package middleware

import (
	"crypto/rand"
	"fmt"
	"math/big"
	"net/http"

	"github.com/google/uuid"
	"github.com/pkg/errors"
)

const AnonIssuer = "anon"

func WithAnonymousUser(funcs ...DefaultUserOptionFunc) DefaultUserOptionFunc {
	return func(opts *DefaultUserOptions) {
		opts.GetSubject = getAnonymousSubject
		opts.GetPreferredUsername = getAnonymousPreferredUsername
		opts.Issuer = AnonIssuer

		for _, fn := range funcs {
			fn(opts)
		}
	}
}

func getAnonymousSubject(r *http.Request) (string, error) {
	uuid, err := uuid.NewUUID()
	if err != nil {
		return "", errors.Wrap(err, "could not generate uuid for anonymous user")
	}

	subject := fmt.Sprintf("%s-%s", AnonIssuer, uuid.String())

	return subject, nil
}

func getAnonymousPreferredUsername(r *http.Request) (string, error) {
	preferredUsername, err := generateRandomPreferredUsername(8)
	if err != nil {
		return "", errors.Wrap(err, "could not generate preferred username for anonymous user")
	}

	return preferredUsername, nil
}

func generateRandomPreferredUsername(size int) (string, error) {
	var letters = []rune("0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ")
	max := big.NewInt(int64(len(letters)))

	b := make([]rune, size)
	for i := range b {
		idx, err := rand.Int(rand.Reader, max)
		if err != nil {
			return "", errors.WithStack(err)
		}
		b[i] = letters[idx.Int64()]
	}

	return fmt.Sprintf("Anon %s", string(b)), nil
}