// Copyright 2018 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 prototext

import (
	"fmt"
	"sort"
	"strconv"
	"unicode/utf8"

	"google.golang.org/protobuf/encoding/protowire"
	"google.golang.org/protobuf/internal/encoding/messageset"
	"google.golang.org/protobuf/internal/encoding/text"
	"google.golang.org/protobuf/internal/errors"
	"google.golang.org/protobuf/internal/fieldnum"
	"google.golang.org/protobuf/internal/flags"
	"google.golang.org/protobuf/internal/mapsort"
	"google.golang.org/protobuf/internal/pragma"
	"google.golang.org/protobuf/proto"
	pref "google.golang.org/protobuf/reflect/protoreflect"
	"google.golang.org/protobuf/reflect/protoregistry"
)

const defaultIndent = "  "

// Format formats the message as a multiline string.
// This function is only intended for human consumption and ignores errors.
// Do not depend on the output being stable. It may change over time across
// different versions of the program.
func Format(m proto.Message) string {
	return MarshalOptions{Multiline: true}.Format(m)
}

// Marshal writes the given proto.Message in textproto format using default
// options. Do not depend on the output being stable. It may change over time
// across different versions of the program.
func Marshal(m proto.Message) ([]byte, error) {
	return MarshalOptions{}.Marshal(m)
}

// MarshalOptions is a configurable text format marshaler.
type MarshalOptions struct {
	pragma.NoUnkeyedLiterals

	// Multiline specifies whether the marshaler should format the output in
	// indented-form with every textual element on a new line.
	// If Indent is an empty string, then an arbitrary indent is chosen.
	Multiline bool

	// Indent specifies the set of indentation characters to use in a multiline
	// formatted output such that every entry is preceded by Indent and
	// terminated by a newline. If non-empty, then Multiline is treated as true.
	// Indent can only be composed of space or tab characters.
	Indent string

	// AllowPartial allows messages that have missing required fields to marshal
	// without returning an error. If AllowPartial is false (the default),
	// Marshal will return error if there are any missing required fields.
	AllowPartial bool

	// EmitUnknown specifies whether to emit unknown fields in the output.
	// If specified, the unmarshaler may be unable to parse the output.
	// The default is to exclude unknown fields.
	EmitUnknown bool

	// Resolver is used for looking up types when expanding google.protobuf.Any
	// messages. If nil, this defaults to using protoregistry.GlobalTypes.
	Resolver interface {
		protoregistry.ExtensionTypeResolver
		protoregistry.MessageTypeResolver
	}
}

// Format formats the message as a string.
// This method is only intended for human consumption and ignores errors.
// Do not depend on the output being stable. It may change over time across
// different versions of the program.
func (o MarshalOptions) Format(m proto.Message) string {
	if m == nil || !m.ProtoReflect().IsValid() {
		return "<nil>" // invalid syntax, but okay since this is for debugging
	}
	o.AllowPartial = true
	o.EmitUnknown = true
	b, _ := o.Marshal(m)
	return string(b)
}

// Marshal writes the given proto.Message in textproto format using options in
// MarshalOptions object. Do not depend on the output being stable. It may
// change over time across different versions of the program.
func (o MarshalOptions) Marshal(m proto.Message) ([]byte, error) {
	const outputASCII = false
	var delims = [2]byte{'{', '}'}

	if o.Multiline && o.Indent == "" {
		o.Indent = defaultIndent
	}
	if o.Resolver == nil {
		o.Resolver = protoregistry.GlobalTypes
	}

	internalEnc, err := text.NewEncoder(o.Indent, delims, outputASCII)
	if err != nil {
		return nil, err
	}

	enc := encoder{internalEnc, o}
	err = enc.marshalMessage(m.ProtoReflect(), false)
	if err != nil {
		return nil, err
	}
	out := enc.Bytes()
	if len(o.Indent) > 0 && len(out) > 0 {
		out = append(out, '\n')
	}
	if o.AllowPartial {
		return out, nil
	}
	return out, proto.CheckInitialized(m)
}

type encoder struct {
	*text.Encoder
	opts MarshalOptions
}

// marshalMessage marshals the given protoreflect.Message.
func (e encoder) marshalMessage(m pref.Message, inclDelims bool) error {
	messageDesc := m.Descriptor()
	if !flags.ProtoLegacy && messageset.IsMessageSet(messageDesc) {
		return errors.New("no support for proto1 MessageSets")
	}

	if inclDelims {
		e.StartMessage()
		defer e.EndMessage()
	}

	// Handle Any expansion.
	if messageDesc.FullName() == "google.protobuf.Any" {
		if e.marshalAny(m) {
			return nil
		}
		// If unable to expand, continue on to marshal Any as a regular message.
	}

	// Marshal known fields.
	fieldDescs := messageDesc.Fields()
	size := fieldDescs.Len()
	for i := 0; i < size; {
		fd := fieldDescs.Get(i)
		if od := fd.ContainingOneof(); od != nil {
			fd = m.WhichOneof(od)
			i += od.Fields().Len()
		} else {
			i++
		}

		if fd == nil || !m.Has(fd) {
			continue
		}

		name := fd.Name()
		// Use type name for group field name.
		if fd.Kind() == pref.GroupKind {
			name = fd.Message().Name()
		}
		val := m.Get(fd)
		if err := e.marshalField(string(name), val, fd); err != nil {
			return err
		}
	}

	// Marshal extensions.
	if err := e.marshalExtensions(m); err != nil {
		return err
	}

	// Marshal unknown fields.
	if e.opts.EmitUnknown {
		e.marshalUnknown(m.GetUnknown())
	}

	return nil
}

// marshalField marshals the given field with protoreflect.Value.
func (e encoder) marshalField(name string, val pref.Value, fd pref.FieldDescriptor) error {
	switch {
	case fd.IsList():
		return e.marshalList(name, val.List(), fd)
	case fd.IsMap():
		return e.marshalMap(name, val.Map(), fd)
	default:
		e.WriteName(name)
		return e.marshalSingular(val, fd)
	}
}

// marshalSingular marshals the given non-repeated field value. This includes
// all scalar types, enums, messages, and groups.
func (e encoder) marshalSingular(val pref.Value, fd pref.FieldDescriptor) error {
	kind := fd.Kind()
	switch kind {
	case pref.BoolKind:
		e.WriteBool(val.Bool())

	case pref.StringKind:
		s := val.String()
		if !utf8.ValidString(s) {
			return errors.InvalidUTF8(string(fd.FullName()))
		}
		e.WriteString(s)

	case pref.Int32Kind, pref.Int64Kind,
		pref.Sint32Kind, pref.Sint64Kind,
		pref.Sfixed32Kind, pref.Sfixed64Kind:
		e.WriteInt(val.Int())

	case pref.Uint32Kind, pref.Uint64Kind,
		pref.Fixed32Kind, pref.Fixed64Kind:
		e.WriteUint(val.Uint())

	case pref.FloatKind:
		// Encoder.WriteFloat handles the special numbers NaN and infinites.
		e.WriteFloat(val.Float(), 32)

	case pref.DoubleKind:
		// Encoder.WriteFloat handles the special numbers NaN and infinites.
		e.WriteFloat(val.Float(), 64)

	case pref.BytesKind:
		e.WriteString(string(val.Bytes()))

	case pref.EnumKind:
		num := val.Enum()
		if desc := fd.Enum().Values().ByNumber(num); desc != nil {
			e.WriteLiteral(string(desc.Name()))
		} else {
			// Use numeric value if there is no enum description.
			e.WriteInt(int64(num))
		}

	case pref.MessageKind, pref.GroupKind:
		return e.marshalMessage(val.Message(), true)

	default:
		panic(fmt.Sprintf("%v has unknown kind: %v", fd.FullName(), kind))
	}
	return nil
}

// marshalList marshals the given protoreflect.List as multiple name-value fields.
func (e encoder) marshalList(name string, list pref.List, fd pref.FieldDescriptor) error {
	size := list.Len()
	for i := 0; i < size; i++ {
		e.WriteName(name)
		if err := e.marshalSingular(list.Get(i), fd); err != nil {
			return err
		}
	}
	return nil
}

// marshalMap marshals the given protoreflect.Map as multiple name-value fields.
func (e encoder) marshalMap(name string, mmap pref.Map, fd pref.FieldDescriptor) error {
	var err error
	mapsort.Range(mmap, fd.MapKey().Kind(), func(key pref.MapKey, val pref.Value) bool {
		e.WriteName(name)
		e.StartMessage()
		defer e.EndMessage()

		e.WriteName("key")
		err = e.marshalSingular(key.Value(), fd.MapKey())
		if err != nil {
			return false
		}

		e.WriteName("value")
		err = e.marshalSingular(val, fd.MapValue())
		if err != nil {
			return false
		}
		return true
	})
	return err
}

// marshalExtensions marshals extension fields.
func (e encoder) marshalExtensions(m pref.Message) error {
	type entry struct {
		key   string
		value pref.Value
		desc  pref.FieldDescriptor
	}

	// Get a sorted list based on field key first.
	var entries []entry
	m.Range(func(fd pref.FieldDescriptor, v pref.Value) bool {
		if !fd.IsExtension() {
			return true
		}
		// For MessageSet extensions, the name used is the parent message.
		name := fd.FullName()
		if messageset.IsMessageSetExtension(fd) {
			name = name.Parent()
		}
		entries = append(entries, entry{
			key:   string(name),
			value: v,
			desc:  fd,
		})
		return true
	})
	// Sort extensions lexicographically.
	sort.Slice(entries, func(i, j int) bool {
		return entries[i].key < entries[j].key
	})

	// Write out sorted list.
	for _, entry := range entries {
		// Extension field name is the proto field name enclosed in [].
		name := "[" + entry.key + "]"
		if err := e.marshalField(name, entry.value, entry.desc); err != nil {
			return err
		}
	}
	return nil
}

// marshalUnknown parses the given []byte and marshals fields out.
// This function assumes proper encoding in the given []byte.
func (e encoder) marshalUnknown(b []byte) {
	const dec = 10
	const hex = 16
	for len(b) > 0 {
		num, wtype, n := protowire.ConsumeTag(b)
		b = b[n:]
		e.WriteName(strconv.FormatInt(int64(num), dec))

		switch wtype {
		case protowire.VarintType:
			var v uint64
			v, n = protowire.ConsumeVarint(b)
			e.WriteUint(v)
		case protowire.Fixed32Type:
			var v uint32
			v, n = protowire.ConsumeFixed32(b)
			e.WriteLiteral("0x" + strconv.FormatUint(uint64(v), hex))
		case protowire.Fixed64Type:
			var v uint64
			v, n = protowire.ConsumeFixed64(b)
			e.WriteLiteral("0x" + strconv.FormatUint(v, hex))
		case protowire.BytesType:
			var v []byte
			v, n = protowire.ConsumeBytes(b)
			e.WriteString(string(v))
		case protowire.StartGroupType:
			e.StartMessage()
			var v []byte
			v, n = protowire.ConsumeGroup(num, b)
			e.marshalUnknown(v)
			e.EndMessage()
		default:
			panic(fmt.Sprintf("prototext: error parsing unknown field wire type: %v", wtype))
		}

		b = b[n:]
	}
}

// marshalAny marshals the given google.protobuf.Any message in expanded form.
// It returns true if it was able to marshal, else false.
func (e encoder) marshalAny(any pref.Message) bool {
	// Construct the embedded message.
	fds := any.Descriptor().Fields()
	fdType := fds.ByNumber(fieldnum.Any_TypeUrl)
	typeURL := any.Get(fdType).String()
	mt, err := e.opts.Resolver.FindMessageByURL(typeURL)
	if err != nil {
		return false
	}
	m := mt.New().Interface()

	// Unmarshal bytes into embedded message.
	fdValue := fds.ByNumber(fieldnum.Any_Value)
	value := any.Get(fdValue)
	err = proto.UnmarshalOptions{
		AllowPartial: true,
		Resolver:     e.opts.Resolver,
	}.Unmarshal(value.Bytes(), m)
	if err != nil {
		return false
	}

	// Get current encoder position. If marshaling fails, reset encoder output
	// back to this position.
	pos := e.Snapshot()

	// Field name is the proto field name enclosed in [].
	e.WriteName("[" + typeURL + "]")
	err = e.marshalMessage(m.ProtoReflect(), true)
	if err != nil {
		e.Reset(pos)
		return false
	}
	return true
}