// swiftlint:disable file_length

import Alamofire
import SwiftUI

@MainActor
class BooruManager: ObservableObject {  // swiftlint:disable:this type_body_length
  // MARK: - Published Properties
  @Published var posts: [BooruPost] = []
  @Published var isLoading = false
  @Published var currentPage = 1
  @Published var searchText = ""
  @Published var endOfData = false
  @Published var selectedPost: BooruPost?
  @Published var flavor: BooruProviderFlavor
  @Published var domain: String
  @Published private(set) var postIndexMap: [String: Int] = [:]
  @Published var provider: BooruProvider
  @Published var historyIndex: Int = -1
  @Published var searchHistory: [BooruSearchQuery] = []
  @Published var isNavigatingHistory = false
  @Published var error: Error?

  // MARK: - Private Properties
  private var currentTask: Task<Void, Never>?
  private let pageCache = NSCache<NSString, BooruPageCacheEntry>()  // swiftlint:disable:this legacy_objc_type
  private let cacheDuration: TimeInterval
  private let credentials: BooruProviderCredentials?
  private let referer: String
  private let userAgent: String?
  private let showHeldMoebooruPosts: Bool
  private var urlCache: [String: URL] = [:]
  private var lastPostCount = 0
  private var cachedMinimumPostID: Int?

  // MARK: - Computed Properties
  var tags: [String] {
    searchText.isEmpty
      ? []
      : searchText
        .components(separatedBy: .whitespaces)
        .filter { !$0.isEmpty }
  }
  var canGoBackInHistory: Bool { historyIndex > 0 }
  var canGoForwardInHistory: Bool { historyIndex < searchHistory.count - 1 }

  // MARK: - Initialisation
  init(
    _ provider: BooruProvider,
    credentials: BooruProviderCredentials? = nil,
    cacheDuration: TimeInterval = BooruPageCacheEntry.defaultExpiration,
    sendUserAgent: Bool = true,
    customUserAgent: String = "",
    showHeldMoebooruPosts: Bool = false
  ) {
    self.provider = provider
    self.flavor = BooruProviderFlavor(provider: provider)
    self.domain = provider.domain
    self.credentials = credentials
    self.cacheDuration = cacheDuration
    self.showHeldMoebooruPosts = showHeldMoebooruPosts
    pageCache.countLimit = 50
    pageCache.totalCostLimit = 50 * 1_024 * 1_024

    self.referer = BooruRequestConfiguration.baseReferer(for: provider.domain)
    self.userAgent = BooruRequestConfiguration.resolvedUserAgent(
      sendUserAgent: sendUserAgent,
      customUserAgent: customUserAgent
    )

    let rootQuery = BooruSearchQuery(
      provider: provider,
      tags: []
    )

    searchHistory.append(rootQuery)

    historyIndex = 0
  }

  // MARK: - Public Methods
  func fetchPosts(page: Int = 1, limit: Int = 100, tags: [String] = [], replace: Bool = false) async
  {
    guard !isLoading else { return }

    let pageValue = flavor == .gelbooru ? page - 1 : page
    guard let url = url(forPosts: pageValue, limit: limit, tags: tags) else { return }
    let cacheKey = "\(url.absoluteString.hashValue)_\(replace)" as NSString  // swiftlint:disable:this legacy_objc_type

    if let cachedEntry = pageCache.object(forKey: cacheKey),
      !cachedEntry.isExpired
    {
      isLoading = true

      defer { isLoading = false }

      updatePosts(cachedEntry.posts, replace: replace)

      return
    }

    isLoading = true

    defer { isLoading = false }

    let finalPosts = await fetchPostsWithRetry(url: url)

    if Task.isCancelled { return }

    let cacheEntry = BooruPageCacheEntry(
      posts: finalPosts,
      timestamp: Date(),
      expiration: cacheDuration
    )

    pageCache.setObject(cacheEntry, forKey: cacheKey, cost: finalPosts.count)

    withAnimation(nil) {
      updatePosts(finalPosts, replace: replace)
    }
  }

  private func fetchPostsWithRetry(url: URL) async -> [BooruPost] {
    let maxAttempts = 4
    var requestURL = url
    var retriedDanbooruWithoutCredentials = false

    for attempt in 1...maxAttempts {
      if Task.isCancelled { return [] }

      do {
        let data = try await self.requestURL(requestURL)

        if Task.isCancelled { return [] }

        let flavor = self.flavor
        let provider = self.provider
        let newPosts = await withCheckedContinuation { continuation in
          DispatchQueue.global(qos: .userInitiated).async {
            let parsedPosts = Self.parsePosts(
              from: data,
              flavor: flavor,
              provider: provider
            )

            continuation.resume(returning: parsedPosts)
          }
        }

        if Task.isCancelled { return [] }

        if !newPosts.isEmpty {
          return newPosts
        }

        if attempt < maxAttempts {
          try await Task.sleep(for: .seconds(0.5 * Double(attempt)))
        }
      } catch {
        if !Task.isCancelled {
          if flavor == .danbooru,
            !retriedDanbooruWithoutCredentials,
            (error as? AFError)?.responseCode == 401,
            let unauthenticatedURL = Self.removingDanbooruCredentials(from: requestURL),
            unauthenticatedURL != requestURL
          {
            retriedDanbooruWithoutCredentials = true
            requestURL = unauthenticatedURL

            debugPrint(
              "BooruManager.fetchPosts(\(attempt)): unauthorized credentials for \(domain),"
                + " retrying without API credentials."
            )

            continue
          }

          self.error = error

          debugPrint("BooruManager.fetchPosts(\(attempt)): \(error)")
        }

        break
      }
    }

    return []
  }

  private static func removingDanbooruCredentials(from url: URL) -> URL? {
    guard var components = URLComponents(url: url, resolvingAgainstBaseURL: false) else {
      return nil
    }
    guard let existingQueryItems = components.queryItems else {
      return components.url
    }

    components.queryItems = existingQueryItems.filter { queryItem in
      queryItem.name != "login" && queryItem.name != "api_key"
    }

    return components.url
  }

  func clearCachedPages() {
    pageCache.removeAllObjects()
    urlCache.removeAll()
  }

  func performSearch(settings: SettingsManager? = nil) async {
    let inputTags = tags

    guard !inputTags.isEmpty else { return }

    if searchHistory.last?.tags == inputTags { return }

    if historyIndex < searchHistory.count - 1 {
      searchHistory = Array(searchHistory[0...historyIndex])
    }

    let query = BooruSearchQuery(
      provider: settings?.preferredBooru ?? provider,
      tags: inputTags
    )

    searchHistory.append(query)

    historyIndex = searchHistory.count - 1

    settings?.appendToSearchHistory(query)

    searchText = inputTags.joined(separator: " ")

    await fetchPosts(page: 1, tags: inputTags, replace: true)
  }

  func loadNextPage() async {
    guard !isLoading else { return }

    currentPage += 1

    await fetchPosts(page: currentPage, tags: tags)

    if historyIndex >= 0, historyIndex < searchHistory.count {
      var currentQuery = searchHistory[historyIndex]

      currentQuery.page = currentPage

      searchHistory[historyIndex] = currentQuery
    }
  }

  func goBackInHistory() {
    guard canGoBackInHistory else { return }

    isNavigatingHistory = true
    historyIndex -= 1

    let previousQuery = searchHistory[historyIndex]

    if previousQuery.provider != provider {
      provider = previousQuery.provider
      flavor = BooruProviderFlavor(provider: provider)
      domain = provider.domain
    }

    searchText = previousQuery.tags.joined(separator: " ")

    cancelCurrentTask()

    currentTask = Task {
      await fetchPosts(page: 1, tags: previousQuery.tags, replace: true)

      isNavigatingHistory = false
    }
  }

  func goForwardInHistory() {
    guard canGoForwardInHistory else { return }

    historyIndex += 1
    isNavigatingHistory = true

    let nextQuery = searchHistory[historyIndex]

    if nextQuery.provider != provider {
      provider = nextQuery.provider
      flavor = BooruProviderFlavor(provider: provider)
      domain = provider.domain
    }

    searchText = nextQuery.tags.joined(separator: " ")

    cancelCurrentTask()

    currentTask = Task {
      await fetchPosts(page: 1, tags: nextQuery.tags, replace: true)

      isNavigatingHistory = false
    }
  }

  func searchTags(name: String) async -> [BooruTag] {
    guard let url = url(forTagsSearch: name) else { return [] }

    do {
      let data = try await requestURL(url)

      guard !Task.isCancelled else { return [] }

      let parsedTags =
        if flavor == .danbooru {
          DanbooruTagParser(data: data).parse()
        } else if flavor == .gelbooru, provider != .safebooru {
          GelbooruAutocompleteTagParser(data: data).parse()
        } else {
          BooruTagXMLParser(data: data).parse()
        }

      return parsedTags.sorted { $0.count > $1.count }
    } catch {
      if (error as? URLError)?.code != .cancelled {
        debugPrint("BooruManager.searchTags: \(error)")
      }

      return []
    }
  }

  // MARK: - Private Methods
  private func moebooruTagString(for tags: [String]) -> String {
    let hasExplicitHoldsFilter = tags.contains { tag in
      tag.lowercased().hasPrefix("holds:")
    }

    if hasExplicitHoldsFilter {
      return tags.joined(separator: "+")
    }

    guard !showHeldMoebooruPosts else {
      return tags.joined(separator: "+")
    }

    return (tags + ["holds:false"]).joined(separator: "+")
  }

  private func hasExplicitSortTag(in tags: [String]) -> Bool {
    tags.contains { tag in
      tag.lowercased().hasPrefix("order:")
    }
  }

  private func danbooruPageToken(for page: Int, tags: [String]) -> String {
    guard page > 1 else { return "1" }
    guard !hasExplicitSortTag(in: tags) else { return String(page) }

    guard let minimumPostID = cachedMinimumPostID else { return String(page) }

    return "b\(minimumPostID)"
  }

  func url(forPosts page: Int, limit: Int, tags: [String]) -> URL? {
    let tagString = tags.joined(separator: "+")
    let pageCacheValue =
      flavor == .danbooru ? danbooruPageToken(for: page, tags: tags) : String(page)
    let cacheKey = "posts_\(pageCacheValue)_\(limit)_\(tagString.hashValue)"

    if let cachedURL = urlCache[cacheKey] {
      return cachedURL
    }

    let url: URL?

    switch flavor {
    case .danbooru:
      var components = URLComponents()

      components.scheme = "https"
      components.host = domain
      components.path = "/posts.json"

      var queryItems = [
        URLQueryItem(name: "page", value: danbooruPageToken(for: page, tags: tags)),
        URLQueryItem(name: "limit", value: String(limit)),
        URLQueryItem(name: "tags", value: tagString),
      ]

      if let validCredentials = credentials {
        let login = validCredentials.login.trimmingCharacters(in: .whitespacesAndNewlines)

        if !validCredentials.apiKey.isEmpty, !login.isEmpty {
          queryItems.append(URLQueryItem(name: "login", value: login))
          queryItems.append(URLQueryItem(name: "api_key", value: validCredentials.apiKey))
        }
      }

      components.queryItems = queryItems
      url = components.url

    case .moebooru:
      var components = URLComponents()
      let moebooruTags = moebooruTagString(for: tags)

      components.scheme = "https"
      components.host = domain
      components.path = "/post.xml"
      components.queryItems = [
        URLQueryItem(name: "page", value: String(page)),
        URLQueryItem(name: "limit", value: String(limit)),
        URLQueryItem(name: "tags", value: moebooruTags),
      ]
      url = components.url

    case .gelbooru:
      var components = URLComponents()

      components.scheme = "https"
      components.host = domain
      components.path = "/index.php"

      var queryItems = [
        URLQueryItem(name: "page", value: "dapi"),
        URLQueryItem(name: "s", value: "post"),
        URLQueryItem(name: "q", value: "index"),
        URLQueryItem(name: "pid", value: String(page)),
        URLQueryItem(name: "limit", value: String(limit)),
        URLQueryItem(name: "tags", value: tagString),
      ]

      if let validCredentials = credentials,
        !validCredentials.apiKey.isEmpty,
        validCredentials.userID != 0
      {
        queryItems.append(URLQueryItem(name: "api_key", value: validCredentials.apiKey))
        queryItems.append(URLQueryItem(name: "user_id", value: String(validCredentials.userID)))
      }

      components.queryItems = queryItems
      url = components.url
    }

    if let constructedURL = url {
      urlCache[cacheKey] = constructedURL
    }

    return url
  }

  private func url(forTags limit: Int, order: String = "count") -> URL? {
    switch flavor {
    case .moebooru:
      var components = URLComponents()

      components.scheme = "https"
      components.host = domain
      components.path = "/tag.xml"
      components.queryItems = [
        URLQueryItem(name: "limit", value: String(limit)),
        URLQueryItem(name: "order", value: order),
      ]

      return components.url

    case .gelbooru:
      var components = URLComponents()

      components.scheme = "https"
      components.host = domain
      components.path = "/index.php"
      components.queryItems = [
        URLQueryItem(name: "page", value: "dapi"),
        URLQueryItem(name: "s", value: "tag"),
        URLQueryItem(name: "q", value: "index"),
        URLQueryItem(name: "limit", value: String(limit)),
        URLQueryItem(name: "orderby", value: order),
      ]

      return components.url

    case .danbooru:
      return nil
    }
  }

  private func url(forTagsSearch name: String) -> URL? {
    switch flavor {
    case .moebooru:
      var components = URLComponents()

      components.scheme = "https"
      components.host = domain
      components.path = "/tag.xml"
      components.queryItems = [
        URLQueryItem(name: "name", value: name),
        URLQueryItem(name: "order", value: "count"),
      ]

      return components.url

    case .gelbooru:
      var components = URLComponents()

      components.scheme = "https"
      components.host = domain
      components.path = "/index.php"

      if provider == .safebooru {
        components.queryItems = [
          URLQueryItem(name: "page", value: "dapi"),
          URLQueryItem(name: "s", value: "tag"),
          URLQueryItem(name: "q", value: "index"),
          URLQueryItem(name: "name_pattern", value: "%\(name)%"),
          URLQueryItem(name: "orderby", value: "count"),
        ]
      } else {
        components.queryItems = [
          URLQueryItem(name: "page", value: "autocomplete2"),
          URLQueryItem(name: "type", value: "tag_query"),
          URLQueryItem(name: "term", value: name),
        ]
      }

      return components.url

    case .danbooru:
      var components = URLComponents()

      components.scheme = "https"
      components.host = domain
      components.path = "/tags.json"
      components.queryItems = [
        URLQueryItem(name: "search[name_matches]", value: "\(name)*"),
        URLQueryItem(name: "limit", value: "50"),
      ]

      return components.url
    }
  }

  nonisolated static func parsePosts(
    from data: Data,
    flavor: BooruProviderFlavor,
    provider: BooruProvider
  ) -> [BooruPost] {
    let parsedPosts =
      flavor == .danbooru
      ? DanbooruPostParser(data: data).parse()
      : BooruPostXMLParser(data: data, provider: provider).parse()

    var seenPostIDs = Set<String>()
    var orderedUniquePosts: [BooruPost] = []

    for post in parsedPosts where seenPostIDs.insert(post.id).inserted {
      orderedUniquePosts.append(post)
    }

    return orderedUniquePosts
  }

  private func updatePosts(_ newPosts: [BooruPost], replace: Bool) {
    if replace {
      posts = []
      currentPage = 1

      postIndexMap.removeAll()

      lastPostCount = 0
      cachedMinimumPostID = nil
    }

    endOfData = newPosts.isEmpty

    guard !endOfData else { return }

    if let nextMinimumPostID = newPosts.lazy.compactMap({ Int($0.id) }).min() {
      cachedMinimumPostID = min(cachedMinimumPostID ?? nextMinimumPostID, nextMinimumPostID)
    }

    withTransaction(Transaction(animation: nil)) {
      let oldCount = self.posts.count

      self.posts += newPosts

      if newPosts.count > 10 || self.posts.count - lastPostCount > 50 {
        for (offset, post) in newPosts.enumerated() {
          self.postIndexMap[post.id] = oldCount + offset
        }

        lastPostCount = self.posts.count
      }
    }
  }

  func requestURL(_ url: URL) async throws -> Data {
    let request = BooruRequestConfiguration.request(
      url: url,
      referer: referer,
      userAgent: userAgent
    )

    return try await AF.request(request)
      .validate(statusCode: 200..<300)
      .serializingData()
      .value
  }

  private func cancelCurrentTask() {
    currentTask?.cancel()

    currentTask = nil
  }

  // MARK: - Deinitialisation
  nonisolated deinit {
    currentTask?.cancel()
    urlCache.removeAll()
  }
}