package pubsub

import (
	"io"

	cskrpubsub "github.com/cskr/pubsub"
)

type PubSubReader struct {
	pubsub  *cskrpubsub.PubSub
	channel chan interface{}
	buf     []byte
	closed  bool
	topic   string
}

func NewPubSubReader(ps *cskrpubsub.PubSub, topic string) *PubSubReader {
	return &PubSubReader{
		pubsub:  ps,
		topic:   topic,
		channel: ps.Sub(topic),
	}
}

func (r *PubSubReader) Read(p []byte) (n int, err error) {
	if r.closed {
		err = io.EOF
		return
	}

	if r.buf == nil {
		data, ok := <-r.channel
		if !ok {
			r.closed = true
			err = io.EOF
			return
		}
		dataBytes := data.([]byte)
		if len(dataBytes) == 0 {
			return
		}
		r.buf = dataBytes
	}

	if r.buf != nil {
		n = len(p)
		if len(r.buf) < n {
			n = len(r.buf)
		}
		copy(p, r.buf[0:n])
		if len(r.buf) == n {
			r.buf = nil
		} else {
			r.buf = r.buf[n:]
		}
		return
	}

	return
}

func (r *PubSubReader) Close() (err error) {
	r.closed = true
	r.pubsub.Unsub(r.channel, r.topic)
	return
}