import XCTest

// Swift port of buildScrollGesturePlan from src/core/scroll-gesture.ts.
//
// This is a deliberate two-place invariant: the daemon keeps the TS implementation (for Android,
// recording, and reported-pixels), and the runner places the gesture with this Swift copy. The
// parity test vectors at the bottom of this file mirror src/core/__tests__/scroll-gesture.test.ts —
// if you change the math in either language, update the other and both vector sets.
//
// All inputs here are positive (reference dims, travel, center), so Swift's `.rounded()`
// (half away from zero) matches JS `Math.round` (half up) on every value computed below.

struct RunnerScrollGesturePlan {
  let x1: Double
  let y1: Double
  let x2: Double
  let y2: Double
  let travelPixels: Double
}

private let runnerDefaultScrollAmount = 0.6
private let runnerDefaultEdgePaddingFraction = 0.05

func runnerScrollGesturePlan(
  direction: String,
  amount: Double?,
  pixels: Double?,
  referenceWidth: Double,
  referenceHeight: Double
) -> RunnerScrollGesturePlan? {
  // Mirror the TS INVALID_ARGS contract: non-positive or non-finite amount/pixels are rejected
  // rather than clamped into a journaled 1px scroll. The daemon validates before sending, so
  // this only triggers for non-daemon wire clients.
  if let amount, !(amount.isFinite && amount > 0) { return nil }
  if let pixels, !(pixels.isFinite && pixels > 0) { return nil }
  let axisLength = (direction == "up" || direction == "down") ? referenceHeight : referenceWidth
  let requestedAmount = amount ?? runnerDefaultScrollAmount
  let requestedPixels: Double =
    pixels.map { max(1, $0.rounded()) } ?? (axisLength * requestedAmount).rounded()
  let edgePadding = max(1, (axisLength * runnerDefaultEdgePaddingFraction).rounded())
  let maxTravelPixels = max(1, axisLength - edgePadding * 2)
  let travelPixels = max(1, min(requestedPixels, maxTravelPixels))
  let halfTravel = (travelPixels / 2).rounded()
  let centerX = (referenceWidth / 2).rounded()
  let centerY = (referenceHeight / 2).rounded()

  func plan(_ x1: Double, _ y1: Double, _ x2: Double, _ y2: Double) -> RunnerScrollGesturePlan {
    RunnerScrollGesturePlan(x1: x1, y1: y1, x2: x2, y2: y2, travelPixels: travelPixels)
  }

  switch direction {
  case "up":
    return plan(centerX, centerY - halfTravel, centerX, centerY + halfTravel)
  case "down":
    return plan(centerX, centerY + halfTravel, centerX, centerY - halfTravel)
  case "left":
    return plan(centerX - halfTravel, centerY, centerX + halfTravel, centerY)
  case "right":
    return plan(centerX + halfTravel, centerY, centerX - halfTravel, centerY)
  default:
    return nil
  }
}