KeychainStorage.swift

//
// A simplified implementation of https://gist.github.com/sturdysturge/e5163a9e95826adbeff9824d5aa1d111
// Which has an associated article here: https://betterprogramming.pub/build-a-secure-swiftui-property-wrapper-for-the-keychain-e0f8e39d554b
// Requires the Keychain Access package: https://github.com/kishikawakatsumi/KeychainAccess
//

import SwiftUI
import KeychainAccess

@propertyWrapper
struct KeychainStorage<Value: Codable>: DynamicProperty {
    private let keychain = Keychain()
    private let valueKey: String
    @State private var value: Value?
    
    init(wrappedValue defaultValue: Value? = nil, _ key: String) {
        valueKey = key

        do {
            if let data = try keychain.getData(key) {
                _value = State(initialValue: try JSONDecoder().decode(Value.self, from: data))
            } else {
                _value = State(initialValue: defaultValue)
            }
        } catch {
            fatalError("\(error)")
        }
    }

    var wrappedValue: Value? {
        get {
            return value
        }
        nonmutating set {
            value = newValue
            
            do {
                if let storeValue = newValue {
                    try keychain.set(JSONEncoder().encode(storeValue), key: valueKey)
                } else {
                    try Keychain().remove(valueKey)
                }
            } catch {
                fatalError("\(error)")
            }
        }
    }
    
    var projectedValue: Binding<Value?> {
      return Binding(get: { wrappedValue }, set: { wrappedValue = $0 })
    }
}