Kurdtvs-Live-Kurdish-TV-Kurdmax/Mastodon/Scene/Share/ViewModel/MosaicImageViewModel.swift

//
//  MosaicImageViewModel.swift
//  Mastodon
//
//  Created by Cirno MainasuK on 2021-2-23.
//

import UIKit
import Combine
import CoreDataStack

struct MosaicImageViewModel {
    
    let metas: [MosaicMeta]
    
    init(mediaAttachments: [Attachment]) {
        var metas: [MosaicMeta] = []
        for element in mediaAttachments where element.type == .image {
            // Display original on the iPad/Mac
            guard let previewURL = element.previewURL else { continue }
            let urlString = UIDevice.current.userInterfaceIdiom == .phone ? previewURL : element.url
            guard let meta = element.meta,
                  let width = meta.original?.width,
                  let height = meta.original?.height,
                  let url = URL(string: urlString) else {
                continue
            }
            let mosaicMeta = MosaicMeta(
                url: url,
                size: CGSize(width: width, height: height),
                blurhash: element.blurhash
            )
            metas.append(mosaicMeta)
        }
        self.metas = metas
    }
    
}

struct MosaicMeta {
    static let edgeMaxLength: CGFloat = 20
    
    let url: URL
    let size: CGSize
    let blurhash: String?
    
    let workingQueue = DispatchQueue(label: "org.joinmastodon.Mastodon.MosaicMeta.working-queue", qos: .userInitiated, attributes: .concurrent)

    func blurhashImagePublisher() -> AnyPublisher<UIImage?, Never> {
        return Future { promise in
            guard let blurhash = blurhash else {
                promise(.success(nil))
                return
            }
            
            let imageSize: CGSize = {
                let aspectRadio = size.width / size.height
                if size.width > size.height {
                    let width: CGFloat = MosaicMeta.edgeMaxLength
                    let height = width / aspectRadio
                    return CGSize(width: width, height: height)
                } else {
                    let height: CGFloat = MosaicMeta.edgeMaxLength
                    let width = height * aspectRadio
                    return CGSize(width: width, height: height)
                }
            }()
            
            workingQueue.async {
                let image = UIImage(blurHash: blurhash, size: imageSize)
                promise(.success(image))
            }
        }
        .eraseToAnyPublisher()
    }
}