package server

import (
	"context"
	"crypto/subtle"
	"net/http"
	"net/url"
	"strings"
	"time"

	"gitea.lab.audasmedia.com.au/sam/email_agent/internal/session"
	"gitea.lab.audasmedia.com.au/sam/email_agent/internal/version"
)

const (
	// csrfCookieName holds the double-submit CSRF token. It is independent of
	// the session so the login form (which has no session yet) is protected too.
	csrfCookieName = "email_agent_csrf"
	sessionTTL     = session.DefaultTTL
)

// ctxKey is the private context key type for request-scoped values.
type ctxKey int

const sessionCtxKey ctxKey = iota

// requireAuth redirects unauthenticated requests to the login screen and
// otherwise puts the session on the request context.
func (s *Server) requireAuth(next http.HandlerFunc) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		sess, ok := s.currentSession(r)
		if !ok {
			target := "/login?next=" + url.QueryEscape(r.URL.RequestURI())
			http.Redirect(w, r, target, http.StatusSeeOther)
			return
		}
		next(w, r.WithContext(context.WithValue(r.Context(), sessionCtxKey, sess)))
	}
}

func (s *Server) currentSession(r *http.Request) (session.Session, bool) {
	c, err := r.Cookie(session.CookieName)
	if err != nil || c.Value == "" {
		return session.Session{}, false
	}
	return s.sessions.Lookup(c.Value)
}

func sessionFrom(r *http.Request) session.Session {
	sess, _ := r.Context().Value(sessionCtxKey).(session.Session)
	return sess
}

// loginSecret is the password the single user must supply. EMAIL_AGENT_PASSWORD
// wins; otherwise the session secret doubles as the password so a single
// configured secret is enough.
func (s *Server) loginSecret() string {
	if s.cfg.Password != "" {
		return s.cfg.Password
	}
	return s.cfg.SessionSecret
}

// csrfToken returns the current double-submit token, minting one when absent.
func (s *Server) csrfToken(w http.ResponseWriter, r *http.Request) string {
	if c, err := r.Cookie(csrfCookieName); err == nil && c.Value != "" {
		return c.Value
	}
	tok, err := session.RandomToken(32)
	if err != nil {
		// crypto/rand failing is fatal for security; surface it rather than
		// issuing an unprotected form.
		s.logger.Error("csrf token generation failed", "error", err)
		return ""
	}
	http.SetCookie(w, &http.Cookie{
		Name:     csrfCookieName,
		Value:    tok,
		Path:     "/",
		HttpOnly: true,
		SameSite: http.SameSiteLaxMode,
		Secure:   s.cfg.IsProduction(),
		MaxAge:   int(sessionTTL.Seconds()),
	})
	return tok
}

// csrfOK verifies the double-submit token from the form or the X-CSRF-Token
// header.
func (s *Server) csrfOK(r *http.Request) bool {
	c, err := r.Cookie(csrfCookieName)
	if err != nil || c.Value == "" {
		return false
	}
	tok := r.FormValue("csrf")
	if tok == "" {
		tok = r.Header.Get("X-CSRF-Token")
	}
	return subtle.ConstantTimeCompare([]byte(tok), []byte(c.Value)) == 1
}

func (s *Server) setSessionCookie(w http.ResponseWriter, value string, expires time.Time) {
	http.SetCookie(w, &http.Cookie{
		Name:     session.CookieName,
		Value:    value,
		Path:     "/",
		HttpOnly: true,
		SameSite: http.SameSiteLaxMode,
		Secure:   s.cfg.IsProduction(),
		Expires:  expires,
		MaxAge:   int(sessionTTL.Seconds()),
	})
}

func (s *Server) clearSessionCookie(w http.ResponseWriter) {
	http.SetCookie(w, &http.Cookie{
		Name:     session.CookieName,
		Value:    "",
		Path:     "/",
		HttpOnly: true,
		SameSite: http.SameSiteLaxMode,
		Secure:   s.cfg.IsProduction(),
		MaxAge:   -1,
	})
}

type loginData struct {
	PartOfDay  string
	Error      string
	Next       string
	CSRFToken  string
	Configured bool
}

func (s *Server) renderLogin(w http.ResponseWriter, r *http.Request, code int, errMsg, next string) {
	// Mint the CSRF cookie before the status line, or Set-Cookie is dropped.
	csrf := s.csrfToken(w, r)
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	w.WriteHeader(code)
	data := loginData{
		PartOfDay:  partOfDay(time.Now()),
		Error:      errMsg,
		Next:       next,
		CSRFToken:  csrf,
		Configured: s.loginSecret() != "",
	}
	if err := s.tmpl.ExecuteTemplate(w, "login.html", data); err != nil {
		s.logger.Error("render login", "error", err)
	}
}

// handleLoginGet renders the sign-in form.
func (s *Server) handleLoginGet(w http.ResponseWriter, r *http.Request) {
	if _, ok := s.currentSession(r); ok {
		http.Redirect(w, r, cleanNext(r.URL.Query().Get("next")), http.StatusSeeOther)
		return
	}
	s.renderLogin(w, r, http.StatusOK, "", cleanNext(r.URL.Query().Get("next")))
}

// handleLoginPost validates the CSRF token and password, then starts a session.
// POST (not GET) means the password is never placed in the URL or browser
// history.
func (s *Server) handleLoginPost(w http.ResponseWriter, r *http.Request) {
	if err := r.ParseForm(); err != nil {
		s.renderLogin(w, r, http.StatusBadRequest, "Could not read the sign-in form.", "/")
		return
	}
	next := cleanNext(r.FormValue("next"))

	if !s.csrfOK(r) {
		s.renderLogin(w, r, http.StatusForbidden, "Your sign-in page expired. Please try again.", next)
		return
	}

	secret := s.loginSecret()
	if secret == "" {
		s.renderLogin(w, r, http.StatusServiceUnavailable, "Login is not configured yet.", next)
		return
	}

	if subtle.ConstantTimeCompare([]byte(r.FormValue("password")), []byte(secret)) != 1 {
		s.logger.Warn("login failed", "remote", r.RemoteAddr)
		s.renderLogin(w, r, http.StatusUnauthorized, "Incorrect password.", next)
		return
	}

	sess, cookie, err := s.sessions.New("Sam")
	if err != nil {
		s.logger.Error("create session", "error", err)
		http.Error(w, "could not start a session", http.StatusInternalServerError)
		return
	}
	s.setSessionCookie(w, cookie, sess.ExpiresAt)
	s.logger.Info("login ok", "user", sess.User, "remote", r.RemoteAddr)
	http.Redirect(w, r, next, http.StatusSeeOther)
}

// handleLogout destroys the session and returns to the login screen.
func (s *Server) handleLogout(w http.ResponseWriter, r *http.Request) {
	_ = r.ParseForm()
	if !s.csrfOK(r) {
		http.Error(w, "invalid CSRF token", http.StatusForbidden)
		return
	}
	if c, err := r.Cookie(session.CookieName); err == nil && c.Value != "" {
		s.sessions.Destroy(c.Value)
	}
	s.clearSessionCookie(w)
	http.Redirect(w, r, "/login", http.StatusSeeOther)
}

type navItem struct {
	Name  string
	Color string
}

type dashboardData struct {
	Greeting   string
	User       string
	CSRFToken  string
	Version    string
	Categories []navItem
	Folders    []navItem
}

// handleDashboard renders the empty inbox shell.
func (s *Server) handleDashboard(w http.ResponseWriter, r *http.Request) {
	sess := sessionFrom(r)
	data := dashboardData{
		Greeting:  partOfDay(time.Now()),
		User:      sess.User,
		CSRFToken: s.csrfToken(w, r),
		Version:   version.Version,
		// Placeholders until FR-14 (editable categories) and FR-9 (folders)
		// land. Colours are the design system's decorative sticker palette.
		Categories: []navItem{
			{Name: "Action", Color: "var(--primary)"},
			{Name: "Important", Color: "var(--sticker-orange)"},
			{Name: "Info", Color: "var(--sticker-sky)"},
			{Name: "Spam", Color: "var(--sticker-red)"},
			{Name: "Newsletter", Color: "var(--sticker-purple)"},
			{Name: "Auto-reply", Color: "var(--sticker-teal)"},
		},
		Folders: []navItem{
			{Name: "Replied-to", Color: "var(--sticker-green)"},
			{Name: "Delete", Color: "var(--sticker-red)"},
			{Name: "Saved", Color: "var(--sticker-teal)"},
		},
	}
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	if err := s.tmpl.ExecuteTemplate(w, "dashboard.html", data); err != nil {
		s.logger.Error("render dashboard", "error", err)
	}
}

// handleInboxPartial is the HTMX fragment for the centre list. Phase 1.2 has no
// mail yet, so it renders the empty state.
func (s *Server) handleInboxPartial(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	if err := s.tmpl.ExecuteTemplate(w, "inbox.html", nil); err != nil {
		s.logger.Error("render inbox partial", "error", err)
	}
}

// cleanNext only allows same-site, absolute-path redirects.
func cleanNext(next string) string {
	if next == "" || !strings.HasPrefix(next, "/") || strings.HasPrefix(next, "//") {
		return "/"
	}
	return next
}

// partOfDay returns the time-aware greeting prefix.
func partOfDay(t time.Time) string {
	switch h := t.Hour(); {
	case h < 12:
		return "Good morning"
	case h < 18:
		return "Good afternoon"
	default:
		return "Good evening"
	}
}