// Copyright (C) 2025, The Duplicati Team
// https://duplicati.com, hello@duplicati.com
// 
// Permission is hereby granted, free of charge, to any person obtaining a 
// copy of this software and associated documentation files (the "Software"), 
// to deal in the Software without restriction, including without limitation 
// the rights to use, copy, modify, merge, publish, distribute, sublicense, 
// and/or sell copies of the Software, and to permit persons to whom the 
// Software is furnished to do so, subject to the following conditions:
// 
// The above copyright notice and this permission notice shall be included in 
// all copies or substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS 
// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE 
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING 
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER 
// DEALINGS IN THE SOFTWARE.

using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Linq;
using System.Net.Security;
using System.Security.Cryptography.X509Certificates;
using System.Threading;
using Duplicati.Library.Interface;

namespace Duplicati.Library.Utility
{
    public static class SystemContextSettings
    {
        private static string defaultTempPath = null;

        private struct SystemSettings
        {
            public string Tempdir;
            public long Buffersize;
        }

        public static string DefaultTempPath
        {
            get
            {
                return defaultTempPath ?? System.IO.Path.GetTempPath();
            }
            set
            {
                if (!System.IO.Directory.Exists(value))
                    throw new FolderMissingException(Strings.TempFolder.TempFolderDoesNotExistError(value));
                defaultTempPath = value;
            }
        }

        public static IDisposable StartSession(string tempdir = null, long buffersize = 0)
        {
            if (buffersize < 1024)
                buffersize = 64 * 1024;

            var systemSettings = new SystemSettings
            {
                Tempdir = string.IsNullOrWhiteSpace(tempdir) ? DefaultTempPath : tempdir,
                Buffersize = buffersize
            };
            return CallContextSettings<SystemSettings>.StartContext(systemSettings);
        }

        public static string Tempdir
        {
            get
            {
                var tf = CallContextSettings<SystemSettings>.Settings.Tempdir;

                if (string.IsNullOrWhiteSpace(tf))
                {
                    tf = DefaultTempPath;
                }
                return tf;
            }
            set
            {
                var st = CallContextSettings<SystemSettings>.Settings;
                st.Tempdir = value;
                CallContextSettings<SystemSettings>.Settings = st;
            }
        }

        public static long Buffersize
        {
            get
            {
                var bs = CallContextSettings<SystemSettings>.Settings.Buffersize;
                if (bs < 1024)
                    bs = 64 * 1024;
                return bs;
            }
        }
    }


    /// <summary>
    /// Class for providing call-context access to http settings
    /// </summary>
    public static class HttpContextSettings
    {
        /// <summary>
        /// Internal struct with properties
        /// </summary>
        private struct HttpSettings
        {
            /// <summary>
            /// Gets or sets the operation timeout.
            /// </summary>
            /// <value>The operation timeout.</value>
            public TimeSpan OperationTimeout;
            /// <summary>
            /// Gets or sets the read write timeout.
            /// </summary>
            /// <value>The read write timeout.</value>
            public TimeSpan ReadWriteTimeout;
            /// <summary>
            /// Gets or sets a value indicating whether http requests are buffered.
            /// </summary>
            /// <value><c>true</c> if buffer requests; otherwise, <c>false</c>.</value>
            public bool BufferRequests;
            /// <summary>
            /// Gets or sets the certificate validator.
            /// </summary>
            /// <value>The certificate validator.</value>
            public SslCertificateValidator CertificateValidator;
        }

        /// <summary>
        /// Starts a new session
        /// </summary>
        /// <returns>The session.</returns>
        /// <param name="operationTimeout">The operation timeout.</param>
        /// <param name="readwriteTimeout">The readwrite timeout.</param>
        /// <param name="bufferRequests">If set to <c>true</c> http requests are buffered.</param>
        public static IDisposable StartSession(TimeSpan operationTimeout = default(TimeSpan), TimeSpan readwriteTimeout = default(TimeSpan), bool bufferRequests = false, bool acceptAnyCertificate = false, string[] allowedCertificates = null)
        {
            // Make sure we always use our own version of the callback
            System.Net.ServicePointManager.ServerCertificateValidationCallback = ServicePointManagerCertificateCallback;

            var httpSettings = new HttpSettings
            {
                OperationTimeout = operationTimeout,
                ReadWriteTimeout = readwriteTimeout,
                BufferRequests = bufferRequests,
                CertificateValidator = acceptAnyCertificate || (allowedCertificates != null)
                    ? new SslCertificateValidator(acceptAnyCertificate, allowedCertificates)
                    : null
            };

            return CallContextSettings<HttpSettings>.StartContext(httpSettings);
        }

        /// <summary>
        /// The callback used to defer the call context, such that each scope can have its own callback
        /// </summary>
        /// <returns><c>true</c>, if point manager certificate callback was serviced, <c>false</c> otherwise.</returns>
        /// <param name="sender">The sender of the validation.</param>
        /// <param name="certificate">The certificate to validate.</param>
        /// <param name="chain">The certificate chain.</param>
        /// <param name="sslPolicyErrors">Errors discovered.</param>
        private static bool ServicePointManagerCertificateCallback(object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors)
        {
            // If we have a custom SSL validator, invoke it
            if (HttpContextSettings.CertificateValidator != null)
                return CertificateValidator.ValidateServerCertificate(sender, certificate, chain, sslPolicyErrors);

            // Default is to only approve certificates without errors
            var result = sslPolicyErrors == SslPolicyErrors.None;

            // Hack: If we have no validator, see if the context is all messed up
            // This is not the right way, but ServicePointManager is not designed right for this
            var any = false;
            foreach (var v in CallContextSettings<HttpSettings>.GetAllInstances())
                if (v.CertificateValidator != null)
                {
                    var t = v.CertificateValidator.ValidateServerCertificate(sender, certificate, chain, sslPolicyErrors);

                    // First instance overrides framework result
                    if (!any)
                        result = t;

                    // If there are more, we see if anyone will accept it
                    else
                        result |= t;

                    any = true;
                }

            return result;
        }

        /// <summary>
        /// Gets the operation timeout.
        /// </summary>
        /// <value>The operation timeout.</value>
        public static TimeSpan OperationTimeout => CallContextSettings<HttpSettings>.Settings.OperationTimeout;
        /// <summary>
        /// Gets the read-write timeout.
        /// </summary>
        /// <value>The read write timeout.</value>
		public static TimeSpan ReadWriteTimeout => CallContextSettings<HttpSettings>.Settings.ReadWriteTimeout;
        /// <summary>
        /// Gets a value indicating whether https requests are buffered.
        /// </summary>
        /// <value><c>true</c> if buffer requests; otherwise, <c>false</c>.</value>
		public static bool BufferRequests => CallContextSettings<HttpSettings>.Settings.BufferRequests;
        /// <summary>
        /// Gets or sets the certificate validator.
        /// </summary>
        /// <value>The certificate validator.</value>
        public static SslCertificateValidator CertificateValidator => CallContextSettings<HttpSettings>.Settings.CertificateValidator;

    }

    /// <summary>
    /// Help class for providing settings in the current call context
    /// </summary>
    public static class CallContextSettings<T>
    {
        /// <summary>
        /// The call context settings for OAuth
        /// </summary>
        private static readonly AsyncLocal<T> _settings = new AsyncLocal<T>();

        /// <summary>
        /// The instances that are currently active
        /// </summary>
        private static readonly ConcurrentDictionary<T, object> _instances = new ConcurrentDictionary<T, object>();

        /// <summary>
        /// Disposable class for setting call context settings
        /// </summary>
        /// <typeparam name="T">The type of the settings</typeparam>
        private sealed class Disposer : IDisposable
        {
            /// <summary>
            /// A flag indicating if the object has been disposed
            /// </summary>
            private bool m_disposed = false;
            /// <summary>
            /// The previous value
            /// </summary>
            private T m_prev;
            /// <summary>
            /// The current value
            /// </summary>
            private T m_current;

            /// <summary>
            /// Initializes a new instance of the <see cref="Disposer"/> class.
            /// </summary>
            /// <param name="current">The current server URL</param>
            /// <param name="prev">The previous server URL</param>
            public Disposer(T current, T prev)
            {
                _settings.Value = m_current = current;
                this.m_prev = prev;
                _instances.TryAdd(current, null);
            }

            /// <inheritdoc/>
            public void Dispose()
            {
                if (m_disposed)
                    return;
                GC.SuppressFinalize(this);
                m_disposed = true;
                if (_settings.Value.Equals(m_current))
                    _settings.Value = m_prev;
                _instances.TryRemove(m_current, out _);
            }
        }

        /// <summary>
        /// Gets or sets the values in the current call context
        /// </summary>
        /// <value>The settings.</value>
        public static T Settings
        {
            get => _settings.Value;
            set => _settings.Value = value;
        }

        /// <summary>
        /// Starts the context wit a default value.
        /// </summary>
        /// <returns>The disposable handle for the context.</returns>
        /// <param name="initial">The initial value.</param>
        public static IDisposable StartContext(T initial = default(T))
            => new Disposer(initial, _settings.Value);

        public static IEnumerable<T> GetAllInstances()
            => _instances.Keys.ToList();

    }
}