package main

import (
	"crypto/subtle"
	"embed"
	"html/template"
	"io/fs"
	"log"
	"net/http"
	"strconv"
	"time"
)

//go:embed templates
var templateFS embed.FS

//go:embed static
var staticFS embed.FS

// recentCount is how many series the "Continue reading" strip shows.
const recentCount = 5

// webHandler serves the browser UI: full pages at / and htmx fragments at /ui/.
// It is a separate handler from bookmarkHandler because the two speak different
// representations (HTML versus JSON) to different clients under different auth.
type webHandler struct {
	store    *Store
	tmpl     *template.Template
	key      []byte
	password string
	limiter  *loginLimiter
}

// listView is what every list-rendering template receives.
type listView struct {
	Tab    string // "all" or "fav"
	Recent []Bookmark
	Items  []Bookmark
}

// loginView is what the login template receives.
type loginView struct {
	Error string
}

// newWebHandler parses every template up front so a broken one kills the
// process at startup rather than the first request that touches it.
func newWebHandler(store *Store, cfg Config) (*webHandler, error) {
	tmpl, err := template.ParseFS(templateFS, "templates/*.html")
	if err != nil {
		return nil, err
	}
	return &webHandler{
		store:    store,
		tmpl:     tmpl,
		key:      sessionKey(cfg.Token),
		password: cfg.WebPassword,
		limiter:  newLoginLimiter(),
	}, nil
}

func (h *webHandler) register(mux *http.ServeMux) {
	mux.HandleFunc("GET /{$}", h.index)
	mux.HandleFunc("POST /login", h.login)
	mux.HandleFunc("POST /logout", h.logout)
	mux.Handle("GET /static/", staticHandler())

	mux.HandleFunc("GET /ui/list", h.requireSession(h.uiList))
}

// staticHandler serves the embedded assets. The vendored htmx build and the
// stylesheet change only on deploy, so a long max-age is safe; a redeploy
// changes the binary and the browser revalidates on its own schedule.
func staticHandler() http.Handler {
	sub, err := fs.Sub(staticFS, "static")
	if err != nil {
		panic("embed static: " + err.Error())
	}
	files := http.FileServer(http.FS(sub))
	return http.StripPrefix("/static/", http.HandlerFunc(
		func(w http.ResponseWriter, r *http.Request) {
			w.Header().Set("Cache-Control", "public, max-age=3600")
			files.ServeHTTP(w, r)
		}))
}

// authed reports whether the request carries a valid session cookie.
func (h *webHandler) authed(r *http.Request) bool {
	c, err := r.Cookie(sessionCookieName)
	return err == nil && verifySession(h.key, c.Value, time.Now().UnixMilli())
}

// requireSession guards the fragment endpoints. It answers 401 rather than
// redirecting, because htmx swaps whatever body it receives into the page and a
// redirected login page would be spliced into the card list.
func (h *webHandler) requireSession(next http.HandlerFunc) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if !h.authed(r) {
			http.Error(w, "unauthorized", http.StatusUnauthorized)
			return
		}
		next(w, r)
	}
}

func (h *webHandler) render(w http.ResponseWriter, status int, name string, data any) {
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	w.WriteHeader(status)
	if err := h.tmpl.ExecuteTemplate(w, name, data); err != nil {
		// The status line is already sent, so this can only be logged.
		log.Printf("render %s: %v", name, err)
	}
}

// index renders the list, or the login page when there is no session. The login
// page is served at / with status 200 rather than as a redirect to a separate
// URL: one page, no redirect loop to reason about.
func (h *webHandler) index(w http.ResponseWriter, r *http.Request) {
	if !h.authed(r) {
		h.render(w, http.StatusOK, "login", loginView{})
		return
	}
	view, err := h.buildListView(r.URL.Query().Get("tab"))
	if err != nil {
		log.Printf("index: %v", err)
		http.Error(w, "internal error", http.StatusInternalServerError)
		return
	}
	h.render(w, http.StatusOK, "app", view)
}

// buildListView loads the list once and derives both the tab-filtered items and
// the recent strip from it. The strip always reflects overall recency, not the
// active tab, so it is built before filtering.
func (h *webHandler) buildListView(tab string) (listView, error) {
	all, err := h.store.List() // already ordered updated_at DESC
	if err != nil {
		return listView{}, err
	}

	recent := all
	if len(recent) > recentCount {
		recent = recent[:recentCount]
	}

	items := all
	if tab == "fav" {
		items = []Bookmark{}
		for _, b := range all {
			if b.Favorite {
				items = append(items, b)
			}
		}
	} else {
		tab = "all"
	}
	return listView{Tab: tab, Recent: recent, Items: items}, nil
}

func (h *webHandler) uiList(w http.ResponseWriter, r *http.Request) {
	view, err := h.buildListView(r.URL.Query().Get("tab"))
	if err != nil {
		log.Printf("ui list: %v", err)
		http.Error(w, "internal error", http.StatusInternalServerError)
		return
	}
	h.render(w, http.StatusOK, "list", view)
}

func (h *webHandler) login(w http.ResponseWriter, r *http.Request) {
	ip := clientIP(r)
	if wait := h.limiter.retryAfter(ip, time.Now()); wait > 0 {
		secs := int(wait.Seconds()) + 1
		w.Header().Set("Retry-After", strconv.Itoa(secs))
		h.render(w, http.StatusTooManyRequests, "login", loginView{
			Error: "Too many attempts. Try again in " +
				strconv.Itoa((secs+59)/60) + " min.",
		})
		return
	}

	if err := r.ParseForm(); err != nil {
		http.Error(w, "invalid form", http.StatusBadRequest)
		return
	}
	got := r.PostFormValue("password")
	if subtle.ConstantTimeCompare([]byte(got), []byte(h.password)) != 1 {
		h.limiter.fail(ip, time.Now())
		h.render(w, http.StatusUnauthorized, "login", loginView{Error: "Wrong password."})
		return
	}

	h.limiter.reset(ip)
	setSessionCookie(w, r, h.key)
	http.Redirect(w, r, "/", http.StatusSeeOther)
}

func (h *webHandler) logout(w http.ResponseWriter, r *http.Request) {
	clearSessionCookie(w, r)
	http.Redirect(w, r, "/", http.StatusSeeOther)
}