86 lines
2.9 KiB
Swift
86 lines
2.9 KiB
Swift
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import Foundation
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import Localization
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/// Negotiates the best supported language for a request from its `Accept-Language` header.
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///
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/// Bound to the module's catalog languages via ``LanguageList``, an instance is invoked like a
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/// function — through ``callAsFunction(forAcceptLanguage:)`` — to resolve a header value to a
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/// supported language identifier, falling back to the default language.
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struct NegotiateLanguage {
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// MARK: Properties
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/// The supported languages and default language, derived from the module's String Catalog.
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private let list: LanguageList
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// MARK: Initializers
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/// Creates a language negotiator backed by the module's String Catalog.
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init() {
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self.list = .init(bundle: .module)
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}
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// MARK: Methods
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/// Picks the best supported language for the given `Accept-Language` header value.
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///
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/// Invoked by calling the instance directly, for example `negotiate(forAcceptLanguage: header)`.
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/// The header is split into its language tags (dropping any `q` weights), then matched against
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/// the supported languages with `Bundle.preferredLocalizations(from:forPreferences:)`. When the
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/// header is absent or matches nothing, the default language is returned.
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/// - Parameter acceptLanguage: the raw `Accept-Language` header value, if any.
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/// - Returns: the identifier of the supported language to serve.
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func callAsFunction(
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forAcceptLanguage acceptLanguage: String?
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) -> String {
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guard let acceptLanguage else {
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return list.default
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}
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let tags = tags(from: acceptLanguage)
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guard !tags.isEmpty else {
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return list.default
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}
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let preferred = Bundle.preferredLocalizations(
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from: list.all,
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forPreferences: tags
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)
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return preferred.first
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?? list.default
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}
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}
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// MARK: - Helpers
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private extension NegotiateLanguage {
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// MARK: Methods
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/// Extracts the ordered language tags from an `Accept-Language` header value.
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///
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/// Each comma-separated entry is reduced to its language tag by dropping the `;q=` weight, and
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/// blank entries are removed. The original order is kept, which mirrors descending preference
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/// closely enough for `preferredLocalizations(from:forPreferences:)` to resolve correctly.
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/// - Parameter acceptLanguage: the raw `Accept-Language` header value.
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/// - Returns: the ordered, weight-stripped language tags.
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func tags(
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from acceptLanguage: String
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) -> [String] {
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acceptLanguage
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.split(separator: ",")
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.map { entry in
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entry
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.split(separator: ";")
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.first
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.map(String.init)?
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.trimmingCharacters(in: .whitespaces) ?? ""
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}
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.filter { !$0.isEmpty }
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}
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}
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