//
//  MainViewController.swift
//  LiveLikeGiphyChallenge
//
//

import UIKit

class MainViewController: UIViewController {
  static private let cellSpacing: CGFloat = 10.0
  private let viewModel = GiphyViewModel()

  fileprivate let stackView: UIStackView = {
    let stackView = UIStackView()
    stackView.distribution = .fill
    stackView.axis = .vertical
    stackView.spacing = cellSpacing
    stackView.translatesAutoresizingMaskIntoConstraints = false
    return stackView
  }()

  fileprivate let searchBar: UISearchBar = {
    let searchBar = UISearchBar(frame: .zero)
    searchBar.searchTextField.placeholder = "Search the gifs you love from Giphy"
    searchBar.returnKeyType = .search
    searchBar.translatesAutoresizingMaskIntoConstraints = false
    searchBar.heightAnchor.constraint(equalToConstant: 50).isActive = true
    return searchBar
  }()

  fileprivate let collectionView: UICollectionView = {
    let layout = UICollectionViewFlowLayout()
    layout.minimumLineSpacing = cellSpacing
    layout.minimumInteritemSpacing = cellSpacing
    let collectionView = UICollectionView(frame: .zero, collectionViewLayout: layout)
    collectionView.register(GiphyCollectionViewCell.self, forCellWithReuseIdentifier: "GiphyCollectionViewCell")
    collectionView.register(ActivityIndicatorCollectionViewCell.self, forCellWithReuseIdentifier: "ActivityIndicatorCollectionViewCell")
    collectionView.translatesAutoresizingMaskIntoConstraints = false
    return collectionView
  }()

  override func viewDidLoad() {
    super.viewDidLoad()
    view.backgroundColor = .white
    setupStackView()
    setupSearchBar()
    setupCollectionView()
    setupViewModel()
  }

  func setupStackView() {
    view.addSubview(stackView)
    stackView.addArrangedSubview(searchBar)
    stackView.addArrangedSubview(collectionView)

    NSLayoutConstraint.activate([
      stackView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor, constant: 20),
      stackView.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: 10),
      stackView.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -10),
      stackView.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 10)
    ])
  }

  func setupCollectionView() {
    collectionView.delegate = self
    collectionView.dataSource = self
  }

  func setupSearchBar() {
    searchBar.delegate = self
  }

  func setupViewModel() {
    viewModel.didFinishLoadingData = { [weak self] success in
      self?.collectionView.reloadData()
    }
    viewModel.fetchGiphyImages()
  }

}

extension MainViewController: UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {
  func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    return viewModel.items.count
  }

  func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    if !viewModel.isLoadingList {
      if let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "GiphyCollectionViewCell", for: indexPath) as? GiphyCollectionViewCell {
        let url = viewModel.items[indexPath.row]
        cell.setupCell(url: url)
        return cell
      }
    } else {
      if let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "ActivityIndicatorCollectionViewCell", for: indexPath) as? ActivityIndicatorCollectionViewCell {
        cell.spinner.startAnimating()
        return cell
      }
    }
    return UICollectionViewCell()
  }

  func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
    let itemsPerRow: CGFloat = UIDevice.current.orientation.isLandscape ? 4 : 2
    let cellSize = collectionView.frame.width / itemsPerRow - MainViewController.cellSpacing
    return CGSize(width: cellSize, height: cellSize)
  }

  func collectionView(_ collectionView: UICollectionView, willDisplay cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {
    viewModel.tryToLoadMore(row: indexPath.row)
  }

}

extension MainViewController: UISearchBarDelegate {
  func searchBar(_ searchBar: UISearchBar, textDidChange searchText: String) {
    scrollToTop()
    DispatchQueue.main.asyncAfter(deadline: .now() + 0.5) {
      self.viewModel.searchTerm = searchText
    }
  }

  func scrollToTop() {
    if !viewModel.items.isEmpty {
      collectionView.scrollToItem(at: IndexPath(item: 0, section: 0), at: .top, animated: true)
    }
  }
}