// Copyright 2023 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

import Foundation
import XCTest

@available(iOS 15.0, macOS 12.0, macCatalyst 15.0, tvOS 15.0, watchOS 8.0, *)
class MockURLProtocol: URLProtocol {
  static var requestHandler: ((URLRequest) throws -> (
    URLResponse,
    AsyncLineSequence<URL.AsyncBytes>?
  ))?

  override class func canInit(with request: URLRequest) -> Bool {
    #if os(watchOS)
      print("MockURLProtocol cannot be used on watchOS.")
      return false
    #else
      return true
    #endif // os(watchOS)
  }

  override class func canonicalRequest(for request: URLRequest) -> URLRequest { return request }

  override func startLoading() {
    guard let requestHandler = MockURLProtocol.requestHandler else {
      fatalError("`requestHandler` is nil.")
    }
    guard let client = client else {
      fatalError("`client` is nil.")
    }

    Task {
      let (response, stream) = try requestHandler(self.request)
      client.urlProtocol(self, didReceive: response, cacheStoragePolicy: .notAllowed)
      if let stream = stream {
        do {
          for try await line in stream {
            guard let data = line.data(using: .utf8) else {
              fatalError("Failed to convert \"\(line)\" to UTF8 data.")
            }
            client.urlProtocol(self, didLoad: data)
            // Add a newline character since AsyncLineSequence strips them when reading line by
            // line;
            // without the following, the whole file is delivered as a single line.
            client.urlProtocol(self, didLoad: "\n".data(using: .utf8)!)
          }
        } catch {
          client.urlProtocol(self, didFailWithError: error)
          XCTFail("Unexpected failure reading lines from stream: \(error.localizedDescription)")
        }
      }
      client.urlProtocolDidFinishLoading(self)
    }
  }

  override func stopLoading() {}
}