// Copyright (C) 2025, The Duplicati Team
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//
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// copy of this software and associated documentation files (the "Software"),
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// Software is furnished to do so, subject to the following conditions:
//
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using System;
using System.Diagnostics;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using CoCoL;
using Duplicati.Library.Main.Volumes;

#nullable enable

namespace Duplicati.Library.Main.Operation.Restore
{

    /// <summary>
    /// Process that decrypts the volumes that the `VolumeDownloader` process has downloaded.
    /// </summary>
    internal class VolumeDecryptor
    {
        /// <summary>
        /// The log tag for this class.
        /// </summary>
        private static readonly string LOGTAG = Logging.Log.LogTagFromType<VolumeDecryptor>();

        /// <summary>
        /// Runs the volume decryptor process.
        /// </summary>
        /// <param name="channels">The named channels for the restore operation.</param>
        /// <param name="backend">The backend manager.</param>
        /// <param name="options">The restore options.</param>
        public static Task Run(Channels channels, IBackendManager backend, Options options)
        {
            return AutomationExtensions.RunTask(
            new
            {
                Input = channels.DecryptRequest.AsRead(),
                Output = channels.VolumeResponse.AsWrite()
            },
            async self =>
            {
                Stopwatch? sw_read = options.InternalProfiling ? new() : null;
                Stopwatch? sw_write = options.InternalProfiling ? new() : null;
                Stopwatch? sw_decrypt = options.InternalProfiling ? new() : null;
                Stopwatch? sw_bvr = options.InternalProfiling ? new() : null;
                Stopwatch? sw_vw = options.InternalProfiling ? new() : null;

                try
                {
                    while (true)
                    {
                        // Get the block request and volume from the `VolumeDownloader` process.
                        sw_read?.Start();
                        var (volume_id, volume_name, volume) = await self.Input.ReadAsync().ConfigureAwait(false);
                        sw_read?.Stop();
                        Logging.Log.WriteExplicitMessage(LOGTAG, "DecryptVolume", null, "Decrypting volume {0} (ID: {1})", volume_name, volume_id);

                        // Decrypt the volume.
                        sw_decrypt?.Start();
                        var tmpfile = backend.DecryptFile(volume, volume_name, options);
                        sw_decrypt?.Stop();
                        Logging.Log.WriteExplicitMessage(LOGTAG, "DecryptVolume", null, "Decrypted volume {0} (ID: {1})", volume_name, volume_id);

                        // TODO These two steps could be moved to another process to allow even more parallelism.
                        sw_bvr?.Start();
                        var bvr = new BlockVolumeReader(options.CompressionModule, tmpfile, options);
                        sw_bvr?.Stop();
                        sw_vw?.Start();
                        var volume_wrapper = new VolumeWrapper(tmpfile, bvr);
                        sw_vw?.Stop();
                        Logging.Log.WriteExplicitMessage(LOGTAG, "BlockVolumeReader", null, "Created BlockVolumeReader for volume {0} (ID: {1})", volume_name, volume_id);

                        sw_write?.Start();
                        // Pass the decrypted volume to the `VolumeDecompressor` process.
                        await self.Output.WriteAsync((volume_id, volume_wrapper)).ConfigureAwait(false);
                        sw_write?.Stop();
                        Logging.Log.WriteExplicitMessage(LOGTAG, "DecryptVolume", null, "Passed decrypted volume {0} (ID: {1}) to next stage", volume_name, volume_id);
                    }
                }
                catch (RetiredException)
                {
                    Logging.Log.WriteVerboseMessage(LOGTAG, "RetiredProcess", null, "Volume decryptor retired");

                    if (options.InternalProfiling)
                    {
                        Logging.Log.WriteProfilingMessage(LOGTAG, "InternalTimings", $"Read: {sw_read!.ElapsedMilliseconds}ms, Decrypt: {sw_decrypt!.ElapsedMilliseconds}ms, BlockVolumeReader: {sw_bvr!.ElapsedMilliseconds}ms, VolumeWrapper: {sw_vw!.ElapsedMilliseconds}ms, Write: {sw_write!.ElapsedMilliseconds}ms");
                    }
                }
                catch (Exception ex)
                {
                    Logging.Log.WriteErrorMessage(LOGTAG, "DecryptionError", ex, "Error during decryption");
                    self.Input.Retire();
                    self.Output.Retire();
                    throw;
                }
            });
        }
    }

}