vds_ios/VDS/Components/Pagination/Pagination.swift

//
//  Pagination.swift
//  VDS
//
//  Created by Bandaru, Krishna Kishore on 01/03/24.
//

import Foundation
import VDSColorTokens
import Combine

@objc(VDSPagination)
open class Pagination: View {
    
    open var onPageDidSelect: ((Int) -> Void)?

    public let previousButton: PaginationButton = .init(type: .previous)
    public let nextButton: PaginationButton = .init(type: .next)
    
    public var total: Int = 0 {
        didSet {
            previousButton.isHidden = true
            nextButton.isHidden = total <= 1
            _selectedPage = 0
            setNeedsUpdate()
        }
    }
    
    public var selectedPage: Int {
        set {
            if newValue >= total {
                _selectedPage = total - 1
            } else if newValue < 0 {
                _selectedPage = 0
            } else {
                _selectedPage = max(newValue - 1, 0)
            }
            setNeedsUpdate()
            updateSelection()
        }
        get {
            _selectedPage
        }
    }

    private var _selectedPage: Int = 0
    private let pageItemCellSize: CGSize = .init(width: 20, height: 16)
    private let spacingBetweenCell: CGFloat = VDSLayout.Spacing.space1X.value
    
    private let containerView: View = View().with {
        $0.translatesAutoresizingMaskIntoConstraints = false
    }
    
    private lazy var flowLayout: UICollectionViewFlowLayout = {
        let layout = UICollectionViewFlowLayout()
        layout.scrollDirection = .horizontal
        layout.minimumInteritemSpacing = spacingBetweenCell
        layout.minimumLineSpacing = spacingBetweenCell
        layout.sectionInset = .zero
        layout.estimatedItemSize = pageItemCellSize
        return layout
    }()
    
    private lazy var collectionView: UICollectionView = {
        let collectionView = UICollectionView(frame: .zero, collectionViewLayout: flowLayout)
        collectionView.isScrollEnabled = false
        collectionView.translatesAutoresizingMaskIntoConstraints = false
        collectionView.delegate = self
        collectionView.dataSource = self
        collectionView.showsHorizontalScrollIndicator = false
        collectionView.showsVerticalScrollIndicator = false
        collectionView.register(PaginationCellItem.self, forCellWithReuseIdentifier: PaginationCellItem.identifier)
        collectionView.backgroundColor = .clear
        return collectionView
    }()
    
    open override func initialSetup() {
        super.initialSetup()
        
        addSubview(containerView)
        containerView.pinToSuperView()
        containerView.widthAnchor.constraint(greaterThanOrEqualToConstant: 288).activate()
        containerView.heightAnchor.constraint(equalToConstant: 44).activate()
        containerView.addSubview(previousButton)
        containerView.addSubview(collectionView)
        containerView.addSubview(nextButton)
        
        previousButton
            .pinTop()
            .pinBottom()
            .pinLeading()
        previousButton.trailingAnchor.constraint(greaterThanOrEqualTo: collectionView.leadingAnchor).activate()
        collectionView.heightAnchor.constraint(equalToConstant: VDSLayout.Spacing.space4X.value).activate()
        collectionView.centerYAnchor.constraint(equalTo: centerYAnchor).activate()
        collectionView.centerXAnchor.constraint(equalTo: centerXAnchor).activate()
        collectionView.trailingAnchor.constraint(greaterThanOrEqualTo: nextButton.leadingAnchor).activate()
        collectionView.widthAnchor.constraint(equalToConstant: 92).activate()
        nextButton
            .pinTop()
            .pinBottom()
            .pinTrailing()
        nextButton.onClick = onbuttonTapped
        previousButton.onClick = onbuttonTapped
        previousButton.isHidden = true
    }
    
    open override func updateView() {
        super.updateView()
        
        nextButton.surface = surface
        previousButton.surface = surface
        collectionView.reloadData()
    }
    
    private func onbuttonTapped(_ sender: UIButton) {
        let isNextAction = sender == nextButton
        if isNextAction {
            _selectedPage += 1
        } else {
            _selectedPage -= 1
        }
        updateSelection()
    }
    
    private func updateSelection() {
        let indexPath = IndexPath(row: selectedPage, section: 0)
        collectionView.scrollToItem(at: indexPath, at: .left, animated: false)
        previousButton.isHidden = selectedPage == 0
        nextButton.isHidden = selectedPage == total - 1
        collectionView.reloadData()
    }
}

extension Pagination: UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {
    
    public func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int { total }

    public func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        guard let cell = collectionView.dequeueReusableCell(withReuseIdentifier: PaginationCellItem.identifier, for: indexPath) as? PaginationCellItem else { return UICollectionViewCell() }
        cell.update(selectedPage, currentIndex: indexPath.row, surface: surface)
        return cell
    }
    
    public func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        _selectedPage = indexPath.row
        updateSelection()
        onPageDidSelect?(indexPath.row)
    }
}