using System.Net;

using Google;

using Google.Cloud.Storage.V1;

namespace Ramstack.FileSystem.Google;

/// <summary>

/// Represents an implementation of <see cref="VirtualFile"/> that maps a file to a Google Cloud Storage object.

/// </summary>

internal sealed class GcsFile : VirtualFile

{

private readonly GoogleFileSystem _fs;

private string? _objectName;

/// <inheritdoc />

public override IVirtualFileSystem FileSystem => _fs;

/// <summary>

/// Initializes a new instance of the <see cref="GcsFile"/> class.

/// </summary>

/// <param name="fileSystem">The file system associated with this file.</param>

/// <param name="path">The path to the file.</param>

public GcsFile(GoogleFileSystem fileSystem, string path) : base(path) =>

_fs = fileSystem;

/// <summary>

/// Initializes a new instance of the <see cref="GcsFile"/> class.

/// </summary>

/// <param name="fileSystem">The file system associated with this file.</param>

/// <param name="path">The path to the file.</param>

/// <param name="properties">The properties of the file, if available.</param>

public GcsFile(GoogleFileSystem fileSystem, string path, VirtualNodeProperties? properties) : base(path, properties) =>

_fs = fileSystem;

/// <inheritdoc />

protected override async ValueTask<VirtualNodeProperties?> GetPropertiesCoreAsync(CancellationToken cancellationToken)

{

try

{

var obj = await _fs.StorageClient

.GetObjectAsync(_fs.BucketName, GetObjectName(), cancellationToken: cancellationToken)

.ConfigureAwait(false);

return VirtualNodeProperties.CreateFileProperties(

creationTime: obj.TimeCreatedDateTimeOffset.GetValueOrDefault(),

lastAccessTime: default,

lastWriteTime: obj.UpdatedDateTimeOffset.GetValueOrDefault(),

length: (long?)obj.Size ?? 0);

}

catch (GoogleApiException e) when (e.HttpStatusCode == HttpStatusCode.NotFound)

{

return null;

}

}

/// <inheritdoc />

protected override async ValueTask<Stream> OpenReadCoreAsync(CancellationToken cancellationToken)

{

var stream = CreateTempFileStream();

await _fs.StorageClient

.DownloadObjectAsync(_fs.BucketName, GetObjectName(), stream, cancellationToken: cancellationToken)

.ConfigureAwait(false);

stream.Position = 0;

return stream;

static FileStream CreateTempFileStream()

{

const int BufferSize = 4096;

const FileOptions Options = FileOptions.DeleteOnClose | FileOptions.Asynchronous;

var path = Path.Combine(Path.GetTempPath(), Path.GetRandomFileName());

return new FileStream(path, FileMode.Create, FileAccess.ReadWrite, FileShare.Read, BufferSize, Options);

}

}

/// <inheritdoc />

protected override ValueTask<Stream> OpenWriteCoreAsync(CancellationToken cancellationToken) =>

new ValueTask<Stream>(new GcsWriteStream(_fs, GetObjectName()));

/// <inheritdoc />

protected override async ValueTask WriteCoreAsync(Stream stream, bool overwrite, CancellationToken cancellationToken)

{

var obj = new global::Google.Apis.Storage.v1.Data.Object

{

Bucket = _fs.BucketName,

Name = GetObjectName()

};

var options = new UploadObjectOptions();

if (!overwrite)

options.IfGenerationMatch = 0;

await _fs.StorageClient

.UploadObjectAsync(obj, stream, options, cancellationToken)

.ConfigureAwait(false);

}

/// <inheritdoc />

protected override async ValueTask DeleteCoreAsync(CancellationToken cancellationToken)

{

try

{

await _fs.StorageClient

.DeleteObjectAsync(_fs.BucketName, GetObjectName(), cancellationToken: cancellationToken)

.ConfigureAwait(false);

}

catch (GoogleApiException e) when (e.HttpStatusCode == HttpStatusCode.NotFound)

{

// Object doesn't exist, which is fine for this operation

}

}

/// <inheritdoc />

protected override ValueTask CopyToCoreAsync(string destinationPath, bool overwrite, CancellationToken cancellationToken) =>

CopyObjectAsync(_fs.BucketName, GetObjectName(), _fs.BucketName, destinationPath[1..], overwrite, cancellationToken);

/// <inheritdoc />

protected override ValueTask CopyToCoreAsync(VirtualFile destination, bool overwrite, CancellationToken cancellationToken)

{

if (destination is GcsFile file)

return CopyObjectAsync(_fs.BucketName, GetObjectName(), file._fs.BucketName, file.GetObjectName(), overwrite, cancellationToken);

return base.CopyToCoreAsync(destination, overwrite, cancellationToken);

}

/// <summary>

/// Returns the object name associated with this file.

/// </summary>

/// <returns>

/// The object name used in Google Cloud Storage.

/// </returns>

internal string GetObjectName() =>

_objectName ??= FullName[1..];

/// <summary>

/// Asynchronously copies a source object to the specified destination.

/// </summary>

/// <param name="sourceBucket">The name of the source GCS bucket.</param>

/// <param name="sourceObjectName">The source object name.</param>

/// <param name="destinationBucket">The name of the destination GCS bucket.</param>

/// <param name="destinationObjectName">The destination object name.</param>

/// <param name="overwrite">A boolean value indicating whether to overwrite the destination object if it already exists.</param>

/// <param name="cancellationToken">An optional cancellation token to cancel the operation.</param>

/// <returns>

/// A <see cref="ValueTask"/> representing the asynchronous operation.

/// </returns>

private async ValueTask CopyObjectAsync(string sourceBucket, string sourceObjectName, string destinationBucket, string destinationObjectName, bool overwrite, CancellationToken cancellationToken)

{

if (sourceBucket == destinationBucket && sourceObjectName == destinationObjectName)

throw new IOException($"Cannot copy a file '{FullName}' to itself.");

var options = new CopyObjectOptions();

if (!overwrite)

options.IfGenerationMatch = 0;

await _fs.StorageClient

.CopyObjectAsync(sourceBucket, sourceObjectName, destinationBucket, destinationObjectName, options, cancellationToken)

.ConfigureAwait(false);

}

}