//
//  DocsView.swift
//  Splits
//
//  Created by Isaac Greene on 6/3/22.
//

import SwiftUI
import LocalAuthentication
import CryptoKit

/// The system username SHA256 hash for the app
/// - Note: This is not a secure way to do it
/// or in any way good practice
/// but this is mainly to test out `SecureField`
let username = "c7ad44cbad762a5da0a452f9e854fdc1e0e7a52a38015f23f3eab1d80b931dd472634dfac71cd34ebc35d16ab7fb8a90c81f975113d6c7538dc69dd8de9077ec".utf8

/// The system password associated with ``username``
///
/// I'm thinking about hashing them, but that would take work.
///
/// It would be more secure though.
/// - Note: Just as with `username` you should not define
/// these unencrypted like they are right now.
let password = "3c9909afec25354d551dae21590bb26e38d53f2173b8d3dc3eee4c047e7ab1c1eb8b85103e3be7ba613b31bb5c9c36214dc9f14a42fd7a2fdb84856bca5c44c2".utf8

/// Holds the views and login for the Docs tab in-app
///
/// Mostly just a long list of sections and calling views
/// - Note: New views are best called in this `struct`
struct DocsView: View {
	enum Field: Hashable {
		case username
		case password
	}

    func hashSHA512(login: String) -> String {
        let loginAsData = Data(login.utf8)
        let loginHashHex = SHA512.hash(data: loginAsData)
        let loginHash = loginHashHex.compactMap { String(format: "%02x", $0) }.joined()
        return String(loginHash)
    }
    
    @State private var pass: String = ""
    @State private var user: String = ""
	@State private var isUnlocked = false
 	@FocusState private var focusedField: Field?
	
	var body: some View {
		NavigationView {
			List {
				NavigationLink("Help", destination: HelpView())
				NavigationLink("Change Log", destination: ChangeLog())
				
				Section(header: Text("Features")) {
					NavigationLink("New", destination: NewFeatures())
					NavigationLink("In Progress", destination: InProgressFeatures())
					NavigationLink("Deprecated", destination: DeprecatedFeatures())
				}
				Section(header: Text("Known Issues")) {
					NavigationLink("Recently Resolved", destination: RecentlyResolved())
					NavigationLink("High Priority", destination: HighPriority())
					NavigationLink("Medium Priority", destination: MediumPriority())
					NavigationLink("Low Priority", destination: LowPriority())
				}
				Section(header: Text("App Information")) {
					NavigationLink("Software License", destination: LicenseView())
					Text("Version: Prerelease Build LVSXT10a.4")
					Text("Release date: 2022-07-06")
					Text("Start date: 2022-03-25")
					Link("Built with SwiftUI \(Image(systemName: "swift"))", destination: URL(string: "https://developer.apple.com/xcode/swiftui")!)
				}
				Section(header: Text("Login")) {
					if (isUnlocked) {
						NavigationLink("Contacts", destination: SecretView())
						Button("Log out") {
							pass = ""
							user = ""
							isUnlocked = false
						}
					} else {
						Button("Log in with biometrics") {
							authenticate()
						}
						SecureField("Username", text: $user)
							.keyboardType(.alphabet)
							.textContentType(.username)
							.submitLabel(.next)
							.focused($focusedField, equals: .username)
							.textContentType(.username)
						SecureField("Password", text: $pass)
							.keyboardType(.numbersAndPunctuation)
							.textContentType(.password)
							.submitLabel(.done)
							.focused($focusedField, equals: .password)
							.textContentType(.password)
						if checkPassword() {
							NavigationLink("Contacts", destination: SecretView())
						}
					}
				}
			}
			.navigationTitle("Docs")
		}
		.onSubmit {
			switch focusedField {
				case .username:
					focusedField = .password
				default:
					()
			}
			if checkPassword() {
				isUnlocked = true
			}
		}
	}
	
	
	/// Compares the `user` SecureField and the `pass` SecureField against ``username`` and ``password``
	///
	/// - Note: come back to this
	/// 
	///
	/// - Returns: `true` if `user` equals `username` *and* `pass` equals `password`, `false` if one or both checks return false.
	func checkPassword() -> Bool {
        if (hashSHA512(login: pass) == String(password) && hashSHA512(login: user) == String(username)) {
			return true
		} else {
			return false
		}
	}
	
	/// Checks wether the user can use biometrics to sign in
	/// and (if true) prompts the user to sign with either FaceID or TouchID
	/// depending on the device.
	///
	/// If the prompt was shown, and the user authenticated correctly
	/// `isUnlocked` is set to `true`
	///
	/// - Note: `authenticate()` has to be called to show the sign-in sheet
	func authenticate() {
		let context = LAContext()
		var error: NSError?

		// check whether biometric authentication is possible
		if context.canEvaluatePolicy(.deviceOwnerAuthenticationWithBiometrics, error: &error) {
			// it's possible, so go ahead and use it
			let reason = "We need authentication before we can show you sensitive data"

			context.evaluatePolicy(.deviceOwnerAuthenticationWithBiometrics, localizedReason: reason) { success, authenticationError in
				// authentication has now completed
				if success {
					isUnlocked = true
				} else {
					()
				}
			}
		} else {
			()
		}
	}
	// getting this to work came from
	// https://www.hackingwithswift.com/books/ios-swiftui/using-touch-id-and-face-id-with-swiftui
	// a truly epic website and it's helped me with
	// just about all of my code questions
}

struct DocsView_Previews: PreviewProvider {
    static var previews: some View {
        DocsView()
    }
}