// Copyright 2010 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

/*
 * Routines for encoding data into the wire format for protocol buffers.
 */

import (
	"errors"
	"reflect"
)

var (
	// errRepeatedHasNil is the error returned if Marshal is called with
	// a struct with a repeated field containing a nil element.
	errRepeatedHasNil = errors.New("proto: repeated field has nil element")

	// errOneofHasNil is the error returned if Marshal is called with
	// a struct with a oneof field containing a nil element.
	errOneofHasNil = errors.New("proto: oneof field has nil value")

	// ErrNil is the error returned if Marshal is called with nil.
	ErrNil = errors.New("proto: Marshal called with nil")

	// ErrTooLarge is the error returned if Marshal is called with a
	// message that encodes to >2GB.
	ErrTooLarge = errors.New("proto: message encodes to over 2 GB")
)

// The fundamental encoders that put bytes on the wire.
// Those that take integer types all accept uint64 and are
// therefore of type valueEncoder.

const maxVarintBytes = 10 // maximum length of a varint

// EncodeVarint returns the varint encoding of x.
// This is the format for the
// int32, int64, uint32, uint64, bool, and enum
// protocol buffer types.
// Not used by the package itself, but helpful to clients
// wishing to use the same encoding.
func EncodeVarint(x uint64) []byte {
	var buf [maxVarintBytes]byte
	var n int
	for n = 0; x > 127; n++ {
		buf[n] = 0x80 | uint8(x&0x7F)
		x >>= 7
	}
	buf[n] = uint8(x)
	n++
	return buf[0:n]
}

// EncodeVarint writes a varint-encoded integer to the Buffer.
// This is the format for the
// int32, int64, uint32, uint64, bool, and enum
// protocol buffer types.
func (p *Buffer) EncodeVarint(x uint64) error {
	for x >= 1<<7 {
		p.buf = append(p.buf, uint8(x&0x7f|0x80))
		x >>= 7
	}
	p.buf = append(p.buf, uint8(x))
	return nil
}

// SizeVarint returns the varint encoding size of an integer.
func SizeVarint(x uint64) int {
	switch {
	case x < 1<<7:
		return 1
	case x < 1<<14:
		return 2
	case x < 1<<21:
		return 3
	case x < 1<<28:
		return 4
	case x < 1<<35:
		return 5
	case x < 1<<42:
		return 6
	case x < 1<<49:
		return 7
	case x < 1<<56:
		return 8
	case x < 1<<63:
		return 9
	}
	return 10
}

// EncodeFixed64 writes a 64-bit integer to the Buffer.
// This is the format for the
// fixed64, sfixed64, and double protocol buffer types.
func (p *Buffer) EncodeFixed64(x uint64) error {
	p.buf = append(p.buf,
		uint8(x),
		uint8(x>>8),
		uint8(x>>16),
		uint8(x>>24),
		uint8(x>>32),
		uint8(x>>40),
		uint8(x>>48),
		uint8(x>>56))
	return nil
}

// EncodeFixed32 writes a 32-bit integer to the Buffer.
// This is the format for the
// fixed32, sfixed32, and float protocol buffer types.
func (p *Buffer) EncodeFixed32(x uint64) error {
	p.buf = append(p.buf,
		uint8(x),
		uint8(x>>8),
		uint8(x>>16),
		uint8(x>>24))
	return nil
}

// EncodeZigzag64 writes a zigzag-encoded 64-bit integer
// to the Buffer.
// This is the format used for the sint64 protocol buffer type.
func (p *Buffer) EncodeZigzag64(x uint64) error {
	// use signed number to get arithmetic right shift.
	return p.EncodeVarint(uint64((x << 1) ^ uint64((int64(x) >> 63))))
}

// EncodeZigzag32 writes a zigzag-encoded 32-bit integer
// to the Buffer.
// This is the format used for the sint32 protocol buffer type.
func (p *Buffer) EncodeZigzag32(x uint64) error {
	// use signed number to get arithmetic right shift.
	return p.EncodeVarint(uint64((uint32(x) << 1) ^ uint32((int32(x) >> 31))))
}

// EncodeRawBytes writes a count-delimited byte buffer to the Buffer.
// This is the format used for the bytes protocol buffer
// type and for embedded messages.
func (p *Buffer) EncodeRawBytes(b []byte) error {
	p.EncodeVarint(uint64(len(b)))
	p.buf = append(p.buf, b...)
	return nil
}

// EncodeStringBytes writes an encoded string to the Buffer.
// This is the format used for the proto2 string type.
func (p *Buffer) EncodeStringBytes(s string) error {
	p.EncodeVarint(uint64(len(s)))
	p.buf = append(p.buf, s...)
	return nil
}

// Marshaler is the interface representing objects that can marshal themselves.
type Marshaler interface {
	Marshal() ([]byte, error)
}

// EncodeMessage writes the protocol buffer to the Buffer,
// prefixed by a varint-encoded length.
func (p *Buffer) EncodeMessage(pb Message) error {
	siz := Size(pb)
	p.EncodeVarint(uint64(siz))
	return p.Marshal(pb)
}

// All protocol buffer fields are nillable, but be careful.
func isNil(v reflect.Value) bool {
	switch v.Kind() {
	case reflect.Interface, reflect.Map, reflect.Ptr, reflect.Slice:
		return v.IsNil()
	}
	return false
}