//
//  ViewController.swift
//  Sample
//
//  Copyright (c) 2014-present, Facebook, Inc.  All rights reserved.
//  This source code is licensed under the BSD-style license found in the
//  LICENSE file in the root directory of this source tree. An additional grant
//  of patent rights can be found in the PATENTS file in the same directory.
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
//  FACEBOOK BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
//  ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
//  CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//

import UIKit
import AsyncDisplayKit

final class ViewController: ASViewController<ASTableNode>, ASTableDataSource, ASTableDelegate {

  struct State {
    var itemCount: Int
    var fetchingMore: Bool
    static let empty = State(itemCount: 20, fetchingMore: false)
  }

  enum Action {
    case beginBatchFetch
    case endBatchFetch(resultCount: Int)
  }

  fileprivate(set) var state: State = .empty

  init() {
    super.init(node: ASTableNode())
    node.delegate = self
    node.dataSource = self
  }

  required init?(coder aDecoder: NSCoder) {
    fatalError("storyboards are incompatible with truth and beauty")
  }

  // MARK: ASTableView data source and delegate.

  func tableView(_ tableView: ASTableView, nodeForRowAt indexPath: IndexPath) -> ASCellNode {
    // Should read the row count directly from table view but
    // https://github.com/facebook/AsyncDisplayKit/issues/1159
    let rowCount = self.tableView(tableView, numberOfRowsInSection: 0)

    if state.fetchingMore && (indexPath as NSIndexPath).row == rowCount - 1 {
      return TailLoadingCellNode()
    }

    let node = ASTextCellNode()
    node.text = String(format: "[%ld.%ld] says hello!", (indexPath as NSIndexPath).section, (indexPath as NSIndexPath).row)

    return node
  }

  func numberOfSections(in tableView: UITableView) -> Int {
    return 1
  }

  func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    var count = state.itemCount
    if state.fetchingMore {
      count += 1
    }
    return count
  }

  func tableView(_ tableView: ASTableView, willBeginBatchFetchWith context: ASBatchContext) {
    /// This call will come in on a background thread. Switch to main
    /// to add our spinner, then fire off our fetch.
    DispatchQueue.main.async {
      let oldState = self.state
      self.state = ViewController.handleAction(.beginBatchFetch, fromState: oldState)
      self.renderDiff(oldState)
    }

    ViewController.fetchDataWithCompletion { resultCount in
      let action = Action.endBatchFetch(resultCount: resultCount)
      let oldState = self.state
      self.state = ViewController.handleAction(action, fromState: oldState)
      self.renderDiff(oldState)
      context.completeBatchFetching(true)
    }
  }

  fileprivate func renderDiff(_ oldState: State) {
    let tableView = node.view
    tableView?.beginUpdates()
	

    // Add or remove items
    let rowCountChange = state.itemCount - oldState.itemCount
    if rowCountChange > 0 {
      let indexPaths = (oldState.itemCount..<state.itemCount).map { index in
        IndexPath(row: index, section: 0)
      }
      tableView?.insertRows(at: indexPaths, with: .none)
    } else if rowCountChange < 0 {
      assertionFailure("Deleting rows is not implemented. YAGNI.")
    }

    // Add or remove spinner.
    if state.fetchingMore != oldState.fetchingMore {
      if state.fetchingMore {
        // Add spinner.
        let spinnerIndexPath = IndexPath(row: state.itemCount, section: 0)
        tableView?.insertRows(at: [ spinnerIndexPath ], with: .none)
      } else {
        // Remove spinner.
        let spinnerIndexPath = IndexPath(row: oldState.itemCount, section: 0)
        tableView?.deleteRows(at: [ spinnerIndexPath ], with: .none)
      }
    }
    tableView?.endUpdates(animated: false, completion: nil)
  }

  /// (Pretend) fetches some new items and calls the
  /// completion handler on the main thread.
  fileprivate static func fetchDataWithCompletion(_ completion: @escaping (Int) -> Void) {
    let time = DispatchTime.now() + Double(Int64(TimeInterval(NSEC_PER_SEC) * 1.0)) / Double(NSEC_PER_SEC)
    DispatchQueue.main.asyncAfter(deadline: time) {
      let resultCount = Int(arc4random_uniform(20))
      completion(resultCount)
    }
  }

  fileprivate static func handleAction(_ action: Action, fromState state: State) -> State {
    var state = state
    switch action {
    case .beginBatchFetch:
      state.fetchingMore = true
    case let .endBatchFetch(resultCount):
      state.itemCount += resultCount
      state.fetchingMore = false
    }
    return state
  }
}