// Copyright 2022 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

#if COCOAPODS
  import GTMSessionFetcher
#else
  import GTMSessionFetcherCore
#endif

/**
 * A Task that lists the entries under a {@link StorageReference}
 */
internal class StorageListTask: StorageTask, StorageTaskManagement {
  private var fetcher: GTMSessionFetcher?
  private var fetcherCompletion: ((Data?, NSError?) -> Void)?
  private var taskCompletion: ((_: StorageListResult?, _: NSError?) -> Void)?
  private let pageSize: Int64?
  private let previousPageToken: String?

  /**
   * Initializes a new List Task.
   *
   * To schedule the task, invoke `[FIRStorageListTask enqueue]`.
   *
   * @param reference The location to invoke List on.
   * @param service GTMSessionFetcherService to use for the RPC.
   * @param queue The queue to schedule the List operation on.
   * @param pageSize An optional pageSize, denoting the maximum size of the result set. If
   * set to `nil`, the backend will use the default page size.
   * @param previousPageToken An optional pageToken, used to resume a previous invocation.
   * @param completion The completion handler to be called with the FIRIMPLStorageListResult.
   */
  internal init(reference: StorageReference,
                fetcherService: GTMSessionFetcherService,
                queue: DispatchQueue,
                pageSize: Int64?,
                previousPageToken: String?,
                completion: ((_ listResult: StorageListResult?, _ error: NSError?) -> Void)?) {
    self.pageSize = pageSize
    self.previousPageToken = previousPageToken
    super.init(reference: reference, service: fetcherService, queue: queue)
    taskCompletion = { (listResult: StorageListResult?, error: NSError?) in
      completion?(listResult, error)
      // Reference self in completion handler in order to retain self until completion is called.
      self.taskCompletion = nil
    }
  }

  deinit {
    self.fetcher?.stopFetching()
  }

  /**
   * Prepares a task and begins execution.
   */
  internal func enqueue() {
    if let completion = taskCompletion {
      taskCompletion = { (listResult: StorageListResult?, error: NSError?) in
        completion(listResult, error)
        // Reference self in completion handler in order to retain self until completion is called.
        self.taskCompletion = nil
      }
    }
    dispatchQueue.async { [weak self] in
      guard let self = self else { return }
      var queryParams = [String: String]()

      let prefix = self.reference.fullPath
      if prefix.count > 0 {
        queryParams["prefix"] = "\(prefix)/"
      }

      // Firebase Storage uses file system semantics and treats slashes as separators. GCS's List API
      // does not prescribe a separator, and hence we need to provide a slash as the delimiter.
      queryParams["delimiter"] = "/"

      // listAll() doesn't set a pageSize as this allows Firebase Storage to determine how many items
      // to return per page. This removes the need to backfill results if Firebase Storage filters
      // objects that are considered invalid (such as items with two consecutive slashes).
      if let pageSize = self.pageSize {
        queryParams["maxResults"] = "\(pageSize)"
      }

      if let previousPageToken = self.previousPageToken {
        queryParams["pageToken"] = previousPageToken
      }

      let root = self.reference.root()
      var request = StorageUtils.defaultRequestForReference(
        reference: root,
        queryParams: queryParams
      )

      request.httpMethod = "GET"
      request.timeoutInterval = self.reference.storage.maxOperationRetryTime

      let fetcher = self.fetcherService.fetcher(with: request)
      fetcher.comment = "ListTask"
      self.fetcher = fetcher

      self.fetcherCompletion = { [weak self] (data: Data?, error: NSError?) in
        guard let self = self else { return }
        var listResult: StorageListResult?
        if let error = error, self.error == nil {
          self.error = StorageErrorCode.error(withServerError: error, ref: self.reference)
        } else {
          if let data = data,
             let responseDictionary = try? JSONSerialization
             .jsonObject(with: data) as? [String: Any] {
            listResult = StorageListResult(with: responseDictionary, reference: self.reference)
          } else {
            self.error = StorageErrorCode.error(withInvalidRequest: data)
          }
        }

        self.taskCompletion?(listResult, self.error)
        self.fetcherCompletion = nil
      }

      self.fetcher?.beginFetch { [weak self] data, error in
        self?.fetcherCompletion?(data, error as? NSError)
      }
    }
  }
}