// 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

///
/// SessionCoordinator is responsible for coordinating the systems in this SDK
/// involved with sending a Session Start event.
///
class SessionCoordinator {
  let identifiers: IdentifierProvider
  let installations: InstallationsProtocol
  let fireLogger: EventGDTLoggerProtocol
  let sampler: SessionSamplerProtocol

  init(identifiers: IdentifierProvider,
       installations: InstallationsProtocol,
       fireLogger: EventGDTLoggerProtocol,
       sampler: SessionSamplerProtocol) {
    self.identifiers = identifiers
    self.installations = installations
    self.fireLogger = fireLogger
    self.sampler = sampler
  }

  // Begins the process of logging a SessionStartEvent to FireLog, while taking into account Data Collection, Sampling, and fetching Settings
  func attemptLoggingSessionStart(event: SessionStartEvent,
                                  callback: @escaping (Result<Void, Error>) -> Void) {
    /// Order of execution
    /// 1. Check if the session can be sent. If yes, move to 2. Else, drop the event.
    /// 2. Fetch the installations Id. If successful, move to 3. Else, drop sending the event.
    /// 3. Log the event. If successful, all is good. Else, log the message with error.
    if sampler.shouldSendEventForSession(sessionId: identifiers.sessionID) {
      installations.installationID { result in
        switch result {
        case let .success(fiid):
          event.setInstallationID(installationId: fiid)
          self.fireLogger.logEvent(event: event) { logResult in
            switch logResult {
            case .success():
              Logger.logInfo("Successfully logged Session Start event to GoogleDataTransport")
              callback(.success(()))
            case let .failure(error):
              Logger
                .logError(
                  "Error logging Session Start event to GoogleDataTransport: \(error)."
                )
              callback(.failure(error))
            }
          }
        case let .failure(error):
          Logger
            .logError(
              "Error getting Firebase Installation ID: \(error). Skip sending event."
            )
          callback(.failure(FirebaseSessionsError.SessionInstallationsError))
        }
      }
    } else {
      Logger
        .logInfo(
          "Session event dropped due to sampling."
        )
      callback(.failure(FirebaseSessionsError.SessionSamplingError))
    }
  }
}