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//
// ErrorChain.swift
// MullvadVPN
//
// Created by pronebird on 07/05/2020.
// Copyright © 2020 Mullvad VPN AB. All rights reserved.
//
import Foundation
/// A protocol describing errors that can be chained together.
protocol ChainedError: LocalizedError {
/// A source error when available.
var source: Error? { get }
}
/// A protocol providing error a way to override error description when printing error chain.
protocol CustomChainedErrorDescriptionProtocol {
/// A custom error description that overrides `localizedDescription` when printing error chain.
var customErrorDescription: String? { get }
}
extension ChainedError {
var source: Error? {
let reflection = Mirror(reflecting: self)
if case .enum = reflection.displayStyle {
for child in reflection.children {
if let associatedError = child.value as? Error {
return associatedError
}
}
}
return nil
}
/// Create a string representation of the entire error chain.
/// An extra `message` is added at the start of the chain when given.
func displayChain(message: String? = nil) -> String {
var s: String
let errorDescription = Self.getErrorDescription(self)
if let message = message {
s = "Error: \(message)\nCaused by: \(errorDescription)"
} else {
s = "Error: \(errorDescription)"
}
for sourceError in makeChainIterator() {
s.append("\nCaused by: \(Self.getErrorDescription(sourceError))")
}
return s
}
private func makeChainIterator() -> AnyIterator<Error> {
var current: Error? = self
return AnyIterator { () -> Error? in
current = (current as? ChainedError)?.source
return current
}
}
private static func getErrorDescription(_ error: Error) -> String {
let anError = error as? CustomChainedErrorDescriptionProtocol
return anError?.customErrorDescription ?? error.localizedDescription
}
}
extension CustomChainedErrorDescriptionProtocol {
var customErrorDescription: String? {
return nil
}
}
/// A type-erasing container type for any `Error` that makes the wrapped error behave like
/// `ChainedError`.
final class AnyChainedError: ChainedError, CustomChainedErrorDescriptionProtocol {
private let wrappedError: Error
init(_ error: Error) {
wrappedError = error
}
var source: Error? {
return (wrappedError as? ChainedError)?.source
}
var errorDescription: String? {
return wrappedError.localizedDescription
}
var customErrorDescription: String? {
return (wrappedError as? CustomChainedErrorDescriptionProtocol)?.customErrorDescription
}
}
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