import CryptoKit
import Intents
import UIKit
import UserNotifications

let APP_GROUP = "group.app.bsky"
typealias ContentHandler = (UNNotificationContent) -> Void

// This extension allows us to do some processing of the received notification
// data before displaying the notification to the user. In our use case, there
// are a few particular things that we want to do:
//
// - Determine whether we should play a sound for the notification
// - Download and display any images for the notification
// - Update the badge count accordingly
//
// The extension may or may not create a new process to handle a notification.
// It is also possible that multiple notifications will be processed by the
// same instance of `NotificationService`, though these will happen in
// parallel.
//
// Because multiple instances of `NotificationService` may exist, we should
// be careful in accessing preferences that will be mutated _by the
// extension itself_. For example, we should not worry about `playChatSound`
// changing, since we never mutate that value within the extension itself.
// However, since we mutate `badgeCount` frequently, we should ensure that
// these updates always run sync with each other and that the have access
// to the most recent values.

class NotificationService: UNNotificationServiceExtension {
  private var contentHandler: ContentHandler?
  private var bestAttempt: UNMutableNotificationContent?

  override func didReceive(
    _ request: UNNotificationRequest,
    withContentHandler contentHandler: @escaping (UNNotificationContent) -> Void
  ) {
    self.contentHandler = contentHandler

    guard let bestAttempt = NSEUtil.createCopy(request.content),
      let reason = request.content.userInfo["reason"] as? String
    else {
      contentHandler(request.content)
      return
    }

    self.bestAttempt = bestAttempt

    if reason == "chat-message" || reason == "chat-reaction" {
      mutateWithChatMessage(bestAttempt)
      // Only apply the title->body swap for chat-message. For chat-reaction,
      // `messageKind` refers to the reacted-to message, so we'd clobber the
      // descriptive reaction body with the title for reactions on system
      // messages.
      if reason == "chat-message" {
        mutateChatMessageBody(bestAttempt, userInfo: request.content.userInfo)
      }
      mutateWithGroupSubtitle(bestAttempt, userInfo: request.content.userInfo)
      let finalContent = createCommunicationNotification(
        from: bestAttempt,
        userInfo: request.content.userInfo
      )
      contentHandler(finalContent)
    } else if reason == "chat-added-to-group"
      || reason == "chat-removed-from-group"
      || reason == "chat-join-request-rejected" {
      mutateWithChatMessage(bestAttempt)
      mutateWithGroupSubtitle(bestAttempt, userInfo: request.content.userInfo)
      mutateWithBadge(bestAttempt)
      contentHandler(bestAttempt)
    } else {
      mutateWithBadge(bestAttempt)
      contentHandler(bestAttempt)
    }
  }

  override func serviceExtensionTimeWillExpire() {
    guard let contentHandler = self.contentHandler,
      let bestAttempt = self.bestAttempt
    else {
      return
    }
    contentHandler(bestAttempt)
  }

  // MARK: Communication Notification

  func createCommunicationNotification(
    from content: UNMutableNotificationContent,
    userInfo: [AnyHashable: Any]
  ) -> UNNotificationContent {
    let senderDisplayName = userInfo["senderDisplayName"] as? String ?? "Unknown"
    let convoId = userInfo["convoId"] as? String
    var avatarImage: INImage?
    if let avatarUrlString = userInfo["senderAvatarUrl"] as? String {
      avatarImage = downloadAvatarImage(from: avatarUrlString)
    }

    let senderHandleValue = userInfo["senderHandle"] as? String
    let senderHandle = INPersonHandle(value: senderHandleValue, type: .unknown)
    let sender = INPerson(
      personHandle: senderHandle,
      nameComponents: nil,
      displayName: senderDisplayName,
      image: avatarImage,
      contactIdentifier: nil,
      customIdentifier: nil
    )

    var speakableGroupName: INSpeakableString?
    if userInfo["convoKind"] as? String == "group",
      let groupName = userInfo["groupName"] as? String,
      !groupName.isEmpty {
      speakableGroupName = INSpeakableString(spokenPhrase: groupName)
    }

    let intent = INSendMessageIntent(
      recipients: nil,
      outgoingMessageType: .outgoingMessageText,
      content: content.body,
      speakableGroupName: speakableGroupName,
      conversationIdentifier: convoId,
      serviceName: nil,
      sender: sender,
      attachments: nil
    )

    // The push payload omits the full recipient list for group convos. Without
    // any signal of multiple recipients, iOS classifies the notification as
    // `MessagingDirect` and ignores `speakableGroupName`. Setting
    // `recipientCount` on the donation metadata is Apple's documented escape
    // hatch for this case, and overrides the (zero-length) recipients array.
    if userInfo["convoKind"] as? String == "group",
      let groupMemberCount = userInfo["groupMemberCount"] as? Int,
      groupMemberCount > 0 {
      let metadata = INSendMessageIntentDonationMetadata()
      metadata.recipientCount = groupMemberCount
      intent.donationMetadata = metadata
    }

    // For group convos, attach the composite group avatar (rendered by the
    // ogcard service) to the `speakableGroupName` parameter so iOS shows it
    // alongside the sender on the Communication Notification.
    // Disabled: the composite avatar renders poorly at notification size.
    // if userInfo["convoKind"] as? String == "group",
    //    let convoAvatarUrlString = userInfo["convoAvatarUrl"] as? String,
    //    let groupImage = downloadAvatarImage(from: convoAvatarUrlString) {
    //   intent.setImage(groupImage, forParameterNamed: \.speakableGroupName)
    // }

    // Set the group image to the sender avatar instead
    if userInfo["convoKind"] as? String == "group",
      let avatarImage {
      intent.setImage(avatarImage, forParameterNamed: \.speakableGroupName)
    }

    let interaction = INInteraction(intent: intent, response: nil)
    interaction.direction = .incoming
    interaction.donate(completion: nil)

    do {
      return try content.updating(from: intent)
    } catch {
      return content
    }
  }

  func downloadAvatarImage(from urlString: String) -> INImage? {
    let thumbnailUrlString = urlString.replacingOccurrences(
      of: "/img/avatar/",
      with: "/img/avatar_thumbnail/"
    )

    guard let url = URL(string: thumbnailUrlString) else { return nil }

    var request = URLRequest(url: url)
    request.timeoutInterval = 5

    var imageData: Data?
    let semaphore = DispatchSemaphore(value: 0)

    let task = URLSession.shared.dataTask(with: request) { data, response, _ in
      if let data = data,
        let httpResponse = response as? HTTPURLResponse,
        httpResponse.statusCode == 200 {
        imageData = data
      }
      semaphore.signal()
    }
    task.resume()
    semaphore.wait()

    guard let data = imageData else { return nil }

    // Back the INImage with a file in the shared App Group container rather
    // than raw image data. `INImage(imageData:)` renders fine on the iPhone
    // itself, but the in-memory bytes are not relayed to paired devices like
    // the Apple Watch. The Watch then receives an INPerson with no usable
    // image and falls back to drawing a monogram from the sender's initials.
    // Pointing the INImage at a file URL the Watch can resolve lets it render
    // the actual avatar.
    if let fileURL = writeAvatarToSharedContainer(data: data, urlString: thumbnailUrlString) {
      return INImage(url: fileURL)
    }

    // Fall back to in-memory data if we could not write to the container. The
    // avatar still shows on the iPhone in that case.
    return INImage(imageData: data)
  }

  // Writes avatar bytes to a file in the shared App Group container so the
  // resulting INImage can be backed by a URL. The system reads this file
  // lazily (including when relaying the notification to the Apple Watch), so
  // it must live in the persistent shared container rather than a temporary
  // directory. Files are named by a stable hash of the source URL, which is
  // content-addressed (the CID changes when a user updates their avatar), so
  // repeated notifications from the same sender reuse one file instead of
  // accumulating duplicates.
  func writeAvatarToSharedContainer(data: Data, urlString: String) -> URL? {
    guard
      let containerURL = FileManager.default.containerURL(
        forSecurityApplicationGroupIdentifier: APP_GROUP
      )
    else {
      return nil
    }

    let avatarsDir = containerURL.appendingPathComponent(
      "notification-avatars",
      isDirectory: true
    )

    let fileName = Insecure.MD5.hash(data: Data(urlString.utf8))
      .map { String(format: "%02x", $0) }
      .joined()
    let fileURL = avatarsDir.appendingPathComponent(fileName)

    // Reuse an already-downloaded avatar if present.
    if FileManager.default.fileExists(atPath: fileURL.path) {
      return fileURL
    }

    do {
      try FileManager.default.createDirectory(
        at: avatarsDir,
        withIntermediateDirectories: true
      )
      try data.write(to: fileURL, options: .atomic)
    } catch {
      return nil
    }

    pruneOldAvatars(in: avatarsDir)

    return fileURL
  }

  // Best-effort, age-based cleanup of the avatar cache. We never delete files
  // right after delivering a notification because the system reads them
  // lazily (the Apple Watch may fetch the avatar seconds later), and the NSE
  // gets no "notification dismissed" callback. Instead we drop files old
  // enough that any device that needed them is long done. Notifications are
  // ephemeral, so a one-day window is comfortably safe.
  //
  // This runs inside the time-limited extension, but the directory holds only
  // a handful of small files. Every step is best-effort: multiple NSE
  // instances may run this concurrently, so a file another instance just
  // removed is expected and harmless (`try?`).
  func pruneOldAvatars(
    in directory: URL,
    olderThan maxAge: TimeInterval = 24 * 60 * 60
  ) {
    let fileManager = FileManager.default
    guard
      let entries = try? fileManager.contentsOfDirectory(
        at: directory,
        includingPropertiesForKeys: [.contentModificationDateKey],
        options: .skipsHiddenFiles
      )
    else {
      return
    }

    let cutoff = Date().addingTimeInterval(-maxAge)
    for fileURL in entries {
      let modified = (try? fileURL.resourceValues(
        forKeys: [.contentModificationDateKey]
      ))?.contentModificationDate
      if let modified, modified < cutoff {
        try? fileManager.removeItem(at: fileURL)
      }
    }
  }

  // MARK: Mutations

  func mutateWithBadge(_ content: UNMutableNotificationContent) {
    NSEUtil.shared.prefsQueue.sync {
      var count = NSEUtil.shared.prefs?.integer(forKey: "badgeCount") ?? 0
      count += 1

      // Set the new badge number for the notification, then store that value for using later
      content.badge = NSNumber(value: count)
      NSEUtil.shared.prefs?.setValue(count, forKey: "badgeCount")
    }
  }

  func mutateWithChatMessage(_ content: UNMutableNotificationContent) {
    if NSEUtil.shared.prefs?.bool(forKey: "playSoundChat") == true {
      mutateWithDmSound(content)
    }
  }

  // For group convos, surface the group name as the notification subtitle.
  // The sender's display name is shown as the title (overridden by
  // `INSendMessageIntent` for chat-message/chat-reaction).
  func mutateWithGroupSubtitle(
    _ content: UNMutableNotificationContent,
    userInfo: [AnyHashable: Any]
  ) {
    guard userInfo["convoKind"] as? String == "group",
      let groupName = userInfo["groupName"] as? String,
      !groupName.isEmpty
    else {
      return
    }
    content.subtitle = groupName
  }

  // System messages (`add_member`, `convo_locked`, `edit_group`, etc.) are
  // delivered through `chat-message` but have a server-rendered description
  // in `title`. iOS overrides the title with the sender name once we apply
  // `INSendMessageIntent`, so we move the title text into the body before
  // building the intent.
  func mutateChatMessageBody(
    _ content: UNMutableNotificationContent,
    userInfo: [AnyHashable: Any]
  ) {
    guard let messageKind = userInfo["messageKind"] as? String,
      messageKind != "message",
      !content.title.isEmpty
    else {
      return
    }
    content.body = content.title
  }

  func mutateWithDefaultSound(_ content: UNMutableNotificationContent) {
    content.sound = UNNotificationSound.default
  }

  func mutateWithDmSound(_ content: UNMutableNotificationContent) {
    content.sound = UNNotificationSound(named: UNNotificationSoundName(rawValue: "dm.aiff"))
  }
}

// NSEUtil's purpose is to create a shared instance of `UserDefaults` across
// `NotificationService` instances. It also includes a queue so that we can process
// updates to `UserDefaults` in parallel.

private class NSEUtil {
  static let shared = NSEUtil()

  var prefs = UserDefaults(suiteName: APP_GROUP)
  var prefsQueue = DispatchQueue(label: "NSEPrefsQueue")

  static func createCopy(_ content: UNNotificationContent) -> UNMutableNotificationContent? {
    return content.mutableCopy() as? UNMutableNotificationContent
  }
}