using System.IO;

namespace EmbyToolbox.Services;

public sealed class SafeFileReplaceService
{
    public async Task ReplaceAsync(
        string originalPath,
        string finalPath,
        string tempOutputPath,
        IProgress<int>? progress,
        CancellationToken cancellationToken)
    {
        if (!File.Exists(tempOutputPath))
        {
            throw new IOException("Временный файл результата не найден.");
        }

        var tempInfo = new FileInfo(tempOutputPath);
        if (tempInfo.Length <= 0)
        {
            throw new IOException("Временный файл результата пуст.");
        }

        var backupPath = originalPath + ".bak_replace_tmp";
        var finalBackupPath = finalPath + ".bak_existing_tmp";
        if (File.Exists(backupPath))
        {
            File.Delete(backupPath);
        }

        if (File.Exists(finalBackupPath))
        {
            File.Delete(finalBackupPath);
        }

        File.Move(originalPath, backupPath, overwrite: false);
        try
        {
            if (!string.Equals(originalPath, finalPath, StringComparison.OrdinalIgnoreCase) && File.Exists(finalPath))
            {
                File.Move(finalPath, finalBackupPath, overwrite: false);
            }

            var sameRoot = string.Equals(Path.GetPathRoot(finalPath), Path.GetPathRoot(tempOutputPath), StringComparison.OrdinalIgnoreCase);
            if (sameRoot)
            {
                File.Move(tempOutputPath, finalPath, overwrite: true);
                progress?.Report(99);
            }
            else
            {
                await CopyWithProgressAsync(tempOutputPath, finalPath, progress, cancellationToken).ConfigureAwait(false);
                File.Delete(tempOutputPath);
            }

            var outInfo = new FileInfo(finalPath);
            if (!outInfo.Exists || outInfo.Length <= 0)
            {
                throw new IOException("Новый файл после замены невалиден.");
            }

            File.Delete(backupPath);
            if (File.Exists(finalBackupPath))
            {
                File.Delete(finalBackupPath);
            }
        }
        catch
        {
            try
            {
                if (File.Exists(finalPath))
                {
                    var i = new FileInfo(finalPath);
                    if (i.Length == 0)
                    {
                        File.Delete(finalPath);
                    }
                }
            }
            catch
            {
                // ignore
            }

            if (File.Exists(backupPath))
            {
                File.Move(backupPath, originalPath, overwrite: true);
            }

            if (File.Exists(finalBackupPath))
            {
                File.Move(finalBackupPath, finalPath, overwrite: true);
            }

            throw;
        }
    }

    private static async Task CopyWithProgressAsync(string src, string dst, IProgress<int>? progress, CancellationToken token)
    {
        const int bufferSize = 1024 * 1024;
        await using var input = new FileStream(src, FileMode.Open, FileAccess.Read, FileShare.Read, bufferSize, useAsync: true);
        await using var output = new FileStream(dst, FileMode.Create, FileAccess.Write, FileShare.None, bufferSize, useAsync: true);
        var total = input.Length;
        var copied = 0L;
        var buffer = new byte[bufferSize];
        while (true)
        {
            var read = await input.ReadAsync(buffer, token).ConfigureAwait(false);
            if (read <= 0)
            {
                break;
            }

            await output.WriteAsync(buffer.AsMemory(0, read), token).ConfigureAwait(false);
            copied += read;
            if (total > 0)
            {
                var frac = copied / (double)total;
                var extra = frac >= 1.0 ? 9 : (int)Math.Floor(frac * 10.0);
                extra = Math.Clamp(extra, 0, 9);
                progress?.Report(90 + extra);
            }
        }
    }
}