grain.social/grain-ios
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@testable import Grain
import SwiftUI
import XCTest
/// The photo strip is scrolled by hand rather than by a ScrollView, so its
/// bounds, snapping and edge fade are all arithmetic this class owns. Getting
/// the clamp wrong lets the strip drift off its own content, which is invisible
/// in a screenshot and obvious the moment you drag.
@MainActor
final class StripScrollStateTests: GrainTestCase {
/// Matches the layout constants: 72pt thumbs, 20pt apart.
private let thumbStride: CGFloat = 92
private let width: CGFloat = 402
/// Five thumbs are 440pt of content in a 402pt window — wider than the
/// window, so there is real scrolling range to clamp against.
private let overflowingCount = 5
/// Two thumbs are 164pt of content, which fits, so the strip must not move.
private let fittingCount = 2
// MARK: - clamp
func testClampRefusesToScrollPastTheStart() {
XCTAssertEqual(
StripScrollState.clamp(200, itemCount: overflowingCount, containerWidth: width),
0
)
}
func testClampRefusesToScrollPastTheEnd() {
// 402 - (5 * 72 + 4 * 20) = -38pt of travel.
XCTAssertEqual(
StripScrollState.clamp(-1000, itemCount: overflowingCount, containerWidth: width),
-38,
accuracy: 0.01
)
}
func testClampLeavesAnOffsetInsideTheRangeAlone() {
XCTAssertEqual(
StripScrollState.clamp(-20, itemCount: overflowingCount, containerWidth: width),
-20,
accuracy: 0.01
)
}
func testContentNarrowerThanTheWindowCannotScroll() {
XCTAssertEqual(StripScrollState.clamp(-50, itemCount: fittingCount, containerWidth: width), 0)
XCTAssertEqual(StripScrollState.clamp(50, itemCount: fittingCount, containerWidth: width), 0)
}
/// Called during layout before the container has been measured, so both
/// degenerate inputs have to return something rather than divide by zero.
func testClampIsZeroWithNoItemsOrNoWidth() {
XCTAssertEqual(StripScrollState.clamp(-50, itemCount: 0, containerWidth: width), 0)
XCTAssertEqual(StripScrollState.clamp(-50, itemCount: overflowingCount, containerWidth: 0), 0)
}
// MARK: - offset(forIndex:)
func testOffsetForAnIndexIsAlwaysInsideTheScrollableRange() {
for index in 0 ..< overflowingCount {
let offset = StripScrollState.offset(
forIndex: index, itemCount: overflowingCount, containerWidth: width
)
XCTAssertLessThanOrEqual(offset, 0)
XCTAssertGreaterThanOrEqual(offset, -38.01)
}
}
func testOffsetMovesLeftAsTheIndexGrows() throws {
let offsets = (0 ..< 12).map {
StripScrollState.offset(forIndex: $0, itemCount: 12, containerWidth: width)
}
for (earlier, later) in zip(offsets, offsets.dropFirst()) {
XCTAssertLessThanOrEqual(later, earlier, "Scrolling forward should never move the strip right")
}
XCTAssertLessThan(try XCTUnwrap(offsets.last), try XCTUnwrap(offsets.first), "The last thumb should sit further along than the first")
}
/// A thumb far enough from either end gets centred exactly.
func testAMiddleThumbIsCentred() {
let index = 6
let offset = StripScrollState.offset(forIndex: index, itemCount: 12, containerWidth: width)
let centreOfThumb = offset + CGFloat(index) * thumbStride + 36
XCTAssertEqual(centreOfThumb, width / 2, accuracy: 0.01)
}
func testOffsetIsZeroWithNoItems() {
XCTAssertEqual(StripScrollState.offset(forIndex: 0, itemCount: 0, containerWidth: width), 0)
}
// MARK: - currentOffset
func testCurrentOffsetTracksTheLiveDrag() {
let state = StripScrollState()
state.baseOffset = -30
state.dragTranslation = -12
XCTAssertEqual(state.currentOffset, -42, accuracy: 0.01)
}
// MARK: - handleDragEnded
func testADragEndSnapsToAThumbAndClearsTheLiveTranslation() {
let state = StripScrollState()
state.dragTranslation = -40
state.handleDragEnded(
translation: -40, predictedEnd: -60,
containerWidth: width, itemCount: 12
)
XCTAssertEqual(state.dragTranslation, 0, "Translation must fold into the base or the strip double-counts it")
let restPositions = (0 ..< 12).map {
StripScrollState.offset(forIndex: $0, itemCount: 12, containerWidth: width)
}
XCTAssertTrue(
restPositions.contains { abs($0 - state.baseOffset) < 0.01 },
"Rest position \(state.baseOffset) is not any thumb's centred offset"
)
}
/// Flicking hard should land further along than releasing dead — the
/// predicted end is the whole point of taking velocity into account.
func testAFastFlickTravelsFurtherThanASlowRelease() {
let gentle = StripScrollState()
gentle.handleDragEnded(translation: -40, predictedEnd: -40, containerWidth: width, itemCount: 12)
let flick = StripScrollState()
flick.handleDragEnded(translation: -40, predictedEnd: -400, containerWidth: width, itemCount: 12)
XCTAssertLessThan(flick.baseOffset, gentle.baseOffset)
}
func testADragCannotEndPastTheEndOfTheContent() {
let state = StripScrollState()
state.handleDragEnded(
translation: -5000, predictedEnd: -9000,
containerWidth: width, itemCount: overflowingCount
)
XCTAssertEqual(state.baseOffset, -38, accuracy: 0.01)
}
// MARK: - scrollToIndex
func testScrollingToAnIndexCentresIt() {
let state = StripScrollState()
state.scrollToIndex(6, itemCount: 12, containerWidth: width, animated: false)
XCTAssertEqual(
state.baseOffset,
StripScrollState.offset(forIndex: 6, itemCount: 12, containerWidth: width),
accuracy: 0.01
)
}
/// Selection changes fire this constantly; re-animating to the position the
/// strip is already in would interrupt an in-flight drag for nothing.
func testScrollingToWhereTheStripAlreadyIsDoesNothing() {
let state = StripScrollState()
let target = StripScrollState.offset(forIndex: 3, itemCount: 12, containerWidth: width)
state.baseOffset = target - 0.2
state.scrollToIndex(3, itemCount: 12, containerWidth: width, animated: false)
XCTAssertEqual(state.baseOffset, target - 0.2, accuracy: 0.001, "A sub-half-point move should be skipped")
}
// MARK: - deleteOpacity
func testTheDeleteButtonIsFullyVisibleForAThumbInView() {
let state = StripScrollState()
XCTAssertEqual(state.deleteOpacity(cellIndex: 0, containerWidth: width), 1, accuracy: 0.01)
XCTAssertEqual(state.deleteOpacity(cellIndex: 1, containerWidth: width), 1, accuracy: 0.01)
}
func testTheDeleteButtonIsGoneForAThumbScrolledOffTheLeft() {
let state = StripScrollState()
state.baseOffset = -400
XCTAssertEqual(state.deleteOpacity(cellIndex: 0, containerWidth: width), 0, accuracy: 0.01)
}
/// The button fades rather than popping, so a thumb partway off the edge
/// has to land strictly between the two extremes.
func testTheDeleteButtonFadesAtTheLeftEdge() {
let state = StripScrollState()
// Leaves the button's centre 7pt inside the clip, mid-fade.
state.baseOffset = -65
let opacity = state.deleteOpacity(cellIndex: 0, containerWidth: width)
XCTAssertGreaterThan(opacity, 0)
XCTAssertLessThan(opacity, 1)
}
func testTheDeleteButtonFadesAtTheRightEdge() {
let state = StripScrollState()
// Cell 0 pushed until only 7pt of it is left inside the right edge.
state.baseOffset = width - 7
let opacity = state.deleteOpacity(cellIndex: 0, containerWidth: width)
XCTAssertGreaterThan(opacity, 0)
XCTAssertLessThan(opacity, 1)
}
func testTheFadeIsMonotonicAsAThumbLeavesTheLeftEdge() {
var previous: CGFloat = 1
for offset in stride(from: CGFloat(-50), through: -75, by: -1) {
let state = StripScrollState()
state.baseOffset = offset
let opacity = state.deleteOpacity(cellIndex: 0, containerWidth: width)
XCTAssertLessThanOrEqual(opacity, previous + 0.001, "Opacity rose while the thumb kept leaving")
previous = opacity
}
XCTAssertEqual(previous, 0, accuracy: 0.01, "The button should be gone by the time the thumb is")
}
}