import SwiftUI

@MainActor
class BooruManager: ObservableObject {
  // MARK: - Published Properties
  @Published var posts: [BooruPost] = []
  @Published var allTags: [BooruTag] = []
  @Published var isLoading = false
  @Published var currentPage = 1
  @Published var searchText = ""
  @Published var endOfData = false
  @Published var cacheSize: String?
  @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] = []

  // MARK: - Private Properties
  private var currentTask: Task<Void, Never>?
  private let tagsCacheFileURL: URL? = FileManager.default.urls(
    for: .cachesDirectory, in: .userDomainMask
  ).first?
  .appendingPathComponent("\(BooruProvider.safebooru.asFileNameComponent)_tags.json")
  private let pageCache = NSCache<NSString, BooruPageCacheEntry>()  // swiftlint:disable:this legacy_objc_type
  private let cacheDuration: TimeInterval = 300

  // MARK: - Computed Properties
  var tags: [String] {
    searchText.isEmpty
      ? []
      : searchText
        .split(separator: " ")
        .map { $0.trimmingCharacters(in: .whitespacesAndNewlines) }
        .filter { !$0.isEmpty }
  }
  var canGoBackInHistory: Bool { historyIndex > 0 }
  var canGoForwardInHistory: Bool { historyIndex < searchHistory.count - 1 }

  // MARK: - Initialisation
  init(_ provider: BooruProvider) {
    self.provider = provider
    self.flavor = BooruProviderFlavor(provider: provider)
    self.domain = provider.domain
    pageCache.countLimit = 50
    pageCache.totalCostLimit = 50 * 1_024 * 1_024

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

    searchHistory.append(rootQuery)
    historyIndex = 0
  }

  // MARK: - Public Methods
  func initializeTags() {
    loadCachedTags()
    fetchAllTags()
    updateTagsCacheSize()
  }

  func fetchPosts(page: Int = 1, limit: Int = 100, tags: [String] = [], replace: Bool = false) async
  {
    guard !isLoading,
      let url = urlForPosts(page: flavor == .gelbooru ? page - 1 : page, limit: limit, tags: tags)
    else { return }

    let cacheKey = "\(url.absoluteString)_\(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

    currentTask?.cancel()

    currentTask = nil
    currentTask = Task {
      defer { isLoading = false }

      do {
        let (data, _) = try await URLSession.shared.data(from: url)

        guard !Task.isCancelled else { return }

        let newPosts = parsePosts(from: data).sorted { $0.id > $1.id }
        let cacheEntry = BooruPageCacheEntry(posts: newPosts, timestamp: Date())

        pageCache.setObject(cacheEntry, forKey: cacheKey)
        updatePosts(newPosts, replace: replace)
      } catch {
        if (error as? URLError)?.code != .cancelled { debugPrint("fetchPosts: \(error)") }
      }
    }
  }

  func clearPageCache() {
    pageCache.removeAllObjects()
  }

  func performSearch(settings: SettingsManager? = nil) {
    if searchHistory.last?.tags == tags { return }

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

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

    searchHistory.append(query)

    historyIndex = searchHistory.count - 1

    settings?.appendToSearchHistory(query)

    searchText = tags.joined(separator: " ")

    currentTask?.cancel()

    currentTask = nil

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

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

    Task {
      await fetchPosts(page: currentPage + 1, tags: tags)

      currentPage += 1

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

        currentQuery.page = currentPage
        searchHistory[historyIndex] = currentQuery
      }
    }
  }

  func goBackInHistory() {
    guard canGoBackInHistory else { return }

    historyIndex -= 1

    let previousQuery = searchHistory[historyIndex]

    searchText = previousQuery.tags.joined(separator: " ")
    currentPage = previousQuery.page
    posts = []

    if tags.isEmpty { clearPageCache() }

    currentTask?.cancel()

    currentTask = nil

    Task {
      await fetchPosts(page: currentPage, tags: previousQuery.tags, replace: true)
    }
  }

  func goForwardInHistory() {
    guard canGoForwardInHistory else { return }

    historyIndex += 1

    let nextQuery = searchHistory[historyIndex]

    searchText = nextQuery.tags.joined(separator: " ")
    currentPage = nextQuery.page
    posts = []

    clearPageCache()
    currentTask?.cancel()

    currentTask = nil

    Task {
      await fetchPosts(page: currentPage, tags: nextQuery.tags, replace: true)
    }
  }

  func fetchAllTags(limit: Int = 0) {
    guard let url = urlForTags(limit: limit) else { return }

    Task {
      do {
        let (data, _) = try await URLSession.shared.data(from: url)

        guard !Task.isCancelled else { return }

        allTags = BooruTagXMLParser(data: data).parse().sorted { $0.count > $1.count }

        saveTagsToCache()
      } catch {
        if (error as? URLError)?.code != .cancelled { debugPrint("fetchAllTags: \(error)") }
      }
    }
  }

  func clearCachedTags() {
    try? tagsCacheFileURL.map { url in
      try FileManager.default.removeItem(at: url)
      updateTagsCacheSize()
    }
  }

  // MARK: - Private Helpers
  private func urlForPosts(page: Int, limit: Int, tags: [String]) -> URL? {
    let tagString = tags.joined(separator: "+")

    switch flavor {
    case .danbooru:
      return URL(string: "https://\(domain)/posts.json?page=\(page)&tags=\(tagString)")

    case .moebooru:
      return URL(string: "https://\(domain)/post.xml?page=\(page)&limit=\(limit)&tags=\(tagString)")

    case .gelbooru:
      return URL(
        string:
          "https://\(domain)/index.php?page=dapi&s=post&q=index&pid=\(page)&limit=\(limit)&tags=\(tagString)"
      )
    }
  }

  private func urlForTags(limit: Int) -> URL? {
    switch flavor {
    case .moebooru:
      return URL(string: "https://\(domain)/tag.xml?limit=\(limit)")

    case .gelbooru:
      return URL(string: "https://\(domain)/index.php?page=dapi&s=tag&q=index&limit=\(limit)")

    case .danbooru:
      return nil
    }
  }

  private func parsePosts(from data: Data) -> [BooruPost] {
    Array(
      Set(
        flavor == .danbooru
          ? DanbooruPostParser(data: data).parse()
          : BooruPostXMLParser(data: data, provider: provider).parse()
      )
    )
  }

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

    endOfData = newPosts.isEmpty

    if !endOfData {
      posts = (posts + newPosts).sorted { $0.id > $1.id }

      postIndexMap.merge(
        Dictionary(uniqueKeysWithValues: newPosts.enumerated().map { ($0.element.id, $0.offset) })
      ) { _, new in new }
    }
  }

  private func saveTagsToCache() {
    try? tagsCacheFileURL.map { url in
      try JSONEncoder().encode(allTags).write(to: url)
      updateTagsCacheSize()
    }
  }

  private func loadCachedTags() {
    guard let url = tagsCacheFileURL else { return }

    if let data = try? Data(contentsOf: url),
      let tags = try? JSONDecoder().decode([BooruTag].self, from: data)
    {
      allTags = tags

      updateTagsCacheSize()
    }
  }

  func updateTagsCacheSize() {
    cacheSize = tagsCacheFileURL.flatMap { url in
      ByteCountFormatter.string(
        fromByteCount: Int64(
          (try? FileManager.default.attributesOfItem(atPath: url.path)[.size] as? Int) ?? 0
        ),
        countStyle: .file
      )
    }
  }

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