// Package web is the hub's website (server-rendered pages, htmx for the live parts) and its API for proxies.
package web

import (
	"context"
	"crypto/subtle"
	"embed"
	"errors"
	"html/template"
	"io/fs"
	"log"
	"net"
	"net/http"
	"strings"
	"sync"
	"time"

	"git.t5de.dev/t5de/t5de-hub/internal/imvu"
	"git.t5de.dev/t5de/t5de-hub/internal/realtime"
	"git.t5de.dev/t5de/t5de-hub/internal/store"
	"git.t5de.dev/t5de/t5de-hub/internal/token"
)

//go:embed templates/*.html
var templateFiles embed.FS

//go:embed static
var staticFiles embed.FS

// Audience is the hub's own API, in its access tokens.
const Audience = "t5de-hub"

// Server is the website and API.
type Server struct {
	Store     *store.Store
	IMVU      *imvu.Client
	Keys      *token.Keys
	Realtime  *realtime.Hub
	PublicURL string // e.g. https://hub.t5de.dev, for links shown to proxies
	Log       *log.Logger

	pages   map[string]*template.Template
	limiter *limiter
}

// Handler is the hub's HTTP handler.
func (s *Server) Handler() (http.Handler, error) {
	if err := s.parseTemplates(); err != nil {
		return nil, err
	}
	s.limiter = &limiter{hits: map[string][]time.Time{}}
	mux := http.NewServeMux()
	static, _ := fs.Sub(staticFiles, "static")
	mux.Handle("GET /static/", http.StripPrefix("/static/", cacheStatic(http.FileServerFS(static))))

	mux.HandleFunc("GET /favicon.ico", func(w http.ResponseWriter, r *http.Request) {
		http.Redirect(w, r, "/static/favicon.svg", http.StatusMovedPermanently)
	})
	mux.HandleFunc("GET /{$}", s.page(s.home))
	mux.HandleFunc("GET /signup", s.page(s.signupForm))
	mux.HandleFunc("POST /signup", s.page(s.signup))
	mux.HandleFunc("GET /signin", s.page(s.signinForm))
	mux.HandleFunc("POST /signin", s.page(s.signin))
	mux.HandleFunc("POST /signout", s.page(s.signout))
	mux.HandleFunc("GET /online", s.page(s.online))
	mux.HandleFunc("GET /online/list", s.page(s.onlineList))

	mux.HandleFunc("GET /account", s.page(s.signedIn(s.account)))
	mux.HandleFunc("POST /account/link", s.page(s.signedIn(s.startLink)))
	mux.HandleFunc("POST /account/link/{imvu}/check", s.page(s.signedIn(s.checkLink)))
	mux.HandleFunc("POST /account/link/{imvu}/cancel", s.page(s.signedIn(s.cancelLink)))
	mux.HandleFunc("POST /account/links/{imvu}/settings", s.page(s.signedIn(s.linkSettings)))
	mux.HandleFunc("POST /account/links/{imvu}/recheck", s.page(s.signedIn(s.recheckLink)))
	mux.HandleFunc("POST /account/links/{imvu}/unlink", s.page(s.signedIn(s.unlink)))
	mux.HandleFunc("POST /account/proxies/signout", s.page(s.signedIn(s.signOutProxies)))
	mux.HandleFunc("GET /device", s.page(s.signedIn(s.deviceForm)))
	mux.HandleFunc("POST /device", s.page(s.signedIn(s.approveDevice)))

	mux.HandleFunc("GET /console", s.page(s.moderator(s.console)))
	mux.HandleFunc("GET /console/online", s.page(s.moderator(s.consoleOnline)))
	mux.HandleFunc("GET /console/people", s.page(s.moderator(s.consolePeople)))
	mux.HandleFunc("GET /console/people/{id}", s.page(s.moderator(s.consolePerson)))
	mux.HandleFunc("POST /console/people/{id}/cap", s.page(s.moderator(s.setCap)))
	mux.HandleFunc("POST /console/people/{id}/ban", s.page(s.moderator(s.ban)))
	mux.HandleFunc("POST /console/people/{id}/unban", s.page(s.moderator(s.unban)))
	mux.HandleFunc("POST /console/people/{id}/role", s.page(s.admin(s.setRole)))

	mux.HandleFunc("GET /.well-known/jwks.json", s.jwks)
	mux.HandleFunc("POST /api/v1/device/code", s.deviceCode)
	mux.HandleFunc("POST /api/v1/device/token", s.deviceToken)
	mux.HandleFunc("POST /api/v1/token/refresh", s.refresh)
	mux.HandleFunc("GET /api/v1/me", s.me)
	mux.HandleFunc("GET /api/v1/realtime", s.realtime)
	return securityHeaders(mux), nil
}

func securityHeaders(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		h := w.Header()
		h.Set("Content-Security-Policy", "default-src 'self'; img-src 'self' https: data:; style-src 'self'; script-src 'self'; "+
			"connect-src 'self'; frame-ancestors 'none'; form-action 'self'; base-uri 'none'; object-src 'none'")
		h.Set("X-Content-Type-Options", "nosniff")
		h.Set("Referrer-Policy", "same-origin")
		h.Set("X-Frame-Options", "DENY")
		next.ServeHTTP(w, r)
	})
}

func cacheStatic(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Cache-Control", "public, max-age=3600")
		next.ServeHTTP(w, r)
	})
}

// request is one page request: who's asking, and what the page shows.
type request struct {
	w      http.ResponseWriter
	r      *http.Request
	person *store.Person // nil when signed out
	csrf   string
	token  string // session token
	flash  string
}

type pageFunc func(q *request) error

// errStatus is an error with the HTTP status to answer with, shown to the person.
type errStatus struct {
	status  int
	message string
}

func (e errStatus) Error() string { return e.message }

func fail(status int, message string) error { return errStatus{status, message} }

const sessionCookie = "t5de_session"

// page wraps a page handler: it finds the session, checks CSRF on POSTs, and shows errors.
func (s *Server) page(fn pageFunc) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		q := &request{w: w, r: r, flash: r.URL.Query().Get("done")}
		if c, err := r.Cookie(sessionCookie); err == nil {
			p, csrf, err := s.Store.Session(r.Context(), c.Value)
			if err == nil && !p.Banned() {
				q.person, q.csrf, q.token = p, csrf, c.Value
			}
		}
		if r.Method == http.MethodPost {
			r.Body = http.MaxBytesReader(w, r.Body, 64<<10)
			sent := r.Header.Get("X-CSRF-Token")
			if sent == "" {
				sent = r.PostFormValue("csrf")
			}
			// Signed in, a form must carry the session's token. Signed out (sign-in and sign-up), browsers' same-site
			// checks apply: the form must come from the hub itself.
			if q.person != nil && subtle.ConstantTimeCompare([]byte(sent), []byte(q.csrf)) != 1 ||
				q.person == nil && !sameOrigin(r) {
				s.showError(q, fail(http.StatusForbidden, "That form expired. Reload the page and try again."))
				return
			}
		}
		if err := fn(q); err != nil {
			s.showError(q, err)
		}
	}
}

func sameOrigin(r *http.Request) bool {
	if site := r.Header.Get("Sec-Fetch-Site"); site != "" {
		return site == "same-origin" || site == "none"
	}
	origin := r.Header.Get("Origin")
	return origin == "" || strings.TrimPrefix(strings.TrimPrefix(origin, "https://"), "http://") == r.Host
}

func (s *Server) signedIn(fn pageFunc) pageFunc {
	return func(q *request) error {
		if q.person == nil {
			http.Redirect(q.w, q.r, "/signin?next="+q.r.URL.RequestURI(), http.StatusSeeOther)
			return nil
		}
		return fn(q)
	}
}

func (s *Server) moderator(fn pageFunc) pageFunc {
	return s.signedIn(func(q *request) error {
		if !q.person.IsModerator() {
			return fail(http.StatusForbidden, "Only moderators can see this.")
		}
		return fn(q)
	})
}

func (s *Server) admin(fn pageFunc) pageFunc {
	return s.signedIn(func(q *request) error {
		if !q.person.IsAdmin() {
			return fail(http.StatusForbidden, "Only admins can do this.")
		}
		return fn(q)
	})
}

func (s *Server) showError(q *request, err error) {
	var e errStatus
	if !errors.As(err, &e) {
		s.Log.Printf("%s %s: %v", q.r.Method, q.r.URL.Path, err)
		e = errStatus{http.StatusInternalServerError, "Something went wrong on our side. Try again in a moment."}
	}
	q.w.WriteHeader(e.status)
	s.render(q, "error", map[string]any{"Message": e.message})
}

// redirect sends the browser on after a form, with a short note to show.
func (q *request) redirect(path, done string) error {
	if done != "" {
		sep := "?"
		if strings.Contains(path, "?") {
			sep = "&"
		}
		path += sep + "done=" + template.URLQueryEscaper(done)
	}
	http.Redirect(q.w, q.r, path, http.StatusSeeOther)
	return nil
}

func clientIP(r *http.Request) string {
	if ip := r.Header.Get("CF-Connecting-IP"); ip != "" {
		return ip
	}
	host, _, err := net.SplitHostPort(r.RemoteAddr)
	if err != nil {
		return r.RemoteAddr
	}
	return host
}

// limiter allows a number of attempts per key in a window (sign-ins, sign-ups, IMVU lookups).
type limiter struct {
	mu   sync.Mutex
	hits map[string][]time.Time
}

func (l *limiter) allow(key string, n int, window time.Duration) bool {
	l.mu.Lock()
	defer l.mu.Unlock()
	now := time.Now()
	recent := l.hits[key][:0]
	for _, t := range l.hits[key] {
		if now.Sub(t) < window {
			recent = append(recent, t)
		}
	}
	if len(recent) >= n {
		l.hits[key] = recent
		return false
	}
	l.hits[key] = append(recent, now)
	if len(l.hits) > 100000 { // forget everything rather than grow without end
		l.hits = map[string][]time.Time{}
	}
	return true
}

func (s *Server) ctx(q *request) context.Context { return q.r.Context() }