//
//  SelfSizingCollectionView.swift
//  VDS
//
//  Created by Matt Bruce on 11/18/22.
//

import Foundation
import UIKit
import Combine

/// UICollectionView subclassed to deal with Changing the size of itself based on its children and layout and changes of its contentSize.
@objc(VDSSelfSizingCollectionView)
public final class SelfSizingCollectionView: UICollectionView {

    //--------------------------------------------------
    // MARK: - Initialization
    //--------------------------------------------------
    
    /// Initializer
    /// - Parameters:
    ///   - frame: Frame needed
    ///   - layout: Layout used for this CollectionView
    public override init(frame: CGRect, collectionViewLayout layout: UICollectionViewLayout) {
        super.init(frame: frame, collectionViewLayout: layout)
        self.initialSetup()
    }

    public required init?(coder: NSCoder) {
        super.init(coder: coder)
        self.initialSetup()
    }
    
    //--------------------------------------------------
    // MARK: - Private Properties
    //--------------------------------------------------
    private var collectionViewHeight: NSLayoutConstraint?
    private var anyCancellable: AnyCancellable?
    private var contentSizeSubject = CurrentValueSubject<CGSize, Never>(.zero)
    
    //--------------------------------------------------
    // MARK: - Public Properties
    //--------------------------------------------------
    public var contentSizePublisher: AnyPublisher<CGSize, Never> {
        contentSizeSubject.eraseToAnyPublisher()
    }
    
    //--------------------------------------------------
    // MARK: - Overrides
    //--------------------------------------------------
 
    /// The natural size for the receiving view, considering only properties of the view itself.
    public override var intrinsicContentSize: CGSize {
        let contentSize = self.contentSize
        return CGSize(width: UIView.noIntrinsicMetric, height: contentSize.height)
    }
    
    /// Overridden to deal with Appearance Changes
    public override func traitCollectionDidChange(_ previousTraitCollection: UITraitCollection?) {
        //print(type(of: self), #function)
        super.traitCollectionDidChange(previousTraitCollection)

        // We need to handle any change that will affect layout and/or anything that affects size of a UILabel
        if self.traitCollection.hasDifferentTextAppearance(comparedTo: previousTraitCollection) {
            self.collectionViewLayout.invalidateLayout()
        }
    }
    
    //--------------------------------------------------
    // MARK: - Private Methods
    //--------------------------------------------------
    private func initialSetup() {
        //ensure this hasn't run before
        guard anyCancellable == nil else { return }
        
        //ensure autoLayout uses intrinsic height
        setContentHuggingPriority(.required, for: .vertical)
        setContentCompressionResistancePriority(.required, for: .vertical)
        collectionViewHeight = height(constant: 0, priority: .defaultHigh)
        
        anyCancellable = self.publisher(for: \.contentSize, options: [.new, .old])
            .sink { [weak self] compare in
                
                guard let self,
                      let currentHeight = self.collectionViewHeight?.constant,
                      compare.height != currentHeight else { return }
                
                self.invalidateIntrinsicContentSize()
                self.collectionViewHeight?.constant = compare.height
                self.contentSizeSubject.send(compare)
            }
    }
    
    deinit {
        anyCancellable?.cancel()
    }
}

extension UITraitCollection {
    
    /// Used within SelfSizingCollectionView to determine if there is an appearance change.
    /// - Parameter traitCollection: TraitCollection to compare.
    /// - Returns: True/False based on the trailCollection passed in.
    public func hasDifferentTextAppearance(comparedTo traitCollection: UITraitCollection?) -> Bool {
        var result = self.preferredContentSizeCategory != traitCollection?.preferredContentSizeCategory
        result = result || self.legibilityWeight != traitCollection?.legibilityWeight
        return result
    }
}