package streams

import (
	"io"

	pubsubutil "git.icedream.tech/icedream/uplink/app/pubsub"
	"github.com/cskr/pubsub"
)

type MetadataExtractor struct {
	io.Reader
	MetadataInterval int

	pubsub *pubsub.PubSub

	blockOffset int

	metadataToRead int
	metadataBuf    []byte
}

func NewMetadataExtractor(r io.Reader, metadataInterval int) *MetadataExtractor {
	return &MetadataExtractor{
		Reader:           r,
		MetadataInterval: metadataInterval,
	}
}

func (me *MetadataExtractor) Data() io.ReadCloser {
	return pubsubutil.NewPubSubReader(me.pubsub, "data")
}

func (me *MetadataExtractor) Metadata() *MetadataStream {
	return &MetadataStream{
		data: me.pubsub.Sub("metadata"),
		me:   me,
	}
}

func (me *MetadataExtractor) close() {
	me.pubsub.Close("metadata", "data")
	me.pubsub.Shutdown()
}

func (mi *MetadataExtractor) Read(data []byte) (n int, err error) {
	if mi.metadataBuf != nil && mi.metadataToRead > 0 {
		n, err = mi.Reader.Read(mi.metadataBuf[len(mi.metadataBuf)-mi.metadataToRead:])
		if err != nil {
			return
		}
		mi.metadataToRead -= n
		if mi.metadataToRead <= 0 {
			var meta map[string]string
			meta, err = decodeMetadata(string(mi.metadataBuf))
			if err != nil {
				return
			}
			me.pubsub.Pub(meta)
			mi.metadataBuf = nil
		}
		return
	}

	bytesToRead := mi.MetadataInterval - mi.blockOffset
	if bytesToRead > len(data) {
		bytesToRead = len(data)
	}
	if bytesToRead > 0 {
		n, err = mi.Reader.Read(data[0:bytesToRead])
		if err != nil {
			return
		}
		mi.blockOffset += n
	}
	if mi.blockOffset == mi.MetadataInterval {
		mi.generateMetadataBuf() // will be read in on next Read call
		mi.blockOffset = 0
	} else if mi.blockOffset > mi.MetadataInterval {
		panic("block offset higher than metadata interval, logical error")
	}
	return
}