feat: implement startCommercial endpoint

Sources/Twitch/API/Endpoints/Ads/StartCommercial.swift

@@ -6,17 +6,26 @@ import Foundation
 
 extension Helix {
   public func startCommercial(broadcasterId: String, length: Int) async throws
-    -> Commercial?
+    -> Commercial
   {
-    var queryItems = [URLQueryItem]()
-    queryItems.append(URLQueryItem(name: "broadcaster_id", value: broadcasterId))
-    queryItems.append(URLQueryItem(name: "length", value: String(length)))
+    return try await self.request(
+      .post("channels/commercial"),
+      jsonBody: StartCommercialRequestBody(broadcasterId: broadcasterId, length: length)
+    ).first!
+  }
+}
+
+private struct StartCommercialRequestBody: Encodable {
+  let broadcasterId: String
+  let length: Int
 
-    return try await self.request(.get("channels"), with: queryItems).first
+  enum CodingKeys: String, CodingKey {
+    case broadcasterId = "broadcaster_id"
+    case length
   }
 }
 
-public struct Commercial: Codable {
+public struct Commercial: Decodable {
   let length: Int
   let message: String
   let retryAfter: Int

Sources/Twitch/API/Endpoints/HelixData.swift

@@ -1 +1 @@
-internal struct HelixData<T>: Codable where T: Codable { let data: [T] }
+internal struct HelixData<T>: Decodable where T: Decodable { let data: [T] }

Sources/Twitch/API/Helix.swift

@@ -17,8 +17,9 @@ public final class Helix {
     self.session = urlSession ?? URLSession(configuration: .default)
   }
 
-  internal func request<T: Codable>(
-    _ request: HelixRequest, with queryItems: [URLQueryItem]? = nil
+  internal func request<T: Decodable>(
+    _ request: HelixRequest, with queryItems: [URLQueryItem]? = nil,
+    jsonBody: Encodable? = nil
   ) async throws -> [T] {
     let (method, endpoint) = request.unwrap()
 
@@ -36,6 +37,11 @@ public final class Helix {
     urlRequest.httpMethod = method
     urlRequest.allHTTPHeaderFields = try? authentication.httpHeaders()
 
+    if let jsonBody {
+      urlRequest.setValue("application/json", forHTTPHeaderField: "Content-Type")
+      urlRequest.httpBody = try JSONEncoder().encode(jsonBody)
+    }
+
     let data = try await self.send(urlRequest)
 
     let result = try? JSONDecoder().decode(HelixData<T>.self, from: data).data