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// untested sections: 1
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package gexec
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import (
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	"io"
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	"sync"
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)
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/*
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PrefixedWriter wraps an io.Writer, emitting the passed in prefix at the beginning of each new line.
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This can be useful when running multiple gexec.Sessions concurrently - you can prefix the log output of each
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session by passing in a PrefixedWriter:
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gexec.Start(cmd, NewPrefixedWriter("[my-cmd] ", GinkgoWriter), NewPrefixedWriter("[my-cmd] ", GinkgoWriter))
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*/
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type PrefixedWriter struct {
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	prefix        []byte
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	writer        io.Writer
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	lock          *sync.Mutex
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	atStartOfLine bool
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}
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func NewPrefixedWriter(prefix string, writer io.Writer) *PrefixedWriter {
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	return &PrefixedWriter{
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		prefix:        []byte(prefix),
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		writer:        writer,
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		lock:          &sync.Mutex{},
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		atStartOfLine: true,
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	}
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}
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func (w *PrefixedWriter) Write(b []byte) (int, error) {
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	w.lock.Lock()
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	defer w.lock.Unlock()
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	toWrite := []byte{}
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	for _, c := range b {
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		if w.atStartOfLine {
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			toWrite = append(toWrite, w.prefix...)
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		}
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		toWrite = append(toWrite, c)
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		w.atStartOfLine = c == '\n'
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	}
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	_, err := w.writer.Write(toWrite)
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	if err != nil {
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		return 0, err
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	}
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	return len(b), nil
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}
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