// Copyright © 2022 Rangeproof Pty Ltd. All rights reserved.

import Foundation
import Combine
import NVActivityIndicatorView
import SessionMessagingKit
import SessionUIKit

final class OpenGroupSuggestionGrid: UIView, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {
    private let itemsPerSection: Int = (UIDevice.current.isIPad ? 4 : 2)
    private var maxWidth: CGFloat
    private var rooms: [OpenGroupAPI.Room] = [] { didSet { update() } }
    private var heightConstraint: NSLayoutConstraint!
    
    var delegate: OpenGroupSuggestionGridDelegate?
    
    // MARK: - UI
    
    private static let cellHeight: CGFloat = 40
    private static let separatorWidth = Values.separatorThickness
    fileprivate static let numHorizontalCells: Int = (UIDevice.current.isIPad ? 4 : 2)
    
    private lazy var layout: LastRowCenteredLayout = {
        let result = LastRowCenteredLayout()
        result.minimumLineSpacing = Values.mediumSpacing
        result.minimumInteritemSpacing = Values.mediumSpacing
        
        return result
    }()
    
    private lazy var collectionView: UICollectionView = {
        let result = UICollectionView(frame: .zero, collectionViewLayout: layout)
        result.themeBackgroundColor = .clear
        result.isScrollEnabled = false
        result.register(view: Cell.self)
        result.dataSource = self
        result.delegate = self
        
        return result
    }()
    
    private let spinner: NVActivityIndicatorView = {
        let result: NVActivityIndicatorView = NVActivityIndicatorView(
            frame: CGRect.zero,
            type: .circleStrokeSpin,
            color: .black,
            padding: nil
        )
        result.set(.width, to: OpenGroupSuggestionGrid.cellHeight)
        result.set(.height, to: OpenGroupSuggestionGrid.cellHeight)
        
        ThemeManager.onThemeChange(observer: result) { [weak result] theme, _ in
            guard let textPrimary: UIColor = theme.color(for: .textPrimary) else { return }
            
            result?.color = textPrimary
        }
        
        return result
    }()

    private lazy var errorView: UIView = {
        let result: UIView = UIView()
        result.isHidden = true
        
        return result
    }()
    
    private lazy var errorImageView: UIImageView = {
        let result: UIImageView = UIImageView(image: #imageLiteral(resourceName: "warning").withRenderingMode(.alwaysTemplate))
        result.themeTintColor = .danger
        
        return result
    }()
    
    private lazy var errorTitleLabel: UILabel = {
        let result: UILabel = UILabel()
        result.font = .systemFont(ofSize: Values.mediumFontSize, weight: .medium)
        result.text = "DEFAULT_OPEN_GROUP_LOAD_ERROR_TITLE".localized()
        result.themeTextColor = .textPrimary
        result.textAlignment = .center
        result.numberOfLines = 0
        
        return result
    }()
    
    private lazy var errorSubtitleLabel: UILabel = {
        let result: UILabel = UILabel()
        result.font = .systemFont(ofSize: Values.smallFontSize, weight: .medium)
        result.text = "DEFAULT_OPEN_GROUP_LOAD_ERROR_SUBTITLE".localized()
        result.themeTextColor = .textPrimary
        result.textAlignment = .center
        result.numberOfLines = 0
        
        return result
    }()
    
    // MARK: - Initialization
    
    init(maxWidth: CGFloat) {
        self.maxWidth = maxWidth
        
        super.init(frame: CGRect.zero)
        
        initialize()
    }
    
    override init(frame: CGRect) {
        preconditionFailure("Use init(maxWidth:) instead.")
    }
    
    required init?(coder: NSCoder) {
        preconditionFailure("Use init(maxWidth:) instead.")
    }
    
    private func initialize() {
        addSubview(collectionView)
        collectionView.pin(to: self)
        
        addSubview(spinner)
        spinner.pin(.top, to: .top, of: self)
        spinner.center(.horizontal, in: self)
        spinner.startAnimating()
        
        addSubview(errorView)
        errorView.pin(.top, to: .top, of: self, withInset: 10)
        errorView.pin( [HorizontalEdge.leading, HorizontalEdge.trailing], to: self)
        
        errorView.addSubview(errorImageView)
        errorImageView.pin(.top, to: .top, of: errorView)
        errorImageView.center(.horizontal, in: errorView)
        errorImageView.set(.width, to: 60)
        errorImageView.set(.height, to: 60)
        
        errorView.addSubview(errorTitleLabel)
        errorTitleLabel.pin(.top, to: .bottom, of: errorImageView, withInset: 10)
        errorTitleLabel.center(.horizontal, in: errorView)
        
        errorView.addSubview(errorSubtitleLabel)
        errorSubtitleLabel.pin(.top, to: .bottom, of: errorTitleLabel, withInset: 20)
        errorSubtitleLabel.center(.horizontal, in: errorView)
        
        heightConstraint = set(.height, to: OpenGroupSuggestionGrid.cellHeight)
        widthAnchor.constraint(greaterThanOrEqualToConstant: OpenGroupSuggestionGrid.cellHeight).isActive = true
        
        OpenGroupManager.getDefaultRoomsIfNeeded()
            .subscribe(on: DispatchQueue.global(qos: .default))
            .receive(on: DispatchQueue.main, immediatelyIfMain: true)
            .sinkUntilComplete(
                receiveCompletion: { [weak self] _ in self?.update() },
                receiveValue: { [weak self] rooms in self?.rooms = rooms }
            )
    }
    
    // MARK: - Updating
    
    private func update() {
        spinner.stopAnimating()
        spinner.isHidden = true
        
        let roomCount: CGFloat = CGFloat(min(rooms.count, 8)) // Cap to a maximum of 8 (4 rows of 2)
        let numRows: CGFloat = ceil(roomCount / CGFloat(OpenGroupSuggestionGrid.numHorizontalCells))
        let height: CGFloat = ((OpenGroupSuggestionGrid.cellHeight * numRows) + ((numRows - 1) * layout.minimumLineSpacing))
        heightConstraint.constant = height
        collectionView.reloadData()
        errorView.isHidden = (roomCount > 0)
    }
    
    public func refreshLayout(with maxWidth: CGFloat) {
        self.maxWidth = maxWidth
        collectionView.collectionViewLayout.invalidateLayout()
    }
    
    // MARK: - Layout
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        let totalItems: Int = collectionView.numberOfItems(inSection: indexPath.section)
        let itemsInFinalRow: Int = (totalItems % OpenGroupSuggestionGrid.numHorizontalCells)
        
        guard indexPath.item >= (totalItems - itemsInFinalRow) && itemsInFinalRow != 0 else {
            let cellWidth: CGFloat = ((maxWidth / CGFloat(OpenGroupSuggestionGrid.numHorizontalCells)) - ((CGFloat(OpenGroupSuggestionGrid.numHorizontalCells) - 1) * layout.minimumInteritemSpacing))
            
            return CGSize(width: cellWidth, height: OpenGroupSuggestionGrid.cellHeight)
        }
        
        // If there isn't an even number of items then we want to calculate proper sizing
        return CGSize(
            width: Cell.calculatedWith(for: rooms[indexPath.item].name),
            height: OpenGroupSuggestionGrid.cellHeight
        )
    }
    
    // MARK: - Data Source
    
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return min(rooms.count, 8) // Cap to a maximum of 8 (4 rows of 2)
    }
    
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell: Cell = collectionView.dequeue(type: Cell.self, for: indexPath)
        cell.room = rooms[indexPath.item]
        
        return cell
    }
    
    // MARK: - Interaction
    
    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        let room = rooms[indexPath.section * itemsPerSection + indexPath.item]
        delegate?.join(room)
    }
}

// MARK: - Cell

extension OpenGroupSuggestionGrid {
    fileprivate final class Cell: UICollectionViewCell {
        private static let labelFont: UIFont = .systemFont(ofSize: Values.smallFontSize)
        private static let imageSize: CGFloat = 30
        private static let itemPadding: CGFloat = Values.smallSpacing
        private static let contentLeftPadding: CGFloat = 7
        private static let contentRightPadding: CGFloat = Values.veryLargeSpacing
        
        fileprivate static func calculatedWith(for title: String) -> CGFloat {
            // FIXME: Do the calculations properly in the 'LastRowCenteredLayout' to handle imageless cells
            return (
                contentLeftPadding +
                imageSize +
                itemPadding +
                NSAttributedString(string: title, attributes: [ .font: labelFont ]).size().width +
                contentRightPadding +
                1   // Not sure why this is needed but it seems things are sometimes truncated without it
            )
        }
        
        var room: OpenGroupAPI.Room? { didSet { update() } }
        
        private lazy var snContentView: UIView = {
            let result: UIView = UIView()
            result.themeBorderColor = .borderSeparator
            result.layer.cornerRadius = Cell.contentViewCornerRadius
            result.layer.borderWidth = 1
            result.set(.height, to: Cell.contentViewHeight)
            
            return result
        }()
        
        private lazy var imageView: UIImageView = {
            let result: UIImageView = UIImageView()
            result.set(.width, to: Cell.imageSize)
            result.set(.height, to: Cell.imageSize)
            result.layer.cornerRadius = (Cell.imageSize / 2)
            result.clipsToBounds = true
            
            return result
        }()
        
        private lazy var label: UILabel = {
            let result: UILabel = UILabel()
            result.font = Cell.labelFont
            result.themeTextColor = .textPrimary
            result.lineBreakMode = .byTruncatingTail
            
            return result
        }()
        
        private static let contentViewInset: CGFloat = 0
        private static var contentViewHeight: CGFloat { OpenGroupSuggestionGrid.cellHeight - 2 * contentViewInset }
        private static var contentViewCornerRadius: CGFloat { contentViewHeight / 2 }
        
        override init(frame: CGRect) {
            super.init(frame: frame)
            
            setUpViewHierarchy()
        }
        
        required init?(coder: NSCoder) {
            super.init(coder: coder)
            
            setUpViewHierarchy()
        }
        
        private func setUpViewHierarchy() {
            backgroundView = UIView()
            backgroundView?.themeBackgroundColor = .backgroundPrimary
            backgroundView?.layer.cornerRadius = Cell.contentViewCornerRadius
            
            selectedBackgroundView = UIView()
            selectedBackgroundView?.themeBackgroundColor = .backgroundSecondary
            selectedBackgroundView?.layer.cornerRadius = Cell.contentViewCornerRadius
            
            addSubview(snContentView)
            
            let stackView = UIStackView(arrangedSubviews: [ imageView, label ])
            stackView.axis = .horizontal
            stackView.spacing = Cell.itemPadding
            snContentView.addSubview(stackView)
            
            stackView.center(.vertical, in: snContentView)
            stackView.pin(.leading, to: .leading, of: snContentView, withInset: Cell.contentLeftPadding)
            
            snContentView.trailingAnchor
                .constraint(
                    greaterThanOrEqualTo: stackView.trailingAnchor,
                    constant: Cell.contentRightPadding
                )
                .isActive = true
            snContentView.pin(to: self)
        }
        
        private func update() {
            guard let room: OpenGroupAPI.Room = room else { return }
            
            label.text = room.name
            
            // Only continue if we have a room image
            guard let imageId: String = room.imageId else {
                imageView.isHidden = true
                return
            }
            
            imageView.image = nil
            
            Publishers
                .MergeMany(
                    Storage.shared
                        .readPublisherFlatMap { db in
                            OpenGroupManager
                                .roomImage(db, fileId: imageId, for: room.token, on: OpenGroupAPI.defaultServer)
                        }
                        .map { ($0, true) }
                        .eraseToAnyPublisher(),
                    // If we have already received the room image then the above will emit first and
                    // we can ignore this 'Just' call which is used to hide the image while loading
                    Just((Data(), false))
                        .setFailureType(to: Error.self)
                        .delay(for: .milliseconds(10), scheduler: DispatchQueue.main)
                        .eraseToAnyPublisher()
                )
                .subscribe(on: DispatchQueue.global(qos: .userInitiated))
                .receive(on: DispatchQueue.main, immediatelyIfMain: true)
                .sinkUntilComplete(
                    receiveValue: { [weak self] imageData, hasData in
                        guard hasData else {
                            // This will emit twice (once with the data and once without it), if we
                            // have actually received the images then we don't want the second emission
                            // to hide the imageView anymore
                            if self?.imageView.image == nil {
                                self?.imageView.isHidden = true
                            }
                            return
                        }
                        
                        self?.imageView.image = UIImage(data: imageData)
                        self?.imageView.isHidden = (self?.imageView.image == nil)
                    }
                )
        }
    }
}

// MARK: - Delegate

protocol OpenGroupSuggestionGridDelegate {
    func join(_ room: OpenGroupAPI.Room)
}

// MARK: - LastRowCenteredLayout

class LastRowCenteredLayout: UICollectionViewFlowLayout {
    override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        // If we have an odd number of items then we want to center the last one horizontally
        let elementAttributes: [UICollectionViewLayoutAttributes]? = super.layoutAttributesForElements(in: rect)
        
        // It looks like on "max" devices the rect we are given can be much larger than the size of the
        // collection view, as a result we need to try and use the collectionView width here instead
        let targetViewWidth: CGFloat = {
            guard let collectionView: UICollectionView = self.collectionView, collectionView.frame.width > 0 else {
                return rect.width
            }
            
            return collectionView.frame.width
        }()
        
        guard
            let remainingItems: Int = elementAttributes.map({ $0.count % OpenGroupSuggestionGrid.numHorizontalCells }),
            remainingItems != 0,
            let lastItems: [UICollectionViewLayoutAttributes] = elementAttributes?.suffix(remainingItems),
            !lastItems.isEmpty
        else { return elementAttributes }
        
        let totalItemWidth: CGFloat = lastItems
            .map { $0.frame.size.width }
            .reduce(0, +)
        let lastRowWidth: CGFloat = (totalItemWidth + (CGFloat(lastItems.count - 1) * minimumInteritemSpacing))
        
        // Offset the start width by half of the remaining space
        var itemXPos: CGFloat = ((targetViewWidth - lastRowWidth) / 2)
        
        lastItems.forEach { item in
            item.frame = CGRect(
                x: itemXPos,
                y: item.frame.origin.y,
                width: item.frame.size.width,
                height: item.frame.size.height
            )
            
            itemXPos += (item.frame.size.width + minimumInteritemSpacing)
        }
        
        return elementAttributes
    }
}