1 import Foundation
2 
3 /**
4  A protocol for errors specyfing its `code` and providing the `description`.
5  */
6 public protocol CodedError: Error, CustomStringConvertible {
7   var code: String { get }
8   var description: String { get }
9 }
10 
11 /**
12  Extends the `CodedError` to make a fallback for `code` and `description`.
13  */
14 public extension CodedError {
15   /**
16    The code is inferred from the class name — e.g. the code of `ModuleNotFoundError` becomes `ERR_MODULE_NOT_FOUND`.
17    To obtain the code, the class name is cut off from generics and `Error` suffix, then it's converted to snake case and uppercased.
18    */
19   var code: String {
20     return errorCodeFromString(String(describing: type(of: self)))
21   }
22 
23   /**
24    The description falls back to object's localized description.
25    */
26   var description: String {
27     return localizedDescription
28   }
29 }
30 
31 /**
32  Basic implementation of `CodedError` protocol,
33  where the code and the description are provided in the initializer.
34  */
35 public struct SimpleCodedError: CodedError {
36   public var code: String
37   public var description: String
38 
39   init(_ code: String, _ description: String) {
40     self.code = code
41     self.description = description
42   }
43 }
44 
45 func errorCodeFromString(_ str: String) -> String {
46   let name = str.replacingOccurrences(of: #"(Error|Exception)?(<.*>)?$"#, with: "", options: .regularExpression)
47   // The pattern is valid, so it'll never throw
48   // swiftlint:disable:next force_try
49   let regex = try! NSRegularExpression(pattern: "(.)([A-Z])", options: [])
50   let range = NSRange(location: 0, length: name.count)
51 
52   return "ERR_" + regex
53     .stringByReplacingMatches(in: name, options: [], range: range, withTemplate: "$1_$2")
54     .uppercased()
55 }
56