package op

import (
	"context"
	"crypto/rand"
	"encoding/base64"
	"errors"
	"fmt"
	"math/big"
	"net/http"
	"strings"
	"time"

	httphelper "github.com/zitadel/oidc/v2/pkg/http"
	"github.com/zitadel/oidc/v2/pkg/oidc"
)

type DeviceAuthorizationConfig struct {
	Lifetime     int
	PollInterval int
	UserFormURL  string
	UserCode     UserCodeConfig
}

type UserCodeConfig struct {
	CharSet      string
	CharAmount   int
	DashInterval int
}

const (
	CharSetBase20 = "BCDFGHJKLMNPQRSTVWXZ"
	CharSetDigits = "0123456789"
)

var (
	UserCodeBase20 = UserCodeConfig{
		CharSet:      CharSetBase20,
		CharAmount:   8,
		DashInterval: 4,
	}
	UserCodeDigits = UserCodeConfig{
		CharSet:      CharSetDigits,
		CharAmount:   9,
		DashInterval: 3,
	}
)

func deviceAuthorizationHandler(o OpenIDProvider) func(http.ResponseWriter, *http.Request) {
	return func(w http.ResponseWriter, r *http.Request) {
		if err := DeviceAuthorization(w, r, o); err != nil {
			RequestError(w, r, err)
		}
	}
}

func DeviceAuthorization(w http.ResponseWriter, r *http.Request, o OpenIDProvider) error {
	storage, err := assertDeviceStorage(o.Storage())
	if err != nil {
		return err
	}

	req, err := ParseDeviceCodeRequest(r, o)
	if err != nil {
		return err
	}

	config := o.DeviceAuthorization()

	deviceCode, err := NewDeviceCode(RecommendedDeviceCodeBytes)
	if err != nil {
		return err
	}
	userCode, err := NewUserCode([]rune(config.UserCode.CharSet), config.UserCode.CharAmount, config.UserCode.CharAmount)
	if err != nil {
		return err
	}

	expires := time.Now().Add(time.Duration(config.Lifetime) * time.Second)
	err = storage.StoreDeviceAuthorization(r.Context(), req.ClientID, deviceCode, userCode, expires, req.Scopes)
	if err != nil {
		return err
	}

	response := &oidc.DeviceAuthorizationResponse{
		DeviceCode:      deviceCode,
		UserCode:        userCode,
		VerificationURI: config.UserFormURL,
	}

	endpoint := o.UserCodeVerificationEndpoint().Absolute(IssuerFromContext(r.Context()))
	response.VerificationURIComplete = fmt.Sprintf("%s?user_code=%s", endpoint, userCode)

	httphelper.MarshalJSON(w, response)
	return nil
}

func ParseDeviceCodeRequest(r *http.Request, o OpenIDProvider) (*oidc.DeviceAuthorizationRequest, error) {
	clientID, _, err := ClientIDFromRequest(r, o)
	if err != nil {
		return nil, err
	}

	req := new(oidc.DeviceAuthorizationRequest)
	if err := o.Decoder().Decode(req, r.Form); err != nil {
		return nil, oidc.ErrInvalidRequest().WithDescription("cannot parse device authentication request").WithParent(err)
	}
	req.ClientID = clientID

	return req, nil
}

// 16 bytes gives 128 bit of entropy.
// results in a 22 character base64 encoded string.
const RecommendedDeviceCodeBytes = 16

func NewDeviceCode(nBytes int) (string, error) {
	bytes := make([]byte, nBytes)
	if _, err := rand.Read(bytes); err != nil {
		return "", fmt.Errorf("%w getting entropy for device code", err)
	}
	return base64.RawURLEncoding.EncodeToString(bytes), nil
}

func NewUserCode(charSet []rune, charAmount, dashInterval int) (string, error) {
	var buf strings.Builder
	if dashInterval > 0 {
		buf.Grow(charAmount + charAmount/dashInterval - 1)
	} else {
		buf.Grow(charAmount)
	}

	max := big.NewInt(int64(len(charSet)))

	for i := 0; i < charAmount; i++ {
		if dashInterval != 0 && i != 0 && i%dashInterval == 0 {
			buf.WriteByte('-')
		}

		bi, err := rand.Int(rand.Reader, max)
		if err != nil {
			return "", fmt.Errorf("%w getting entropy for user code", err)
		}

		buf.WriteRune(charSet[int(bi.Int64())])
	}

	return buf.String(), nil
}

func DeviceAccessToken(w http.ResponseWriter, r *http.Request, exchanger Exchanger) {
	if err := deviceAccessToken(w, r, exchanger); err != nil {
		RequestError(w, r, err)
	}
}

func deviceAccessToken(w http.ResponseWriter, r *http.Request, exchanger Exchanger) error {
	// use a limited context timeout shorter as the default
	// poll interval of 5 seconds.
	ctx, cancel := context.WithTimeout(r.Context(), 4*time.Second)
	defer cancel()
	r = r.WithContext(ctx)

	clientID, clientAuthenticated, err := ClientIDFromRequest(r, exchanger)
	if err != nil {
		return err
	}

	req, err := ParseDeviceAccessTokenRequest(r, exchanger)
	if err != nil {
		return err
	}
	state, authReq, err := CheckDeviceAuthorizationState(ctx, clientID, req.DeviceCode, exchanger)
	if err != nil {
		return err
	}

	client, err := exchanger.Storage().GetClientByClientID(ctx, clientID)
	if err != nil {
		return err
	}
	if !clientAuthenticated {
		if m := client.AuthMethod(); m != oidc.AuthMethodNone { // Livio: Does this mean "public" client?
			return oidc.ErrInvalidClient().WithParent(ErrNoClientCredentials).
				WithDescription(fmt.Sprintf("required client auth method: %s", m))
		}
	}

	resp, err := CreateTokenResponse(ctx, authReq, client, exchanger, true, state.AuthCode, "")
	if err != nil {
		return err
	}

	httphelper.MarshalJSON(w, resp)
	return nil
}

func ParseDeviceAccessTokenRequest(r *http.Request, exchanger Exchanger) (*oidc.DeviceAccessTokenRequest, error) {
	req := new(oidc.DeviceAccessTokenRequest)
	if err := exchanger.Decoder().Decode(req, r.PostForm); err != nil {
		return nil, err
	}
	return req, nil
}

func CheckDeviceAuthorizationState(ctx context.Context, clientID, deviceCode string, exchanger Exchanger) (*DeviceAuthorizationState, AuthRequest, error) {
	storage, err := assertDeviceStorage(exchanger.Storage())
	if err != nil {
		return nil, nil, err
	}

	state, err := storage.GetDeviceAuthorizatonState(ctx, clientID, deviceCode)
	if errors.Is(err, context.DeadlineExceeded) {
		return nil, nil, oidc.ErrSlowDown().WithParent(err)
	}
	if err != nil {
		return nil, nil, err
	}
	if state.Denied {
		return state, nil, oidc.ErrAccessDenied()
	}
	if state.AuthCode != "" {
		return state, nil, nil
	}
	if time.Now().After(state.Expires) {
		return state, nil, oidc.ErrExpiredDeviceCode()
	}
	authReq, err := AuthRequestByCode(ctx, exchanger.Storage(), state.AuthCode)
	return state, authReq, err
}

func userCodeVerificationHandler(o OpenIDProvider) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		UserCodeVerification(w, r, o)
	}
}

type UserCodeVerificationRequest struct {
	Code        string `schema:"code"`
	UserCode    string `schema:"user_code"`
	RedirectURL string `schema:"redirect_url"`
}

func UserCodeVerification(w http.ResponseWriter, r *http.Request, o OpenIDProvider) {
	if err := userCodeVerification(w, r, o); err != nil {
		RequestError(w, r, err)
	}
}

func userCodeVerification(w http.ResponseWriter, r *http.Request, o OpenIDProvider) (err error) {
	req, err := ParseUserCodeVerificationRequest(r, o.Decoder())
	if err != nil {
		return err
	}

	storage, err := assertDeviceStorage(o.Storage())
	if err != nil {
		return err
	}

	ctx := r.Context()
	if err := storage.CompleteDeviceAuthorization(ctx, req.Code, req.UserCode); err != nil {
		return err
	}

	if req.RedirectURL != "" {
		http.Redirect(w, r, req.RedirectURL, http.StatusSeeOther)
	}

	fmt.Fprintln(w, "Authorization successfull, please return to your device")
	return nil
}

func ParseUserCodeVerificationRequest(r *http.Request, decoder httphelper.Decoder) (*UserCodeVerificationRequest, error) {
	if err := r.ParseForm(); err != nil {
		return nil, oidc.ErrInvalidRequest().WithDescription("cannot parse form").WithParent(err)
	}

	req := new(UserCodeVerificationRequest)
	if err := decoder.Decode(req, r.Form); err != nil {
		return nil, oidc.ErrInvalidRequest().WithDescription("cannot parse user code form").WithParent(err)
	}
	if req.Code == "" {
		return nil, oidc.ErrInvalidRequest().WithDescription("\"code\" missing in form")
	}
	if req.UserCode == "" {
		return nil, oidc.ErrInvalidRequest().WithDescription("\"user_code\" missing in form")
	}

	return req, nil
}