package webui

import (
	"crypto/sha256"
	"encoding/base64"
	"encoding/json"
	"net/http"
	"strconv"

	"github.com/go-webauthn/webauthn/webauthn"
	"mailgoserver/internal/db"
)

// mailboxWebauthnSessionCookie mirrors webauthnSessionCookie but kept separate so an
// in-progress admin passkey ceremony and an in-progress mailbox one (e.g. different
// browser tabs) can never collide.
const mailboxWebauthnSessionCookie = "mailgoserver_mailbox_webauthn_session"

// mailboxWebauthnUser adapts a Mailbox + its stored credentials to webauthn.User,
// mirroring webauthnUser.
type mailboxWebauthnUser struct {
	mailbox *db.Mailbox
	creds   []db.MailboxWebAuthnCredential
}

func (u *mailboxWebauthnUser) WebAuthnID() []byte {
	sum := sha256.Sum256([]byte("mailbox-" + strconv.FormatInt(u.mailbox.ID, 10)))
	return sum[:]
}
func (u *mailboxWebauthnUser) WebAuthnName() string        { return u.mailbox.Email }
func (u *mailboxWebauthnUser) WebAuthnDisplayName() string { return u.mailbox.Email }
func (u *mailboxWebauthnUser) WebAuthnCredentials() []webauthn.Credential {
	out := make([]webauthn.Credential, 0, len(u.creds))
	for _, c := range u.creds {
		var cred webauthn.Credential
		if err := json.Unmarshal([]byte(c.CredentialData), &cred); err == nil {
			out = append(out, cred)
		}
	}
	return out
}

func (a *App) mailboxWebauthnUserFor(mbox *db.Mailbox) (*mailboxWebauthnUser, error) {
	creds, err := a.DB.ListMailboxWebAuthnCredentials(mbox.ID)
	if err != nil {
		return nil, err
	}
	return &mailboxWebauthnUser{mailbox: mbox, creds: creds}, nil
}

func saveMailboxWebauthnSession(w http.ResponseWriter, s *webauthn.SessionData) error {
	b, err := json.Marshal(s)
	if err != nil {
		return err
	}
	http.SetCookie(w, &http.Cookie{
		Name: mailboxWebauthnSessionCookie, Value: base64.URLEncoding.EncodeToString(b),
		Path: "/", HttpOnly: true, SameSite: http.SameSiteLaxMode, MaxAge: 5 * 60,
	})
	return nil
}

func loadMailboxWebauthnSession(r *http.Request) (*webauthn.SessionData, error) {
	c, err := r.Cookie(mailboxWebauthnSessionCookie)
	if err != nil {
		return nil, err
	}
	raw, err := base64.URLEncoding.DecodeString(c.Value)
	if err != nil {
		return nil, err
	}
	var s webauthn.SessionData
	if err := json.Unmarshal(raw, &s); err != nil {
		return nil, err
	}
	return &s, nil
}

func clearMailboxWebauthnSession(w http.ResponseWriter) {
	http.SetCookie(w, &http.Cookie{Name: mailboxWebauthnSessionCookie, Value: "", Path: "/", MaxAge: -1})
}

func (a *App) webmailPasskeyRegisterBegin(w http.ResponseWriter, r *http.Request) {
	mbox := mailboxFromContext(r)
	wa, err := a.buildWebAuthn()
	if err != nil {
		writeJSON(w, http.StatusInternalServerError, M{"error": "WebAuthn is not configured correctly: " + err.Error()})
		return
	}
	wu, err := a.mailboxWebauthnUserFor(mbox)
	if err != nil {
		writeJSON(w, http.StatusInternalServerError, M{"error": "Could not load account"})
		return
	}
	creation, session, err := wa.BeginRegistration(wu)
	if err != nil {
		writeJSON(w, http.StatusInternalServerError, M{"error": err.Error()})
		return
	}
	if err := saveMailboxWebauthnSession(w, session); err != nil {
		writeJSON(w, http.StatusInternalServerError, M{"error": "Could not start registration"})
		return
	}
	writeJSON(w, http.StatusOK, creation)
}

func (a *App) webmailPasskeyRegisterFinish(w http.ResponseWriter, r *http.Request) {
	mbox := mailboxFromContext(r)
	wa, err := a.buildWebAuthn()
	if err != nil {
		writeJSON(w, http.StatusInternalServerError, M{"error": err.Error()})
		return
	}
	session, err := loadMailboxWebauthnSession(r)
	if err != nil {
		writeJSON(w, http.StatusBadRequest, M{"error": "Registration session expired — try again"})
		return
	}
	wu, err := a.mailboxWebauthnUserFor(mbox)
	if err != nil {
		writeJSON(w, http.StatusInternalServerError, M{"error": "Could not load account"})
		return
	}
	cred, err := wa.FinishRegistration(wu, *session, r)
	clearMailboxWebauthnSession(w)
	if err != nil {
		writeJSON(w, http.StatusBadRequest, M{"error": err.Error()})
		return
	}
	data, err := json.Marshal(cred)
	if err != nil {
		writeJSON(w, http.StatusInternalServerError, M{"error": "Could not save passkey"})
		return
	}
	name := r.URL.Query().Get("name")
	if name == "" {
		name = "Passkey"
	}
	if err := a.DB.CreateMailboxWebAuthnCredential(mbox.ID, name, base64.URLEncoding.EncodeToString(cred.ID), string(data)); err != nil {
		writeJSON(w, http.StatusInternalServerError, M{"error": "Could not save passkey"})
		return
	}
	_ = a.DB.LogAuthAttempt("mailbox_mfa", mbox.Email, a.requestIP(r), true, "Passkey added: "+name)
	writeJSON(w, http.StatusOK, M{"success": true})
}

func (a *App) webmailPasskeyRemove(w http.ResponseWriter, r *http.Request) {
	mbox := mailboxFromContext(r)
	if err := a.DB.DeleteMailboxWebAuthnCredential(pathID(r), mbox.ID); err != nil {
		setFlash(w, "error", "Could not remove passkey")
	} else {
		_ = a.DB.LogAuthAttempt("mailbox_mfa", mbox.Email, a.requestIP(r), true, "Passkey removed")
		setFlash(w, "success", "Passkey removed")
	}
	http.Redirect(w, r, MailboxPrefix+"/account", http.StatusFound)
}

// webmailPasskeyLoginBegin starts the passkey ceremony for the mailbox that's already
// passed its password and is now at the MFA step.
func (a *App) webmailPasskeyLoginBegin(w http.ResponseWriter, r *http.Request) {
	mailboxID := pendingMailboxMFAID(r)
	if mailboxID == 0 {
		writeJSON(w, http.StatusUnauthorized, M{"error": "No login in progress"})
		return
	}
	mbox, err := a.DB.GetMailboxByID(mailboxID)
	if err != nil || mbox == nil {
		writeJSON(w, http.StatusUnauthorized, M{"error": "No login in progress"})
		return
	}
	wa, err := a.buildWebAuthn()
	if err != nil {
		writeJSON(w, http.StatusInternalServerError, M{"error": err.Error()})
		return
	}
	wu, err := a.mailboxWebauthnUserFor(mbox)
	if err != nil || len(wu.creds) == 0 {
		writeJSON(w, http.StatusBadRequest, M{"error": "No passkeys registered"})
		return
	}
	assertion, session, err := wa.BeginLogin(wu)
	if err != nil {
		writeJSON(w, http.StatusInternalServerError, M{"error": err.Error()})
		return
	}
	if err := saveMailboxWebauthnSession(w, session); err != nil {
		writeJSON(w, http.StatusInternalServerError, M{"error": "Could not start login"})
		return
	}
	writeJSON(w, http.StatusOK, assertion)
}

func (a *App) webmailPasskeyLoginFinish(w http.ResponseWriter, r *http.Request) {
	mailboxID := pendingMailboxMFAID(r)
	if mailboxID == 0 {
		writeJSON(w, http.StatusUnauthorized, M{"error": "No login in progress"})
		return
	}
	mbox, err := a.DB.GetMailboxByID(mailboxID)
	if err != nil || mbox == nil {
		writeJSON(w, http.StatusUnauthorized, M{"error": "No login in progress"})
		return
	}
	wa, err := a.buildWebAuthn()
	if err != nil {
		writeJSON(w, http.StatusInternalServerError, M{"error": err.Error()})
		return
	}
	session, err := loadMailboxWebauthnSession(r)
	if err != nil {
		writeJSON(w, http.StatusBadRequest, M{"error": "Login session expired — try again"})
		return
	}
	wu, err := a.mailboxWebauthnUserFor(mbox)
	if err != nil {
		writeJSON(w, http.StatusInternalServerError, M{"error": "Could not load account"})
		return
	}
	if _, err := wa.FinishLogin(wu, *session, r); err != nil {
		clearMailboxWebauthnSession(w)
		_ = a.DB.LogAuthAttempt("webmail_login", mbox.Email, a.requestIP(r), false, "Passkey verification failed")
		writeJSON(w, http.StatusUnauthorized, M{"error": "Passkey verification failed"})
		return
	}
	clearMailboxWebauthnSession(w)

	token, err := a.DB.CreateMailboxSession(mbox.ID, true, sessionTTL)
	if err != nil {
		writeJSON(w, http.StatusInternalServerError, M{"error": "Could not start session"})
		return
	}
	_ = a.DB.LogAuthAttempt("webmail_login", mbox.Email, a.requestIP(r), true, "Login successful (passkey)")
	clearMailboxPendingMFACookie(w)
	setMailboxSessionCookie(w, token, r.TLS != nil)
	writeJSON(w, http.StatusOK, M{"success": true})
}