82 lines
2.8 KiB
Swift
82 lines
2.8 KiB
Swift
import Foundation
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/// Durable MAM position. The archive UID is the primary synchronization
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/// anchor; the timestamp is retained as a compatibility fallback for legacy
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/// snapshots and servers that have expired an old UID.
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struct ArchiveSyncCheckpoint: Codable, Equatable, Sendable {
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let timestamp: Date
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let cursor: String?
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init(timestamp: Date, cursor: String? = nil) {
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self.timestamp = timestamp
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self.cursor = Self.normalizedCursor(cursor)
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}
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func advances(over previous: ArchiveSyncCheckpoint?) -> Bool {
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guard let previous else { return true }
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return timestamp > previous.timestamp || cursor != previous.cursor
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}
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static func normalizedCursor(_ value: String?) -> String? {
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guard let value = value?.trimmingCharacters(in: .whitespacesAndNewlines),
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!value.isEmpty else { return nil }
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return value
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}
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}
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struct ArchiveSyncRequestPosition: Equatable, Sendable {
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let start: Date?
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let after: String?
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}
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/// Keeps cursor-based catch-up and the timestamp fallback deterministic and
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/// independently testable from Martin's callback lifecycle.
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enum ArchiveSyncCursorPolicy {
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static func requestPosition(
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checkpoint: ArchiveSyncCheckpoint?,
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resumeAfter: String?,
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overlap: TimeInterval
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) -> ArchiveSyncRequestPosition {
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let after = ArchiveSyncCheckpoint.normalizedCursor(resumeAfter)
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?? checkpoint?.cursor
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if let after {
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return ArchiveSyncRequestPosition(start: nil, after: after)
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}
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return ArchiveSyncRequestPosition(
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start: checkpoint?.timestamp.addingTimeInterval(-overlap),
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after: nil
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)
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}
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static func resolvedCheckpoint(
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previous: ArchiveSyncCheckpoint?,
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cursor: String?,
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highWatermark: Date?,
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queryStartedAt: Date,
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caughtUp: Bool
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) -> ArchiveSyncCheckpoint {
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let previousTimestamp = previous?.timestamp ?? .distantPast
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let boundedHighWatermark = min(highWatermark ?? previousTimestamp, queryStartedAt)
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let timestamp = caughtUp
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? max(previousTimestamp, queryStartedAt)
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: max(previousTimestamp, boundedHighWatermark)
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return ArchiveSyncCheckpoint(
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timestamp: timestamp,
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cursor: ArchiveSyncCheckpoint.normalizedCursor(cursor) ?? previous?.cursor
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)
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}
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static func shouldFallbackFromStoredCursor(
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requestedAfter: String?,
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checkpoint: ArchiveSyncCheckpoint?,
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hasCompletedPage: Bool,
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fallbackAlreadyUsed: Bool
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) -> Bool {
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guard !fallbackAlreadyUsed,
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!hasCompletedPage,
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let requestedAfter = ArchiveSyncCheckpoint.normalizedCursor(requestedAfter),
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requestedAfter == checkpoint?.cursor else { return false }
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return true
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}
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}
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