using static MFiles.Grpc.Samples.MFilesValues;

namespace MFiles.Grpc.Samples.Recipes;

/// <summary>
/// Recipe "download-file": download the files of a document's latest version to a folder.
/// Arguments: [document ID, default 437] [folder, default a "mfiles-grpc-samples" folder in TEMP]
/// </summary>
public static class DownloadFile
{
    /// <summary>Bytes per DownloadFile_ReadBlock call; the server allows at most 4 MiB.</summary>
    private const int BlockSize = 4 * 1024 * 1024;

    public static async Task RunAsync(MFilesSettings settings, string[] args)
    {
        int id = RecipeHelpers.IntArg(args, 0, 437);
        string folder = RecipeHelpers.StringArg(args, 1) ?? Path.Combine(Path.GetTempPath(), "mfiles-grpc-samples");
        Directory.CreateDirectory(folder);
        await using var connection = await MFilesConnection.ConnectAsync(settings, RecipeHelpers.ClientName);
        var objects = new IRPCObjectOperations.IRPCObjectOperationsClient(connection.CallInvoker);

        // The latest version lists the files.
        var latest = (await objects.GetObjectInfoAndPropertiesAsync(new GetObjectInfoAndPropertiesRequest
        {
            ObjId = ObjId(0, id),
            LatestVersion = true,
        })).ObjectInfo;
        Console.WriteLine(RecipeHelpers.Describe(latest));

        foreach (var file in latest.VersionInfo.Files)
        {
            string name = $"{file.Title}.{file.Extension}";
            // A title can contain characters that are not allowed in file names, such as "/".
            string path = Path.Combine(folder, SafeFileName(name));
            long size = await DownloadAsync(objects, latest.ObjectInfo.ObjId, file.FileVer, path);
            Console.WriteLine($"  Downloaded {name} ({size} bytes) to {path}");
        }
    }

    /// <summary>Replaces the characters Windows does not allow in file names.</summary>
    private static string SafeFileName(string name) =>
        string.Concat(name.Select(c => "<>:\"/\\|?*".Contains(c) ? '_' : c));

    // [START download-file]
    /// <summary>
    /// Downloads one file version in blocks: DownloadFile_Begin opens a download session,
    /// DownloadFile_ReadBlock reads it, DownloadFile_Stop closes it.
    /// </summary>
    private static async Task<long> DownloadAsync(IRPCObjectOperations.IRPCObjectOperationsClient objects,
        ObjID objId, FileVer fileVer, string path)
    {
        var begin = await objects.DownloadFile_BeginAsync(new DownloadFile_BeginRequest
        {
            ObjFileVer = new ObjFileVer { ObjId = objId, FileVer = fileVer },
            Format = FileFormat.Native,
            PrepareFileForDownloading = true,
        });
        try
        {
            await using var output = System.IO.File.Create(path);
            long size = begin.FileOutline.Size;
            for (long offset = 0; offset < size;)
            {
                var block = await objects.DownloadFile_ReadBlockAsync(new DownloadFile_ReadBlockRequest
                {
                    DownloadId = begin.DownloadId,
                    BlockSize = (uint)Math.Min(BlockSize, size - offset),
                    Offset = offset,
                });
                if (block.Data.IsEmpty)
                    throw new IOException($"The server returned no data at offset {offset} of {size}.");
                block.Data.WriteTo(output);
                offset += block.Data.Length;
            }
            return size;
        }
        finally
        {
            await objects.DownloadFile_StopAsync(new DownloadFile_StopRequest { DownloadId = begin.DownloadId });
        }
    }
    // [END download-file]
}