// Copyright 2019 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 protocmp provides protobuf specific options for the
// [github.com/google/go-cmp/cmp] package.
//
// The primary feature is the [Transform] option, which transform [proto.Message]
// types into a [Message] map that is suitable for cmp to introspect upon.
// All other options in this package must be used in conjunction with [Transform].
package protocmp

import (
	"reflect"
	"strconv"

	"github.com/google/go-cmp/cmp"

	"google.golang.org/protobuf/encoding/protowire"
	"google.golang.org/protobuf/internal/genid"
	"google.golang.org/protobuf/internal/msgfmt"
	"google.golang.org/protobuf/proto"
	"google.golang.org/protobuf/reflect/protoreflect"
	"google.golang.org/protobuf/reflect/protoregistry"
	"google.golang.org/protobuf/runtime/protoiface"
	"google.golang.org/protobuf/runtime/protoimpl"
)

var (
	enumV2Type    = reflect.TypeOf((*protoreflect.Enum)(nil)).Elem()
	messageV1Type = reflect.TypeOf((*protoiface.MessageV1)(nil)).Elem()
	messageV2Type = reflect.TypeOf((*proto.Message)(nil)).Elem()
)

// Enum is a dynamic representation of a protocol buffer enum that is
// suitable for [cmp.Equal] and [cmp.Diff] to compare upon.
type Enum struct {
	num protoreflect.EnumNumber
	ed  protoreflect.EnumDescriptor
}

// Descriptor returns the enum descriptor.
// It returns nil for a zero Enum value.
func (e Enum) Descriptor() protoreflect.EnumDescriptor {
	return e.ed
}

// Number returns the enum value as an integer.
func (e Enum) Number() protoreflect.EnumNumber {
	return e.num
}

// Equal reports whether e1 and e2 represent the same enum value.
func (e1 Enum) Equal(e2 Enum) bool {
	if e1.ed.FullName() != e2.ed.FullName() {
		return false
	}
	return e1.num == e2.num
}

// String returns the name of the enum value if known (e.g., "ENUM_VALUE"),
// otherwise it returns the formatted decimal enum number (e.g., "14").
func (e Enum) String() string {
	if ev := e.ed.Values().ByNumber(e.num); ev != nil {
		return string(ev.Name())
	}
	return strconv.Itoa(int(e.num))
}

const (
	// messageTypeKey indicates the protobuf message type.
	// The value type is always messageMeta.
	// From the public API, it presents itself as only the type, but the
	// underlying data structure holds arbitrary metadata about the message.
	messageTypeKey = "@type"

	// messageInvalidKey indicates that the message is invalid.
	// The value is always the boolean "true".
	messageInvalidKey = "@invalid"
)

type messageMeta struct {
	m   proto.Message
	md  protoreflect.MessageDescriptor
	xds map[string]protoreflect.ExtensionDescriptor
}

func (t messageMeta) String() string {
	return string(t.md.FullName())
}

func (t1 messageMeta) Equal(t2 messageMeta) bool {
	return t1.md.FullName() == t2.md.FullName()
}

// Message is a dynamic representation of a protocol buffer message that is
// suitable for [cmp.Equal] and [cmp.Diff] to directly operate upon.
//
// Every populated known field (excluding extension fields) is stored in the map
// with the key being the short name of the field (e.g., "field_name") and
// the value determined by the kind and cardinality of the field.
//
// Singular scalars are represented by the same Go type as [protoreflect.Value],
// singular messages are represented by the [Message] type,
// singular enums are represented by the [Enum] type,
// list fields are represented as a Go slice, and
// map fields are represented as a Go map.
//
// Every populated extension field is stored in the map with the key being the
// full name of the field surrounded by brackets (e.g., "[extension.full.name]")
// and the value determined according to the same rules as known fields.
//
// Every unknown field is stored in the map with the key being the field number
// encoded as a decimal string (e.g., "132") and the value being the raw bytes
// of the encoded field (as the [protoreflect.RawFields] type).
//
// Message values must not be created by or mutated by users.
type Message map[string]interface{}

// Unwrap returns the original message value.
// It returns nil if this Message was not constructed from another message.
func (m Message) Unwrap() proto.Message {
	mm, _ := m[messageTypeKey].(messageMeta)
	return mm.m
}

// Descriptor return the message descriptor.
// It returns nil for a zero Message value.
func (m Message) Descriptor() protoreflect.MessageDescriptor {
	mm, _ := m[messageTypeKey].(messageMeta)
	return mm.md
}

// ProtoReflect returns a reflective view of m.
// It only implements the read-only operations of [protoreflect.Message].
// Calling any mutating operations on m panics.
func (m Message) ProtoReflect() protoreflect.Message {
	return (reflectMessage)(m)
}

// ProtoMessage is a marker method from the legacy message interface.
func (m Message) ProtoMessage() {}

// Reset is the required Reset method from the legacy message interface.
func (m Message) Reset() {
	panic("invalid mutation of a read-only message")
}

// String returns a formatted string for the message.
// It is intended for human debugging and has no guarantees about its
// exact format or the stability of its output.
func (m Message) String() string {
	switch {
	case m == nil:
		return "<nil>"
	case !m.ProtoReflect().IsValid():
		return "<invalid>"
	default:
		return msgfmt.Format(m)
	}
}

type option struct{}

// Transform returns a [cmp.Option] that converts each [proto.Message] to a [Message].
// The transformation does not mutate nor alias any converted messages.
//
// The google.protobuf.Any message is automatically unmarshaled such that the
// "value" field is a [Message] representing the underlying message value
// assuming it could be resolved and properly unmarshaled.
//
// This does not directly transform higher-order composite Go types.
// For example, []*foopb.Message is not transformed into []Message,
// but rather the individual message elements of the slice are transformed.
//
// Note that there are currently no custom options for Transform,
// but the use of an unexported type keeps the future open.
func Transform(...option) cmp.Option {
	// addrType returns a pointer to t if t isn't a pointer or interface.
	addrType := func(t reflect.Type) reflect.Type {
		if k := t.Kind(); k == reflect.Interface || k == reflect.Ptr {
			return t
		}
		return reflect.PtrTo(t)
	}

	// TODO: Should this transform protoreflect.Enum types to Enum as well?
	return cmp.FilterPath(func(p cmp.Path) bool {
		ps := p.Last()
		if isMessageType(addrType(ps.Type())) {
			return true
		}

		// Check whether the concrete values of an interface both satisfy
		// the Message interface.
		if ps.Type().Kind() == reflect.Interface {
			vx, vy := ps.Values()
			if !vx.IsValid() || vx.IsNil() || !vy.IsValid() || vy.IsNil() {
				return false
			}
			return isMessageType(addrType(vx.Elem().Type())) && isMessageType(addrType(vy.Elem().Type()))
		}

		return false
	}, cmp.Transformer("protocmp.Transform", func(v interface{}) Message {
		// For user convenience, shallow copy the message value if necessary
		// in order for it to implement the message interface.
		if rv := reflect.ValueOf(v); rv.IsValid() && rv.Kind() != reflect.Ptr && !isMessageType(rv.Type()) {
			pv := reflect.New(rv.Type())
			pv.Elem().Set(rv)
			v = pv.Interface()
		}

		m := protoimpl.X.MessageOf(v)
		switch {
		case m == nil:
			return nil
		case !m.IsValid():
			return Message{messageTypeKey: messageMeta{m: m.Interface(), md: m.Descriptor()}, messageInvalidKey: true}
		default:
			return transformMessage(m)
		}
	}))
}

func isMessageType(t reflect.Type) bool {
	// Avoid transforming the Message itself.
	if t == reflect.TypeOf(Message(nil)) || t == reflect.TypeOf((*Message)(nil)) {
		return false
	}
	return t.Implements(messageV1Type) || t.Implements(messageV2Type)
}

func transformMessage(m protoreflect.Message) Message {
	mx := Message{}
	mt := messageMeta{m: m.Interface(), md: m.Descriptor(), xds: make(map[string]protoreflect.FieldDescriptor)}

	// Handle known and extension fields.
	m.Range(func(fd protoreflect.FieldDescriptor, v protoreflect.Value) bool {
		s := fd.TextName()
		if fd.IsExtension() {
			mt.xds[s] = fd
		}
		switch {
		case fd.IsList():
			mx[s] = transformList(fd, v.List())
		case fd.IsMap():
			mx[s] = transformMap(fd, v.Map())
		default:
			mx[s] = transformSingular(fd, v)
		}
		return true
	})

	// Handle unknown fields.
	for b := m.GetUnknown(); len(b) > 0; {
		num, _, n := protowire.ConsumeField(b)
		s := strconv.Itoa(int(num))
		b2, _ := mx[s].(protoreflect.RawFields)
		mx[s] = append(b2, b[:n]...)
		b = b[n:]
	}

	// Expand Any messages.
	if mt.md.FullName() == genid.Any_message_fullname {
		// TODO: Expose Transform option to specify a custom resolver?
		s, _ := mx[string(genid.Any_TypeUrl_field_name)].(string)
		b, _ := mx[string(genid.Any_Value_field_name)].([]byte)
		mt, err := protoregistry.GlobalTypes.FindMessageByURL(s)
		if mt != nil && err == nil {
			m2 := mt.New()
			err := proto.UnmarshalOptions{AllowPartial: true}.Unmarshal(b, m2.Interface())
			if err == nil {
				mx[string(genid.Any_Value_field_name)] = transformMessage(m2)
			}
		}
	}

	mx[messageTypeKey] = mt
	return mx
}

func transformList(fd protoreflect.FieldDescriptor, lv protoreflect.List) interface{} {
	t := protoKindToGoType(fd.Kind())
	rv := reflect.MakeSlice(reflect.SliceOf(t), lv.Len(), lv.Len())
	for i := 0; i < lv.Len(); i++ {
		v := reflect.ValueOf(transformSingular(fd, lv.Get(i)))
		rv.Index(i).Set(v)
	}
	return rv.Interface()
}

func transformMap(fd protoreflect.FieldDescriptor, mv protoreflect.Map) interface{} {
	kfd := fd.MapKey()
	vfd := fd.MapValue()
	kt := protoKindToGoType(kfd.Kind())
	vt := protoKindToGoType(vfd.Kind())
	rv := reflect.MakeMapWithSize(reflect.MapOf(kt, vt), mv.Len())
	mv.Range(func(k protoreflect.MapKey, v protoreflect.Value) bool {
		kv := reflect.ValueOf(transformSingular(kfd, k.Value()))
		vv := reflect.ValueOf(transformSingular(vfd, v))
		rv.SetMapIndex(kv, vv)
		return true
	})
	return rv.Interface()
}

func transformSingular(fd protoreflect.FieldDescriptor, v protoreflect.Value) interface{} {
	switch fd.Kind() {
	case protoreflect.EnumKind:
		return Enum{num: v.Enum(), ed: fd.Enum()}
	case protoreflect.MessageKind, protoreflect.GroupKind:
		return transformMessage(v.Message())
	case protoreflect.BytesKind:
		// The protoreflect API does not specify whether an empty bytes is
		// guaranteed to be nil or not. Always return non-nil bytes to avoid
		// leaking information about the concrete proto.Message implementation.
		if len(v.Bytes()) == 0 {
			return []byte{}
		}
		return v.Bytes()
	default:
		return v.Interface()
	}
}

func protoKindToGoType(k protoreflect.Kind) reflect.Type {
	switch k {
	case protoreflect.BoolKind:
		return reflect.TypeOf(bool(false))
	case protoreflect.Int32Kind, protoreflect.Sint32Kind, protoreflect.Sfixed32Kind:
		return reflect.TypeOf(int32(0))
	case protoreflect.Int64Kind, protoreflect.Sint64Kind, protoreflect.Sfixed64Kind:
		return reflect.TypeOf(int64(0))
	case protoreflect.Uint32Kind, protoreflect.Fixed32Kind:
		return reflect.TypeOf(uint32(0))
	case protoreflect.Uint64Kind, protoreflect.Fixed64Kind:
		return reflect.TypeOf(uint64(0))
	case protoreflect.FloatKind:
		return reflect.TypeOf(float32(0))
	case protoreflect.DoubleKind:
		return reflect.TypeOf(float64(0))
	case protoreflect.StringKind:
		return reflect.TypeOf(string(""))
	case protoreflect.BytesKind:
		return reflect.TypeOf([]byte(nil))
	case protoreflect.EnumKind:
		return reflect.TypeOf(Enum{})
	case protoreflect.MessageKind, protoreflect.GroupKind:
		return reflect.TypeOf(Message{})
	default:
		panic("invalid kind")
	}
}