encoder.go

package toolbox

import (
	"encoding/json"
	"fmt"
	"gopkg.in/yaml.v2"
	"io"
)

//Encoder writes an instance to output stream
type Encoder interface {
	//Encode encodes  an instance to output stream
	Encode(object interface{}) error
}

//Marshaler represents byte to object converter
type Marshaler interface {
	//Marshal converts bytes to attributes of owner struct
	Marshal() (data []byte, err error)
}

//EncoderFactory create an encoder for an output stream
type EncoderFactory interface {
	//Create creates an encoder for an output stream
	Create(writer io.Writer) Encoder
}

type jsonEncoderFactory struct{}

func (e jsonEncoderFactory) Create(writer io.Writer) Encoder {
	return json.NewEncoder(writer)
}

//NewJSONEncoderFactory creates new NewJSONEncoderFactory
func NewJSONEncoderFactory() EncoderFactory {
	return &jsonEncoderFactory{}
}

type marshalerEncoderFactory struct {
}

func (f *marshalerEncoderFactory) Create(writer io.Writer) Encoder {
	return &marshalerEncoder{writer: writer}
}

type marshalerEncoder struct {
	writer io.Writer
}

func (e *marshalerEncoder) Encode(v interface{}) error {
	result, casted := v.(Marshaler)
	if !casted {
		return fmt.Errorf("failed to decode - unable cast %T to %s", v, (*Marshaler)(nil))
	}
	bytes, err := result.Marshal()
	if err != nil {
		return err
	}
	var totalByteWritten int = 0
	var bytesLen = len(bytes)
	for i := 0; i < bytesLen; i++ {
		bytesWritten, err := e.writer.Write(bytes[totalByteWritten:])
		if err != nil {
			return fmt.Errorf("failed to write data %v", err)
		}
		totalByteWritten = totalByteWritten + bytesWritten
		if totalByteWritten == bytesLen {
			break
		}
	}
	if totalByteWritten != bytesLen {
		return fmt.Errorf("failed to write all data, written %v, expected: %v", totalByteWritten, bytesLen)
	}
	return nil
}

//NewMarshalerEncoderFactory create a new encoder factory for marsheler struct
func NewMarshalerEncoderFactory() EncoderFactory {
	return &marshalerEncoderFactory{}
}

type yamlEncoderFactory struct{}

func (e yamlEncoderFactory) Create(writer io.Writer) Encoder {
	return &yamlEncoder{writer}
}

type yamlEncoder struct {
	io.Writer
}

//Encode converts source into yaml format to write itto writer
func (d *yamlEncoder) Encode(source interface{}) error {
	data, err := yaml.Marshal(source)
	if err != nil {
		return err
	}
	var dataSize = len(data)
	for i := 0; i < dataSize; i++ {
		written, err := d.Writer.Write(data)
		if err != nil {
			return err
		}
		if len(data) == written {
			break
		}
		data = data[written:]
	}
	return err
}

//NewYamlEncoderFactory create a new yaml encoder factory
func NewYamlEncoderFactory() EncoderFactory {
	return &yamlEncoderFactory{}
}