package util

import "math"

func ShortDistance(w, h uint32, x1, y1, x2, y2 float64) float64 {
	return math.Hypot(deltas(w, h, x1, y1, x2, y2))
}

func NextTravelCoord(w, h uint32, x1, y1, x2, y2, delta float64) (float64, float64, bool) {
	deltaX, deltaY := deltas(w, h, x1, y1, x2, y2)
	distance := math.Hypot(deltaX, deltaY)
	if distance <= delta {
		return x2, y2, true
	}
	// TODO: refactor - remove extra vars
	xa := 0.
	ya := 0.
	xb := deltaX
	yb := deltaY
	d := distance
	d2 := delta
	xc := xa - (d2*(xa-xb))/d
	yc := ya - (d2*(ya-yb))/d

	// ---
	var tx, ty float64

	if math.Abs(x2-x1) > float64(w/2) {
		// moving across X boundary
		if x2 < x1 {
			// moving across higher border
			tx = math.Mod(x1+xc, float64(w))
		} else {
			// moving across lower border
			tx = x1 - xc
			if tx < 0 {
				tx = float64(w) + tx
			}
		}
	} else {
		if x2 < x1 {
			tx = x1 - xc
		} else {
			tx = x1 + xc
		}
	}

	if math.Abs(y2-y1) > float64(h/2) {
		// moving across Y boundary
		if y2 < y1 {
			// moving across higher border
			ty = math.Mod(y1+yc, float64(h))
		} else {
			// moving across lower border
			ty = y1 - yc
			if ty < 0 {
				ty = float64(h) + ty
			}
		}
	} else {
		if y2 < y1 {
			ty = y1 - yc
		} else {
			ty = y1 + yc
		}
	}

	return tx, ty, false
}

func deltas(w, h uint32, x1, y1, x2, y2 float64) (float64, float64) {
	dx := math.Abs(x2 - x1)
	dy := math.Abs(y2 - y1)
	if dx > float64(w/2) {
		dx = float64(h) - dx
	}
	if dy > float64(h/2) {
		dy = float64(h) - dy
	}
	return dx, dy
}