package cml04eventer

import (
	"bytes"
	"encoding/gob"
	"encoding/json"

	"github.com/nsqio/go-nsq"
	"github.com/pkg/errors"
)

type Marshaler interface {
	Marshal(topic string, msg *Event) ([]byte, error)
}

type Unmarshaler interface {
	Unmarshal(*nsq.Message) (*Event, error)
}

type JSONMarshaler struct{}

func (j JSONMarshaler) Marshal(topic string, msg *Event) ([]byte, error) {
	// buffer holder
	buf := new(bytes.Buffer)
	// create encoder
	encoder := json.NewEncoder(buf)
	// encode message
	if err := encoder.Encode(msg); err != nil {
		return nil, errors.Wrap(err, "cannot encode message")
	}
	// return encoded message
	return buf.Bytes(), nil
}

func (j JSONMarshaler) Unmarshal(nsqMsg *nsq.Message) (*Event, error) {
	// buffer holder
	buf := new(bytes.Buffer)
	// write message data to buffer
	_, err := buf.Write(nsqMsg.Body)
	if err != nil {
		return nil, errors.Wrap(err, "cannot write nsq message data to buffer")
	}
	// create decoder
	decoder := json.NewDecoder(buf)
	// decode event from buffer message
	var decodedEvent Event
	// decode message
	if err := decoder.Decode(&decodedEvent); err != nil {
		return nil, errors.Wrap(err, "cannot decode message")
	}
	// return decoded message
	return &decodedEvent, nil
}

type GobMarshaler struct{}

func (g GobMarshaler) Marshal(topic string, msg *Event) ([]byte, error) {
	// buffer holder
	buf := new(bytes.Buffer)
	// create encoder
	encoder := gob.NewEncoder(buf)
	// encode message
	if err := encoder.Encode(msg); err != nil {
		return nil, errors.Wrap(err, "cannot encode message")
	}
	// return encoded message
	return buf.Bytes(), nil
}

func (g GobMarshaler) Unmarshal(nsqMsg *nsq.Message) (*Event, error) {
	// buffer holder
	buf := new(bytes.Buffer)
	// write message data to buffer
	_, err := buf.Write(nsqMsg.Body)
	if err != nil {
		return nil, errors.Wrap(err, "cannot write nsq message data to buffer")
	}
	// create decoder
	decoder := gob.NewDecoder(buf)
	// decode event from buffer message
	var decodedEvent Event
	// decode message
	if err := decoder.Decode(&decodedEvent); err != nil {
		return nil, errors.Wrap(err, "cannot decode message")
	}
	// return decoded message
	return &decodedEvent, nil
}