Replace static UserAgent with UserAgent extensions (#764)

Author: VladislavFitz

Sources/AlgoliaSearchClient/Helpers/UserAgent/UserAgent.swift

@@ -33,6 +33,14 @@ extension UserAgent: CustomStringConvertible {
 
 }
 
+extension UserAgent: UserAgentExtending {
+  
+  public var userAgentExtension: String {
+    return description
+  }
+  
+}
+
 extension UserAgent {
 
   static var library: UserAgent {

Sources/AlgoliaSearchClient/Helpers/UserAgent/UserAgentController.swift

@@ -9,11 +9,32 @@ import Foundation
 
 public struct UserAgentController {
 
-  public internal(set) static var userAgents: [UserAgent] = [.operatingSystem, .library]
+  public static var userAgents: [UserAgent] {
+    extensions.compactMap { $0 as? UserAgent }
+  }
+  
+  public internal(set) static var extensions: [UserAgentExtending] = [UserAgent.operatingSystem, UserAgent.library]
+  
+  public static var httpHeaderValue: String {
+    return extensions.map(\.userAgentExtension).joined(separator: "; ")
+  }
 
-  /// Append user agent info which will be includede in each API call.
+  /// Append user agent to include into each API call.
+  @available(*, deprecated, message: "Use `append(_ userAgentExtension: UserAgentExtending)` instead")
   public static func append(userAgent: UserAgent) {
-    userAgents.append(userAgent)
+    extensions.append(userAgent)
+  }
+  
+  /// Append user agent to include into each API call.
+  public static func append(_ userAgentExtension: UserAgentExtending) {
+    extensions.append(userAgentExtension)
   }
 
 }
+
+public protocol UserAgentExtending {
+  
+  var userAgentExtension: String { get }
+  
+}
+

Sources/AlgoliaSearchClient/Transport/HTTP/HTTPRequestBuilder.swift

@@ -31,8 +31,7 @@ class HTTPRequestBuilder {
 
     let timeout = command.requestOptions?.timeout(for: command.callType) ?? configuration.timeout(for: command.callType)
     var request = URLRequest(command: command).setIfNotNil(\.credentials, to: credentials)
-    let userAgentsValue = UserAgentController.userAgents.map(\.description).joined(separator: "; ")
-    request.addValue(userAgentsValue, forHTTPHeaderField: HTTPHeaderKey.userAgent.rawValue)
+    request.addValue(UserAgentController.httpHeaderValue, forHTTPHeaderField: HTTPHeaderKey.userAgent.rawValue)
     return HTTPRequest(requester: requester,
                        retryStrategy: retryStrategy,
                        request: request,