package streams

import (
	"io"
)

type MetadataInjector struct {
	io.Writer
	offset           int
	MetadataInterval int
	metadata         Metadata
}

func NewMetadataInjector(w io.Writer, metadataInterval int) *MetadataInjector {
	return &MetadataInjector{
		Writer:           w,
		MetadataInterval: metadataInterval,
	}
}

func (mi *MetadataInjector) SetMetadata(metadata Metadata) {
	mi.metadata = metadata
}

func (mi *MetadataInjector) writeMetadata() (n int, err error) {
	// the metadata generated here will be read on the next Read call
	metadataBytes := mi.metadata.Bytes()
	lenByte := (len(metadataBytes) + 15) / 16
	metadataBuf := make([]byte, int(lenByte)*16+1)
	metadataBuf[0] = byte(lenByte)
	copy(metadataBuf[1:], metadataBytes)

	if len(mi.metadata) > 0 {
		mi.metadata = Metadata{}
	}

	return mi.Writer.Write(metadataBuf)
}

func (mi *MetadataInjector) Write(data []byte) (n int, err error) {
	for n < len(data) {
		restLen := len(data) - n
		toWrite := mi.MetadataInterval - mi.offset
		if toWrite > restLen {
			toWrite = restLen
		}

		if toWrite <= 0 {
			_, err = mi.writeMetadata()
			if err != nil {
				return
			}
			mi.offset = 0
			continue
		}

		outBytes := make([]byte, toWrite)
		copy(outBytes, data[n:n+toWrite])
		cn, cerr := mi.Writer.Write(outBytes)
		n += cn
		mi.offset += cn
		if cerr != nil {
			err = cerr
			return
		}
	}
	return
}