package safecast

import (
	"math"
)

// Number is a constraint for all integers and floats
type Number interface {
	~int | ~int8 | ~int16 | ~int32 | ~int64 | ~uint | ~uint8 | ~uint16 | ~uint32 | ~uint64 | ~float32 | ~float64 | ~uintptr

	// TODO(ccoVeille): consider using complex, but not sure if there is a need
}

func isNegative[T Number](t T) bool {
	return t < 0
}

func sameSign[T1, T2 Number](a T1, b T2) bool {
	return isNegative(a) == isNegative(b)
}

func isUnsigned[T Number]() bool {
	v := -1
	return T(v) >= 0
}
func isFloat[T Number]() bool {
	v := 0.1
	return T(v) != 0
}

func isFloat32[T Number]() bool {
	if !isFloat[T]() {
		return false
	}
	v := math.SmallestNonzeroFloat64
	return T(v*0.9) == 0
}

func isFloat64[T Number]() bool {
	return isFloat[T]() && !isFloat32[T]()
}

func sizeOf[T Number]() uint64 {
	if isFloat32[T]() {
		return 4
	}

	x := uint16(1 << 8)
	y := uint32(2 << 16)
	z := uint64(4 << 32)

	return 1 + uint64(T(x))>>8 + uint64(T(y))>>16 + uint64(T(z))>>32
}

func minOf[T Number]() any {
	switch {
	case isFloat64[T]():
		return float64(-math.MaxFloat64)
	case isFloat32[T]():
		return float32(-math.MaxFloat32)
	case isUnsigned[T]():
		return T(0)
	}
	v := int64(1) << (8*sizeOf[T]() - 1)
	return T(v)
}

func maxOf[T Number]() any {
	switch {
	case isFloat64[T]():
		return float64(math.MaxFloat64)
	// there is no case for float64, as nothing can overflow it
	case isFloat32[T]():
		return float32(math.MaxFloat32)
	}
	v := uint64(1)<<(8*sizeOf[T]()-1) - 1
	if isUnsigned[T]() {
		v = v*2 + 1
	}

	return T(v)
}