package rss

import (
	"encoding/gob"
	"encoding/xml"
	"fmt"
	"os"
	"sync"
)

type Feed struct {
	addChannel       chan *Channel
	XMLName          xml.Name `xml:"rss"`
	Version          string   `xml:"version,attr"`
	ContentNamespace string   `xml:"xmlns:content,attr"`
	Channels         []*Channel
	wg               sync.WaitGroup
}

func (f *Feed) start() {
	f.wg.Done()

	for channel := range f.addChannel {
		f.Channels = append(f.Channels, channel)
	}
}

func initFeed() *Feed {
	feed := &Feed{
		addChannel:       make(chan *Channel),
		Version:          "2.0",
		ContentNamespace: "http://purl.org/rss/1.0/modules/content/",
	}

	return feed
}

func (f *Feed) check() error {
	if f.Channels == nil {
		return fmt.Errorf("error: feed has no channels")
	}

	for _, channel := range f.Channels {
		if err := channel.check(); err != nil {
			return fmt.Errorf("error checking channel: %v", err)
		}
	}

	return nil
}

func NewFeed() *Feed {
	feed := initFeed()

	feed.wg.Add(1)
	go feed.start()
	feed.wg.Wait()

	return feed
}

func (f *Feed) AddChannel(c *Channel) {
	f.addChannel <- c
}

func (f *Feed) Save(filename string) error {
	file, err := os.Create(filename)
	if err != nil {
		return fmt.Errorf("error creating file %v: %v", filename, err)
	}
	defer file.Close()

	if err := gob.NewEncoder(file).Encode(f); err != nil {
		return fmt.Errorf("error encoding feed in file %v: %v", filename, err)
	}

	return nil
}

func OpenFeed(filename string) (*Feed, error) {
	file, err := os.Open(filename)
	if err != nil {
		return nil, fmt.Errorf("error opening file %v: %v", filename, err)
	}
	defer file.Close()

	feed := initFeed()
	feed.wg.Add(1)
	go feed.start()
	feed.wg.Wait()

	if err := gob.NewDecoder(file).Decode(feed); err != nil {
		return nil, fmt.Errorf("error decoding file %v: %v", filename, err)
	}

	return nil, nil
}