// Copyright 2020 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

/// Possible errors with model downloading.
public enum DownloadError: Error, Equatable {
  /// No model with this name found on server.
  case notFound
  /// Caller does not have necessary permissions for this operation.
  case permissionDenied
  /// Conditions not met to perform download.
  case failedPrecondition
  /// Not enough space for model on device.
  case notEnoughSpace
  /// Malformed model name.
  case invalidArgument
  /// Other errors with description.
  case internalError(description: String)
}

/// Possible errors with locating model on device.
public enum DownloadedModelError: Error {
  /// File system error.
  case fileIOError
  /// Model not found on device.
  case notFound
}

/// Possible ways to get a custom model.
public enum ModelDownloadType {
  /// Get local model stored on device.
  case localModel
  /// Get local model on device and update to latest model from server in the background.
  case localModelUpdateInBackground
  /// Get latest model from server.
  case latestModel
}

/// Downloader to manage custom model downloads.
public struct ModelDownloader {
  /// Downloads a custom model to device or gets a custom model already on device, w/ optional handler for progress.
  public func getModel(name modelName: String, downloadType: ModelDownloadType,
                       conditions: ModelDownloadConditions,
                       progressHandler: ((Float) -> Void)? = nil,
                       completion: @escaping (Result<CustomModel, DownloadError>) -> Void) {
    // TODO: Model download
    let modelSize = Int()
    let modelPath = String()
    let modelHash = String()

    let customModel = CustomModel(
      name: modelName,
      size: modelSize,
      path: modelPath,
      hash: modelHash
    )
    completion(.success(customModel))
    completion(.failure(.notFound))
  }

  /// Gets all downloaded models.
  public func listDownloadedModels(completion: @escaping (Result<Set<CustomModel>,
    DownloadedModelError>) -> Void) {
    let customModels = Set<CustomModel>()
    // TODO: List downloaded models
    completion(.success(customModels))
    completion(.failure(.notFound))
  }

  /// Deletes a custom model from device.
  public func deleteDownloadedModel(name modelName: String,
                                    completion: @escaping (Result<Void, DownloadedModelError>)
                                      -> Void) {
    // TODO: Delete previously downloaded model
    completion(.success(()))
    completion(.failure(.notFound))
  }
}