using System.Formats.Tar;
using System.IO;
using ZstdSharp;

namespace ParadoxSaveParser.WebAPI;

/// <summary>
/// Uploaded save is a zstd-compressed tar with files of the original save inside.
/// Game data is stored in entry with name from <see cref="GameSaveEntryNames"/>.
/// </summary>
public static class SaveArchive
{
    public static Task<long> GetGameDataSize(IOPath archivePath, Game game, CancellationToken ct)
    {
        return WithGameDataEntry(archivePath, game, ct,
            entry => Task.FromResult(entry.Length));
    }

    public static Task ExtractGameData(IOPath archivePath, Game game, Stream dest, long maxBytes,
        CancellationToken ct)
    {
        return WithGameDataEntry(archivePath, game, ct, async entry =>
        {
            if (entry.Length > maxBytes)
                throw new InvalidDataException(
                    $"Game data size ({entry.Length} bytes) exceeds limit ({maxBytes} bytes)");
            if (entry.DataStream is not null)
                await entry.DataStream.CopyToAsync(dest, ct);
            return true;
        });
    }

    private static async Task<T> WithGameDataEntry<T>(IOPath archivePath, Game game, CancellationToken ct,
        Func<TarEntry, Task<T>> action)
    {
        if (!GameSaveEntryNames.Map.TryGetValue(game, out string? entryName))
            throw new ArgumentOutOfRangeException(nameof(game), game, "No game data entry name for game");

        await using var file = File.OpenRead(archivePath);
        await using var zstd = new DecompressionStream(file);
        await using var tar = new TarReader(zstd);
        while (await tar.GetNextEntryAsync(copyData: false, ct) is { } entry)
        {
            if (entry.EntryType is not (TarEntryType.RegularFile or TarEntryType.V7RegularFile))
                continue;
            if (System.IO.Path.GetFileName(entry.Name) == entryName)
                return await action(entry);
        }

        throw new InvalidDataException($"Invalid save format: no '{entryName}' entry found");
    }
}