//
// Copyright 2020-2022 Sean C Foley
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//

package ipaddr

import (
	"fmt"
	"math/big"
	"unsafe"

	"github.com/seancfoley/ipaddress-go/ipaddr/addrerr"
)

type IPv4SegInt = uint8
type IPv4SegmentValueProvider func(segmentIndex int) IPv4SegInt

// WrapIPv4SegmentValueProvider converts the given IPv4SegmentValueProvider to a SegmentValueProvider.
func WrapIPv4SegmentValueProvider(f IPv4SegmentValueProvider) SegmentValueProvider {
	if f == nil {
		return nil
	}
	return func(segmentIndex int) SegInt {
		return SegInt(f(segmentIndex))
	}
}

// WrapSegmentValueProviderForIPv4 converts the given SegmentValueProvider to an IPv4SegmentValueProvider.
// Values that do not fit IPv4SegInt are truncated.
func WrapSegmentValueProviderForIPv4(f SegmentValueProvider) IPv4SegmentValueProvider {
	if f == nil {
		return nil
	}
	return func(segmentIndex int) IPv4SegInt {
		return IPv4SegInt(f(segmentIndex))
	}
}

const useIPv4SegmentCache = true

type ipv4SegmentValues struct {
	value      IPv4SegInt
	upperValue IPv4SegInt
	prefLen    PrefixLen
	cache      divCache
}

func (seg *ipv4SegmentValues) getAddrType() addrType {
	return ipv4Type
}

func (seg *ipv4SegmentValues) includesZero() bool {
	return seg.value == 0
}

func (seg *ipv4SegmentValues) includesMax() bool {
	return seg.upperValue == 0xff
}

func (seg *ipv4SegmentValues) isMultiple() bool {
	return seg.value != seg.upperValue
}

func (seg *ipv4SegmentValues) getCount() *big.Int {
	return big.NewInt(int64(seg.upperValue-seg.value) + 1)
}

func (seg *ipv4SegmentValues) getBitCount() BitCount {
	return IPv4BitsPerSegment
}

func (seg *ipv4SegmentValues) getByteCount() int {
	return IPv4BytesPerSegment
}

func (seg *ipv4SegmentValues) getValue() *BigDivInt {
	return big.NewInt(int64(seg.value))
}

func (seg *ipv4SegmentValues) getUpperValue() *BigDivInt {
	return big.NewInt(int64(seg.upperValue))
}

func (seg *ipv4SegmentValues) getDivisionValue() DivInt {
	return DivInt(seg.value)
}

func (seg *ipv4SegmentValues) getUpperDivisionValue() DivInt {
	return DivInt(seg.upperValue)
}

func (seg *ipv4SegmentValues) getDivisionPrefixLength() PrefixLen {
	return seg.prefLen
}

func (seg *ipv4SegmentValues) deriveNew(val, upperVal DivInt, prefLen PrefixLen) divisionValues {
	return newIPv4SegmentPrefixedValues(IPv4SegInt(val), IPv4SegInt(upperVal), prefLen)
}

func (seg *ipv4SegmentValues) derivePrefixed(prefLen PrefixLen) divisionValues {
	return newIPv4SegmentPrefixedValues(seg.value, seg.upperValue, prefLen)
}

func (seg *ipv4SegmentValues) deriveNewSeg(val SegInt, prefLen PrefixLen) divisionValues {
	return newIPv4SegmentPrefixedVal(IPv4SegInt(val), prefLen)
}

func (seg *ipv4SegmentValues) deriveNewMultiSeg(val, upperVal SegInt, prefLen PrefixLen) divisionValues {
	return newIPv4SegmentPrefixedValues(IPv4SegInt(val), IPv4SegInt(upperVal), prefLen)
}

func (seg *ipv4SegmentValues) getCache() *divCache {
	return &seg.cache
}

func (seg *ipv4SegmentValues) getSegmentValue() SegInt {
	return SegInt(seg.value)
}

func (seg *ipv4SegmentValues) getUpperSegmentValue() SegInt {
	return SegInt(seg.upperValue)
}

func (seg *ipv4SegmentValues) calcBytesInternal() (bytes, upperBytes []byte) {
	bytes = []byte{byte(seg.value)}
	if seg.isMultiple() {
		upperBytes = []byte{byte(seg.upperValue)}
	} else {
		upperBytes = bytes
	}
	return
}

func (seg *ipv4SegmentValues) bytesInternal(upper bool) []byte {
	if upper {
		return []byte{byte(seg.upperValue)}
	}
	return []byte{byte(seg.value)}
}

var _ divisionValues = &ipv4SegmentValues{}

var zeroIPv4Seg = NewIPv4Segment(0)
var zeroIPv4SegZeroPrefix = NewIPv4PrefixedSegment(0, cacheBitCount(0))
var zeroIPv4SegPrefixBlock = NewIPv4RangePrefixedSegment(0, IPv4MaxValuePerSegment, cacheBitCount(0))

// IPv4AddressSegment represents a segment of an IPv4 address.
// An IPv4 segment contains a single value or a range of sequential values, a prefix length, and it has bit length of 8 bits.
//
// Like strings, segments are immutable, which also makes them concurrency-safe.
//
// See AddressSegment for more details regarding segments.
type IPv4AddressSegment struct {
	ipAddressSegmentInternal
}

func (seg *IPv4AddressSegment) init() *IPv4AddressSegment {
	if seg.divisionValues == nil {
		return zeroIPv4Seg
	}
	return seg
}

// GetIPv4SegmentValue returns the lower value.  Same as GetSegmentValue but returned as a IPv4SegInt.
func (seg *IPv4AddressSegment) GetIPv4SegmentValue() IPv4SegInt {
	return IPv4SegInt(seg.GetSegmentValue())
}

// GetIPv4UpperSegmentValue returns the lower value.  Same as GetUpperSegmentValue but returned as a IPv4SegInt.
func (seg *IPv4AddressSegment) GetIPv4UpperSegmentValue() IPv4SegInt {
	return IPv4SegInt(seg.GetUpperSegmentValue())
}

// Contains returns whether this is same type and version as the given segment and whether it contains all values in the given segment.
func (seg *IPv4AddressSegment) Contains(other AddressSegmentType) bool {
	if seg == nil {
		return other == nil || other.ToSegmentBase() == nil
	}
	return seg.init().contains(other)
}

// Equal returns whether the given segment is equal to this segment.
// Two segments are equal if they match:
//  - type/version: IPv4
//  - value range
// Prefix lengths are ignored.
func (seg *IPv4AddressSegment) Equal(other AddressSegmentType) bool {
	if seg == nil {
		return other == nil || other.ToDiv() == nil
	}
	return seg.init().equal(other)
}

// Compare returns a negative integer, zero, or a positive integer if this address segment is less than, equal, or greater than the given item.
// Any address item is comparable to any other.  All address items use CountComparator to compare.
func (seg *IPv4AddressSegment) Compare(item AddressItem) int {
	if seg != nil {
		seg = seg.init()
	}
	return CountComparator.Compare(seg, item)
}

// CompareSize compares the counts of two segments, the number of individual values within.
//
// Rather than calculating counts with GetCount, there can be more efficient ways of determining whether one represents more individual values than another.
//
// CompareSize returns a positive integer if this segment has a larger count than the one given, zero if they are the same, or a negative integer if the other has a larger count.
func (seg *IPv4AddressSegment) CompareSize(other AddressItem) int {
	if seg == nil {
		if isNilItem(other) {
			return 0
		}
		// we have size 0, other has size >= 1
		return -1
	}
	return seg.init().compareSize(other)
}

// PrefixContains returns whether the prefix values in the prefix of the given segment are also prefix values in this segment.
// It returns whether the prefix of this segment contains the prefix of the given segment.
func (seg *IPv4AddressSegment) PrefixContains(other AddressSegmentType, prefixLength BitCount) bool {
	return seg.init().ipAddressSegmentInternal.PrefixContains(other, prefixLength)
}

// PrefixEqual returns whether the prefix bits of this segment match the same bits of the given segment.
// It returns whether the two segments share the same range of prefix values using the given prefix length.
func (seg *IPv4AddressSegment) PrefixEqual(other AddressSegmentType, prefixLength BitCount) bool {
	return seg.init().ipAddressSegmentInternal.PrefixEqual(other, prefixLength)
}

// GetBitCount returns the number of bits in each value comprising this address item, which is 8.
func (seg *IPv4AddressSegment) GetBitCount() BitCount {
	return IPv4BitsPerSegment
}

// GetByteCount returns the number of bytes required for each value comprising this address item, which is 1.
func (seg *IPv4AddressSegment) GetByteCount() int {
	return IPv4BytesPerSegment
}

// GetMaxValue gets the maximum possible value for this type or version of segment, determined by the number of bits.
//
// For the highest range value of this particular segment, use GetUpperSegmentValue.
func (seg *IPv4AddressSegment) GetMaxValue() IPv4SegInt {
	return 0xff
}

// GetLower returns a segment representing just the lowest value in the range, which will be the same segment if it represents a single value.
func (seg *IPv4AddressSegment) GetLower() *IPv4AddressSegment {
	return seg.init().getLower().ToIPv4()
}

// GetUpper returns a segment representing just the highest value in the range, which will be the same segment if it represents a single value.
func (seg *IPv4AddressSegment) GetUpper() *IPv4AddressSegment {
	return seg.init().getUpper().ToIPv4()
}

// IsMultiple returns whether this segment represents multiple values.
func (seg *IPv4AddressSegment) IsMultiple() bool {
	return seg != nil && seg.isMultiple()
}

// GetCount returns the count of possible distinct values for this item.
// If not representing multiple values, the count is 1.
//
// For instance, a segment with the value range of 3-7 has count 5.
//
// Use IsMultiple if you simply want to know if the count is greater than 1.
func (seg *IPv4AddressSegment) GetCount() *big.Int {
	if seg == nil {
		return bigZero()
	}
	return seg.getCount()
}

// GetPrefixCountLen returns the count of the number of distinct prefix values for the given prefix length in the range of values of this segment.
func (seg *IPv4AddressSegment) GetPrefixCountLen(segmentPrefixLength BitCount) *big.Int {
	return seg.init().ipAddressSegmentInternal.GetPrefixCountLen(segmentPrefixLength)
}

// GetPrefixValueCountLen returns the same value as GetPrefixCountLen as an integer.
func (seg *IPv4AddressSegment) GetPrefixValueCountLen(segmentPrefixLength BitCount) SegIntCount {
	return seg.init().ipAddressSegmentInternal.GetPrefixValueCountLen(segmentPrefixLength)
}

// IsOneBit returns true if the bit in the lower value of this segment at the given index is 1, where index 0 is the most significant bit.
func (seg *IPv4AddressSegment) IsOneBit(segmentBitIndex BitCount) bool {
	return seg.init().ipAddressSegmentInternal.IsOneBit(segmentBitIndex)
}

// Bytes returns the lowest value in the address segment range as a byte slice.
func (seg *IPv4AddressSegment) Bytes() []byte {
	return seg.init().ipAddressSegmentInternal.Bytes()
}

// UpperBytes returns the highest value in the address segment range as a byte slice.
func (seg *IPv4AddressSegment) UpperBytes() []byte {
	return seg.init().ipAddressSegmentInternal.UpperBytes()
}

// CopyBytes copies the lowest value in the address segment range into a byte slice.
//
// If the value can fit in the given slice, the value is copied into that slice and a length-adjusted sub-slice is returned.
// Otherwise, a new slice is created and returned with the value.
func (seg *IPv4AddressSegment) CopyBytes(bytes []byte) []byte {
	return seg.init().ipAddressSegmentInternal.CopyBytes(bytes)
}

// CopyUpperBytes copies the highest value in the address segment range into a byte slice.
//
// If the value can fit in the given slice, the value is copied into that slice and a length-adjusted sub-slice is returned.
// Otherwise, a new slice is created and returned with the value.
func (seg *IPv4AddressSegment) CopyUpperBytes(bytes []byte) []byte {
	return seg.init().ipAddressSegmentInternal.CopyUpperBytes(bytes)
}

// GetPrefixValueCount returns the count of prefixes in this segment for its prefix length, or the total count if it has no prefix length.
func (seg *IPv4AddressSegment) GetPrefixValueCount() SegIntCount {
	return seg.init().ipAddressSegmentInternal.GetPrefixValueCount()
}

// MatchesWithPrefixMask applies the network mask of the given bit-length to this segment and then compares the result with the given value masked by the same mask,
//returning true if the resulting range matches the given single value.
func (seg *IPv4AddressSegment) MatchesWithPrefixMask(value IPv4SegInt, networkBits BitCount) bool {
	return seg.init().ipAddressSegmentInternal.MatchesWithPrefixMask(SegInt(value), networkBits)
}

// GetBlockMaskPrefixLen returns the prefix length if this address segment is equivalent to the mask for a CIDR prefix block.
// Otherwise, it returns nil.
// A CIDR network mask is a segment with all ones in the network bits and then all zeros in the host bits.
// A CIDR host mask is a segment with all zeros in the network bits and then all ones in the host bits.
// The prefix length is the bit-length of the network bits.
//
// Also, keep in mind that the prefix length returned by this method is not equivalent to the prefix length of this segment.
// The prefix length returned here indicates the whether the value of this segment can be used as a mask for the network and host
// bits of any other segment.  Therefore, the two values can be different values, or one can be nil while the other is not.
//
// This method applies only to the lower value of the range if this segment represents multiple values.
func (seg *IPv4AddressSegment) GetBlockMaskPrefixLen(network bool) PrefixLen {
	return seg.init().ipAddressSegmentInternal.GetBlockMaskPrefixLen(network)
}

// GetTrailingBitCount returns the number of consecutive trailing one or zero bits.
// If ones is true, returns the number of consecutive trailing zero bits.
// Otherwise, returns the number of consecutive trailing one bits.
//
// This method applies only to the lower value of the range if this segment represents multiple values.
func (seg *IPv4AddressSegment) GetTrailingBitCount(ones bool) BitCount {
	return seg.init().ipAddressSegmentInternal.GetTrailingBitCount(ones)
}

// GetLeadingBitCount returns the number of consecutive leading one or zero bits.
// If ones is true, returns the number of consecutive leading one bits.
// Otherwise, returns the number of consecutive leading zero bits.
//
// This method applies only to the lower value of the range if this segment represents multiple values.
func (seg *IPv4AddressSegment) GetLeadingBitCount(ones bool) BitCount {
	return seg.init().ipAddressSegmentInternal.GetLeadingBitCount(ones)
}

// ToPrefixedNetworkSegment returns a segment with the network bits matching this segment but the host bits converted to zero.
// The new segment will be assigned the given prefix length.
func (seg *IPv4AddressSegment) ToPrefixedNetworkSegment(segmentPrefixLength PrefixLen) *IPv4AddressSegment {
	return seg.init().toPrefixedNetworkDivision(segmentPrefixLength).ToIPv4()
}

// ToNetworkSegment returns a segment with the network bits matching this segment but the host bits converted to zero.
// The new segment will have no assigned prefix length.
func (seg *IPv4AddressSegment) ToNetworkSegment(segmentPrefixLength PrefixLen) *IPv4AddressSegment {
	return seg.init().toNetworkDivision(segmentPrefixLength, false).ToIPv4()
}

// ToPrefixedHostSegment returns a segment with the host bits matching this segment but the network bits converted to zero.
// The new segment will be assigned the given prefix length.
func (seg *IPv4AddressSegment) ToPrefixedHostSegment(segmentPrefixLength PrefixLen) *IPv4AddressSegment {
	return seg.init().toPrefixedHostDivision(segmentPrefixLength).ToIPv4()
}

// ToHostSegment returns a segment with the host bits matching this segment but the network bits converted to zero.
// The new segment will have no assigned prefix length.
func (seg *IPv4AddressSegment) ToHostSegment(segmentPrefixLength PrefixLen) *IPv4AddressSegment {
	return seg.init().toHostDivision(segmentPrefixLength, false).ToIPv4()
}

// Iterator provides an iterator to iterate through the individual address segments of this address segment.
//
// When iterating, the prefix length is preserved.  Remove it using WithoutPrefixLen prior to iterating if you wish to drop it from all individual address segments.
//
// Call IsMultiple to determine if this instance represents multiple address segments, or GetValueCount for the count.
func (seg *IPv4AddressSegment) Iterator() Iterator[*IPv4AddressSegment] {
	if seg == nil {
		return ipv4SegmentIterator{nilSegIterator()}
	}
	return ipv4SegmentIterator{seg.init().iterator()}
}

// PrefixBlockIterator provides an iterator to iterate through the individual prefix blocks, one for each prefix of this address segment.
// Each iterated address segment will be a prefix block with the same prefix length as this address segment.
//
// If this address segment has no prefix length, then this is equivalent to Iterator.
func (seg *IPv4AddressSegment) PrefixBlockIterator() Iterator[*IPv4AddressSegment] {
	return ipv4SegmentIterator{seg.init().prefixBlockIterator()}
}

// PrefixedBlockIterator provides an iterator to iterate through the individual prefix blocks of the given prefix length in this segment,
// one for each prefix of this address or subnet.
//
// It is similar to PrefixBlockIterator except that this method allows you to specify the prefix length.
func (seg *IPv4AddressSegment) PrefixedBlockIterator(segmentPrefixLen BitCount) Iterator[*IPv4AddressSegment] {
	return ipv4SegmentIterator{seg.init().prefixedBlockIterator(segmentPrefixLen)}
}

// PrefixIterator provides an iterator to iterate through the individual prefixes of this segment,
// each iterated element spanning the range of values for its prefix.
//
// It is similar to the prefix block iterator, except for possibly the first and last iterated elements, which might not be prefix blocks,
// instead constraining themselves to values from this segment.
//
// If this address segment has no prefix length, then this is equivalent to Iterator.
func (seg *IPv4AddressSegment) PrefixIterator() Iterator[*IPv4AddressSegment] {
	return ipv4SegmentIterator{seg.init().prefixIterator()}
}

// IsPrefixed returns whether this segment has an associated prefix length.
func (seg *IPv4AddressSegment) IsPrefixed() bool {
	return seg != nil && seg.isPrefixed()
}

// WithoutPrefixLen returns a segment with the same value range but without a prefix length.
func (seg *IPv4AddressSegment) WithoutPrefixLen() *IPv4AddressSegment {
	if !seg.IsPrefixed() {
		return seg
	}
	return seg.withoutPrefixLen().ToIPv4()
}

// ReverseBits returns a segment with the bits reversed.
//
// If this segment represents a range of values that cannot be reversed, then this returns an error.
//
// To be reversible, a range must include all values except possibly the largest and/or smallest, which reverse to themselves.
// Otherwise the result is not contiguous and thus cannot be represented by a sequential range of values.
//
// If perByte is true, the bits are reversed within each byte, otherwise all the bits are reversed.
func (seg *IPv4AddressSegment) ReverseBits(_ bool) (res *IPv4AddressSegment, err addrerr.IncompatibleAddressError) {
	if seg.divisionValues == nil {
		res = seg
		return
	}
	if seg.isMultiple() {
		if isReversible := seg.isReversibleRange(false); isReversible {
			res = seg.WithoutPrefixLen()
			return
		}
		err = &incompatibleAddressError{addressError{key: "ipaddress.error.reverseRange"}}
		return
	}
	oldVal := IPv4SegInt(seg.GetSegmentValue())
	val := IPv4SegInt(reverseUint8(uint8(oldVal)))
	if oldVal == val && !seg.isPrefixed() {
		res = seg
	} else {
		res = NewIPv4Segment(val)
	}
	return
}

// ReverseBytes returns a segment with the bytes reversed, which for an IPv4 segment is always the original segment.
func (seg *IPv4AddressSegment) ReverseBytes() (*IPv4AddressSegment, addrerr.IncompatibleAddressError) {
	return seg, nil
}

func (seg *IPv4AddressSegment) isJoinableTo(low *IPv4AddressSegment) bool {
	// if the high segment has a range, the low segment must match the full range,
	// otherwise it is not possible to create an equivalent range when joining
	return !seg.isMultiple() || low.IsFullRange()
}

// Join joins this segment with another IPv4 segment to produce an IPv6 segment.
func (seg *IPv4AddressSegment) Join(low *IPv4AddressSegment) (*IPv6AddressSegment, addrerr.IncompatibleAddressError) {
	prefixLength := seg.getJoinedSegmentPrefixLen(low.GetSegmentPrefixLen())
	if !seg.isJoinableTo(low) {
		return nil, &incompatibleAddressError{addressError: addressError{key: "ipaddress.error.invalidMixedRange"}}
	}
	return NewIPv6RangePrefixedSegment(
		IPv6SegInt((seg.GetSegmentValue()<<8)|low.getSegmentValue()),
		IPv6SegInt((seg.GetUpperSegmentValue()<<8)|low.getUpperSegmentValue()),
		prefixLength), nil
}

func (seg *IPv4AddressSegment) getJoinedSegmentPrefixLen(lowBits PrefixLen) PrefixLen {
	highBits := seg.GetSegmentPrefixLen()
	if lowBits == nil {
		return nil
	}
	lowBitCount := lowBits.bitCount()
	if lowBitCount == 0 {
		return highBits
	}
	return cacheBitCount(lowBitCount + IPv4BitsPerSegment)
}

// ToDiv converts to an AddressDivision, a polymorphic type usable with all address segments and divisions.
// Afterwards, you can convert back with ToIPv4.
//
// ToDiv can be called with a nil receiver, enabling you to chain this method with methods that might return a nil pointer.
func (seg *IPv4AddressSegment) ToDiv() *AddressDivision {
	return seg.ToIP().ToDiv()
}

// ToSegmentBase converts to an AddressSegment, a polymorphic type usable with all address segments.
// Afterwards, you can convert back with ToIPv4.
//
// ToSegmentBase can be called with a nil receiver, enabling you to chain this method with methods that might return a nil pointer.
func (seg *IPv4AddressSegment) ToSegmentBase() *AddressSegment {
	return seg.ToIP().ToSegmentBase()
}

// ToIP converts to an IPAddressSegment, a polymorphic type usable with all IP address segments.
// Afterwards, you can convert back with ToIPv4.
//
// ToIP can be called with a nil receiver, enabling you to chain this method with methods that might return a nil pointer.
func (seg *IPv4AddressSegment) ToIP() *IPAddressSegment {
	if seg == nil {
		return nil
	}
	return (*IPAddressSegment)(seg.init())
}

// GetString produces a normalized string to represent the segment.
// If the segment is a CIDR network prefix block for its prefix length, then the string contains only the lower value of the block range.
// Otherwise, the explicit range will be printed.
//
// The string returned is useful in the context of creating strings for address sections or full addresses,
// in which case the radix and bit-length can be deduced from the context.
// The String method produces strings more appropriate when no context is provided.
func (seg *IPv4AddressSegment) GetString() string {
	if seg == nil {
		return nilString()
	}
	return seg.init().getString()
}

// GetWildcardString produces a normalized string to represent the segment, favouring wildcards and range characters while ignoring any network prefix length.
// The explicit range of a range-valued segment will be printed.
//
// The string returned is useful in the context of creating strings for address sections or full addresses,
// in which case the radix and the bit-length can be deduced from the context.
// The String method produces strings more appropriate when no context is provided.
func (seg *IPv4AddressSegment) GetWildcardString() string {
	if seg == nil {
		return nilString()
	}
	return seg.init().getWildcardString()
}

// Format implements [fmt.Formatter] interface. It accepts the formats
//  - 'v' for the default address and section format (either the normalized or canonical string),
//  - 's' (string) for the same,
//  - 'b' (binary), 'o' (octal with 0 prefix), 'O' (octal with 0o prefix),
//  - 'd' (decimal), 'x' (lowercase hexadecimal), and
//  - 'X' (uppercase hexadecimal).
// Also supported are some of fmt's format flags for integral types.
// Sign control is not supported since addresses and sections are never negative.
// '#' for an alternate format is supported, which adds a leading zero for octal, and for hexadecimal it adds
// a leading "0x" or "0X" for "%#x" and "%#X" respectively.
// Also supported is specification of minimum digits precision, output field width,
// space or zero padding, and '-' for left or right justification.
func (seg IPv4AddressSegment) Format(state fmt.State, verb rune) {
	seg.init().ipAddressSegmentInternal.Format(state, verb)
}

// String produces a string that is useful when a segment string is provided with no context.  It uses the decimal radix.
// GetWildcardString is more appropriate in context with other segments or divisions.  It does not use a string prefix and uses '*' for full-range segments.
// GetString is more appropriate in context with prefix lengths, it uses zeros instead of wildcards with full prefix block ranges alongside prefix lengths.
func (seg *IPv4AddressSegment) String() string {
	if seg == nil {
		return nilString()
	}
	return seg.init().toString()
}

// NewIPv4Segment constructs a segment of an IPv4 address with the given value.
func NewIPv4Segment(val IPv4SegInt) *IPv4AddressSegment {
	return newIPv4Segment(newIPv4SegmentVal(val))
}

// NewIPv4RangeSegment constructs a segment of an IPv4 subnet with the given range of sequential values.
func NewIPv4RangeSegment(val, upperVal IPv4SegInt) *IPv4AddressSegment {
	return newIPv4Segment(newIPv4SegmentPrefixedValues(val, upperVal, nil))
}

// NewIPv4PrefixedSegment constructs a segment of an IPv4 address with the given value and assigned prefix length.
func NewIPv4PrefixedSegment(val IPv4SegInt, prefixLen PrefixLen) *IPv4AddressSegment {
	return newIPv4Segment(newIPv4SegmentPrefixedVal(val, prefixLen))
}

// NewIPv4RangePrefixedSegment constructs a segment of an IPv4 subnet with the given range of sequential values and assigned prefix length.
func NewIPv4RangePrefixedSegment(val, upperVal IPv4SegInt, prefixLen PrefixLen) *IPv4AddressSegment {
	return newIPv4Segment(newIPv4SegmentPrefixedValues(val, upperVal, prefixLen))
}

func newIPv4Segment(vals *ipv4SegmentValues) *IPv4AddressSegment {
	return &IPv4AddressSegment{
		ipAddressSegmentInternal{
			addressSegmentInternal{
				addressDivisionInternal{
					addressDivisionBase{
						vals,
					},
				},
			},
		},
	}
}

type ipv4DivsBlock struct {
	block []ipv4SegmentValues
}

var (
	allRangeValsIPv4 = &ipv4SegmentValues{
		upperValue: IPv4MaxValuePerSegment,
		cache: divCache{
			isSinglePrefBlock: &falseVal,
		},
	}
	allPrefixedCacheIPv4   = makePrefixCache()
	segmentCacheIPv4       = makeSegmentCache()
	segmentPrefixCacheIPv4 = makeDivsBlock()
	prefixBlocksCacheIPv4  = makeDivsBlock()
)

func makeDivsBlock() []*ipv4DivsBlock {
	if useIPv4SegmentCache {
		return make([]*ipv4DivsBlock, IPv4BitsPerSegment+1)
	}
	return nil
}

func makePrefixCache() (allPrefixedCacheIPv4 []ipv4SegmentValues) {
	if useIPv4SegmentCache {
		allPrefixedCacheIPv4 = make([]ipv4SegmentValues, IPv4BitsPerSegment+1)
		for i := range allPrefixedCacheIPv4 {
			vals := &allPrefixedCacheIPv4[i]
			vals.upperValue = IPv4MaxValuePerSegment
			vals.prefLen = cacheBitCount(i)
			vals.cache.isSinglePrefBlock = &falseVal
		}
		allPrefixedCacheIPv4[0].cache.isSinglePrefBlock = &trueVal
	}
	return
}

func makeSegmentCache() (segmentCacheIPv4 []ipv4SegmentValues) {
	if useIPv4SegmentCache {
		segmentCacheIPv4 = make([]ipv4SegmentValues, IPv4MaxValuePerSegment+1)
		for i := range segmentCacheIPv4 {
			vals := &segmentCacheIPv4[i]
			segi := IPv4SegInt(i)
			vals.value = segi
			vals.upperValue = segi
			vals.cache.isSinglePrefBlock = &falseVal
		}
	}
	return
}

func newIPv4SegmentVal(value IPv4SegInt) *ipv4SegmentValues {
	if useIPv4SegmentCache {
		result := &segmentCacheIPv4[value]
		return result
	}
	return &ipv4SegmentValues{
		value:      value,
		upperValue: value,
		cache: divCache{
			isSinglePrefBlock: &falseVal,
		},
	}
}

func newIPv4SegmentPrefixedVal(value IPv4SegInt, prefLen PrefixLen) (result *ipv4SegmentValues) {
	if prefLen == nil {
		return newIPv4SegmentVal(value)
	}
	segmentPrefixLength := prefLen.bitCount()
	if segmentPrefixLength < 0 {
		segmentPrefixLength = 0
	} else if segmentPrefixLength > IPv4BitsPerSegment {
		segmentPrefixLength = IPv4BitsPerSegment
	}
	prefLen = cacheBitCount(segmentPrefixLength) // this ensures we use the prefix length cache for all segments
	if useIPv4SegmentCache {
		prefixIndex := segmentPrefixLength
		cache := segmentPrefixCacheIPv4
		block := (*ipv4DivsBlock)(atomicLoadPointer((*unsafe.Pointer)(unsafe.Pointer(&cache[prefixIndex]))))
		if block == nil {
			block = &ipv4DivsBlock{make([]ipv4SegmentValues, IPv4MaxValuePerSegment+1)}
			vals := block.block
			var isSinglePrefBlock *bool
			if prefixIndex == IPv4BitsPerSegment {
				isSinglePrefBlock = &trueVal
			} else {
				isSinglePrefBlock = &falseVal
			}
			for i := range vals {
				value := &vals[i]
				segi := IPv4SegInt(i)
				value.value = segi
				value.upperValue = segi
				value.prefLen = prefLen
				value.cache.isSinglePrefBlock = isSinglePrefBlock
			}
			dataLoc := (*unsafe.Pointer)(unsafe.Pointer(&cache[prefixIndex]))
			atomicStorePointer(dataLoc, unsafe.Pointer(block))
		}
		result = &block.block[value]
		return result
	}
	var isSinglePrefBlock *bool
	if segmentPrefixLength == IPv4BitsPerSegment {
		isSinglePrefBlock = &trueVal
	} else {
		isSinglePrefBlock = &falseVal
	}
	return &ipv4SegmentValues{
		value:      value,
		upperValue: value,
		prefLen:    prefLen,
		cache: divCache{
			isSinglePrefBlock: isSinglePrefBlock,
		},
	}
}

func newIPv4SegmentPrefixedValues(value, upperValue IPv4SegInt, prefLen PrefixLen) *ipv4SegmentValues {
	var isSinglePrefBlock *bool
	if prefLen == nil {
		if value == upperValue {
			return newIPv4SegmentVal(value)
		} else if value > upperValue {
			value, upperValue = upperValue, value
		}
		if useIPv4SegmentCache && value == 0 && upperValue == IPv4MaxValuePerSegment {
			return allRangeValsIPv4
		}
		isSinglePrefBlock = &falseVal
	} else {
		if value == upperValue {
			return newIPv4SegmentPrefixedVal(value, prefLen)
		} else if value > upperValue {
			value, upperValue = upperValue, value
		}
		segmentPrefixLength := prefLen.bitCount()
		if segmentPrefixLength < 0 {
			segmentPrefixLength = 0
		} else if segmentPrefixLength > IPv4BitsPerSegment {
			segmentPrefixLength = IPv4BitsPerSegment
		}
		prefLen = cacheBitCount(segmentPrefixLength) // this ensures we use the prefix length cache for all segments
		if useIPv4SegmentCache {
			// cache is the prefix block for any prefix length
			shiftBits := uint(IPv4BitsPerSegment - segmentPrefixLength)
			nmask := ^IPv4SegInt(0) << shiftBits
			prefixBlockLower := value & nmask
			hmask := ^nmask
			prefixBlockUpper := value | hmask
			if value == prefixBlockLower && upperValue == prefixBlockUpper {
				valueIndex := value >> shiftBits
				cache := prefixBlocksCacheIPv4
				prefixIndex := segmentPrefixLength
				block := (*ipv4DivsBlock)(atomicLoadPointer((*unsafe.Pointer)(unsafe.Pointer(&cache[prefixIndex]))))
				var result *ipv4SegmentValues
				if block == nil {
					block = &ipv4DivsBlock{make([]ipv4SegmentValues, 1<<uint(segmentPrefixLength))}
					vals := block.block
					for i := range vals {
						value := &vals[i]
						segi := IPv4SegInt(i << shiftBits)
						value.value = segi
						value.upperValue = segi | hmask
						value.prefLen = prefLen
						value.cache.isSinglePrefBlock = &trueVal
					}
					dataLoc := (*unsafe.Pointer)(unsafe.Pointer(&cache[prefixIndex]))
					atomicStorePointer(dataLoc, unsafe.Pointer(block))
				}
				result = &block.block[valueIndex]
				return result
			}
			if value == 0 {
				// cache is 0-255 for any prefix length
				if upperValue == IPv4MaxValuePerSegment {
					result := &allPrefixedCacheIPv4[segmentPrefixLength]
					return result
				}
			}
			isSinglePrefBlock = &falseVal
		}
	}
	return &ipv4SegmentValues{
		value:      value,
		upperValue: upperValue,
		prefLen:    prefLen,
		cache: divCache{
			isSinglePrefBlock: isSinglePrefBlock,
		},
	}
}