using Launcher.Next.Core;

namespace Launcher.Next.Infrastructure;

/// <summary>
/// Reads a catalog descriptor only. The returned source is later copied into
/// local immutable staging by <see cref="IPackageSynchronizer"/>; it is never
/// an active launch root.
/// </summary>
public sealed class FileSystemCatalogPackageAcquirer(string catalogRoot) : IPackageCatalogPackageAcquirer
{
    private const int MaxFiles = 256;
    private const long MaxBytes = 512L * 1024 * 1024;

    public async Task<CatalogPackage?> AcquireAsync(PackageRequirement requirement, CancellationToken cancellationToken)
    {
        var root = Path.GetFullPath(catalogRoot);
        var candidate = Path.GetFullPath(Path.Combine(root, requirement.PackageId, requirement.RequiredVersion));
        if (!Directory.Exists(root) || IsReparsePoint(root) || !IsWithin(root, candidate) || !Directory.Exists(candidate) || IsReparsePoint(candidate))
            return null;

        var manifestPath = Path.Combine(candidate, "package.manifest.json");
        if (!File.Exists(manifestPath) || IsReparsePoint(manifestPath))
            return null;

        var manifest = PackageManifestJson.Parse(await File.ReadAllTextAsync(manifestPath, cancellationToken));
        if (manifest.Files.Count > MaxFiles || manifest.Files.Sum(file => file.Length) > MaxBytes ||
            manifest.Files.Any(file => string.IsNullOrWhiteSpace(file.Path) || Path.IsPathRooted(file.Path) ||
                                      file.Path.Split(Path.DirectorySeparatorChar, Path.AltDirectorySeparatorChar).Any(segment => segment is ".." or ".")))
            return null;
        return new CatalogPackage(manifest, candidate);
    }

    private static bool IsWithin(string root, string candidate) =>
        candidate.StartsWith(Path.TrimEndingDirectorySeparator(root) + Path.DirectorySeparatorChar, StringComparison.OrdinalIgnoreCase);

    private static bool IsReparsePoint(string path) =>
        (File.GetAttributes(path) & FileAttributes.ReparsePoint) != 0;
}