// Copyright 2021 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.

#if canImport(SwiftUI)
  import FirebaseAnalytics
  import SwiftUI

  /// Custom view modifier to allow for easily logging screen view events.
  @available(iOS 13, *)
  @available(tvOS, unavailable)
  @available(macOS, unavailable)
  @available(macCatalyst, unavailable)
  @available(watchOS, unavailable)
  internal struct LoggedAnalyticsModifier: ViewModifier {
    /// The name of the view to log in the `AnalyticsParameterScreenName` parameter.
    let screenName: String

    /// The name of the view to log in the `AnalyticsParameterScreenClass` parameter.
    let screenClass: String

    /// Extra parameters to log with the screen view event.
    let extraParameters: [String: Any]

    func body(content: Content) -> some View {
      // Take the content and add an onAppear action to know when the view has appeared on screen.
      content.onAppear {
        // Log the event appearing, adding the appropriate keys and values needed for screen
        // view events.
        var parameters = extraParameters
        parameters[AnalyticsParameterScreenName] = screenName
        parameters[AnalyticsParameterScreenClass] = screenClass
        Analytics.logEvent(AnalyticsEventScreenView, parameters: parameters)
      }
    }
  }

  @available(iOS 13, *)
  @available(tvOS, unavailable)
  @available(macOS, unavailable)
  @available(macCatalyst, unavailable)
  @available(watchOS, unavailable)
  public extension View {
    /// Logs `screen_view` events in Google Analytics for Firebase when this view appears on screen.
    /// - Parameters:
    ///   - name: Current screen name logged with the `screen_view` event.
    ///   - class: Current screen class or struct logged with the `screen_view` event.
    ///   - extraParameters: Any additional parameters to be logged. These extra parameters must
    ///       follow the same rules as described in the `Analytics.logEvent(_:parameters:)` docs.
    /// - Returns: A view with a custom `ViewModifier` used to log `screen_view` events when this
    ///    view appears on screen.
    func analyticsScreen(name: String,
                         class: String = "View",
                         extraParameters: [String: Any] = [:]) -> some View {
      // `self` is the view, we're just adding an `LoggedAnalyticsModifier` modifier on it.
      modifier(LoggedAnalyticsModifier(screenName: name,
                                       screenClass: `class`,
                                       extraParameters: extraParameters))
    }
  }
#endif