package main

import (
	"encoding/base64"
	"encoding/json"
	"fmt"
	"strings"
)

func userIDFromJWT(token string) (string, error) {
	parts := strings.Split(token, ".")
	if len(parts) < 2 {
		return "", fmt.Errorf("token is not a JWT")
	}
	payload, err := base64.RawURLEncoding.DecodeString(parts[1])
	if err != nil {
		return "", err
	}
	var claims map[string]any
	if err := json.Unmarshal(payload, &claims); err != nil {
		return "", err
	}
	sub, _ := claims["sub"].(string)
	if sub == "" {
		return "", fmt.Errorf("token has no sub claim")
	}
	return sub, nil
}