import Foundation
import UIKit

final class FileProcessing {
    static let shared = FileProcessing()

    static var fileFolder: URL {
        // swiftlint:disable:next force_unwrapping
        let documentsURL = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!
        return documentsURL.appendingPathComponent(Const.fileFolder)
    }

    func createThumbnail(id: String, localUrl: URL) -> URL? {
        // make path for thumbnail
        let thumbnailUrl = FileProcessing.fileFolder.appendingPathComponent(id).appendingPathExtension("png")

        // check if thumbnail already exists
        if FileManager.default.fileExists(atPath: thumbnailUrl.path) {
            return thumbnailUrl
        }

        // create thumbnail if not exists
        switch localUrl.lastPathComponent.attachmentType {
        case .image:
            guard let image = UIImage(contentsOfFile: localUrl.path) else { return nil }
            let targetSize = CGSize(width: Const.attachmentPreviewSize, height: Const.attachmentPreviewSize)
            guard let thumbnail = scaleAndCropImage(image, targetSize) else { return nil }
            guard let data = thumbnail.pngData() else { return nil }
            do {
                try data.write(to: thumbnailUrl)
                return thumbnailUrl
            } catch {
                return nil
            }

        default:
            return nil
        }
    }
}

private extension FileProcessing {
    func scaleAndCropImage(_ img: UIImage, _ size: CGSize) -> UIImage? {
        guard let cgImage = img.cgImage else {
            return nil
        }
        let contextImage: UIImage = .init(cgImage: cgImage)
        var contextSize: CGSize = contextImage.size

        var posX: CGFloat = 0.0
        var posY: CGFloat = 0.0
        let cgwidth: CGFloat = size.width
        let cgheight: CGFloat = size.height

        // Check and handle if the image is wider than the requested size
        if contextSize.width > contextSize.height {
            posX = ((contextSize.width - contextSize.height) / 2)
            contextSize.width = contextSize.height
        } else if contextSize.width < contextSize.height {
            // Check and handle if the image is taller than the requested size
            posY = ((contextSize.height - contextSize.width) / 2)
            contextSize.height = contextSize.width
        }

        let rect: CGRect = .init(x: posX, y: posY, width: cgwidth, height: cgheight)
        guard let contextCg = contextImage.cgImage, let imgRef = contextCg.cropping(to: rect) else {
            return nil
        }
        let image: UIImage = .init(cgImage: imgRef, scale: img.scale, orientation: img.imageOrientation)
        return image
    }
}