// Package feed generates RSS 2.0 / Atom feeds from blog posts.
package feed

import (
	"encoding/xml"
	"time"

	"ridgwaysystems.org/website/internal/blog"
)

// --- RSS 2.0 ---

type rssChannel struct {
	XMLName       xml.Name  `xml:"channel"`
	Title         string    `xml:"title"`
	Link          string    `xml:"link"`
	Description   string    `xml:"description"`
	Language      string    `xml:"language"`
	LastBuildDate string    `xml:"lastBuildDate"`
	AtomLink      atomLink  `xml:"atom:link"`
	Items         []rssItem `xml:"item"`
}

type atomLink struct {
	Href string `xml:"href,attr"`
	Rel  string `xml:"rel,attr"`
	Type string `xml:"type,attr"`
}

type rssItem struct {
	Title       string `xml:"title"`
	Link        string `xml:"link"`
	Description string `xml:"description"`
	PubDate     string `xml:"pubDate"`
	GUID        string `xml:"guid"`
}

type rssFeed struct {
	XMLName xml.Name   `xml:"rss"`
	Version string     `xml:"version,attr"`
	Atom    string     `xml:"xmlns:atom,attr"`
	Channel rssChannel `xml:"channel"`
}

// RSS generates RSS 2.0 XML for the given posts.
func RSS(siteURL, siteTitle, siteDesc string, posts []*blog.Post) ([]byte, error) {
	var items []rssItem
	for _, p := range posts {
		postURL := siteURL + "/blog/" + p.Slug
		items = append(items, rssItem{
			Title:       p.Title,
			Link:        postURL,
			Description: p.Description,
			PubDate:     p.ParsedDate.Format(time.RFC1123Z),
			GUID:        postURL,
		})
	}

	feed := rssFeed{
		Version: "2.0",
		Atom:    "http://www.w3.org/2005/Atom",
		Channel: rssChannel{
			Title:         siteTitle,
			Link:          siteURL,
			Description:   siteDesc,
			Language:      "en-us",
			LastBuildDate: time.Now().Format(time.RFC1123Z),
			AtomLink: atomLink{
				Href: siteURL + "/blog/feed.xml",
				Rel:  "self",
				Type: "application/rss+xml",
			},
			Items: items,
		},
	}

	out, err := xml.MarshalIndent(feed, "", "  ")
	if err != nil {
		return nil, err
	}
	return append([]byte(xml.Header), out...), nil
}