package handlers

import (
	"bytes"

	"github.com/go-webauthn/webauthn/protocol"
	"github.com/go-webauthn/webauthn/webauthn"

	"github.com/authelia/authelia/v4/internal/middlewares"
	"github.com/authelia/authelia/v4/internal/model"
	"github.com/authelia/authelia/v4/internal/regulation"
)

// WebauthnAssertionGET handler starts the assertion ceremony.
func WebauthnAssertionGET(ctx *middlewares.AutheliaCtx) {
	var (
		w    *webauthn.WebAuthn
		user *model.WebauthnUser
		err  error
	)

	userSession := ctx.GetSession()

	if w, err = newWebauthn(ctx); err != nil {
		ctx.Logger.Errorf("Unable to configure %s during assertion challenge for user '%s': %+v", regulation.AuthTypeWebauthn, userSession.Username, err)

		respondUnauthorized(ctx, messageMFAValidationFailed)

		return
	}

	if user, err = getWebAuthnUser(ctx, userSession); err != nil {
		ctx.Logger.Errorf("Unable to create %s assertion challenge for user '%s': %+v", regulation.AuthTypeWebauthn, userSession.Username, err)

		respondUnauthorized(ctx, messageMFAValidationFailed)

		return
	}

	var opts = []webauthn.LoginOption{
		webauthn.WithAllowedCredentials(user.WebAuthnCredentialDescriptors()),
	}

	extensions := map[string]any{}

	if user.HasFIDOU2F() {
		extensions["appid"] = w.Config.RPOrigins[0]
	}

	if len(extensions) != 0 {
		opts = append(opts, webauthn.WithAssertionExtensions(extensions))
	}

	var assertion *protocol.CredentialAssertion

	if assertion, userSession.Webauthn, err = w.BeginLogin(user, opts...); err != nil {
		ctx.Logger.Errorf("Unable to create %s assertion challenge for user '%s': %+v", regulation.AuthTypeWebauthn, userSession.Username, err)

		respondUnauthorized(ctx, messageMFAValidationFailed)

		return
	}

	if err = ctx.SaveSession(userSession); err != nil {
		ctx.Logger.Errorf(logFmtErrSessionSave, "assertion challenge", regulation.AuthTypeWebauthn, userSession.Username, err)

		respondUnauthorized(ctx, messageMFAValidationFailed)

		return
	}

	if err = ctx.SetJSONBody(assertion); err != nil {
		ctx.Logger.Errorf(logFmtErrWriteResponseBody, regulation.AuthTypeWebauthn, userSession.Username, err)

		respondUnauthorized(ctx, messageMFAValidationFailed)

		return
	}
}

// WebauthnAssertionPOST handler completes the assertion ceremony after verifying the challenge.
func WebauthnAssertionPOST(ctx *middlewares.AutheliaCtx) {
	var (
		err error
		w   *webauthn.WebAuthn

		bodyJSON bodySignWebauthnRequest
	)

	if err = ctx.ParseBody(&bodyJSON); err != nil {
		ctx.Logger.Errorf(logFmtErrParseRequestBody, regulation.AuthTypeWebauthn, err)

		respondUnauthorized(ctx, messageMFAValidationFailed)

		return
	}

	userSession := ctx.GetSession()

	if userSession.Webauthn == nil {
		ctx.Logger.Errorf("Webauthn session data is not present in order to handle assertion for user '%s'. This could indicate a user trying to POST to the wrong endpoint, or the session data is not present for the browser they used.", userSession.Username)

		respondUnauthorized(ctx, messageMFAValidationFailed)

		return
	}

	if w, err = newWebauthn(ctx); err != nil {
		ctx.Logger.Errorf("Unable to configure %s during assertion challenge for user '%s': %+v", regulation.AuthTypeWebauthn, userSession.Username, err)

		respondUnauthorized(ctx, messageMFAValidationFailed)

		return
	}

	var (
		assertionResponse *protocol.ParsedCredentialAssertionData
		credential        *webauthn.Credential
		user              *model.WebauthnUser
	)

	if assertionResponse, err = protocol.ParseCredentialRequestResponseBody(bytes.NewReader(ctx.PostBody())); err != nil {
		ctx.Logger.Errorf("Unable to parse %s assertionfor user '%s': %+v", regulation.AuthTypeWebauthn, userSession.Username, err)

		respondUnauthorized(ctx, messageMFAValidationFailed)

		return
	}

	if user, err = getWebAuthnUser(ctx, userSession); err != nil {
		ctx.Logger.Errorf("Unable to load %s devices for assertion challenge for user '%s': %+v", regulation.AuthTypeWebauthn, userSession.Username, err)

		respondUnauthorized(ctx, messageMFAValidationFailed)

		return
	}

	if credential, err = w.ValidateLogin(user, *userSession.Webauthn, assertionResponse); err != nil {
		_ = markAuthenticationAttempt(ctx, false, nil, userSession.Username, regulation.AuthTypeWebauthn, err)

		respondUnauthorized(ctx, messageMFAValidationFailed)

		return
	}

	var found bool

	for _, device := range user.Devices {
		if bytes.Equal(device.KID.Bytes(), credential.ID) {
			device.UpdateSignInInfo(w.Config, ctx.Clock.Now(), credential.Authenticator.SignCount)

			found = true

			if err = ctx.Providers.StorageProvider.UpdateWebauthnDeviceSignIn(ctx, device.ID, device.RPID, device.LastUsedAt, device.SignCount, device.CloneWarning); err != nil {
				ctx.Logger.Errorf("Unable to save %s device signin count for assertion challenge for user '%s': %+v", regulation.AuthTypeWebauthn, userSession.Username, err)

				respondUnauthorized(ctx, messageMFAValidationFailed)

				return
			}

			break
		}
	}

	if !found {
		ctx.Logger.Errorf("Unable to save %s device signin count for assertion challenge for user '%s' device '%x' count '%d': unable to find device", regulation.AuthTypeWebauthn, userSession.Username, credential.ID, credential.Authenticator.SignCount)

		respondUnauthorized(ctx, messageMFAValidationFailed)

		return
	}

	if err = ctx.Providers.SessionProvider.RegenerateSession(ctx.RequestCtx); err != nil {
		ctx.Logger.Errorf(logFmtErrSessionRegenerate, regulation.AuthTypeWebauthn, userSession.Username, err)

		respondUnauthorized(ctx, messageMFAValidationFailed)

		return
	}

	if err = markAuthenticationAttempt(ctx, true, nil, userSession.Username, regulation.AuthTypeWebauthn, nil); err != nil {
		respondUnauthorized(ctx, messageMFAValidationFailed)

		return
	}

	userSession.SetTwoFactorWebauthn(ctx.Clock.Now(),
		assertionResponse.Response.AuthenticatorData.Flags.UserPresent(),
		assertionResponse.Response.AuthenticatorData.Flags.UserVerified())

	if err = ctx.SaveSession(userSession); err != nil {
		ctx.Logger.Errorf(logFmtErrSessionSave, "removal of the assertion challenge and authentication time", regulation.AuthTypeWebauthn, userSession.Username, err)

		respondUnauthorized(ctx, messageMFAValidationFailed)

		return
	}

	if bodyJSON.Workflow == workflowOpenIDConnect {
		handleOIDCWorkflowResponse(ctx, bodyJSON.TargetURL, bodyJSON.WorkflowID)
	} else {
		Handle2FAResponse(ctx, bodyJSON.TargetURL)
	}
}