// Copyright 2020 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package internal_gengo

import (
	"strings"

	"google.golang.org/protobuf/compiler/protogen"
	"google.golang.org/protobuf/internal/genid"
)

// Specialized support for well-known types are hard-coded into the generator
// as opposed to being injected in adjacent .go sources in the generated package
// in order to support specialized build systems like Bazel that always generate
// dynamically from the source .proto files.

func genMessageKnownFunctions(g *protogen.GeneratedFile, f *fileInfo, m *messageInfo) {
	switch m.Desc.FullName() {
	case genid.Any_message_fullname:
		g.P("// MarshalFrom marshals src into dst as the underlying message")
		g.P("// using the provided marshal options.")
		g.P("//")
		g.P("// If no options are specified, call dst.MarshalFrom instead.")
		g.P("func MarshalFrom(dst *Any, src ", protoPackage.Ident("Message"), ", opts ", protoPackage.Ident("MarshalOptions"), ") error {")
		g.P("	const urlPrefix = \"type.googleapis.com/\"")
		g.P("	if src == nil {")
		g.P("		return ", protoimplPackage.Ident("X"), ".NewError(\"invalid nil source message\")")
		g.P("	}")
		g.P("	b, err := opts.Marshal(src)")
		g.P("	if err != nil {")
		g.P("		return err")
		g.P("	}")
		g.P("	dst.TypeUrl = urlPrefix + string(src.ProtoReflect().Descriptor().FullName())")
		g.P("	dst.Value = b")
		g.P("	return nil")
		g.P("}")
		g.P()

		g.P("// UnmarshalTo unmarshals the underlying message from src into dst")
		g.P("// using the provided unmarshal options.")
		g.P("// It reports an error if dst is not of the right message type.")
		g.P("//")
		g.P("// If no options are specified, call src.UnmarshalTo instead.")
		g.P("func UnmarshalTo(src *Any, dst ", protoPackage.Ident("Message"), ", opts ", protoPackage.Ident("UnmarshalOptions"), ") error {")
		g.P("	if src.GetTypeUrl() == \"\" {")
		g.P("		return ", protoimplPackage.Ident("X"), ".NewError(\"invalid empty type URL\")")
		g.P("	}")
		g.P("	if !src.MessageIs(dst) {")
		g.P("		got := dst.ProtoReflect().Descriptor().FullName()")
		g.P("		want := src.MessageName()")
		g.P("		return ", protoimplPackage.Ident("X"), ".NewError(\"mismatching message types: got %q, want %q\", got, want)")
		g.P("	}")
		g.P("	return opts.Unmarshal(src.GetValue(), dst)")
		g.P("}")
		g.P()

		g.P("// UnmarshalNew unmarshals the underlying message from src into dst,")
		g.P("// which is newly created message using a type resolved from the type URL.")
		g.P("// The message type is resolved according to opt.Resolver,")
		g.P("// which should implement protoregistry.MessageTypeResolver.")
		g.P("// It reports an error if the underlying message type could not be resolved.")
		g.P("//")
		g.P("// If no options are specified, call src.UnmarshalNew instead.")
		g.P("func UnmarshalNew(src *Any, opts ", protoPackage.Ident("UnmarshalOptions"), ") (dst ", protoPackage.Ident("Message"), ", err error) {")
		g.P("	if src.GetTypeUrl() == \"\" {")
		g.P("		return nil, ", protoimplPackage.Ident("X"), ".NewError(\"invalid empty type URL\")")
		g.P("	}")
		g.P("	if opts.Resolver == nil {")
		g.P("		opts.Resolver = ", protoregistryPackage.Ident("GlobalTypes"))
		g.P("	}")
		g.P("	r, ok := opts.Resolver.(", protoregistryPackage.Ident("MessageTypeResolver"), ")")
		g.P("	if !ok {")
		g.P("		return nil, ", protoregistryPackage.Ident("NotFound"))
		g.P("	}")
		g.P("	mt, err := r.FindMessageByURL(src.GetTypeUrl())")
		g.P("	if err != nil {")
		g.P("		if err == ", protoregistryPackage.Ident("NotFound"), " {")
		g.P("			return nil, err")
		g.P("		}")
		g.P("		return nil, ", protoimplPackage.Ident("X"), ".NewError(\"could not resolve %q: %v\", src.GetTypeUrl(), err)")
		g.P("	}")
		g.P("	dst = mt.New().Interface()")
		g.P("	return dst, opts.Unmarshal(src.GetValue(), dst)")
		g.P("}")
		g.P()

		g.P("// MessageIs reports whether the underlying message is of the same type as m.")
		g.P("func (x *Any) MessageIs(m ", protoPackage.Ident("Message"), ") bool {")
		g.P("	if m == nil {")
		g.P("		return false")
		g.P("	}")
		g.P("	url := x.GetTypeUrl()")
		g.P("	name := string(m.ProtoReflect().Descriptor().FullName())")
		g.P("	if !", stringsPackage.Ident("HasSuffix"), "(url, name) {")
		g.P("		return false")
		g.P("	}")
		g.P("	return len(url) == len(name) || url[len(url)-len(name)-1] == '/'")
		g.P("}")
		g.P()

		g.P("// MessageName reports the full name of the underlying message,")
		g.P("// returning an empty string if invalid.")
		g.P("func (x *Any) MessageName() ", protoreflectPackage.Ident("FullName"), " {")
		g.P("	url := x.GetTypeUrl()")
		g.P("	name := ", protoreflectPackage.Ident("FullName"), "(url)")
		g.P("	if i := ", stringsPackage.Ident("LastIndexByte"), "(url, '/'); i >= 0 {")
		g.P("		name = name[i+len(\"/\"):]")
		g.P("	}")
		g.P("	if !name.IsValid() {")
		g.P("		return \"\"")
		g.P("	}")
		g.P("	return name")
		g.P("}")
		g.P()

		g.P("// MarshalFrom marshals m into x as the underlying message.")
		g.P("func (x *Any) MarshalFrom(m ", protoPackage.Ident("Message"), ") error {")
		g.P("	return MarshalFrom(x, m, ", protoPackage.Ident("MarshalOptions"), "{})")
		g.P("}")
		g.P()

		g.P("// UnmarshalTo unmarshals the contents of the underlying message of x into m.")
		g.P("// It resets m before performing the unmarshal operation.")
		g.P("// It reports an error if m is not of the right message type.")
		g.P("func (x *Any) UnmarshalTo(m ", protoPackage.Ident("Message"), ") error {")
		g.P("	return UnmarshalTo(x, m, ", protoPackage.Ident("UnmarshalOptions"), "{})")
		g.P("}")
		g.P()

		g.P("// UnmarshalNew unmarshals the contents of the underlying message of x into")
		g.P("// a newly allocated message of the specified type.")
		g.P("// It reports an error if the underlying message type could not be resolved.")
		g.P("func (x *Any) UnmarshalNew() (", protoPackage.Ident("Message"), ", error) {")
		g.P("	return UnmarshalNew(x, ", protoPackage.Ident("UnmarshalOptions"), "{})")
		g.P("}")
		g.P()

	case genid.Timestamp_message_fullname:
		g.P("// Now constructs a new Timestamp from the current time.")
		g.P("func Now() *Timestamp {")
		g.P("	return New(", timePackage.Ident("Now"), "())")
		g.P("}")
		g.P()

		g.P("// New constructs a new Timestamp from the provided time.Time.")
		g.P("func New(t ", timePackage.Ident("Time"), ") *Timestamp {")
		g.P("	return &Timestamp{Seconds: int64(t.Unix()), Nanos: int32(t.Nanosecond())}")
		g.P("}")
		g.P()

		g.P("// AsTime converts x to a time.Time.")
		g.P("func (x *Timestamp) AsTime() ", timePackage.Ident("Time"), " {")
		g.P("	return ", timePackage.Ident("Unix"), "(int64(x.GetSeconds()), int64(x.GetNanos())).UTC()")
		g.P("}")
		g.P()

		g.P("// IsValid reports whether the timestamp is valid.")
		g.P("// It is equivalent to CheckValid == nil.")
		g.P("func (x *Timestamp) IsValid() bool {")
		g.P("	return x.check() == 0")
		g.P("}")
		g.P()

		g.P("// CheckValid returns an error if the timestamp is invalid.")
		g.P("// In particular, it checks whether the value represents a date that is")
		g.P("// in the range of 0001-01-01T00:00:00Z to 9999-12-31T23:59:59Z inclusive.")
		g.P("func (x *Timestamp) CheckValid() error {")
		g.P("	switch x.check() {")
		g.P("	case invalidUnderflow:")
		g.P("		return ", protoimplPackage.Ident("X"), ".NewError(\"timestamp (%v) before 0001-01-01\", x)")
		g.P("	case invalidOverflow:")
		g.P("		return ", protoimplPackage.Ident("X"), ".NewError(\"timestamp (%v) after 9999-12-31\", x)")
		g.P("	case invalidNanos:")
		g.P("		return ", protoimplPackage.Ident("X"), ".NewError(\"timestamp (%v) has out-of-range nanos\", x)")
		g.P("	default:")
		g.P("		return nil")
		g.P("	}")
		g.P("}")
		g.P()

		g.P("const invalidUnderflow = 1")
		g.P("const invalidOverflow = 2")
		g.P("const invalidNanos = 3")
		g.P()

		g.P("func (x *Timestamp) check() uint {")
		g.P("	const minTimestamp = -62135596800  // Seconds between 1970-01-01T00:00:00Z and 0001-01-01T00:00:00Z, inclusive")
		g.P("	const maxTimestamp = +253402300799 // Seconds between 1970-01-01T00:00:00Z and 9999-12-31T23:59:59Z, inclusive")
		g.P("	secs := x.GetSeconds()")
		g.P("	nanos := x.GetNanos()")
		g.P("	switch {")
		g.P("	case secs < minTimestamp:")
		g.P("		return invalidUnderflow")
		g.P("	case secs > maxTimestamp:")
		g.P("		return invalidOverflow")
		g.P("	case nanos < 0 || nanos >= 1e9:")
		g.P("		return invalidNanos")
		g.P("	default:")
		g.P("		return 0")
		g.P("	}")
		g.P("}")
		g.P()

	case genid.Duration_message_fullname:
		g.P("// New constructs a new Duration from the provided time.Duration.")
		g.P("func New(d ", timePackage.Ident("Duration"), ") *Duration {")
		g.P("	nanos := d.Nanoseconds()")
		g.P("	secs := nanos / 1e9")
		g.P("	nanos -= secs * 1e9")
		g.P("	return &Duration{Seconds: int64(secs), Nanos: int32(nanos)}")
		g.P("}")
		g.P()

		g.P("// AsDuration converts x to a time.Duration,")
		g.P("// returning the closest duration value in the event of overflow.")
		g.P("func (x *Duration) AsDuration() ", timePackage.Ident("Duration"), " {")
		g.P("	secs := x.GetSeconds()")
		g.P("	nanos := x.GetNanos()")
		g.P("	d := ", timePackage.Ident("Duration"), "(secs) * ", timePackage.Ident("Second"))
		g.P("	overflow := d/", timePackage.Ident("Second"), " != ", timePackage.Ident("Duration"), "(secs)")
		g.P("	d += ", timePackage.Ident("Duration"), "(nanos) * ", timePackage.Ident("Nanosecond"))
		g.P("	overflow = overflow || (secs < 0 && nanos < 0 && d > 0)")
		g.P("	overflow = overflow || (secs > 0 && nanos > 0 && d < 0)")
		g.P("	if overflow {")
		g.P("		switch {")
		g.P("		case secs < 0:")
		g.P("			return ", timePackage.Ident("Duration"), "(", mathPackage.Ident("MinInt64"), ")")
		g.P("		case secs > 0:")
		g.P("			return ", timePackage.Ident("Duration"), "(", mathPackage.Ident("MaxInt64"), ")")
		g.P("		}")
		g.P("	}")
		g.P("	return d")
		g.P("}")
		g.P()

		g.P("// IsValid reports whether the duration is valid.")
		g.P("// It is equivalent to CheckValid == nil.")
		g.P("func (x *Duration) IsValid() bool {")
		g.P("	return x.check() == 0")
		g.P("}")
		g.P()

		g.P("// CheckValid returns an error if the duration is invalid.")
		g.P("// In particular, it checks whether the value is within the range of")
		g.P("// -10000 years to +10000 years inclusive.")
		g.P("func (x *Duration) CheckValid() error {")
		g.P("	switch x.check() {")
		g.P("	case invalidUnderflow:")
		g.P("		return ", protoimplPackage.Ident("X"), ".NewError(\"duration (%v) exceeds -10000 years\", x)")
		g.P("	case invalidOverflow:")
		g.P("		return ", protoimplPackage.Ident("X"), ".NewError(\"duration (%v) exceeds +10000 years\", x)")
		g.P("	case invalidNanosRange:")
		g.P("		return ", protoimplPackage.Ident("X"), ".NewError(\"duration (%v) has out-of-range nanos\", x)")
		g.P("	case invalidNanosSign:")
		g.P("		return ", protoimplPackage.Ident("X"), ".NewError(\"duration (%v) has seconds and nanos with different signs\", x)")
		g.P("	default:")
		g.P("		return nil")
		g.P("	}")
		g.P("}")
		g.P()

		g.P("const invalidUnderflow = 1")
		g.P("const invalidOverflow = 2")
		g.P("const invalidNanosRange = 3")
		g.P("const invalidNanosSign = 4")
		g.P()

		g.P("func (x *Duration) check() uint {")
		g.P("	const absDuration = 315576000000 // 10000yr * 365.25day/yr * 24hr/day * 60min/hr * 60sec/min")
		g.P("	secs := x.GetSeconds()")
		g.P("	nanos := x.GetNanos()")
		g.P("	switch {")
		g.P("	case secs < -absDuration:")
		g.P("		return invalidUnderflow")
		g.P("	case secs > +absDuration:")
		g.P("		return invalidOverflow")
		g.P("	case nanos <= -1e9 || nanos >= +1e9:")
		g.P("		return invalidNanosRange")
		g.P("	case (secs > 0 && nanos < 0) || (secs < 0 && nanos > 0):")
		g.P("		return invalidNanosSign")
		g.P("	default:")
		g.P("		return 0")
		g.P("	}")
		g.P("}")
		g.P()

	case genid.Struct_message_fullname:
		g.P("// NewStruct constructs a Struct from a general-purpose Go map.")
		g.P("// The map keys must be valid UTF-8.")
		g.P("// The map values are converted using NewValue.")
		g.P("func NewStruct(v map[string]interface{}) (*Struct, error) {")
		g.P("	x := &Struct{Fields: make(map[string]*Value, len(v))}")
		g.P("	for k, v := range v {")
		g.P("		if !", utf8Package.Ident("ValidString"), "(k) {")
		g.P("			return nil, ", protoimplPackage.Ident("X"), ".NewError(\"invalid UTF-8 in string: %q\", k)")
		g.P("		}")
		g.P("		var err error")
		g.P("		x.Fields[k], err = NewValue(v)")
		g.P("		if err != nil {")
		g.P("			return nil, err")
		g.P("		}")
		g.P("	}")
		g.P("	return x, nil")
		g.P("}")
		g.P()

		g.P("// AsMap converts x to a general-purpose Go map.")
		g.P("// The map values are converted by calling Value.AsInterface.")
		g.P("func (x *Struct) AsMap() map[string]interface{} {")
		g.P("	vs := make(map[string]interface{})")
		g.P("	for k, v := range x.GetFields() {")
		g.P("		vs[k] = v.AsInterface()")
		g.P("	}")
		g.P("	return vs")
		g.P("}")
		g.P()

		g.P("func (x *Struct) MarshalJSON() ([]byte, error) {")
		g.P("	return ", protojsonPackage.Ident("Marshal"), "(x)")
		g.P("}")
		g.P()

		g.P("func (x *Struct) UnmarshalJSON(b []byte) error {")
		g.P("	return ", protojsonPackage.Ident("Unmarshal"), "(b, x)")
		g.P("}")
		g.P()

	case genid.ListValue_message_fullname:
		g.P("// NewList constructs a ListValue from a general-purpose Go slice.")
		g.P("// The slice elements are converted using NewValue.")
		g.P("func NewList(v []interface{}) (*ListValue, error) {")
		g.P("	x := &ListValue{Values: make([]*Value, len(v))}")
		g.P("	for i, v := range v {")
		g.P("		var err error")
		g.P("		x.Values[i], err = NewValue(v)")
		g.P("		if err != nil {")
		g.P("			return nil, err")
		g.P("		}")
		g.P("	}")
		g.P("	return x, nil")
		g.P("}")
		g.P()

		g.P("// AsSlice converts x to a general-purpose Go slice.")
		g.P("// The slice elements are converted by calling Value.AsInterface.")
		g.P("func (x *ListValue) AsSlice() []interface{} {")
		g.P("	vs := make([]interface{}, len(x.GetValues()))")
		g.P("	for i, v := range x.GetValues() {")
		g.P("		vs[i] = v.AsInterface()")
		g.P("	}")
		g.P("	return vs")
		g.P("}")
		g.P()

		g.P("func (x *ListValue) MarshalJSON() ([]byte, error) {")
		g.P("	return ", protojsonPackage.Ident("Marshal"), "(x)")
		g.P("}")
		g.P()

		g.P("func (x *ListValue) UnmarshalJSON(b []byte) error {")
		g.P("	return ", protojsonPackage.Ident("Unmarshal"), "(b, x)")
		g.P("}")
		g.P()

	case genid.Value_message_fullname:
		g.P("// NewValue constructs a Value from a general-purpose Go interface.")
		g.P("//")
		g.P("//	╔════════════════════════╤════════════════════════════════════════════╗")
		g.P("//	║ Go type                │ Conversion                                 ║")
		g.P("//	╠════════════════════════╪════════════════════════════════════════════╣")
		g.P("//	║ nil                    │ stored as NullValue                        ║")
		g.P("//	║ bool                   │ stored as BoolValue                        ║")
		g.P("//	║ int, int32, int64      │ stored as NumberValue                      ║")
		g.P("//	║ uint, uint32, uint64   │ stored as NumberValue                      ║")
		g.P("//	║ float32, float64       │ stored as NumberValue                      ║")
		g.P("//	║ string                 │ stored as StringValue; must be valid UTF-8 ║")
		g.P("//	║ []byte                 │ stored as StringValue; base64-encoded      ║")
		g.P("//	║ map[string]interface{} │ stored as StructValue                      ║")
		g.P("//	║ []interface{}          │ stored as ListValue                        ║")
		g.P("//	╚════════════════════════╧════════════════════════════════════════════╝")
		g.P("//")
		g.P("// When converting an int64 or uint64 to a NumberValue, numeric precision loss")
		g.P("// is possible since they are stored as a float64.")
		g.P("func NewValue(v interface{}) (*Value, error) {")
		g.P("	switch v := v.(type) {")
		g.P("	case nil:")
		g.P("		return NewNullValue(), nil")
		g.P("	case bool:")
		g.P("		return NewBoolValue(v), nil")
		g.P("	case int:")
		g.P("		return NewNumberValue(float64(v)), nil")
		g.P("	case int32:")
		g.P("		return NewNumberValue(float64(v)), nil")
		g.P("	case int64:")
		g.P("		return NewNumberValue(float64(v)), nil")
		g.P("	case uint:")
		g.P("		return NewNumberValue(float64(v)), nil")
		g.P("	case uint32:")
		g.P("		return NewNumberValue(float64(v)), nil")
		g.P("	case uint64:")
		g.P("		return NewNumberValue(float64(v)), nil")
		g.P("	case float32:")
		g.P("		return NewNumberValue(float64(v)), nil")
		g.P("	case float64:")
		g.P("		return NewNumberValue(float64(v)), nil")
		g.P("	case string:")
		g.P("		if !", utf8Package.Ident("ValidString"), "(v) {")
		g.P("			return nil, ", protoimplPackage.Ident("X"), ".NewError(\"invalid UTF-8 in string: %q\", v)")
		g.P("		}")
		g.P("		return NewStringValue(v), nil")
		g.P("	case []byte:")
		g.P("		s := ", base64Package.Ident("StdEncoding"), ".EncodeToString(v)")
		g.P("		return NewStringValue(s), nil")
		g.P("	case map[string]interface{}:")
		g.P("		v2, err := NewStruct(v)")
		g.P("		if err != nil {")
		g.P("			return nil, err")
		g.P("		}")
		g.P("		return NewStructValue(v2), nil")
		g.P("	case []interface{}:")
		g.P("		v2, err := NewList(v)")
		g.P("		if err != nil {")
		g.P("			return nil, err")
		g.P("		}")
		g.P("		return NewListValue(v2), nil")
		g.P("	default:")
		g.P("		return nil, ", protoimplPackage.Ident("X"), ".NewError(\"invalid type: %T\", v)")
		g.P("	}")
		g.P("}")
		g.P()

		g.P("// NewNullValue constructs a new null Value.")
		g.P("func NewNullValue() *Value {")
		g.P("	return &Value{Kind: &Value_NullValue{NullValue: NullValue_NULL_VALUE}}")
		g.P("}")
		g.P()

		g.P("// NewBoolValue constructs a new boolean Value.")
		g.P("func NewBoolValue(v bool) *Value {")
		g.P("	return &Value{Kind: &Value_BoolValue{BoolValue: v}}")
		g.P("}")
		g.P()

		g.P("// NewNumberValue constructs a new number Value.")
		g.P("func NewNumberValue(v float64) *Value {")
		g.P("	return &Value{Kind: &Value_NumberValue{NumberValue: v}}")
		g.P("}")
		g.P()

		g.P("// NewStringValue constructs a new string Value.")
		g.P("func NewStringValue(v string) *Value {")
		g.P("	return &Value{Kind: &Value_StringValue{StringValue: v}}")
		g.P("}")
		g.P()

		g.P("// NewStructValue constructs a new struct Value.")
		g.P("func NewStructValue(v *Struct) *Value {")
		g.P("	return &Value{Kind: &Value_StructValue{StructValue: v}}")
		g.P("}")
		g.P()

		g.P("// NewListValue constructs a new list Value.")
		g.P("func NewListValue(v *ListValue) *Value {")
		g.P("	return &Value{Kind: &Value_ListValue{ListValue: v}}")
		g.P("}")
		g.P()

		g.P("// AsInterface converts x to a general-purpose Go interface.")
		g.P("//")
		g.P("// Calling Value.MarshalJSON and \"encoding/json\".Marshal on this output produce")
		g.P("// semantically equivalent JSON (assuming no errors occur).")
		g.P("//")
		g.P("// Floating-point values (i.e., \"NaN\", \"Infinity\", and \"-Infinity\") are")
		g.P("// converted as strings to remain compatible with MarshalJSON.")
		g.P("func (x *Value) AsInterface() interface{} {")
		g.P("	switch v := x.GetKind().(type) {")
		g.P("	case *Value_NumberValue:")
		g.P("		if v != nil {")
		g.P("			switch {")
		g.P("			case ", mathPackage.Ident("IsNaN"), "(v.NumberValue):")
		g.P("				return \"NaN\"")
		g.P("			case ", mathPackage.Ident("IsInf"), "(v.NumberValue, +1):")
		g.P("				return \"Infinity\"")
		g.P("			case ", mathPackage.Ident("IsInf"), "(v.NumberValue, -1):")
		g.P("				return \"-Infinity\"")
		g.P("			default:")
		g.P("				return v.NumberValue")
		g.P("			}")
		g.P("		}")
		g.P("	case *Value_StringValue:")
		g.P("		if v != nil {")
		g.P("			return v.StringValue")
		g.P("		}")
		g.P("	case *Value_BoolValue:")
		g.P("		if v != nil {")
		g.P("			return v.BoolValue")
		g.P("		}")
		g.P("	case *Value_StructValue:")
		g.P("		if v != nil {")
		g.P("			return v.StructValue.AsMap()")
		g.P("		}")
		g.P("	case *Value_ListValue:")
		g.P("		if v != nil {")
		g.P("			return v.ListValue.AsSlice()")
		g.P("		}")
		g.P("	}")
		g.P("	return nil")
		g.P("}")
		g.P()

		g.P("func (x *Value) MarshalJSON() ([]byte, error) {")
		g.P("	return ", protojsonPackage.Ident("Marshal"), "(x)")
		g.P("}")
		g.P()

		g.P("func (x *Value) UnmarshalJSON(b []byte) error {")
		g.P("	return ", protojsonPackage.Ident("Unmarshal"), "(b, x)")
		g.P("}")
		g.P()

	case genid.FieldMask_message_fullname:
		g.P("// New constructs a field mask from a list of paths and verifies that")
		g.P("// each one is valid according to the specified message type.")
		g.P("func New(m ", protoPackage.Ident("Message"), ", paths ...string) (*FieldMask, error) {")
		g.P("	x := new(FieldMask)")
		g.P("	return x, x.Append(m, paths...)")
		g.P("}")
		g.P()

		g.P("// Union returns the union of all the paths in the input field masks.")
		g.P("func Union(mx *FieldMask, my *FieldMask, ms ...*FieldMask) *FieldMask {")
		g.P("	var out []string")
		g.P("	out = append(out, mx.GetPaths()...)")
		g.P("	out = append(out, my.GetPaths()...)")
		g.P("	for _, m := range ms {")
		g.P("		out = append(out, m.GetPaths()...)")
		g.P("	}")
		g.P("	return &FieldMask{Paths: normalizePaths(out)}")
		g.P("}")
		g.P()

		g.P("// Intersect returns the intersection of all the paths in the input field masks.")
		g.P("func Intersect(mx *FieldMask, my *FieldMask, ms ...*FieldMask) *FieldMask {")
		g.P("	var ss1, ss2 []string // reused buffers for performance")
		g.P("	intersect := func(out, in []string) []string {")
		g.P("		ss1 = normalizePaths(append(ss1[:0], in...))")
		g.P("		ss2 = normalizePaths(append(ss2[:0], out...))")
		g.P("		out = out[:0]")
		g.P("		for i1, i2 := 0, 0; i1 < len(ss1) && i2 < len(ss2); {")
		g.P("			switch s1, s2 := ss1[i1], ss2[i2]; {")
		g.P("			case hasPathPrefix(s1, s2):")
		g.P("				out = append(out, s1)")
		g.P("				i1++")
		g.P("			case hasPathPrefix(s2, s1):")
		g.P("				out = append(out, s2)")
		g.P("				i2++")
		g.P("			case lessPath(s1, s2):")
		g.P("				i1++")
		g.P("			case lessPath(s2, s1):")
		g.P("				i2++")
		g.P("			}")
		g.P("		}")
		g.P("		return out")
		g.P("	}")
		g.P()
		g.P("	out := Union(mx, my, ms...).GetPaths()")
		g.P("	out = intersect(out, mx.GetPaths())")
		g.P("	out = intersect(out, my.GetPaths())")
		g.P("	for _, m := range ms {")
		g.P("		out = intersect(out, m.GetPaths())")
		g.P("	}")
		g.P("	return &FieldMask{Paths: normalizePaths(out)}")
		g.P("}")
		g.P()

		g.P("// IsValid reports whether all the paths are syntactically valid and")
		g.P("// refer to known fields in the specified message type.")
		g.P("func (x *FieldMask) IsValid(m ", protoPackage.Ident("Message"), ") bool {")
		g.P("	paths := x.GetPaths()")
		g.P("	return numValidPaths(m, paths) == len(paths)")
		g.P("}")
		g.P()

		g.P("// Append appends a list of paths to the mask and verifies that each one")
		g.P("// is valid according to the specified message type.")
		g.P("// An invalid path is not appended and breaks insertion of subsequent paths.")
		g.P("func (x *FieldMask) Append(m ", protoPackage.Ident("Message"), ", paths ...string) error {")
		g.P("	numValid := numValidPaths(m, paths)")
		g.P("	x.Paths = append(x.Paths, paths[:numValid]...)")
		g.P("	paths = paths[numValid:]")
		g.P("	if len(paths) > 0 {")
		g.P("		name := m.ProtoReflect().Descriptor().FullName()")
		g.P("		return ", protoimplPackage.Ident("X"), ".NewError(\"invalid path %q for message %q\", paths[0], name)")
		g.P("	}")
		g.P("	return nil")
		g.P("}")
		g.P()

		g.P("func numValidPaths(m ", protoPackage.Ident("Message"), ", paths []string) int {")
		g.P("	md0 := m.ProtoReflect().Descriptor()")
		g.P("	for i, path := range paths {")
		g.P("		md := md0")
		g.P("		if !rangeFields(path, func(field string) bool {")
		g.P("			// Search the field within the message.")
		g.P("			if md == nil {")
		g.P("				return false // not within a message")
		g.P("			}")
		g.P("			fd := md.Fields().ByName(", protoreflectPackage.Ident("Name"), "(field))")
		g.P("			// The real field name of a group is the message name.")
		g.P("			if fd == nil {")
		g.P("				gd := md.Fields().ByName(", protoreflectPackage.Ident("Name"), "(", stringsPackage.Ident("ToLower"), "(field)))")
		g.P("				if gd != nil && gd.Kind() == ", protoreflectPackage.Ident("GroupKind"), " && string(gd.Message().Name()) == field {")
		g.P("					fd = gd")
		g.P("				}")
		g.P("			} else if fd.Kind() == ", protoreflectPackage.Ident("GroupKind"), " && string(fd.Message().Name()) != field {")
		g.P("				fd = nil")
		g.P("			}")
		g.P("			if fd == nil {")
		g.P("				return false // message has does not have this field")
		g.P("			}")
		g.P()
		g.P("			// Identify the next message to search within.")
		g.P("			md = fd.Message() // may be nil")
		g.P("			if fd.IsMap() {")
		g.P("				md = fd.MapValue().Message() // may be nil")
		g.P("			}")
		g.P("			return true")
		g.P("		}) {")
		g.P("			return i")
		g.P("		}")
		g.P("	}")
		g.P("	return len(paths)")
		g.P("}")
		g.P()

		g.P("// Normalize converts the mask to its canonical form where all paths are sorted")
		g.P("// and redundant paths are removed.")
		g.P("func (x *FieldMask) Normalize() {")
		g.P("	x.Paths = normalizePaths(x.Paths)")
		g.P("}")
		g.P()
		g.P("func normalizePaths(paths []string) []string {")
		g.P("	", sortPackage.Ident("Slice"), "(paths, func(i, j int) bool {")
		g.P("		return lessPath(paths[i], paths[j])")
		g.P("	})")
		g.P()
		g.P("	// Elide any path that is a prefix match on the previous.")
		g.P("	out := paths[:0]")
		g.P("	for _, path := range paths {")
		g.P("		if len(out) > 0 && hasPathPrefix(path, out[len(out)-1]) {")
		g.P("			continue")
		g.P("		}")
		g.P("		out = append(out, path)")
		g.P("	}")
		g.P("	return out")
		g.P("}")
		g.P()

		g.P("// hasPathPrefix is like strings.HasPrefix, but further checks for either")
		g.P("// an exact matche or that the prefix is delimited by a dot.")
		g.P("func hasPathPrefix(path, prefix string) bool {")
		g.P("	return ", stringsPackage.Ident("HasPrefix"), "(path, prefix) && (len(path) == len(prefix) || path[len(prefix)] == '.')")
		g.P("}")
		g.P()

		g.P("// lessPath is a lexicographical comparison where dot is specially treated")
		g.P("// as the smallest symbol.")
		g.P("func lessPath(x, y string) bool {")
		g.P("	for i := 0; i < len(x) && i < len(y); i++ {")
		g.P("		if x[i] != y[i] {")
		g.P("			return (x[i] - '.') < (y[i] - '.')")
		g.P("		}")
		g.P("	}")
		g.P("	return len(x) < len(y)")
		g.P("}")
		g.P()

		g.P("// rangeFields is like strings.Split(path, \".\"), but avoids allocations by")
		g.P("// iterating over each field in place and calling a iterator function.")
		g.P("func rangeFields(path string, f func(field string) bool) bool {")
		g.P("	for {")
		g.P("		var field string")
		g.P("		if i := ", stringsPackage.Ident("IndexByte"), "(path, '.'); i >= 0 {")
		g.P("			field, path = path[:i], path[i:]")
		g.P("		} else {")
		g.P("			field, path = path, \"\"")
		g.P("		}")
		g.P()
		g.P("		if !f(field) {")
		g.P("			return false")
		g.P("		}")
		g.P()
		g.P("		if len(path) == 0 {")
		g.P("			return true")
		g.P("		}")
		g.P("		path = ", stringsPackage.Ident("TrimPrefix"), "(path, \".\")")
		g.P("	}")
		g.P("}")
		g.P()

	case genid.BoolValue_message_fullname,
		genid.Int32Value_message_fullname,
		genid.Int64Value_message_fullname,
		genid.UInt32Value_message_fullname,
		genid.UInt64Value_message_fullname,
		genid.FloatValue_message_fullname,
		genid.DoubleValue_message_fullname,
		genid.StringValue_message_fullname,
		genid.BytesValue_message_fullname:
		funcName := strings.TrimSuffix(m.GoIdent.GoName, "Value")
		typeName := strings.ToLower(funcName)
		switch typeName {
		case "float":
			typeName = "float32"
		case "double":
			typeName = "float64"
		case "bytes":
			typeName = "[]byte"
		}

		g.P("// ", funcName, " stores v in a new ", m.GoIdent, " and returns a pointer to it.")
		g.P("func ", funcName, "(v ", typeName, ") *", m.GoIdent, " {")
		g.P("	return &", m.GoIdent, "{Value: v}")
		g.P("}")
		g.P()
	}
}