// 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 proto

import (
	"google.golang.org/protobuf/encoding/protowire"
	"google.golang.org/protobuf/internal/encoding/messageset"
	"google.golang.org/protobuf/reflect/protoreflect"
	"google.golang.org/protobuf/runtime/protoiface"
)

// Size returns the size in bytes of the wire-format encoding of m.
func Size(m Message) int {
	return MarshalOptions{}.Size(m)
}

// Size returns the size in bytes of the wire-format encoding of m.
func (o MarshalOptions) Size(m Message) int {
	// Treat a nil message interface as an empty message; nothing to output. 
	if m == nil {
		return 0
	}

	return o.size(m. ProtoReflect())
}

// size is a centralized function that all size operations go through. 
// For profiling purposes, avoid changing the name of this function or
// introducing other code paths for size that do not go through this. 
func (o MarshalOptions) size(m protoreflect. Message) (size int) {
	methods := protoMethods(m)
	if methods ! = nil && methods. Size ! = nil {
		out := methods. Size(protoiface. SizeInput{
			Message: m,
		})
		return out. Size
	}
	if methods ! = nil && methods. Marshal ! = nil {
		// This is not efficient, but we don't have any choice. 
		// This case is mainly used for legacy types with a Marshal method. 
		out, _ := methods. Marshal(protoiface. MarshalInput{
			Message: m,
		})
		return len(out. Buf)
	}
	return o.sizeMessageSlow(m)
}

func (o MarshalOptions) sizeMessageSlow(m protoreflect. Message) (size int) {
	if messageset. IsMessageSet(m. Descriptor()) {
		return o.sizeMessageSet(m)
	}
	m.Range(func(fd protoreflect. FieldDescriptor, v protoreflect. Value) bool {
		size += o.sizeField(fd, v)
		return true
	})
	size += len(m. GetUnknown())
	return size
}

func (o MarshalOptions) sizeField(fd protoreflect. FieldDescriptor, value protoreflect. Value) (size int) {
	num := fd. Number()
	switch {
	case fd. IsList():
		return o.sizeList(num, fd, value. List())
	case fd. IsMap():
		return o.sizeMap(num, fd, value. Map())
	default:
		return protowire. SizeTag(num) + o.sizeSingular(num, fd. Kind(), value)
	}
}

func (o MarshalOptions) sizeList(num protowire. Number, fd protoreflect. FieldDescriptor, list protoreflect. List) (size int) {
	if fd. IsPacked() && list. Len() > 0 {
		content := 0
		for i, llen := 0, list. Len(); i < llen; i++ {
			content += o.sizeSingular(num, fd. Kind(), list. Get(i))
		}
		return protowire. SizeTag(num) + protowire. SizeBytes(content)
	}

	for i, llen := 0, list. Len(); i < llen; i++ {
		size += protowire. SizeTag(num) + o.sizeSingular(num, fd. Kind(), list. Get(i))
	}
	return size
}

func (o MarshalOptions) sizeMap(num protowire. Number, fd protoreflect. FieldDescriptor, mapv protoreflect. Map) (size int) {
	mapv. Range(func(key protoreflect. MapKey, value protoreflect. Value) bool {
		size += protowire. SizeTag(num)
		size += protowire. SizeBytes(o.sizeField(fd. MapKey(), key. Value()) + o.sizeField(fd. MapValue(), value))
		return true
	})
	return size
}
