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A slopfork of Sam Henri Gold's Twitter client, reskinned like Tweetie 2 / Twitter for iPhone circa 2012. Personal use.
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/// Post text typeset into an attributed string: links on every entity, Twitter's bold/italic as inline presentation/// intents, and each entity tagged with ``PostEntityAttribute``.package struct TypesetPostText: Equatable, Sendable { /// A stretch of the text that is either all one entity (a mention, tag or link) or has none, so a view can tag /// each entity's runs. package struct Segment: Equatable, Sendable { package let text: AttributedString package let entity: PostEntity?
/// The screen name, when this segment is a mention. package var mention: String? { if case .mention(let screenName) = entity { screenName } else { nil } } }
package let input: PostTextInput package let attributedString: AttributedString /// The text split around entities, in order; empty when it has none. package let segments: [Segment]
package var hasEntities: Bool { !segments.isEmpty }
/// Typesetting is deterministic, so equal inputs are equal outputs. package static func == (lhs: TypesetPostText, rhs: TypesetPostText) -> Bool { lhs.input == rhs.input }}
/// Parses and typesets post text, and keeps what it built.////// Modeled on the transcript app's payload transform: the work is a pure function of an `Equatable` input, it runs/// off the main actor, and its results live in a cache keyed by the input itself (never a hash of it), so a row the/// lazy stack recycles finds its text on its first frame. Views read ``cachedOrInline(_:)`` synchronously and fall/// back to ``prepare(_:)`` for text too long to typeset inside a frame.package enum PostTextTypesetter { /// Text up to this many UTF-16 units typesets inline on a cache miss: a few hundred microseconds, cheaper than a /// placeholder frame and the restyle that follows it. Longer text (note posts run to 25,000 characters) goes off /// the main actor. package static let inlineBudget = 600
private static let cache = Mutex(GenerationalCache<PostTextInput, TypesetPostText>(capacity: 2_000))
/// The cached result for `input`, if it was typeset before. package static func cached(_ input: PostTextInput) -> TypesetPostText? { cache.withLock { $0[input] } }
/// The cached result, or one built now when `input` is within ``inlineBudget``; `nil` means call ``prepare(_:)``. package static func cachedOrInline(_ input: PostTextInput) -> TypesetPostText? { if let hit = cached(input) { return hit } guard input.text.utf16.count <= inlineBudget else { return nil } return typeset(input) }
/// Typesets `input` on the caller's thread, through the cache. package static func typeset(_ input: PostTextInput) -> TypesetPostText { if let hit = cached(input) { return hit } // Built outside the lock: racing builders produce equal values. let value = build(input) cache.withLock { $0[input] = value } return value }
/// Typesets `input` off the main actor, through the cache. @concurrent package static func prepare(_ input: PostTextInput) async -> TypesetPostText { typeset(input) }
/// Fills the cache ahead of display, e.g. when a page of posts arrives. @concurrent package static func prewarm(_ inputs: [PostTextInput]) async { for input in inputs { if Task.isCancelled { return } _ = typeset(input) } }
/// Parse and typeset without the cache. package static func build(_ input: PostTextInput) -> TypesetPostText { let pieces = PostTextParser.pieces(for: input) var string = AttributedString() var segments: [TypesetPostText.Segment] = [] var pending = AttributedString() let hasEntities = pieces.contains { $0.entity != nil }
for piece in pieces { var run = AttributedString(piece.text) if let entity = piece.entity { run.link = entity.destination run[PostEntityAttribute.self] = entity } if let intent = piece.emphasis.presentationIntent { run.inlinePresentationIntent = intent } string.append(run) guard hasEntities else { continue } if let entity = piece.entity { if !pending.characters.isEmpty { segments.append(.init(text: pending, entity: nil)) pending = AttributedString() } segments.append(.init(text: run, entity: entity)) } else { pending.append(run) } } if hasEntities, !pending.characters.isEmpty { segments.append(.init(text: pending, entity: nil)) } return TypesetPostText(input: input, attributedString: string, segments: segments) }}
/// Two generations of entries: lookups promote from the old one, and when the new one fills it becomes the old one./// An approximate LRU with O(1) work per operation and no per-entry bookkeeping.struct GenerationalCache<Key: Hashable, Value> { let capacity: Int private var current: [Key: Value] = [:] private var previous: [Key: Value] = [:]
init(capacity: Int) { self.capacity = capacity }
subscript(key: Key) -> Value? { mutating get { if let value = current[key] { return value } guard let value = previous.removeValue(forKey: key) else { return nil } insert(value, for: key) return value } set { if let newValue { insert(newValue, for: key) } else { current[key] = nil } } }
private mutating func insert(_ value: Value, for key: Key) { current[key] = value if current.count >= capacity { previous = current current = [:] current.reserveCapacity(capacity) } }}
extension GenerationalCache: Sendable where Key: Sendable, Value: Sendable {}