Tusker/Tusker/Screens/Search/SearchResultsViewController.swift

//
//  SearchResultsViewController.swift
//  Tusker
//
//  Created by Shadowfacts on 9/14/19.
//  Copyright © 2019 Shadowfacts. All rights reserved.
//

import UIKit
import Combine
import Pachyderm

fileprivate let accountCell = "accountCell"
fileprivate let statusCell = "statusCell"
fileprivate let hashtagCell = "hashtagCell"

protocol SearchResultsViewControllerDelegate: class {
    func selectedSearchResult(account accountID: String)
    func selectedSearchResult(hashtag: Hashtag)
    func selectedSearchResult(status statusID: String)
}

extension SearchResultsViewControllerDelegate {
    func selectedSearchResult(account accountID: String) {}
    func selectedSearchResult(hashtag: Hashtag) {}
    func selectedSearchResult(status statusID: String) {}
}

class SearchResultsViewController: EnhancedTableViewController {

    weak var exploreNavigationController: UINavigationController?
    weak var delegate: SearchResultsViewControllerDelegate?
    
    var dataSource: UITableViewDiffableDataSource<Section, Item>!

    var activityIndicator: UIActivityIndicatorView!
    
    var onlySections: [Section] = Section.allCases
    
    let searchSubject = PassthroughSubject<String?, Never>()
    var currentQuery: String?
    
    init() {
        super.init(style: .grouped)
        
        title = NSLocalizedString("Search", comment: "search screen title")
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()

        tableView.register(UINib(nibName: "AccountTableViewCell", bundle: .main), forCellReuseIdentifier: accountCell)
        tableView.register(UINib(nibName: "TimelineStatusTableViewCell", bundle: .main), forCellReuseIdentifier: statusCell)
        tableView.register(UINib(nibName: "HashtagTableViewCell", bundle: .main), forCellReuseIdentifier: hashtagCell)
        
        dataSource = DataSource(tableView: tableView, cellProvider: { (tableView, indexPath, item) -> UITableViewCell? in
            switch item {
            case let .account(id):
                let cell = tableView.dequeueReusableCell(withIdentifier: accountCell, for: indexPath) as! AccountTableViewCell
                cell.updateUI(accountID: id)
                cell.delegate = self
                return cell
            case let .hashtag(tag):
                let cell = tableView.dequeueReusableCell(withIdentifier: hashtagCell, for: indexPath) as! HashtagTableViewCell
                cell.updateUI(hashtag: tag)
                cell.delegate = self
                return cell
            case let .status(id, state):
                let cell = tableView.dequeueReusableCell(withIdentifier: statusCell, for: indexPath) as! TimelineStatusTableViewCell
                cell.updateUI(statusID: id, state: state)
                cell.delegate = self
                return cell
            }
        })
        
        activityIndicator = UIActivityIndicatorView(style: .large)
        activityIndicator.translatesAutoresizingMaskIntoConstraints = false
        activityIndicator.isHidden = true
        view.addSubview(activityIndicator)
        NSLayoutConstraint.activate([
            activityIndicator.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            activityIndicator.topAnchor.constraint(equalTo: view.topAnchor, constant: 8)
        ])

        _ = searchSubject
            .debounce(for: .milliseconds(500), scheduler: RunLoop.main)
            .map { $0?.trimmingCharacters(in: .whitespacesAndNewlines) }
            .filter { $0 != self.currentQuery }
            .sink(receiveValue: performSearch(query:))

        userActivity = UserActivityManager.searchActivity()
    }
    
    override func targetViewController(forAction action: Selector, sender: Any?) -> UIViewController? {
        // if we're showing a view controller, we need to go up to the explore VC's nav controller
        // the UISearchController that is our parent is not part of the normal VC hierarchy and itself doesn't have a parent
        if action == #selector(UIViewController.show(_:sender:)),
            let exploreNavController = exploreNavigationController {
            return exploreNavController
        }
        return super.targetViewController(forAction: action, sender: sender)
    }
    
    func performSearch(query: String?) {
        guard let query = query, !query.isEmpty else {
            self.dataSource.apply(NSDiffableDataSourceSnapshot<Section, Item>())
            return
        }
        self.currentQuery = query

        if self.dataSource.snapshot().numberOfItems == 0 {
            activityIndicator.isHidden = false
            activityIndicator.startAnimating()
        }

        let request = MastodonController.client.search(query: query, resolve: true, limit: 10)
        MastodonController.client.run(request) { (response) in
            guard case let .success(results, _) = response else { fatalError() }

            DispatchQueue.main.async {
                self.activityIndicator.isHidden = true
                self.activityIndicator.stopAnimating()
            }

            guard self.currentQuery == query else { return }

            var snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
            if self.onlySections.contains(.accounts) && !results.accounts.isEmpty {
                snapshot.appendSections([.accounts])
                snapshot.appendItems(results.accounts.map { .account($0.id) }, toSection: .accounts)
                MastodonCache.addAll(accounts: results.accounts)
            }
            if self.onlySections.contains(.hashtags) && !results.hashtags.isEmpty {
                snapshot.appendSections([.hashtags])
                snapshot.appendItems(results.hashtags.map { .hashtag($0) }, toSection: .hashtags)
            }
            if self.onlySections.contains(.statuses) && !results.statuses.isEmpty {
                snapshot.appendSections([.statuses])
                snapshot.appendItems(results.statuses.map { .status($0.id, .unknown) }, toSection: .statuses)
                MastodonCache.addAll(statuses: results.statuses)
                MastodonCache.addAll(accounts: results.statuses.map { $0.account })
            }
            self.dataSource.apply(snapshot)
        }
    }
    
    // MARK: - Table view delegate
    
    override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
        if let delegate = delegate {
            switch dataSource.itemIdentifier(for: indexPath) {
            case nil:
                return
            case let .account(id):
                delegate.selectedSearchResult(account: id)
            case let .hashtag(hashtag):
                delegate.selectedSearchResult(hashtag: hashtag)
            case let .status(id, _):
                delegate.selectedSearchResult(status: id)
            }
        } else {
            super.tableView(tableView, didSelectRowAt: indexPath)
        }
    }

}

extension SearchResultsViewController {
    enum Section: CaseIterable {
        case accounts
        case hashtags
        case statuses

        var displayName: String {
            switch self {
            case .accounts:
                return NSLocalizedString("People", comment: "accounts search results section")
            case .hashtags:
                return NSLocalizedString("Hashtags", comment: "hashtag search results section")
            case .statuses:
                return NSLocalizedString("Posts", comment: "statuses search results section")
            }
        }
    }
    enum Item: Hashable {
        case account(String)
        case hashtag(Hashtag)
        case status(String, StatusState)
    }
    
    class DataSource: UITableViewDiffableDataSource<Section, Item> {
        override func tableView(_ tableView: UITableView, titleForHeaderInSection sectionIndex: Int) -> String? {
            let currentSnapshot = snapshot()
            for section in Section.allCases where currentSnapshot.indexOfSection(section) == sectionIndex {
                return section.displayName
            }
            return nil
        }
    }
}

extension SearchResultsViewController: UISearchResultsUpdating {
    func updateSearchResults(for searchController: UISearchController) {
        searchSubject.send(searchController.searchBar.text)
    }
}

extension SearchResultsViewController: UISearchBarDelegate {
    func searchBarTextDidEndEditing(_ searchBar: UISearchBar) {
        // perform a search immedaitely when the search button is pressed
        performSearch(query: searchBar.text?.trimmingCharacters(in: .whitespacesAndNewlines))
    }
}

extension SearchResultsViewController: StatusTableViewCellDelegate {
    func statusCellCollapsedStateChanged(_ cell: BaseStatusTableViewCell) {
        tableView.beginUpdates()
        tableView.endUpdates()
    }
}