// Package api serves the read-only public surface: site settings, posts,
// archive, tags and RSS. Nothing here requires authentication.
package api

import (
	"encoding/xml"
	"errors"
	"html"
	"net/http"
	"strings"
	"time"

	"oneblog/internal/config"
	"oneblog/internal/httpx"
	"oneblog/internal/model"
	"oneblog/internal/store"
)

type API struct {
	Store *store.Store
	Cfg   *config.Config
}

func (a *API) Routes() http.Handler {
	mux := http.NewServeMux()
	mux.HandleFunc("/api/health", func(w http.ResponseWriter, r *http.Request) {
		httpx.OK(w, map[string]any{"ok": true, "driver": a.Cfg.Driver})
	})
	mux.HandleFunc("/api/site", a.site)
	mux.HandleFunc("/api/posts", a.listPosts)
	mux.HandleFunc("/api/posts/", a.getPost)
	mux.HandleFunc("/api/archive", a.archive)
	mux.HandleFunc("/api/tags", a.tags)
	return mux
}

// Mount registers the feed routes on the root mux, where they are not
// shadowed by the SPA catch-all.
func (a *API) Mount(root *http.ServeMux) {
	root.Handle("/api/", a.Routes())
	root.HandleFunc("/rss.xml", a.RSS)
	root.HandleFunc("/feed", a.RSS)
	root.HandleFunc("/feed.xml", a.RSS)
}

func (a *API) site(w http.ResponseWriter, r *http.Request) {
	st, err := a.Store.GetSettings()
	if err != nil {
		httpx.ServerError(w, err)
		return
	}
	httpx.OK(w, st)
}

func listOptions(r *http.Request, defSize int) store.ListOptions {
	return store.ListOptions{
		Kind:   httpx.QueryString(r, "kind"),
		Tag:    httpx.QueryString(r, "tag"),
		Query:  httpx.QueryString(r, "q"),
		Page:   httpx.QueryInt(r, "page", 1),
		Size:   httpx.QueryInt(r, "size", defSize),
		Status: model.StatusPublished,
	}
}

func (a *API) listPosts(w http.ResponseWriter, r *http.Request) {
	page, err := a.Store.List(listOptions(r, 10))
	if err != nil {
		httpx.ServerError(w, err)
		return
	}
	httpx.OK(w, page)
}

func (a *API) getPost(w http.ResponseWriter, r *http.Request) {
	slug := strings.TrimPrefix(r.URL.Path, "/api/posts/")
	slug = strings.TrimSuffix(slug, "/")
	if slug == "" {
		a.listPosts(w, r)
		return
	}
	p, err := a.Store.GetBySlug(slug)
	if err != nil {
		if errors.Is(err, store.ErrNotFound) {
			httpx.NotFound(w)
			return
		}
		httpx.ServerError(w, err)
		return
	}
	if p.Status != model.StatusPublished {
		httpx.NotFound(w)
		return
	}
	httpx.OK(w, p)
}

func (a *API) archive(w http.ResponseWriter, r *http.Request) {
	years, err := a.Store.Archive()
	if err != nil {
		httpx.ServerError(w, err)
		return
	}
	httpx.OK(w, map[string]any{"years": years})
}

func (a *API) tags(w http.ResponseWriter, r *http.Request) {
	tags, err := a.Store.ListTags()
	if err != nil {
		httpx.ServerError(w, err)
		return
	}
	if tags == nil {
		tags = []model.Tag{}
	}
	httpx.OK(w, map[string]any{"tags": tags})
}

// ---------- RSS ----------

type rssItem struct {
	XMLName     xml.Name `xml:"item"`
	Title       string   `xml:"title"`
	Link        string   `xml:"link"`
	Description string   `xml:"description"`
	PubDate     string   `xml:"pubDate"`
	GUID        string   `xml:"guid"`
	Category    []string `xml:"category,omitempty"`
}

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

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

// RSS renders the site feed.
func (a *API) RSS(w http.ResponseWriter, r *http.Request) {
	settings, err := a.Store.GetSettings()
	if err != nil {
		httpx.ServerError(w, err)
		return
	}
	page, err := a.Store.List(store.ListOptions{Status: model.StatusPublished, Page: 1, Size: 30})
	if err != nil {
		httpx.ServerError(w, err)
		return
	}
	base := strings.TrimSuffix(a.Cfg.SiteURL, "/")

	feed := rssFeed{
		Version: "2.0",
		Channel: rssChannel{
			Title:       orDefault(settings.SiteTitle, "ONE"),
			Link:        base + "/",
			Description: orDefault(settings.SiteDesc, ""),
			Language:    "zh-CN",
			LastBuild:   time.Now().UTC().Format(time.RFC1123Z),
			Items:       []rssItem{},
		},
	}
	for _, p := range page.Items {
		title := p.Title
		if p.Kind == model.KindShort || title == "" {
			title = shortTitle(p)
		}
		desc := p.Summary
		if desc == "" {
			desc = trimRunes(stripTags(p.ContentHTML), 160)
		}
		item := rssItem{
			Title:       title,
			Link:        base + "/post/" + p.Slug,
			Description: desc,
			PubDate:     rssDate(p.PublishedAt),
			GUID:        base + "/post/" + p.Slug,
			Category:    p.Tags,
		}
		if p.Kind == model.KindShort {
			item.Title = "[短] " + title
		}
		feed.Channel.Items = append(feed.Channel.Items, item)
	}

	out, err := xml.MarshalIndent(feed, "", "  ")
	if err != nil {
		httpx.ServerError(w, err)
		return
	}
	w.Header().Set("Content-Type", "application/rss+xml; charset=utf-8")
	w.WriteHeader(http.StatusOK)
	_, _ = w.Write([]byte(xml.Header))
	_, _ = w.Write(out)
	_, _ = w.Write([]byte("\n"))
}

func shortTitle(p model.Post) string {
	s := strings.TrimSpace(stripTags(p.ContentHTML))
	if s == "" {
		return "无题"
	}
	return trimRunes(s, 40)
}

func stripTags(s string) string {
	var b strings.Builder
	in := false
	for _, r := range s {
		switch {
		case r == '<':
			in = true
		case r == '>':
			in = false
		case !in:
			b.WriteRune(r)
		}
	}
	return html.UnescapeString(strings.TrimSpace(b.String()))
}

func trimRunes(s string, n int) string {
	runes := []rune(s)
	if len(runes) <= n {
		return s
	}
	return string(runes[:n]) + "…"
}

func rssDate(rfc3339 string) string {
	t, err := time.Parse(time.RFC3339, rfc3339)
	if err != nil {
		return time.Now().UTC().Format(time.RFC1123Z)
	}
	return t.UTC().Format(time.RFC1123Z)
}

func orDefault(s, def string) string {
	if strings.TrimSpace(s) == "" {
		return def
	}
	return s
}