using System;
using System.IO;
using System.Security.Cryptography;
using System.Threading;
using System.Threading.Tasks;

namespace StellaOps.Scanner.Sbomer.BuildXPlugin.Surface;

internal static class SurfaceCasLayout
{
    internal const string DefaultBucket = "scanner-artifacts";
    internal const string DefaultRootPrefix = "scanner";
    private const string Sha256 = "sha256";

    public static string NormalizeDigest(string? digest)
    {
        if (string.IsNullOrWhiteSpace(digest))
        {
            throw new BuildxPluginException("Surface artefact digest cannot be empty.");
        }

        var trimmed = digest.Trim();
        return trimmed.Contains(':', StringComparison.Ordinal)
            ? trimmed
            : $"{Sha256}:{trimmed}";
    }

    public static string ExtractDigestValue(string normalizedDigest)
    {
        var parts = normalizedDigest.Split(':', 2, StringSplitOptions.TrimEntries | StringSplitOptions.RemoveEmptyEntries);
        return parts.Length == 2 ? parts[1] : normalizedDigest;
    }

    public static string BuildObjectKey(string rootPrefix, SurfaceCasKind kind, string normalizedDigest)
    {
        var digestValue = ExtractDigestValue(normalizedDigest);
        var prefix = kind switch
        {
            SurfaceCasKind.LayerFragments => "surface/payloads/layer-fragments",
            SurfaceCasKind.EntryTraceGraph => "surface/payloads/entrytrace",
            SurfaceCasKind.EntryTraceNdjson => "surface/payloads/entrytrace",
            SurfaceCasKind.Manifest => "surface/manifests",
            _ => "surface/unknown"
        };

        var extension = kind switch
        {
            SurfaceCasKind.LayerFragments => "layer-fragments.json",
            SurfaceCasKind.EntryTraceGraph => "entrytrace.graph.json",
            SurfaceCasKind.EntryTraceNdjson => "entrytrace.ndjson",
            SurfaceCasKind.Manifest => "surface.manifest.json",
            _ => "artifact.bin"
        };

        var normalizedRoot = string.IsNullOrWhiteSpace(rootPrefix)
            ? string.Empty
            : rootPrefix.Trim().Trim('/');

        var relative = $"{prefix}/{digestValue}/{extension}";
        return string.IsNullOrWhiteSpace(normalizedRoot) ? relative : $"{normalizedRoot}/{relative}";
    }

    public static string BuildCasUri(string bucket, string objectKey)
    {
        var normalizedBucket = string.IsNullOrWhiteSpace(bucket) ? DefaultBucket : bucket.Trim();
        var normalizedKey = string.IsNullOrWhiteSpace(objectKey) ? string.Empty : objectKey.Trim().TrimStart('/');
        return $"cas://{normalizedBucket}/{normalizedKey}";
    }

    public static string ComputeDigest(ReadOnlySpan<byte> content)
    {
        Span<byte> hash = stackalloc byte[32];
        SHA256.HashData(content, hash);
        return $"{Sha256}:{Convert.ToHexString(hash).ToLowerInvariant()}";
    }

    public static async Task<string> WriteBytesAsync(string rootDirectory, string objectKey, byte[] bytes, CancellationToken cancellationToken)
    {
        if (string.IsNullOrWhiteSpace(rootDirectory))
        {
            throw new BuildxPluginException("Surface cache root must be provided.");
        }

        var normalizedRoot = Path.GetFullPath(rootDirectory);
        var relativePath = objectKey.Replace('/', Path.DirectorySeparatorChar);
        var fullPath = Path.Combine(normalizedRoot, relativePath);
        var directory = Path.GetDirectoryName(fullPath);
        if (!string.IsNullOrWhiteSpace(directory))
        {
            Directory.CreateDirectory(directory);
        }

        await using var stream = new FileStream(
            fullPath,
            FileMode.Create,
            FileAccess.Write,
            FileShare.Read,
            bufferSize: 64 * 1024,
            options: FileOptions.Asynchronous | FileOptions.SequentialScan);
        await stream.WriteAsync(bytes.AsMemory(0, bytes.Length), cancellationToken).ConfigureAwait(false);
        await stream.FlushAsync(cancellationToken).ConfigureAwait(false);
        return fullPath;
    }
}

internal enum SurfaceCasKind
{
    LayerFragments,
    EntryTraceGraph,
    EntryTraceNdjson,
    Manifest
}