damus

nostr ios client
git clone git://jb55.com/damus
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PreviewCache.swift (1437B)

      1 //
      2 //  PreviewCache.swift
      3 //  damus
      4 //
      5 //  Created by William Casarin on 2023-01-02.
      6 //
      7 
      8 import Foundation
      9 import LinkPresentation
     10 
     11 class CachedMetadata {
     12     let meta: LPLinkMetadata
     13     var intrinsic_height: CGFloat?
     14     
     15     init(meta: LPLinkMetadata) {
     16         self.meta = meta
     17         self.intrinsic_height = nil
     18     }
     19 }
     20 
     21 enum Preview {
     22     case value(CachedMetadata)
     23     case failed
     24     
     25     init(meta: LPLinkMetadata?) {
     26         if let meta {
     27             self = .value(CachedMetadata(meta: meta))
     28         } else {
     29             self = .failed
     30         }
     31     }
     32     
     33     static func fetch_metadata(for url: URL) async -> LPLinkMetadata? {
     34         // iOS 15 is crashing for some reason
     35         guard #available(iOS 16, *) else {
     36             return nil
     37         }
     38         
     39         let provider = LPMetadataProvider()
     40         
     41         do {
     42             return try await provider.startFetchingMetadata(for: url)
     43         } catch {
     44             return nil
     45         }
     46     }
     47     
     48 }
     49 
     50 enum PreviewState {
     51     case not_loaded
     52     case loading
     53     case loaded(Preview)
     54     
     55     var should_preload: Bool {
     56         switch self {
     57         case .loaded:
     58             return false
     59         case .loading:
     60             return false
     61         case .not_loaded:
     62             return true
     63         }
     64     }
     65 }
     66 
     67 class PreviewCache {
     68     private var previews: [NoteId: Preview] = [:]
     69     
     70     func lookup(_ evid: NoteId) -> Preview? {
     71         return previews[evid]
     72     }
     73 }