mvm_core_ui/MVMCoreUI/BaseControllers/ThreeLayerTableViewController.swift

//
//  ThreeLayerTableViewController.swift
//  MVMCoreUI
//
//  Created by Scott Pfeil on 4/18/19.
//  Copyright © 2019 Verizon Wireless. All rights reserved.
//

import UIKit
import MVMAnimationFramework

open class ThreeLayerTableViewController: ProgrammaticTableViewController {
    // The three main views
    private var topView: UIView?
    private var bottomView: UIView?
    private var headerView: UIView?
    private var footerView: UIView?
    private var safeAreaView: UIView?
    var useMargins: Bool = true
    var bottomViewOutsideOfScrollArea: Bool = false
    private var topViewBottomConstraint: NSLayoutConstraint?
    private var bottomViewTopConstraint: NSLayoutConstraint?
    
    //MARK: - MFViewController
    open override func updateViews() {
        super.updateViews()
        let width = view.bounds.width
        if let topView = topView as? MVMCoreViewProtocol {
            topView.updateView(width)
            showHeader(width)
        }
        if let bottomView = bottomView as? MVMCoreViewProtocol {
            bottomView.updateView(width)
            showFooter(width)
        }
        self.tableView?.reloadData()
    }
    
    open override func handleNewData() {
        createViewForTableHeader()
        createViewForTableFooter()
        tableView?.reloadData()
        super.handleNewData()
    }
    
    override open func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        setNoSectionHeadersFooters()
    }
    
    //MARK: - Spacing
    // If both are subclassed to return a value, then the buttons will not be pinned towards the bottom because neither spacing would try to fill the screen.
    /// Space between the top view and the table sections, nil to fill. 0 default
    open func spaceBelowTopView() -> CGFloat? {
        return 0
    }
    
    /// Space between the bottom view and the table sections, nil to fill. nil default
    open func spaceAboveBottomView() -> CGFloat? {
        return nil
    }
    
    /// can override to return a minimum fill space.
    open func minimumFillSpace() -> CGFloat {
        return 0
    }
    
    open override func updateViewConstraints() {
        super.updateViewConstraints()
        
        guard let tableView = tableView else { return }
        
        let minimumSpace: CGFloat = minimumFillSpace()
        var currentSpace: CGFloat = 0
        var totalMinimumSpace: CGFloat = 0

        var fillTop = false
        if spaceBelowTopView() == nil, self.tableView?.tableHeaderView != nil {
            fillTop = true
            currentSpace += topViewBottomConstraint?.constant ?? 0
            totalMinimumSpace += minimumSpace
        }
        
        var fillBottom = false
        if spaceAboveBottomView() == nil, !bottomViewOutsideOfScrollArea, self.tableView?.tableFooterView != nil {
            fillBottom = true
            currentSpace += bottomViewTopConstraint?.constant ?? 0
            totalMinimumSpace += minimumSpace
        }
        
        guard fillTop || fillBottom else { return }
        
        let newSpace = MVMCoreUIUtility.getVariableConstraintHeight(currentSpace, in: tableView, minimumHeight: totalMinimumSpace)
        
        // If the bottom view is outside of the scroll, then only the top view constraint is being used, so we have to double it to account for the bottom constraint not being there when we compare to the new value.
        var currentSpaceForCompare: CGFloat = currentSpace
        if fillTop && bottomViewOutsideOfScrollArea {
            currentSpaceForCompare = currentSpace * 2;
        }
        
        let width = view.bounds.width
        if !MVMCoreGetterUtility.cgfequalwiththreshold(newSpace, currentSpaceForCompare, 0.1) {
            if fillTop && fillBottom {
                // space both
                let half = newSpace / 2
                topViewBottomConstraint?.constant = half
                bottomViewTopConstraint?.constant = half
                showHeader(width)
                showFooter(width)
            } else if fillTop {
                // Only top is spaced (half the size if the bottom view is out of the scroll because it needs to be sized as if there are two spacers but there is only one.
                if bottomViewOutsideOfScrollArea {
                    topViewBottomConstraint?.constant = newSpace / 2
                } else {
                    topViewBottomConstraint?.constant = newSpace
                }
                showHeader(width)
            } else if fillBottom {
                // Only bottom is spaced.
                bottomViewTopConstraint?.constant = newSpace
                showFooter(width)
            }
        }
    }
    
    //MARK: - Header Footer
    /// Gets the top view and adds it to a spacing view, headerView, and then calls showHeader.
    open func createViewForTableHeader() {
        let topView = viewForTop()
        self.topView = topView
        
        let headerView = MVMCoreUICommonViewsUtility.commonView()
        headerView.addSubview(topView)
        topView.topAnchor.constraint(equalTo: headerView.topAnchor).isActive = true
        topView.leftAnchor.constraint(equalTo: headerView.leftAnchor).isActive = true
        headerView.rightAnchor.constraint(equalTo: topView.rightAnchor).isActive = true
        topViewBottomConstraint = headerView.bottomAnchor.constraint(equalTo: topView.bottomAnchor, constant: spaceBelowTopView() ?? 0)
        topViewBottomConstraint?.isActive = true
        self.headerView = headerView
        showHeader(nil)
    }

    /// Gets the bottom view and adds it to a spacing view, footerView, and then calls showFooter.
    open func createViewForTableFooter() {
        let bottomView = viewForBottom()
        self.bottomView = bottomView
        
        let footerView = MVMCoreUICommonViewsUtility.commonView()
        footerView.addSubview(bottomView)
        bottomViewTopConstraint = bottomView.topAnchor.constraint(equalTo: footerView.topAnchor, constant: spaceAboveBottomView() ?? 0)
        bottomViewTopConstraint?.isActive = true
        bottomView.leftAnchor.constraint(equalTo: footerView.leftAnchor).isActive = true
        footerView.rightAnchor.constraint(equalTo: bottomView.rightAnchor).isActive = true
        footerView.bottomAnchor.constraint(equalTo: bottomView.bottomAnchor).isActive = true
        self.footerView = footerView
        showFooter(nil)
    }
    
    /// Takes the current headerView and adds it to the tableHeaderView
    func showHeader(_ sizingWidth: CGFloat?) {
        headerView?.removeFromSuperview()
        tableView?.tableHeaderView = nil
        guard let headerView = headerView else {
            return
        }
        
        // This extra view is needed because of the wonkiness of apple's table header. Things breaks if using autolayout.
        headerView.setNeedsLayout()
        headerView.layoutIfNeeded()
        MVMCoreUIUtility.sizeView(toFit: headerView)
        let tableHeaderView = UIView(frame: CGRect(x: 0, y: 0, width: MVMCoreUIUtility.getWidth(), height: headerView.frame.height))
        tableHeaderView.addSubview(headerView)
        NSLayoutConstraint.constraintPinSubview(toSuperview: headerView)
        tableView?.tableHeaderView = tableHeaderView
    }
    
    /// Takes the current footerView and adds it to the tableFooterView
    func showFooter(_ sizingWidth: CGFloat?) {
        footerView?.removeFromSuperview()
        safeAreaView?.removeFromSuperview()
        guard let footerView = footerView, let tableView = tableView else {
            return
        }
        
        if bottomViewOutsideOfScrollArea {
            // put bottom view outside of scrolling area.
            bottomConstraint?.isActive = false
            view.addSubview(footerView)
            footerView.topAnchor.constraint(equalTo: tableView.bottomAnchor).isActive = true
            footerView.leftAnchor.constraint(equalTo: view.leftAnchor).isActive = true
            view.rightAnchor.constraint(equalTo: footerView.rightAnchor).isActive = true
            view.safeAreaLayoutGuide.bottomAnchor.constraint(equalTo: footerView.bottomAnchor).isActive = true
            safeAreaView = MVMCoreUICommonViewsUtility.getAndSetupSafeAreaView(on: view)
            safeAreaView?.backgroundColor = bottomView?.backgroundColor
        } else {
            bottomConstraint?.isActive = true
            var y: CGFloat?
            if let tableFooterView = tableView.tableFooterView {
                // if footer already exists, use the same y location to avoid strange moving animation
                y = tableFooterView.frame.minY
            }
            
            // This extra view is needed because of the wonkiness of apple's table footer. Things breaks if using autolayout.
            MVMCoreUIUtility.sizeView(toFit: footerView)
            let tableFooterView = UIView(frame: CGRect(x: 0, y: y ?? 0, width: MVMCoreUIUtility.getWidth(), height: footerView.frame.height))
            tableFooterView.addSubview(footerView)
            NSLayoutConstraint.constraintPinSubview(toSuperview: footerView)
            tableView.tableFooterView = tableFooterView
        }
    }
    
    //MARK: - Functions to subclass
    /// Subclass for a top view.
    open func viewForTop() -> UIView {
        let view = MVMCoreUICommonViewsUtility.commonView()
        // Small height is needed to stop apple from adding padding for grouped tables when no header.
        view.heightAnchor.constraint(equalToConstant: 1).isActive = true
        return view
    }
        
    /// Subclass for a bottom view.
    open func viewForBottom() -> UIView {
        // Default spacing is standard when no buttons.
        let view = MVMCoreUICommonViewsUtility.commonView()
        view.heightAnchor.constraint(equalToConstant: PaddingDefaultVerticalSpacing).isActive = true
        return view
    }
    
    deinit {
        tableView?.delegate = nil
    }
}