import Foundation
import XCTest
import RastrilloNative

final class BackoffTests: XCTestCase {
  func testDoublesFromHalfASecondToTenWithEqualJitter() {
    var high = Backoff(random: { $0.upperBound })
    XCTAssertEqual((0..<7).map { _ in high.next() }, [0.5, 1, 2, 4, 8, 10, 10])
    var low = Backoff(random: { $0.lowerBound })
    XCTAssertEqual((0..<6).map { _ in low.next() }, [0.25, 0.5, 1, 2, 4, 5])
    var real = Backoff()
    for expected in [0.5, 1.0, 2.0, 4.0] {
      let delay = real.next()
      XCTAssertTrue((expected / 2...expected).contains(delay), "\(delay) outside [\(expected / 2), \(expected)]")
    }
  }

  func testRetryAfterIsAFloorCappedAtFiveMinutes() {
    var backoff = Backoff(random: { $0.upperBound })
    XCTAssertEqual(backoff.next(retryAfter: 30), 30)
    XCTAssertEqual(backoff.next(retryAfter: 3600), 300)
    XCTAssertEqual(backoff.next(retryAfter: 0.1), 2, "A short Retry-After must not undercut the backoff")
  }

  func testResetsOnSuccessAndAfterAStableConnectionOnly() {
    var backoff = Backoff(random: { $0.upperBound })
    _ = backoff.next(); _ = backoff.next(); _ = backoff.next()
    backoff.opened(at: 100)
    backoff.ended(at: 103)
    XCTAssertEqual(backoff.next(), 4, "A connection that dropped quickly must keep backing off")
    backoff.opened(at: 200)
    backoff.ended(at: 206)
    XCTAssertEqual(backoff.next(), 0.5)
    _ = backoff.next()
    backoff.reset()
    XCTAssertEqual(backoff.next(), 0.5)
  }

  /// The stable clock starts when the stream opens, not when the attempt
  /// starts: a slow refusal or a long access check must not count.
  func testAnAttemptThatNeverOpenedIsNeverStable() {
    var backoff = Backoff(random: { $0.upperBound })
    _ = backoff.next(); _ = backoff.next()
    backoff.ended(at: 1_000)
    XCTAssertEqual(backoff.next(), 2, "An attempt that never opened reset the backoff")
    backoff.opened(at: 2_000)
    backoff.ended(at: 2_006)
    _ = backoff.next()
    backoff.ended(at: 9_000)
    XCTAssertEqual(backoff.next(), 1, "An earlier open was counted for a later attempt")
  }
}