1import Photos
2import SwiftUI
3
4/// Implement a RandomAccessCollection for a PHFetchResult.
5///
6/// This wrapper allows us to use a PHFetchResult in a SwiftUI ForEach loop,
7/// for example:
8///
9/// ```swift
10/// let fetchResult = PHAsset.fetchAssets(…)
11/// let collection = PHFetchResultCollection(fetchResult: fetchResult)
12///
13/// var body: some View  {
14///     ForEach(collection, id: \.localIdentifier) {
15///         ...
16///     }
17/// }
18/// ```
19///
20/// This collection vends the IndexedPHAsset struct, which tells us both
21/// what asset we're on and where we are -- this is necessary for performance
22/// reasons.  See the comment above the ForEach in PHAssetHStack.
23///
24/// This is based on code written by Slava Semeniuk on Stack Overflow:
25/// https://stackoverflow.com/q/62745595/1558022
26
27struct IndexedPHAsset {
28    var position: Int
29    var asset: PHAsset
30}
31
32struct PHFetchResultCollection: RandomAccessCollection, Equatable {
33    typealias Element = IndexedPHAsset
34    typealias Index = Int
35
36    let fetchResult: PHFetchResult<PHAsset>
37
38    init(_ fetchResult: PHFetchResult<PHAsset>) {
39        self.fetchResult = fetchResult
40    }
41    
42    var startIndex: Int { 0 }
43    var endIndex: Int { fetchResult.count }
44
45    subscript(position: Int) -> IndexedPHAsset {
46        IndexedPHAsset(
47            position: position,
48            asset: fetchResult.object(at: position)
49        )
50    }
51}
52
53struct PHFetchResultCollection_Previews: PreviewProvider {
54    static var resultCollection: PHFetchResultCollection {
55        let options = PHFetchOptions()
56        options.sortDescriptors = [NSSortDescriptor(key: "creationDate", ascending: false)]
57        options.fetchLimit = 3
58        
59        let fetchResult: PHFetchResult<PHAsset> = PHAsset.fetchAssets(with: options)
60        
61        return PHFetchResultCollection(fetchResult)
62    }
63    
64    static var previews: some View {
65        VStack {
66            Text("These dates should be in descending order:")
67            
68            ForEach(self.resultCollection, id: \.asset.localIdentifier) { indexedAsset in
69                Text("\(indexedAsset.asset.creationDate?.ISO8601Format() ?? "(unknown)")")
70            }
71        }
72    }
73}