// Package webclient provides the webmail HTTP client (default: 0.0.0.0:8080).
package webclient

import (
	"crypto/hmac"
	"crypto/sha256"
	"encoding/hex"
	"fmt"
	"html/template"
	"io/fs"
	"log"
	"net/http"
	"time"

	"ghb.freebede.com/nahakubuilder/mailgosend/internal/auth"
	"ghb.freebede.com/nahakubuilder/mailgosend/internal/config"
	appCrypto "ghb.freebede.com/nahakubuilder/mailgosend/internal/crypto"
	"ghb.freebede.com/nahakubuilder/mailgosend/internal/db"
	"ghb.freebede.com/nahakubuilder/mailgosend/internal/models"
	"ghb.freebede.com/nahakubuilder/mailgosend/internal/storage"
)

// Deps groups all dependencies for the webclient.
type Deps struct {
	DB       *db.DB
	Crypt    *appCrypto.Crypto
	Sessions *auth.SessionStore
	Brute    *auth.BruteGuard
	Store    *storage.Store
	Cfg      *config.Config
	FS       fs.FS // embed.FS sub-rooted at web/client
}

// Server handles all webclient HTTP routes.
type Server struct {
	deps *Deps
	mux  *http.ServeMux
}

// New creates a webclient Server and registers all routes.
func New(deps *Deps) *Server {
	s := &Server{deps: deps, mux: http.NewServeMux()}
	s.setupRoutes()
	return s
}

// Handler returns the HTTP handler.
func (s *Server) Handler() http.Handler {
	return logMiddleware(s.mux)
}

// ---- Routing ----

func (s *Server) setupRoutes() {
	m := s.mux

	// Public
	m.HandleFunc("GET /login", s.loginGet)
	m.HandleFunc("POST /login", s.loginPost)
	m.HandleFunc("GET /login/mfa", s.mfaGet)
	m.HandleFunc("POST /login/mfa", s.mfaPost)
	m.HandleFunc("GET /logout", s.logout)

	// Root redirect
	m.HandleFunc("GET /{$}", s.require(s.rootRedirect))

	// Mailbox + message routes
	m.HandleFunc("GET /mail/{boxid}", s.require(s.mailboxView))
	m.HandleFunc("GET /mail/{boxid}/{uid}", s.require(s.messageView))
	m.HandleFunc("POST /mail/{boxid}/{uid}/flag", s.require(s.messageFlag))
	m.HandleFunc("POST /mail/{boxid}/{uid}/trash", s.require(s.messageTrash))
	m.HandleFunc("POST /mail/{boxid}/{uid}/move", s.require(s.messageMove))
	m.HandleFunc("POST /mail/{boxid}/expunge", s.require(s.mailboxExpunge))

	// Compose
	m.HandleFunc("GET /compose", s.require(s.composeGet))
	m.HandleFunc("POST /compose", s.require(s.composeSend))

	// Settings
	m.HandleFunc("GET /settings", s.require(s.settingsGet))
	m.HandleFunc("POST /settings/password", s.require(s.settingsPassword))
	m.HandleFunc("POST /settings/display", s.require(s.settingsDisplay))
	m.HandleFunc("GET /settings/mfa/enroll", s.require(s.mfaEnrollGet))
	m.HandleFunc("POST /settings/mfa/enroll", s.require(s.mfaEnrollPost))
	m.HandleFunc("POST /settings/mfa/disable", s.require(s.mfaDisable))

	// Static assets
	static, _ := fs.Sub(s.deps.FS, "static")
	m.Handle("GET /static/", http.StripPrefix("/static/", http.FileServer(http.FS(static))))
}

// ---- Middleware ----

func (s *Server) require(next http.HandlerFunc) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if s.currentUser(r) == nil {
			http.Redirect(w, r, "/login", http.StatusSeeOther)
			return
		}
		next(w, r)
	}
}

func (s *Server) currentUser(r *http.Request) *models.User {
	_, user, err := s.deps.Sessions.Get(r)
	if err != nil || user == nil || !user.Enabled {
		return nil
	}
	return user
}

func logMiddleware(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		start := time.Now()
		next.ServeHTTP(w, r)
		log.Printf("[webmail] %s %s %s", r.Method, r.URL.Path, time.Since(start))
	})
}

// ---- Template rendering ----

type basePage struct {
	Flash        string
	Error        string
	CSRF         string
	User         *models.User
	Mailboxes    []*models.Mailbox
	CurrentBoxID int64 // 0 = no mailbox selected (compose, settings, etc.)
}

func (s *Server) newBase(r *http.Request, flash, errMsg string) basePage {
	user := s.currentUser(r)
	sessObj, _, _ := s.deps.Sessions.Get(r)
	var csrf string
	if sessObj != nil {
		csrf = s.csrfToken(sessObj.TokenHash)
	}

	var boxes []*models.Mailbox
	if user != nil {
		boxes, _ = s.deps.DB.ListMailboxes(r.Context(), user.ID)
	}
	return basePage{Flash: flash, Error: errMsg, CSRF: csrf, User: user, Mailboxes: boxes}
}

func (s *Server) render(w http.ResponseWriter, page string, data any) {
	t, err := template.New("").Funcs(tmplFuncs).ParseFS(
		s.deps.FS,
		"templates/base.html",
		"templates/"+page+".html",
	)
	if err != nil {
		log.Printf("[webmail] template parse %s: %v", page, err)
		http.Error(w, "template error", http.StatusInternalServerError)
		return
	}
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	w.Header().Set("X-Content-Type-Options", "nosniff")
	w.Header().Set("X-Frame-Options", "SAMEORIGIN")
	if err := t.ExecuteTemplate(w, "base", data); err != nil {
		log.Printf("[webmail] template exec %s: %v", page, err)
	}
}

// redirect sends 303 with optional flash/error query param.
func redirect(w http.ResponseWriter, r *http.Request, path, flash, errMsg string) {
	target := path
	if flash != "" {
		target += "?flash=" + template.URLQueryEscaper(flash)
	} else if errMsg != "" {
		target += "?error=" + template.URLQueryEscaper(errMsg)
	}
	http.Redirect(w, r, target, http.StatusSeeOther)
}

func flashFrom(r *http.Request) (flash, errMsg string) {
	return r.URL.Query().Get("flash"), r.URL.Query().Get("error")
}

// ---- CSRF ----

// csrfToken returns an HMAC-SHA256 token valid for the current clock-hour.
func (s *Server) csrfToken(sessionHash string) string {
	return computeCSRF(sessionHash, s.deps.Cfg.SessionSecret, time.Now().UTC())
}

func computeCSRF(sessionHash string, secret []byte, t time.Time) string {
	h := hmac.New(sha256.New, secret)
	h.Write([]byte(sessionHash))
	h.Write([]byte(t.Format("2006-01-02-15")))
	return hex.EncodeToString(h.Sum(nil))
}

// checkCSRF validates the CSRF token from the form field "_csrf".
func (s *Server) checkCSRF(r *http.Request, sessionHash string) bool {
	got := r.FormValue("_csrf")
	if got == "" {
		return false
	}
	now := time.Now().UTC()
	cur := computeCSRF(sessionHash, s.deps.Cfg.SessionSecret, now)
	if hmac.Equal([]byte(got), []byte(cur)) {
		return true
	}
	prev := computeCSRF(sessionHash, s.deps.Cfg.SessionSecret, now.Add(-time.Hour))
	return hmac.Equal([]byte(got), []byte(prev))
}

// validateCSRF checks CSRF and writes 403 on failure. Returns false on failure.
func (s *Server) validateCSRF(w http.ResponseWriter, r *http.Request) bool {
	if err := r.ParseForm(); err != nil {
		http.Error(w, "bad request", http.StatusBadRequest)
		return false
	}
	sess, _, _ := s.deps.Sessions.Get(r)
	if sess == nil {
		http.Error(w, "unauthenticated", http.StatusForbidden)
		return false
	}
	if !s.checkCSRF(r, sess.TokenHash) {
		http.Error(w, "CSRF validation failed", http.StatusForbidden)
		return false
	}
	return true
}

// ---- Template funcs ----

var tmplFuncs = template.FuncMap{
	"humanBytes": humanBytes,
	"shortTime":  func(t time.Time) string { return t.Format("2006-01-02 15:04") },
	"shortDate": func(t time.Time) string {
		now := time.Now()
		if t.Year() == now.Year() && t.Month() == now.Month() && t.Day() == now.Day() {
			return t.Format("15:04")
		}
		return t.Format("Jan 2")
	},
	"isZero":  func(t time.Time) bool { return t.IsZero() },
	"add":     func(a, b int) int { return a + b },
	"truncate": func(s string, n int) string {
		r := []rune(s)
		if len(r) <= n {
			return s
		}
		return string(r[:n]) + "..."
	},
	"mailboxLabel": mailboxLabel,
	"safeHTML":     func(s string) template.HTML { return template.HTML(s) }, //nolint:gosec
}

func mailboxLabel(mboxType string) string {
	switch mboxType {
	case "inbox":
		return "Inbox"
	case "sent":
		return "Sent"
	case "drafts":
		return "Drafts"
	case "trash":
		return "Trash"
	case "spam":
		return "Spam"
	case "archive":
		return "Archive"
	}
	return ""
}

func humanBytes(b int64) string {
	const unit = 1024
	if b < unit {
		return fmt.Sprintf("%d B", b)
	}
	div, exp := int64(unit), 0
	for n := b / unit; n >= unit; n /= unit {
		div *= unit
		exp++
	}
	return fmt.Sprintf("%.1f %cB", float64(b)/float64(div), "KMGTPE"[exp])
}