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1//
2// KeyDecodingStrategy.swift
3// URLQueryItemCoder
4//
5// Created by Kyle Hughes on 4/10/23.
6//
7
8/// The strategy to use for automatically changing the value of keys before decoding.
9public enum KeyDecodingStrategy: Sendable {
10 /// Convert from "snake_case_keys" to "camelCaseKeys" before attempting to match a key with the one specified by
11 /// each type.
12 ///
13 /// The conversion to upper case uses `Locale.system`, also known as the ICU "root" locale. This means the result
14 /// is consistent regardless of the current user's locale and language preferences.
15 ///
16 /// Converting from snake case to camel case:
17 ///
18 /// 1. Capitalizes the word starting after each `_`
19 /// 2. Removes all `_`
20 /// 3. Preserves starting and ending `_` (as these are often used to indicate private variables or other metadata).
21 ///
22 /// For example, `one_two_three` becomes `oneTwoThree`. `_one_two_three_` becomes `_oneTwoThree_`.
23 ///
24 /// - Note: Using a key decoding strategy has a nominal performance cost, as each string key has to be inspected
25 /// for the `_` character.
26 case convertFromSnakeCase
27
28 /// Provide a custom conversion from the key in the encoded JSON to the keys specified by the decoded types.
29 ///
30 /// The full path to the current decoding position is provided for context (in case you need to locate this key
31 /// within the payload). The returned key is used in place of the last component in the coding path before decoding.
32 ///
33 /// If the result of the conversion is a duplicate key, then only one value will be present in the container for
34 /// the type to decode from.
35 case custom(@Sendable (_ codingPath: [CodingKey]) -> CodingKey)
36
37 /// Use the keys specified by each type.
38 ///
39 /// This is the default strategy.
40 case useDefaultKeys
41
42 // MARK: Public Static Interface
43
44 /// The default decoding strategy.
45 ///
46 /// Equals `.useDefaultKeys`.
47 public static let `default`: Self = .useDefaultKeys
48
49 // MARK: Internal Instance Interface
50
51 internal func encode(_ key: any CodingKey, at codingPath: [any CodingKey]) -> any CodingKey {
52 switch self {
53 case .convertFromSnakeCase:
54 return StringCodingKey(stringValue: key.stringValue.convertToSnakeCase())
55 case let .custom(encoder):
56 return encoder(codingPath + [key])
57 case .useDefaultKeys:
58 return key
59 }
60 }
61}
62