html/wrap.go

package html

import (
	"bytes"
	"errors"
	"io"
	"unicode"
)

type wrapper struct {
	out                                                       *indentWriter
	width                                                     int
	line, word                                                *bytes.Buffer
	inWord, inTag, inSingleQuote, inQuote, lastSpace, started bool
	err                                                       error
}

func newWrapper(out io.Writer, width int, indent string) *wrapper {
	return &wrapper{
		out:   newIndentWriter(out, indent),
		width: width,
		line:  bytes.NewBuffer(nil),
		word:  bytes.NewBuffer(nil),
	}
}

func (w *wrapper) feed() error {
	withSpace := w.lastSpace && w.line.Len() > 0
	l := w.line.Len() + w.word.Len()
	if withSpace && w.word.Len() > 0 {
		l++
	}

	feedLine := l > w.width && w.line.Len() > 0
	if feedLine {
		if w.started {
			if _, err := w.out.Write([]byte{'\n'}); err != nil {
				return err
			}
		}

		if _, err := io.Copy(w.out, w.line); err != nil {
			return err
		}

		w.line.Reset()
		w.started = true
	}

	if !feedLine && withSpace {
		w.line.WriteRune(' ')
	}

	io.Copy(w.line, w.word)
	w.word.Reset()
	return nil
}

func (w *wrapper) Write(p []byte) (int, error) {
	if w.err != nil {
		return 0, w.err
	}

	runes := bytes.NewBuffer(nil)
	if n, err := runes.Write(p); err != nil {
		w.err = err
		return n, w.err
	}

	for {
		r, _, err := runes.ReadRune()
		if errors.Is(err, io.EOF) {
			return len(p), nil
		}

		if err != nil {
			w.err = err
			return len(p), w.err
		}

		if r == unicode.ReplacementChar {
			continue
		}

		if w.inSingleQuote {
			w.inSingleQuote = r != '\''
			w.word.WriteRune(r)
			continue
		}

		if w.inQuote {
			w.inQuote = r != '"'
			w.word.WriteRune(r)
			continue
		}

		if w.inTag {
			w.inSingleQuote = r == '\''
			w.inQuote = r == '"'
			w.inTag = r != '>'
			if w.inTag || !unicode.IsSpace(r) {
				w.word.WriteRune(r)
			}

			if !w.inTag {
				if err := w.feed(); err != nil {
					w.err = err
					return len(p), w.err
				}

				w.lastSpace = unicode.IsSpace(r)
			}

			continue
		}

		if w.inWord {
			w.inTag = r == '<'
			w.inWord = !w.inTag && !unicode.IsSpace(r)
			if !w.inWord {
				if err := w.feed(); err != nil {
					w.err = err
					return len(p), w.err
				}

				w.lastSpace = unicode.IsSpace(r)
			}

			if w.inWord || w.inTag {
				w.word.WriteRune(r)
			}

			continue
		}

		if unicode.IsSpace(r) {
			w.lastSpace = true
			continue
		}

		w.word.WriteRune(r)
		w.inTag = r == '<'
		w.inWord = !w.inTag
	}

	return len(p), w.err
}

func (w *wrapper) Flush() error {
	if w.err != nil {
		return w.err
	}

	if w.inTag || w.inWord {
		if err := w.feed(); err != nil {
			w.err = err
			return err
		}
	}

	w.width = 0
	if err := w.feed(); err != nil {
		w.err = err
		return err
	}

	w.err = w.out.Flush()
	return w.err
}