// This is Free Software under GNU Affero General Public License v >= 3.0
// without warranty, see README.md and license for details.
//
// SPDX-License-Identifier: AGPL-3.0-or-later
// License-Filename: LICENSES/AGPL-3.0.txt
//
// Copyright (C) 2024 by via donau
//   – Österreichische Wasserstraßen-Gesellschaft mbH
// Software engineering by Intevation GmbH
//
// Author(s):
//  * Sascha L. Teichmann <sascha.teichmann@intevation.de>

package common

// Delta returns a function which returns its argument when called
// the first time and the delta to the last call afterwards.
func Delta() func(int64) int64 {
	var last int64
	first := true
	return func(x int64) (y int64) {
		if first {
			first = false
			y = x
			last = x
		} else {
			y = x - last
			last = x
		}
		return
	}
}