using System;
using System.Collections.Generic;
using System.Linq;
using System.Security.Cryptography;
using System.Text;
using Jose;
using Newtonsoft.Json;

namespace Sony.Filtr.AppleMusic
{
    public class AppleMusicTokenGenerator
    {
        private readonly string _privateKey;
        private readonly string _kid;
        private readonly string _iss;

        public AppleMusicTokenGenerator(string privateKey, string kid, string iss)
        {
            _privateKey = privateKey;
            _kid = kid;
            _iss = iss;
        }

        public string GetJwtToken()
        {

            var headers = JsonConvert.SerializeObject(new Dictionary<string, object>()
            {
                { "alg", "ES256" },
                { "kid", _kid },
            });

            var issued = DateTimeOffset.UtcNow.ToUnixTimeSeconds();
            var expiresAt = DateTimeOffset.UtcNow.AddMonths(3).ToUnixTimeSeconds();

            var payload = JsonConvert.SerializeObject(new Dictionary<string, object>()
            {
                { "iss", _iss },
                { "iat", issued },
                { "exp", expiresAt }
            });

            using (ECDsa key = ECDsa.Create())
            {
                key.ImportPkcs8PrivateKey(Convert.FromBase64String(_privateKey), out _);

                var headerBase64 = Convert.ToBase64String(Encoding.UTF8.GetBytes(headers));
                var payloadBasae64 = Convert.ToBase64String(Encoding.UTF8.GetBytes(payload));
                var unsignedJwtData = $"{headerBase64}.{payloadBasae64}";
                byte[] encodedRequest = Encoding.UTF8.GetBytes(unsignedJwtData);

                byte[] signature = key.SignData(encodedRequest, HashAlgorithmName.SHA256);

                return $"{unsignedJwtData}.{Convert.ToBase64String(signature)}";
            }
        }
    }
}