61 lines
2.3 KiB
Swift
61 lines
2.3 KiB
Swift
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import Foundation
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/// Decides which districts auto-expand into hub-and-spoke each tick.
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///
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/// Rules: a district expands only if it has at least two endpoints (a single-IP
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/// org has nothing to fan out) and ranks among the busiest `topK` above
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/// `floorBytes`. Once chosen it stays expanded for `ttlTicks` ticks, so a burst
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/// leaves a smooth tail instead of flickering collapsed the moment it idles.
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///
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/// Pure and deterministic given its input — no SpriteKit, fully unit-testable.
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public final class ExpansionPolicy {
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public struct District: Sendable {
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public let key: String
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public let bytes: UInt64
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public let endpointCount: Int
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public init(key: String, bytes: UInt64, endpointCount: Int) {
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self.key = key
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self.bytes = bytes
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self.endpointCount = endpointCount
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}
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}
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private let topK: Int
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private let ttlTicks: Int
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private let floorBytes: UInt64
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private var ttl: [String: Int] = [:]
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public init(topK: Int = 4, ttlTicks: Int = 4, floorBytes: UInt64 = 8 * 1024) {
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self.topK = topK
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self.ttlTicks = ttlTicks
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self.floorBytes = floorBytes
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}
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/// Advance one tick over the full set of currently-known districts (include
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/// idle ones so their tail can decay). Returns the set of keys to render
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/// expanded.
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public func update(_ districts: [District]) -> Set<String> {
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// Decay every existing timer.
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for key in ttl.keys { ttl[key] = max(0, (ttl[key] ?? 0) - 1) }
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// Refresh the busiest multi-endpoint districts.
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var winners = 0
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for d in districts.sorted(by: { $0.bytes > $1.bytes }) {
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guard winners < topK else { break }
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if d.bytes >= floorBytes && d.endpointCount >= 2 {
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ttl[d.key] = ttlTicks
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winners += 1
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}
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}
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// Expanded = live timer AND still has something to fan out.
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let endpointCounts = Dictionary(districts.map { ($0.key, $0.endpointCount) },
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uniquingKeysWith: { a, _ in a })
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var expanded = Set<String>()
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for (key, remaining) in ttl where remaining > 0 {
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if (endpointCounts[key] ?? 0) >= 2 { expanded.insert(key) }
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}
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return expanded
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}
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}
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