Supports streaming with reader

[rnotorni]

#59

Supports Streaming with Transfer.

[kyokomi]

@rnotorni Thanks for the PR. I'm sorry, but I can't merge this PR because I have a policy of not using non-standard packages.

Instead, I am thinking of exporting emojize so that emojiTransfer can be created as a separate library from kyokomi/emoji, but what do you think?

+func Emojize(x string) string {
-func emojize(x string) string {
	str, ok := emojiCode()[x]
	if ok {
		return str + ReplacePadding
	}
	if match := flagRegexp.FindStringSubmatch(x); len(match) == 2 {
		return regionalIndicator(match[1][0]) + regionalIndicator(match[1][1])
	}
	return x
}

(I'm not very good at English, so sorry if I didn't communicate well)

[rnotorni]

@kyokomi That's a good policy! I think it would be nice to exporting the emojize, although it is different from the purpose of this PR.

Wrapping a Reader and Writer for emoji is possible with standard packages only. However, if the feature deviates from the role of this repository, it should not be implemented.

After all, I don't know if it's okay to support streaming without defining the role of this repository.

(Don't worry I'm not good at English.)

[kyokomi]

@rnotorni Exported here.

For example, if you import github.com/kyokomi/emoji as the emojitransfer package and create emojiTransfer, this is what you will get.

This code is your idea, so if you want to publish it on github, I would prefer that you publish it on your github.

package emojitransfer

import (
	"bytes"
	"unicode"

	"github.com/kyokomi/emoji/v2"
	"golang.org/x/text/transform"
)

type emojiTransfer struct {
	atEOF    bool
	emojiBuf *bytes.Buffer
	buf      []byte
	transform.NopResetter
}

// NewEmojiTransfer return transform.Transfer implementd.
func NewEmojiTransfer() transform.Transformer {
	return &emojiTransfer{}
}

func (e *emojiTransfer) Transform(dst, src []byte, atEOF bool) (int, int, error) {
	e.atEOF = atEOF
	if e.buf == nil {
		e.buf = e.encode(bytes.NewBuffer(src)).Bytes()
	}

	n := copy(dst, e.buf)
	if len(e.buf) <= n {
		e.buf = nil
		return n, len(src), nil
	}
	e.buf = e.buf[n:]
	return n, 0, transform.ErrShortDst
}

func (e *emojiTransfer) replaceEmoji(input *bytes.Buffer) string {
	emojiStr := bytes.NewBufferString(":")
	for {
		i, _, err := input.ReadRune()
		if err != nil {
			return e.replaceNotFindEnd(emojiStr)
		}

		if i == ':' && emojiStr.Len() == 1 {
			return emojiStr.String() + e.replaceEmoji(input)
		}

		emojiStr.WriteRune(i)
		switch {
		case unicode.IsSpace(i):
			return emojiStr.String()
		case i == ':':
			return emoji.Emojize(emojiStr.String())
		}
	}
}

func (e *emojiTransfer) replaceNotFindEnd(emojiBuf *bytes.Buffer) string {
	if e.atEOF {
		return emojiBuf.String()
	}
	e.emojiBuf = emojiBuf
	return ""
}

func (e *emojiTransfer) mergeBuf(input *bytes.Buffer) *bytes.Buffer {
	if e.emojiBuf == nil {
		return input
	}
	return bytes.NewBuffer(append(e.emojiBuf.Bytes(), input.Bytes()...))
}

func (e *emojiTransfer) encode(input *bytes.Buffer) *bytes.Buffer {
	target := e.mergeBuf(input)
	e.emojiBuf = nil

	output := &bytes.Buffer{}
	output.Grow(input.Len())

	for {
		i, _, err := target.ReadRune()
		if err != nil {
			break
		}
		switch i {
		default:
			output.WriteRune(i)
		case ':':
			output.WriteString(e.replaceEmoji(target))
		}
	}
	return output
}

[rnotorni]

This code is your idea, so if you want to publish it on github, I would prefer that you publish it on your github.

That's right.

Thank you for your response!