// Copyright (C) 2024, The Duplicati Team
// https://duplicati.com, hello@duplicati.com
// 
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// Software is furnished to do so, subject to the following conditions:
// 
// The above copyright notice and this permission notice shall be included in 
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// 
// 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 
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using System;
using System.Collections.Generic;
using System.Linq;
using System.Net.Security;
using System.Security.Cryptography.X509Certificates;

using Duplicati.Library.Interface;
using Duplicati.Library.Logging;

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
            {
                lock (CallContextSettings<SystemSettings>._lock)
                {
                    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.ValidateServerCertficate(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.ValidateServerCertficate(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 settings that are stored in the call context, which are not serializable
        /// </summary>
        private static readonly Dictionary<string, T> _settings = new Dictionary<string, T>();

        /// <summary>
        /// The context setting types that are used and need their private setting key
        /// to prevent overwriting each others settings.
        /// </summary>
        private static string contextSettingsType = null;

        /// <summary>
        /// Lock for protecting the dictionary
        /// </summary>
        public static readonly object _lock = new object();

        /// <summary>
        /// Gets or sets the values in the current call context
        /// </summary>
        /// <value>The settings.</value>
        public static T Settings
        {
            get
            {
                var key = ContextID;
                if (string.IsNullOrWhiteSpace(key))
                    return default(T);


                if (!_settings.TryGetValue(key, out T res))
                    lock (_lock) // if not present but context id is not null, wait
                        if (!_settings.TryGetValue(key, out res))
                            return default(T);

                return res;
            }
            set
            {
                var key = ContextID;
                if (!string.IsNullOrWhiteSpace(key))
                    lock (_lock)
                        _settings[key] = 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(string settingsKey, T initial = default(T))
        {
            contextSettingsType = settingsKey;
            var res = new ContextGuard();
            Settings = initial;
            return res;
        }

        /// <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))
        {
            return StartContext(typeof(T).ToString(), initial);
        }

        /// <summary>
        /// Gets all instances currently registered
        /// </summary>
        internal static T[] GetAllInstances()
        {
            lock (_lock)
                return _settings.Values.ToArray();
        }

        /// <summary>
        /// Help class for providing a way to release resources associated with a call context
        /// </summary>
        private class ContextGuard : IDisposable
        {
            /// <summary>
            /// Randomly generated identifier
            /// </summary>
            private readonly string ID = Guid.NewGuid().ToString();

            /// <summary>
            /// Initializes a new instance of the
            /// <see cref="T:Duplicati.Library.Utility.CallContextSettings`1.ContextGuard"/> class,
            /// and sets up the call context
            /// </summary>
            public ContextGuard()
            {
                CallContext.SetData(contextSettingsType, ID);
            }

            /// <summary>
            /// Releases all resource used by the
            /// <see cref="T:Duplicati.Library.Utility.CallContextSettings`1.ContextGuard"/> object.
            /// </summary>
            /// <remarks>Call <see cref="Dispose"/> when you are finished using the
            /// <see cref="T:Duplicati.Library.Utility.CallContextSettings`1.ContextGuard"/>. The <see cref="Dispose"/>
            /// method leaves the <see cref="T:Duplicati.Library.Utility.CallContextSettings`1.ContextGuard"/> in an
            /// unusable state. After calling <see cref="Dispose"/>, you must release all references to the
            /// <see cref="T:Duplicati.Library.Utility.CallContextSettings`1.ContextGuard"/> so the garbage collector
            /// can reclaim the memory that the
            /// <see cref="T:Duplicati.Library.Utility.CallContextSettings`1.ContextGuard"/> was occupying.</remarks>
            public void Dispose()
            {
                lock (_lock)
                {
                    // Release the resources, if any
                    _settings.Remove(ID);
                }

                CallContext.SetData(contextSettingsType, null);
            }
        }

        /// <summary>
        /// Gets the context ID for this call.
        /// </summary>
        /// <value>The context identifier.</value>
        private static string ContextID
        {
            get
            {
                return contextSettingsType != null ? CallContext.GetData(contextSettingsType) as string : null;
            }
        }
    }
}