import Foundation
import UIKit

enum VideoCallDeclineClient {
  private static let uuidPattern =
    #"^[0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{12}$"#

  /// `POST /video-call/decline` from the CallKit callback. The process is
  /// awake here even when the user never opens the app afterwards.
  static func send(extra: [String: Any], handle: String) {
    let fields = declineFields(extra: extra, handle: handle)
    guard let request = makeRequest(
      baseUrl: prefsString("apiBaseUrl") ?? prefsString("customBaseUrl"),
      token: prefsString("token"),
      hwId: UIDevice.current.identifierForVendor?.uuidString,
      fields: fields
    ) else {
      NSLog(
        "[EatvioVoIP] decline POST skipped conversation=\(fields.conversationUuid) ended=\(fields.endedPush)"
      )
      return
    }

    let task = EatvioBackgroundTask()
    task.begin(name: "video-call-decline")
    let urlTask = URLSession.shared.dataTask(with: request) { _, response, error in
      let code = (response as? HTTPURLResponse)?.statusCode ?? -1
      NSLog(
        "[EatvioVoIP] decline POST status=\(code) conversation=\(fields.conversationUuid) error=\(error?.localizedDescription ?? "-")"
      )
      task.end()
    }
    urlTask.resume()
  }

  static func makeRequest(
    baseUrl: String?,
    token: String?,
    hwId: String?,
    fields: VideoCallDeclineFields
  ) -> URLRequest? {
    if fields.endedPush { return nil }
    let conversation = fields.conversationUuid.trimmingCharacters(in: .whitespacesAndNewlines)
    let authToken = token?.trimmingCharacters(in: .whitespacesAndNewlines) ?? ""
    let deviceId = hwId?.trimmingCharacters(in: .whitespacesAndNewlines) ?? ""
    var root = baseUrl?.trimmingCharacters(in: .whitespacesAndNewlines) ?? ""
    while root.hasSuffix("/") {
      root.removeLast()
    }
    guard !conversation.isEmpty, !authToken.isEmpty else { return nil }
    guard deviceId.count >= 8, deviceId.count <= 64 else { return nil }
    guard root.hasPrefix("http://") || root.hasPrefix("https://") else { return nil }
    guard let encoded = conversation.addingPercentEncoding(withAllowedCharacters: .urlPathAllowed),
      let url = URL(string: "\(root)/api/v2/chat/\(encoded)/video-call/decline")
    else { return nil }

    var body: [String: String] = ["hw_id": deviceId]
    if let callId = fields.callId {
      body["call_id"] = callId
    }
    guard let data = try? JSONSerialization.data(withJSONObject: body) else { return nil }

    var request = URLRequest(url: url)
    request.httpMethod = "POST"
    request.timeoutInterval = 10
    request.setValue("Bearer \(authToken)", forHTTPHeaderField: "Authorization")
    request.setValue("application/json", forHTTPHeaderField: "Accept")
    request.setValue("application/json; charset=utf-8", forHTTPHeaderField: "Content-Type")
    request.httpBody = data
    return request
  }

  private static func declineFields(extra: [String: Any], handle: String) -> VideoCallDeclineFields {
    let conversation = firstString(extra, keys: ["conversationUuid", "conversation_uuid"])
      ?? handle.trimmingCharacters(in: .whitespacesAndNewlines)
    let rawCallId = firstString(extra, keys: ["call_id", "callId"])
    return VideoCallDeclineFields(
      conversationUuid: conversation,
      callId: backendCallId(rawCallId, conversation: conversation),
      endedPush: marksEndedPush(extra["endedPush"])
    )
  }

  private static func backendCallId(_ callId: String?, conversation: String) -> String? {
    let id = callId?.trimmingCharacters(in: .whitespacesAndNewlines) ?? ""
    guard let regex = try? NSRegularExpression(pattern: uuidPattern),
      regex.firstMatch(in: id, range: NSRange(id.startIndex..., in: id)) != nil
    else { return nil }
    if id.compare(conversation.trimmingCharacters(in: .whitespacesAndNewlines), options: .caseInsensitive) == .orderedSame {
      return nil
    }
    return id
  }

  private static func firstString(_ extra: [String: Any], keys: [String]) -> String? {
    for key in keys {
      guard let value = extra[key] as? String else { continue }
      let trimmed = value.trimmingCharacters(in: .whitespacesAndNewlines)
      if !trimmed.isEmpty { return trimmed }
    }
    return nil
  }

  private static func marksEndedPush(_ value: Any?) -> Bool {
    if let bool = value as? Bool { return bool }
    if let number = value as? NSNumber { return number.intValue != 0 }
    if let text = value as? String {
      let normalized = text.trimmingCharacters(in: .whitespacesAndNewlines).lowercased()
      return normalized == "true" || normalized == "1"
    }
    return false
  }

  private static func prefsString(_ key: String) -> String? {
    let value = UserDefaults.standard.string(forKey: "flutter.\(key)")?
      .trimmingCharacters(in: .whitespacesAndNewlines)
    if let value, !value.isEmpty { return value }
    return nil
  }
}

struct VideoCallDeclineFields {
  var conversationUuid: String
  var callId: String?
  var endedPush: Bool
}

private final class EatvioBackgroundTask {
  private let lock = NSLock()
  private var id: UIBackgroundTaskIdentifier = .invalid

  func begin(name: String) {
    let taskId = UIApplication.shared.beginBackgroundTask(withName: name) { [weak self] in
      self?.end()
    }
    lock.lock()
    id = taskId
    lock.unlock()
  }

  func end() {
    lock.lock()
    let current = id
    id = .invalid
    lock.unlock()
    guard current != .invalid else { return }
    UIApplication.shared.endBackgroundTask(current)
  }
}