Support using an arbitrary Codable value with AppStorage, with syntactic sugar to avoid referring directly to wrapped value.

AppStorageCodable.swift

//
//  AppStorageCodable.swift
//
//
//  Created by Jesse Hemingway on 9/4/24.
//

import Foundation
import SwiftUI

/**
 Support arbitrary Codable values with AppStorage,
 including syntactic sugar to avoid referring directly to wrapped value.

 Example usage:
 ```
 struct ExampleStruct: Codable {
     var id: Int = 0
     var name: String = "John"
 }

 class ExampleVendor: ObservableObject {
     @AppStorage("example")
     @AppStorageCodable
     var example: ExampleStruct = .init()
 }

 func testAppStorageCodable() {
     let exampleVendor = ExampleVendor()
     print("Example id: \(exampleVendor.example.id), name: \(exampleVendor.example.name)")
 }
 ```
 */
@propertyWrapper
@dynamicMemberLookup
public struct AppStorageCodable<Value: Codable> {
    public var wrappedValue: Value

    public init(wrappedValue: Value) {
        self.wrappedValue = wrappedValue
    }

    subscript<T>(dynamicMember keyPath: WritableKeyPath<Value, T>) -> T {
        get { wrappedValue[keyPath: keyPath] }
        set { wrappedValue[keyPath: keyPath] = newValue }
    }
}

extension AppStorageCodable: RawRepresentable {
    public typealias RawValue = String

    public var rawValue: RawValue {
        guard let data = try? JSONEncoder().encode(wrappedValue),
              let string = String(data: data, encoding: .utf8) else { return "" }
        return string
    }

    public init?(rawValue: RawValue) {
        guard let data = rawValue.data(using: .utf8),
              let decoded = try? JSONDecoder().decode(Value.self, from: data) else { return nil }
        wrappedValue = decoded
    }
}

extension AppStorageCodable: Equatable where Value: Equatable {}