grain.social/grain-ios
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@testable import Grain
import Nuke
import XCTest
final class ImagePrefetchPlanningTests: GrainTestCase {
// MARK: - Helpers
private func photo(index: Int) -> (thumb: String, fullsize: String) {
(thumb: "https://cdn.example.com/thumb/\(index).jpg", fullsize: "https://cdn.example.com/full/\(index).jpg")
}
private func photos(_ count: Int) -> [(thumb: String, fullsize: String)] {
(0 ..< count).map { photo(index: $0) }
}
private func urls(from requests: [ImageRequest]) -> [String] {
requests.compactMap { $0.url?.absoluteString }
}
// MARK: - Carousel: Empty / Edge Cases
func testCarousel_emptyPhotos_returnsEmpty() {
let result = ImagePrefetchPlanning.carouselPrefetchRequests(photos: [], currentPage: 0)
XCTAssertTrue(result.all.isEmpty)
}
func testCarousel_outOfBoundsPage_returnsEmpty() {
let result = ImagePrefetchPlanning.carouselPrefetchRequests(photos: photos(3), currentPage: 10)
XCTAssertTrue(result.all.isEmpty)
}
func testCarousel_negativePage_returnsEmpty() {
let result = ImagePrefetchPlanning.carouselPrefetchRequests(photos: photos(3), currentPage: -1)
XCTAssertTrue(result.all.isEmpty)
}
// MARK: - Carousel: Page 0
func testCarousel_singlePhoto_page0_prefetchesOnlyThatFullsize() {
let result = ImagePrefetchPlanning.carouselPrefetchRequests(photos: photos(1), currentPage: 0)
XCTAssertEqual(urls(from: result.high), ["https://cdn.example.com/full/0.jpg"])
XCTAssertTrue(result.normal.isEmpty)
XCTAssertTrue(result.low.isEmpty)
}
func testCarousel_twoPhotos_page0_prefetchesBothFullsize() {
let result = ImagePrefetchPlanning.carouselPrefetchRequests(photos: photos(2), currentPage: 0)
XCTAssertEqual(urls(from: result.high), [
"https://cdn.example.com/full/0.jpg",
"https://cdn.example.com/full/1.jpg",
])
}
func testCarousel_fivePhotos_page0_prefetchesOnlyFirstTwo() {
let result = ImagePrefetchPlanning.carouselPrefetchRequests(photos: photos(5), currentPage: 0)
XCTAssertEqual(urls(from: result.high).count, 2)
XCTAssertTrue(result.normal.isEmpty)
}
// MARK: - Carousel: Page 1
func testCarousel_threePhotos_page1_prefetchesThirdFullsizeAndAllThumbs() {
let result = ImagePrefetchPlanning.carouselPrefetchRequests(photos: photos(3), currentPage: 1)
XCTAssertEqual(urls(from: result.high), ["https://cdn.example.com/full/2.jpg"])
XCTAssertEqual(urls(from: result.normal).count, 3) // all 3 thumbs
XCTAssertTrue(urls(from: result.normal).allSatisfy { $0.contains("/thumb/") })
}
func testCarousel_twoPhotos_page1_noThirdFullsize_stillPrefetchesThumbs() {
let result = ImagePrefetchPlanning.carouselPrefetchRequests(photos: photos(2), currentPage: 1)
XCTAssertTrue(result.high.isEmpty)
XCTAssertEqual(urls(from: result.normal).count, 2) // both thumbs
}
// MARK: - Carousel: Page 2+
func testCarousel_tenPhotos_page5_prefetchesNextAtHighRestAtNormal() {
let result = ImagePrefetchPlanning.carouselPrefetchRequests(photos: photos(10), currentPage: 5)
XCTAssertEqual(urls(from: result.high), ["https://cdn.example.com/full/6.jpg"])
XCTAssertEqual(urls(from: result.normal).count, 3) // 7, 8, 9
}
func testCarousel_lastPage_returnsEmpty() {
let result = ImagePrefetchPlanning.carouselPrefetchRequests(photos: photos(3), currentPage: 2)
XCTAssertTrue(result.high.isEmpty)
XCTAssertTrue(result.normal.isEmpty)
}
// MARK: - Feed: Edge Cases
func testFeed_emptyGalleries_returnsEmpty() {
let result = ImagePrefetchPlanning.feedPrefetchRequests(galleries: [], currentIndex: 0)
XCTAssertTrue(result.all.isEmpty)
}
func testFeed_atLastGallery_returnsEmpty() {
let galleries: [(firstThumb: String?, firstFullsize: String?)] = [
(firstThumb: "t0", firstFullsize: "f0"),
]
let result = ImagePrefetchPlanning.feedPrefetchRequests(galleries: galleries, currentIndex: 0)
XCTAssertTrue(result.all.isEmpty)
}
// MARK: - Feed: Look-ahead
func testFeed_tenGalleries_atIndex3_prefetchesNext3() {
let galleries: [(firstThumb: String?, firstFullsize: String?)] = (0 ..< 10).map { i in
(firstThumb: "https://cdn.example.com/thumb/\(i).jpg",
firstFullsize: "https://cdn.example.com/full/\(i).jpg")
}
let result = ImagePrefetchPlanning.feedPrefetchRequests(galleries: galleries, currentIndex: 3)
// High: thumb 4, fullsize 4, thumb 5
// Normal: fullsize 5
// Low: fullsize 6, thumb 6
let allUrls = urls(from: result.all)
XCTAssertTrue(allUrls.contains("https://cdn.example.com/full/4.jpg"))
XCTAssertTrue(allUrls.contains("https://cdn.example.com/full/5.jpg"))
XCTAssertTrue(allUrls.contains("https://cdn.example.com/full/6.jpg"))
XCTAssertTrue(allUrls.contains("https://cdn.example.com/thumb/4.jpg"))
}
func testFeed_galleryWithNoPhotos_skipsGracefully() {
let galleries: [(firstThumb: String?, firstFullsize: String?)] = [
(firstThumb: "t0", firstFullsize: "f0"),
(firstThumb: nil, firstFullsize: nil), // gallery with no photos
(firstThumb: "t2", firstFullsize: "f2"),
]
let result = ImagePrefetchPlanning.feedPrefetchRequests(galleries: galleries, currentIndex: 0)
// Should still get gallery at index 2
let allUrls = urls(from: result.all)
XCTAssertTrue(allUrls.contains("t2"))
XCTAssertFalse(allUrls.contains("nil"))
}
// MARK: - Stories: Edge Cases
func testStory_emptyCurrentStories_returnsEmpty() {
let result = ImagePrefetchPlanning.storyPrefetchRequests(
currentStories: [],
currentStoryIndex: 0,
nextAuthorStories: nil,
secondNextAuthorStories: nil,
thirdNextFirstStory: nil,
fourthNextFirstStory: nil
)
XCTAssertTrue(result.all.isEmpty)
}
// MARK: - Stories: Priority Order
func testStory_fiveStories_atIndex0_prefetchesCorrectPriorities() {
let stories = photos(5)
let nextAuthor = photos(3)
let result = ImagePrefetchPlanning.storyPrefetchRequests(
currentStories: stories,
currentStoryIndex: 0,
nextAuthorStories: nextAuthor,
secondNextAuthorStories: nil,
thirdNextFirstStory: nil,
fourthNextFirstStory: nil
)
let highUrls = Set(urls(from: result.high))
// High fullsizes: stories 1, 2 of current + first of next author
XCTAssertTrue(highUrls.contains("https://cdn.example.com/full/1.jpg"))
XCTAssertTrue(highUrls.contains("https://cdn.example.com/full/2.jpg"))
XCTAssertTrue(highUrls.contains("https://cdn.example.com/full/0.jpg"))
// High thumbs: every reachable thumb (current + next author)
for i in 0 ..< 5 {
XCTAssertTrue(highUrls.contains("https://cdn.example.com/thumb/\(i).jpg"))
}
// Normal: stories 3, 4 of current (rest of stack — fullsize only)
XCTAssertEqual(urls(from: result.normal), [
"https://cdn.example.com/full/3.jpg",
"https://cdn.example.com/full/4.jpg",
])
}
func testStory_lastStoryOfAuthor_onlyPrefetchesNextAuthor() {
let stories = photos(1)
let nextAuthor = photos(2)
let result = ImagePrefetchPlanning.storyPrefetchRequests(
currentStories: stories,
currentStoryIndex: 0,
nextAuthorStories: nextAuthor,
secondNextAuthorStories: nil,
thirdNextFirstStory: nil,
fourthNextFirstStory: nil
)
let highUrls = Set(urls(from: result.high))
// High fullsize: only next author's first (no more current stories)
XCTAssertTrue(highUrls.contains("https://cdn.example.com/full/0.jpg"))
XCTAssertFalse(highUrls.contains("https://cdn.example.com/full/1.jpg"))
// High thumbs: current + next author thumbs
XCTAssertTrue(highUrls.contains("https://cdn.example.com/thumb/0.jpg"))
XCTAssertTrue(highUrls.contains("https://cdn.example.com/thumb/1.jpg"))
}
func testStory_noNextAuthorData_skipsThatTier() {
let stories = photos(3)
let result = ImagePrefetchPlanning.storyPrefetchRequests(
currentStories: stories,
currentStoryIndex: 0,
nextAuthorStories: nil,
secondNextAuthorStories: nil,
thirdNextFirstStory: nil,
fourthNextFirstStory: nil
)
let highUrls = Set(urls(from: result.high))
// High fullsize: only current stories 1, 2 (no next author tier)
XCTAssertTrue(highUrls.contains("https://cdn.example.com/full/1.jpg"))
XCTAssertTrue(highUrls.contains("https://cdn.example.com/full/2.jpg"))
// High thumbs: only current author's thumbs
XCTAssertTrue(highUrls.contains("https://cdn.example.com/thumb/0.jpg"))
XCTAssertTrue(highUrls.contains("https://cdn.example.com/thumb/1.jpg"))
XCTAssertTrue(highUrls.contains("https://cdn.example.com/thumb/2.jpg"))
XCTAssertTrue(result.low.isEmpty)
}
func testStory_fullPriorityChain() {
let current = photos(2)
let nextAuthor = [(thumb: "https://next/t0", fullsize: "https://next/f0")]
let secondNext = [(thumb: "https://second/t0", fullsize: "https://second/f0"),
(thumb: "https://second/t1", fullsize: "https://second/f1")]
let third = (thumb: "https://third/t0", fullsize: "https://third/f0")
let fourth = (thumb: "https://fourth/t0", fullsize: "https://fourth/f0")
let result = ImagePrefetchPlanning.storyPrefetchRequests(
currentStories: current,
currentStoryIndex: 0,
nextAuthorStories: nextAuthor,
secondNextAuthorStories: secondNext,
thirdNextFirstStory: third,
fourthNextFirstStory: fourth
)
let highUrls = Set(urls(from: result.high))
// High fullsizes: current story 1 + next author first
XCTAssertTrue(highUrls.contains("https://cdn.example.com/full/1.jpg"))
XCTAssertTrue(highUrls.contains("https://next/f0"))
// High thumbs: every reachable thumb at every tier
XCTAssertTrue(highUrls.contains("https://cdn.example.com/thumb/0.jpg"))
XCTAssertTrue(highUrls.contains("https://cdn.example.com/thumb/1.jpg"))
XCTAssertTrue(highUrls.contains("https://next/t0"))
XCTAssertTrue(highUrls.contains("https://second/t0"))
XCTAssertTrue(highUrls.contains("https://second/t1"))
XCTAssertTrue(highUrls.contains("https://third/t0"))
XCTAssertTrue(highUrls.contains("https://fourth/t0"))
// Normal: second-next author stories 0, 1 (fullsize only)
XCTAssertEqual(urls(from: result.normal).count, 2)
// Low: third + fourth author firsts (fullsize only)
XCTAssertEqual(urls(from: result.low).count, 2)
}
// MARK: - Priority correctness
func testCarousel_page0_allRequestsAreHighPriority() {
let result = ImagePrefetchPlanning.carouselPrefetchRequests(photos: photos(5), currentPage: 0)
XCTAssertTrue(result.high.allSatisfy { $0.priority == .high })
XCTAssertTrue(result.normal.isEmpty)
XCTAssertTrue(result.low.isEmpty)
}
func testCarousel_page1_thumbsAreNormalPriority() {
let result = ImagePrefetchPlanning.carouselPrefetchRequests(photos: photos(5), currentPage: 1)
XCTAssertTrue(result.high.allSatisfy { $0.priority == .high })
XCTAssertTrue(result.normal.allSatisfy { $0.priority == .normal })
}
func testFeed_priorityDescentAcrossOffsets() {
let galleries: [(firstThumb: String?, firstFullsize: String?)] = (0 ..< 10).map { i in
(firstThumb: "https://cdn.example.com/thumb/\(i).jpg",
firstFullsize: "https://cdn.example.com/full/\(i).jpg")
}
let result = ImagePrefetchPlanning.feedPrefetchRequests(galleries: galleries, currentIndex: 3)
XCTAssertTrue(urls(from: result.high).contains("https://cdn.example.com/full/4.jpg"))
XCTAssertTrue(urls(from: result.normal).contains("https://cdn.example.com/full/5.jpg"))
XCTAssertTrue(urls(from: result.low).contains("https://cdn.example.com/full/6.jpg"))
}
// MARK: - Story boundary: currentStoryIndex at end
func testStory_atLastIndex_noCurrentPrefetchButNextAuthorStill() {
let stories = photos(3)
let nextAuthor = photos(2)
let result = ImagePrefetchPlanning.storyPrefetchRequests(
currentStories: stories,
currentStoryIndex: 2,
nextAuthorStories: nextAuthor,
secondNextAuthorStories: nil,
thirdNextFirstStory: nil,
fourthNextFirstStory: nil
)
let highUrls = urls(from: result.high)
XCTAssertFalse(highUrls.contains("https://cdn.example.com/full/3.jpg"))
XCTAssertTrue(highUrls.contains("https://cdn.example.com/full/0.jpg"))
}
// MARK: - No duplicate URLs
func testCarousel_page0_noDuplicateURLs() {
let result = ImagePrefetchPlanning.carouselPrefetchRequests(photos: photos(5), currentPage: 0)
let allUrls = urls(from: result.all)
XCTAssertEqual(allUrls.count, Set(allUrls).count)
}
func testFeed_noDuplicateURLs() {
let galleries: [(firstThumb: String?, firstFullsize: String?)] = (0 ..< 10).map { i in
(firstThumb: "https://cdn.example.com/thumb/\(i).jpg",
firstFullsize: "https://cdn.example.com/full/\(i).jpg")
}
let result = ImagePrefetchPlanning.feedPrefetchRequests(galleries: galleries, currentIndex: 3)
let allUrls = urls(from: result.all)
XCTAssertEqual(allUrls.count, Set(allUrls).count)
}
}