package journal

import (
	"encoding/binary"
	"io"
	"net"
	"slices"
)

var (
	wireProtocolAttributeSeparator  = []byte{'='}
	wireProtocolAttributeTerminator = []byte{'\n'}
)

// WireWrite is the lowest-level routine. It writes a journal entry using the
// native wire protocol documented at https://systemd.io/JOURNAL_NATIVE_PROTOCOL/ .
// Invalid attributes are silently skipped. It appends to buf as needed.
//
// As long as w supports the net.buffersWriter interface, the write will be
// atomic, and this function is safe to use across goroutines. Otherwise,
// writes may be interleaved.
func WireWrite(buf *net.Buffers, w io.Writer, attrs []Attr) error {
	*buf = slices.Grow(*buf, len(*buf)+len(attrs)*4)
	for i := range attrs {
		key := attrs[i].Key.key
		if key == "" {
			// silently discard invalid attributes
			continue
		}

		*buf = append(*buf, []byte(key))
		if attrs[i].UseTextProto() {
			*buf = append(*buf, wireProtocolAttributeSeparator)
			*buf = append(*buf, attrs[i].Value)
		} else {
			var valueSize [9]byte
			valueSize[0] = '\n'
			binary.LittleEndian.PutUint64(valueSize[1:], uint64(len(attrs[i].Value)))
			*buf = append(*buf, valueSize[:])
			*buf = append(*buf, attrs[i].Value)
		}
		*buf = append(*buf, wireProtocolAttributeTerminator)
	}
	_, err := buf.WriteTo(w)
	return err
}