// Copyright (C) 2019-2025, Lux Industries, Inc. All rights reserved.
// See the file LICENSE for licensing terms.

package math

import (
	"errors"

	"golang.org/x/exp/constraints"
)

var (
	ErrOverflow  = errors.New("overflow")
	ErrUnderflow = errors.New("underflow")

	// Deprecated: Add64 is deprecated. Use Add[uint64] instead.
	Add64 = Add[uint64]

	// Deprecated: Mul64 is deprecated. Use Mul[uint64] instead.
	Mul64 = Mul[uint64]
)

// MaxUint returns the maximum value of an unsigned integer of type T.
func MaxUint[T constraints.Unsigned]() T {
	return ^T(0)
}

// Add returns:
// 1) a + b
// 2) If there is overflow, an error
func Add[T constraints.Unsigned](a, b T) (T, error) {
	if a > MaxUint[T]()-b {
		return 0, ErrOverflow
	}
	return a + b, nil
}

// Sub returns:
// 1) a - b
// 2) If there is underflow, an error
func Sub[T constraints.Unsigned](a, b T) (T, error) {
	if a < b {
		return 0, ErrUnderflow
	}
	return a - b, nil
}

// Mul returns:
// 1) a * b
// 2) If there is overflow, an error
func Mul[T constraints.Unsigned](a, b T) (T, error) {
	if b != 0 && a > MaxUint[T]()/b {
		return 0, ErrOverflow
	}
	return a * b, nil
}

// AbsDiff returns the absolute difference between a and b.
func AbsDiff[T constraints.Unsigned](a, b T) T {
	return max(a, b) - min(a, b)
}

// SafeAdd returns x+y and whether overflow occurred.
func SafeAdd(x, y uint64) (uint64, bool) {
	sum := x + y
	return sum, sum < x
}

// SafeSub returns x-y and whether underflow occurred.
func SafeSub(x, y uint64) (uint64, bool) {
	return x - y, x < y
}

// SafeMul returns x*y and whether overflow occurred.
func SafeMul(x, y uint64) (uint64, bool) {
	if x == 0 || y == 0 {
		return 0, false
	}
	result := x * y
	return result, result/y != x
}