package api

import (
	"encoding/xml"
	"html"
	"net/http"
	"strings"
	"time"
	"unicode/utf8"

	"git.golem15.com/golem15/sm-journal-plugin/models"
	"git.golem15.com/golem15/summercms/modules/backpack"
)

// RSS is GET /_journal/api/v1/rss. Empty or disabled settings still yield a
// well-formed RSS 2.0 document (D-14).
func RSS(app *backpack.App) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		db, err := gdb(app)
		if err != nil {
			http.Error(w, "Internal server error", http.StatusInternalServerError)
			return
		}
		var settings models.Settings
		if err := db.WithContext(r.Context()).First(&settings, 1).Error; err != nil {
			settings = models.Settings{RSSLanguage: "en-us", RSSPostsPerFeed: 20, RSSEnabled: true}
		}
		limit := settings.RSSPostsPerFeed
		if limit <= 0 {
			limit = 20
		}
		var posts []models.Post
		if err := applyPublished(db.WithContext(r.Context()).Model(&models.Post{})).
			Preload("User").Preload("Categories").
			Order("published_at DESC").Limit(limit).Find(&posts).Error; err != nil {
			http.Error(w, "Internal server error", http.StatusInternalServerError)
			return
		}
		title := "Journal"
		if settings.RSSTitle != nil && strings.TrimSpace(*settings.RSSTitle) != "" {
			title = strings.TrimSpace(*settings.RSSTitle)
		}
		desc := ""
		if settings.RSSDescription != nil {
			desc = *settings.RSSDescription
		}
		site := requestOrigin(r, app)
		self := site + r.URL.RequestURI()
		var b strings.Builder
		b.WriteString(`<?xml version="1.0" encoding="utf-8"?>` + "\n")
		b.WriteString(`<rss version="2.0" xmlns:atom="http://www.w3.org/2005/Atom" xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:content="http://purl.org/rss/1.0/modules/content/" xmlns:media="http://search.yahoo.com/mrss/">` + "\n")
		b.WriteString("<channel>\n")
		writeXMLTag(&b, "title", title)
		writeXMLTag(&b, "link", site+"/")
		writeXMLTag(&b, "description", desc)
		if settings.RSSLanguage != "" {
			writeXMLTag(&b, "language", settings.RSSLanguage)
		}
		if settings.RSSCopyright != nil && strings.TrimSpace(*settings.RSSCopyright) != "" {
			writeXMLTag(&b, "copyright", *settings.RSSCopyright)
		}
		writeXMLTag(&b, "lastBuildDate", time.Now().UTC().Format(time.RFC1123Z))
		writeXMLTag(&b, "generator", "Golem15 Journal")
		b.WriteString(`<atom:link rel="self" href="` + xmlEsc(self) + `" type="application/rss+xml" />` + "\n")
		if settings.RSSImageURL != nil && strings.TrimSpace(*settings.RSSImageURL) != "" {
			b.WriteString("<image>\n")
			writeXMLTag(&b, "url", *settings.RSSImageURL)
			writeXMLTag(&b, "title", title)
			writeXMLTag(&b, "link", site+"/")
			b.WriteString("</image>\n")
		}
		for i := range posts {
			p := &posts[i]
			postURL := site + "/blog/" + p.Slug
			summary := p.Excerpt
			if strings.TrimSpace(summary) == "" {
				summary = truncateRunes(stripTags(p.ContentHTML), 300)
			}
			b.WriteString("<item>\n")
			writeXMLTag(&b, "title", p.Title)
			writeXMLTag(&b, "link", postURL)
			b.WriteString(`<guid isPermaLink="true">` + xmlEsc(postURL) + "</guid>\n")
			if p.PublishedAt != nil {
				writeXMLTag(&b, "pubDate", p.PublishedAt.UTC().Format(time.RFC1123Z))
			}
			b.WriteString("<description><![CDATA[" + cdata(summary) + "]]></description>\n")
			if settings.RSSIncludeContent && p.ContentHTML != "" {
				b.WriteString("<content:encoded><![CDATA[" + cdata(p.ContentHTML) + "]]></content:encoded>\n")
			}
			if p.User != nil {
				creator := strings.TrimSpace(p.User.FirstName + " " + p.User.LastName)
				if creator != "" {
					b.WriteString("<dc:creator>" + xmlEsc(creator) + "</dc:creator>\n")
				}
			}
			for _, cat := range p.Categories {
				writeXMLTag(&b, "category", cat.Name)
			}
			b.WriteString("</item>\n")
		}
		b.WriteString("</channel>\n</rss>\n")
		w.Header().Set("Content-Type", "application/rss+xml; charset=utf-8")
		w.WriteHeader(http.StatusOK)
		_, _ = w.Write([]byte(b.String()))
	}
}

func writeXMLTag(b *strings.Builder, name, value string) {
	b.WriteString("<" + name + ">" + xmlEsc(value) + "</" + name + ">\n")
}

func xmlEsc(s string) string {
	var b strings.Builder
	_ = xml.EscapeText(&b, []byte(s))
	return b.String()
}

func cdata(s string) string {
	return strings.ReplaceAll(s, "]]>", "]]&gt;")
}

func requestOrigin(r *http.Request, app *backpack.App) string {
	if app != nil && app.Config != nil {
		if u := strings.TrimRight(strings.TrimSpace(app.Config.String("url")), "/"); u != "" {
			return u
		}
	}
	scheme := "http"
	if r.TLS != nil {
		scheme = "https"
	}
	return scheme + "://" + r.Host
}

func truncateRunes(s string, n int) string {
	if utf8.RuneCountInString(s) <= n {
		return s
	}
	runes := []rune(html.UnescapeString(s))
	if len(runes) > n {
		return string(runes[:n])
	}
	return s
}