package main

import (
	"cmp"
	"encoding/xml"
	"net/http"
	"time"
)

const feedItems = 20

type rss struct {
	XMLName xml.Name   `xml:"rss"`
	Version string     `xml:"version,attr"`
	DC      string     `xml:"xmlns:dc,attr"` // Dublin Core, for dc:creator
	Channel rssChannel `xml:"channel"`
}

type rssChannel struct {
	Title         string    `xml:"title"`
	Link          string    `xml:"link"`
	Description   string    `xml:"description"`
	LastBuildDate string    `xml:"lastBuildDate,omitempty"`
	Items         []rssItem `xml:"item"`
}

type rssItem struct {
	Title       string `xml:"title"`
	Link        string `xml:"link"`
	GUID        string `xml:"guid"`
	PubDate     string `xml:"pubDate"`
	Description string `xml:"description,omitempty"`
	// RSS's own <author> must be an email address; dc:creator takes a name.
	Creator string `xml:"dc:creator"`
}

func (a *app) feed(w http.ResponseWriter, r *http.Request) {
	idx, err := a.store.Index()
	if err != nil {
		a.serverError(w, err)
		return
	}
	ch := rssChannel{
		Title:       a.siteName,
		Link:        a.siteURL + "/",
		Description: "Posts from " + a.siteName,
	}
	defaultAuthor := a.config.Get().DefaultAuthor
	for i, p := range idx.posts {
		if i == feedItems {
			break
		}
		if i == 0 {
			ch.LastBuildDate = p.Date.Format(time.RFC1123Z)
		}
		link := a.siteURL + "/posts/" + p.Slug
		ch.Items = append(ch.Items, rssItem{
			Title:       p.Title,
			Link:        link,
			GUID:        link,
			PubDate:     p.Date.Format(time.RFC1123Z),
			Description: p.Summary,
			Creator:     cmp.Or(p.Author, defaultAuthor),
		})
	}
	out, err := xml.MarshalIndent(rss{Version: "2.0", DC: "http://purl.org/dc/elements/1.1/", Channel: ch}, "", "  ")
	if err != nil {
		a.serverError(w, err)
		return
	}
	w.Header().Set("Content-Type", "application/rss+xml; charset=utf-8")
	w.Write([]byte(xml.Header))
	w.Write(out)
}