using console_spo_utils.Model;
using Microsoft.SharePoint.Client;
using System.Collections.Concurrent;
using System.Text;
using System.Text.Json;
using System.Web;
using Microsoft.Extensions.Logging;
using console_spo_utils.Interfaces.Services;

namespace console_spo_utils.Services
{
    internal sealed class SharePointAuthenticationManager : IDisposable, ISharePointAuthenticationManager
    {
        private readonly ILogger<SharePointAuthenticationManager> logger;
        private readonly ISiteOptions siteOptions;

        public SharePointAuthenticationManager(
            ILogger<SharePointAuthenticationManager> logger,
            ISiteOptions siteOptions)
        {
            this.logger = logger;
            this.siteOptions = siteOptions;
        }

        private static readonly HttpClient HttpClient = new();
        
        private static readonly SemaphoreSlim SemaphoreSlimTokens = new(1);
        private AutoResetEvent tokenResetEvent = null;
        private readonly ConcurrentDictionary<string, string> tokenCache = new();
        private bool disposedValue;

        #region CSOM
        public ClientContext GetContext(Uri web)
        {
            var context = new ClientContext(web);

            context.ExecutingWebRequest += (sender, e) =>
            {
                var accessToken = EnsureAccessTokenAsync(new Uri($"{web.Scheme}://{web.DnsSafeHost}"),
                        siteOptions.GetUser(),
                        new System.Net.NetworkCredential(string.Empty, siteOptions.GetPassword()).Password)
                    .GetAwaiter()
                    .GetResult();
                e.WebRequestExecutor.RequestHeaders["Authorization"] = "Bearer " + accessToken;
            };

            return context;
        }

        public async Task<string> EnsureAccessTokenAsync(Uri resourceUri, string userPrincipalName, string userPassword)
        {
            var accessTokenFromCache = TokenFromCache(resourceUri, tokenCache);
            if (accessTokenFromCache == null)
            {
                await SemaphoreSlimTokens.WaitAsync();
                try
                {
                    // No async methods are allowed in a lock section
                    var accessToken = await AcquireTokenAsync(resourceUri, userPrincipalName, userPassword);
                    logger.LogInformation($"Successfully requested new access token resource {resourceUri.DnsSafeHost} for user {userPrincipalName}");
                    AddTokenToCache(resourceUri, tokenCache, accessToken);

                    // Register a thread to invalidate the access token once's it's expired
                    tokenResetEvent = new AutoResetEvent(false);
                    var wi = new TokenWaitInfo();
                    wi.Handle = ThreadPool.RegisterWaitForSingleObject(
                        tokenResetEvent,
                        (state, timedOut) =>
                        {
                            if (!timedOut)
                            {
                                var internalWaitToken = (TokenWaitInfo)state;
                                if (internalWaitToken?.Handle is not null)
                                {
                                    internalWaitToken.Handle.Unregister(null);
                                }
                            }
                            else
                            {
                                try
                                {
                                    // Take a lock to ensure no other threads are updating the SharePoint Access token at this time
                                    SemaphoreSlimTokens.Wait();
                                    RemoveTokenFromCache(resourceUri, tokenCache);
                                    logger.LogInformation($"Cached token for resource {resourceUri.DnsSafeHost} and user {userPrincipalName} expired");
                                }
                                catch (Exception ex)
                                {
                                    logger.LogInformation($"Something went wrong during cache token invalidation: {ex.Message}");
                                    RemoveTokenFromCache(resourceUri, tokenCache);
                                }
                                finally
                                {
                                    SemaphoreSlimTokens.Release();
                                }
                            }
                        },
                        wi,
                        (uint)CalculateThreadSleep(accessToken).TotalMilliseconds,
                        true
                    );

                    return accessToken;

                }
                finally
                {
                    SemaphoreSlimTokens.Release();
                }
            }
            else
            {
                logger.LogInformation("OK - Execution Query");
                return accessTokenFromCache;
            }
        }

        private async Task<string> AcquireTokenAsync(Uri resourceUri, string username, string password)
        {
            var resource = $"{resourceUri.Scheme}://{resourceUri.DnsSafeHost}";

            var clientId = siteOptions.DefaultAadAppId;
            var body = $"resource={resource}&client_id={clientId}&grant_type=password&username={HttpUtility.UrlEncode(username)}&password={HttpUtility.UrlEncode(password)}";
            using var stringContent = new StringContent(body, Encoding.UTF8, "application/x-www-form-urlencoded");
            var result = await HttpClient.PostAsync(siteOptions.TokenEndpoint, stringContent).ContinueWith((response) =>
            {
                return response.Result.Content.ReadAsStringAsync().Result;
            }).ConfigureAwait(false);

            var tokenResult = JsonSerializer.Deserialize<JsonElement>(result);
            var token = tokenResult.GetProperty("access_token").GetString();
            return token;
        }

        private static string TokenFromCache(Uri web, ConcurrentDictionary<string, string> tokenCache)
        {
            if (tokenCache.TryGetValue(web.DnsSafeHost, out var accessToken))
            {
                return accessToken;
            }

            return null;
        }

        private static void AddTokenToCache(Uri web, ConcurrentDictionary<string, string> tokenCache, string newAccessToken)
        {
            if (tokenCache.TryGetValue(web.DnsSafeHost, out var currentAccessToken))
            {
                tokenCache.TryUpdate(web.DnsSafeHost, newAccessToken, currentAccessToken);
            }
            else
            {
                tokenCache.TryAdd(web.DnsSafeHost, newAccessToken);
            }
        }

        private static void RemoveTokenFromCache(Uri web, ConcurrentDictionary<string, string> tokenCache)
        {
            tokenCache.TryRemove(web.DnsSafeHost, out _);
        }

        private static TimeSpan CalculateThreadSleep(string accessToken)
        {
            var token = new System.IdentityModel.Tokens.Jwt.JwtSecurityToken(accessToken);
            var lease = GetAccessTokenLease(token.ValidTo);
            lease = TimeSpan.FromSeconds(lease.TotalSeconds - TimeSpan.FromMinutes(5).TotalSeconds > 0 ? lease.TotalSeconds - TimeSpan.FromMinutes(5).TotalSeconds : lease.TotalSeconds);
            return lease;
        }

        private static TimeSpan GetAccessTokenLease(DateTime expiresOn)
        {
            var now = DateTime.UtcNow;
            var expires = expiresOn.Kind == DateTimeKind.Utc ? expiresOn : TimeZoneInfo.ConvertTimeToUtc(expiresOn);
            var lease = expires - now;
            return lease;
        }

        private void Dispose(bool disposing)
        {
            if (disposedValue)
            {
                return;
            }
            if (disposing)
            {
                if (tokenResetEvent is not null)
                {
                    tokenResetEvent.Set();
                    tokenResetEvent.Dispose();
                }
            }

            disposedValue = true;
        }

        public void Dispose()
        {
            // Do not change this code. Put cleanup code in 'Dispose(bool disposing)' method
            Dispose(disposing: true);
            GC.SuppressFinalize(this);
        }
        #endregion
    }
}