? "None"
print("No team company: \(result)")

// ============================================
// Type casting: upcasting and downcasting in a media library
// ============================================
class MediaItem {
    let title: String
    init(title: String) { self.title = title }
}
class Movie: MediaItem {
    let director: String
    init(title: String, director: String) {
        self.director = director
        super.init(title: title)
    }
}
class Song: MediaItem {
    let artist: String
    init(title: String, artist: String) {
        self.artist = artist
        super.init(title: title)
    }
}
let library: [MediaItem] = [
    Movie(title: "Inception", director: "Nolan"),
    Song(title: "Bohemian Rhapsody", artist: "Queen"),
    Movie(title: "Interstellar", director: "Nolan"),
]
var movieCount = 0
var songCount = 0
for item in library {
    if item is Movie { movieCount += 1 }
    else if item is Song { songCount += 1 }
}
print("Movies: \(movieCount), Songs: \(songCount)")
for item in library {
    if let movie = item as? Movie {
        print("Movie: \(movie.title), Dir: \(movie.director)")
    } else if let song = item as? Song {
        print("Song: \(song.title), Artist: \(song.artist)")
    }
}

// ============================================
// Any array storing mixed types + safe retrieval
// ============================================
var mixedArray: [Any] = []
mixedArray.append(42)
mixedArray.append("Hello")
mixedArray.append(3.14)
mixedArray.append(true)
mixedArray.append([1, 2, 3])
for (index, item) in mixedArray.enumerated() {
    switch item {
    case let num as Int:
        print("[\(index)] Int: \(num)")
    case let str as String:
        print("[\(index)] String: \(str)")
    case let d as Double:
        print("[\(index)] Double: \(d)")
    case let b as Bool:
        print("[\(index)] Bool: \(b)")
    case let arr as [Int]:
        print("[\(index)] [Int]: \(arr)")
    default:
        print("[\(index)] Unknown")
    }
}

// ============================================
// Using some to hide the concrete return type
// ============================================
protocol Shape {
    func area() -> Double
}
struct Circle: Shape {
    let radius: Double
    func area() -> Double { .pi * radius * radius }
}
struct Rectangle: Shape {
    let width: Double
    let height: Double
    func area() -> Double { width * height }
}
func makeShape(isCircle: Bool) -> some Shape {
    if isCircle {
        return Circle(radius: 5)
    } else {
        return Rectangle(width: 3, height: 4)
    }
}
let shape1 = makeShape(isCircle: true)
let shape2 = makeShape(isCircle: false)
print("Circle area: \(shape1.area())")
print("Rectangle area: \(shape2.area())")

// ============================================
// Full example: JSON configuration parser
// Uses optional chaining + type casting + Any
// ============================================
import Foundation
// 1. Simulated JSON data
let json: [String: Any] = [
    "app": [
        "name": "WeatherApp",
        "version": 2.1,
        "settings": [
            "theme": "dark",
            "units": "metric",
            "notifications": true
        ],
        "authors": ["Alice", "Bob"]
    ],
    "debug": nil
]
// 2. Safe parsing function
func parseConfig(_ json: [String: Any]) {
    // Optional chaining + type casting
    guard let app = json["app"] as? [String: Any] else {
        print("Invalid configuration")
        return
    }
    let name = app["name"] as? String ?? "Unknown"
    let version = app["version"] as? Double ?? 0.0
    let theme = (app["settings"] as? [String: Any])?["theme"] as? String ?? "light"
    let notifications = (app["settings"] as? [String: Any])?["notifications"] as? Bool ?? false
    let authors = app["authors"] as? [String] ?? []
    print("App: \(name) v\(version)")
    print("Theme: \(theme)")
    print("Notifications: \(notifications)")
    print("Authors: \(authors.joined(separator: ", "))")
    // is check for nil
    if json["debug"] is NSNull {
        print("Debug: disabled")
    }
}
parseConfig(json)