// SPDX-License-Identifier: BUSL-1.1
// Sprint: SPRINT_5200_0001_0001 - Starter Policy Template
// Task: T7 - Policy Pack Distribution

using System.Collections.Immutable;
using System.IO.Compression;
using System.Security.Cryptography;
using System.Text;
using System.Text.Json;
using Microsoft.Extensions.Logging;

namespace StellaOps.Policy.Registry.Distribution;

/// <summary>
/// Service for exporting and importing policy packs as offline bundles.
/// Supports air-gapped environments where OCI registries are not available.
/// </summary>
public sealed class PolicyPackOfflineBundleService
{
    private const string SchemaVersion = "1.0.0";
    private const string BlobsDirectory = "blobs/sha256";
    private const string ManifestFile = "index.json";

    private readonly ILogger<PolicyPackOfflineBundleService> _logger;
    private readonly TimeProvider _timeProvider;

    private static readonly JsonSerializerOptions JsonOptions = new(JsonSerializerDefaults.Web)
    {
        WriteIndented = true
    };

    public PolicyPackOfflineBundleService(
        ILogger<PolicyPackOfflineBundleService>? logger = null,
        TimeProvider? timeProvider = null)
    {
        _logger = logger ?? Microsoft.Extensions.Logging.Abstractions.NullLogger<PolicyPackOfflineBundleService>.Instance;
        _timeProvider = timeProvider ?? TimeProvider.System;
    }

    /// <summary>
    /// Exports a policy pack to an offline bundle.
    /// </summary>
    public async Task<PolicyPackBundleExportResult> ExportAsync(
        PolicyPackBundleExportRequest request,
        string outputPath,
        CancellationToken cancellationToken = default)
    {
        ArgumentNullException.ThrowIfNull(request);
        ArgumentException.ThrowIfNullOrWhiteSpace(outputPath);

        if (request.PackContent.Length == 0)
        {
            return new PolicyPackBundleExportResult
            {
                Success = false,
                Error = "Pack content cannot be empty"
            };
        }

        try
        {
            _logger.LogInformation(
                "Exporting policy pack {PackName}:{PackVersion} to {OutputPath}",
                request.PackName, request.PackVersion, outputPath);

            // Create temp directory for bundle layout
            var tempDir = Path.Combine(Path.GetTempPath(), $"stellaops-policy-bundle-{Guid.NewGuid():N}");
            Directory.CreateDirectory(tempDir);
            var blobsDir = Path.Combine(tempDir, BlobsDirectory);
            Directory.CreateDirectory(blobsDir);

            try
            {
                var artifacts = new List<PolicyPackBundleArtifact>();

                // Export main pack content
                var packDigest = ComputeDigest(request.PackContent);
                var packPath = Path.Combine(blobsDir, packDigest);
                await File.WriteAllBytesAsync(packPath, request.PackContent, cancellationToken).ConfigureAwait(false);

                artifacts.Add(new PolicyPackBundleArtifact
                {
                    Digest = $"sha256:{packDigest}",
                    MediaType = "application/vnd.stellaops.policy-pack.yaml.v1",
                    Size = request.PackContent.Length,
                    Path = $"{BlobsDirectory}/{packDigest}",
                    Annotations = ImmutableDictionary<string, string>.Empty
                        .Add("stellaops.policy.pack.name", request.PackName)
                        .Add("stellaops.policy.pack.version", request.PackVersion)
                        .Add("org.opencontainers.image.title", $"{request.PackName}.yaml")
                });

                // Export overrides
                if (request.Overrides?.Count > 0)
                {
                    foreach (var (env, content) in request.Overrides)
                    {
                        var overrideDigest = ComputeDigest(content);
                        var overridePath = Path.Combine(blobsDir, overrideDigest);
                        await File.WriteAllBytesAsync(overridePath, content, cancellationToken).ConfigureAwait(false);

                        artifacts.Add(new PolicyPackBundleArtifact
                        {
                            Digest = $"sha256:{overrideDigest}",
                            MediaType = "application/vnd.stellaops.policy-pack.override.v1+json",
                            Size = content.Length,
                            Path = $"{BlobsDirectory}/{overrideDigest}",
                            Annotations = ImmutableDictionary<string, string>.Empty
                                .Add("stellaops.policy.pack.override.env", env)
                                .Add("org.opencontainers.image.title", $"overrides/{env}.yaml")
                        });
                    }
                }

                // Export attestation if provided
                if (request.Attestation?.Length > 0)
                {
                    var attestDigest = ComputeDigest(request.Attestation);
                    var attestPath = Path.Combine(blobsDir, attestDigest);
                    await File.WriteAllBytesAsync(attestPath, request.Attestation, cancellationToken).ConfigureAwait(false);

                    artifacts.Add(new PolicyPackBundleArtifact
                    {
                        Digest = $"sha256:{attestDigest}",
                        MediaType = "application/vnd.stellaops.policy-pack.attestation.v1+json",
                        Size = request.Attestation.Length,
                        Path = $"{BlobsDirectory}/{attestDigest}",
                        Annotations = ImmutableDictionary<string, string>.Empty
                            .Add("org.opencontainers.image.title", "attestation.dsse.json")
                    });
                }

                // Create manifest
                var manifest = new PolicyPackBundleManifest
                {
                    SchemaVersion = SchemaVersion,
                    CreatedAt = _timeProvider.GetUtcNow(),
                    PackName = request.PackName,
                    PackVersion = request.PackVersion,
                    Artifacts = artifacts.ToImmutableArray(),
                    Metrics = new PolicyPackBundleMetrics
                    {
                        ArtifactCount = artifacts.Count,
                        OverrideCount = request.Overrides?.Count ?? 0,
                        HasAttestation = request.Attestation?.Length > 0,
                        TotalSize = artifacts.Sum(a => a.Size)
                    },
                    ManifestDigest = "" // Will be set after serialization
                };

                var manifestJson = JsonSerializer.Serialize(manifest, JsonOptions);
                var manifestDigest = ComputeDigest(Encoding.UTF8.GetBytes(manifestJson));
                manifest = manifest with { ManifestDigest = $"sha256:{manifestDigest}" };
                manifestJson = JsonSerializer.Serialize(manifest, JsonOptions);

                await File.WriteAllTextAsync(
                    Path.Combine(tempDir, ManifestFile),
                    manifestJson,
                    cancellationToken).ConfigureAwait(false);

                // Create tar.gz
                using (var fs = File.Create(outputPath))
                using (var gzip = new GZipStream(fs, CompressionLevel.Optimal))
                {
                    await CreateTarAsync(tempDir, gzip, cancellationToken).ConfigureAwait(false);
                }

                var bundleDigest = ComputeFileDigest(outputPath);

                _logger.LogInformation(
                    "Bundle exported: {ArtifactCount} artifacts, {TotalSize:N0} bytes",
                    manifest.Metrics.ArtifactCount, manifest.Metrics.TotalSize);

                return new PolicyPackBundleExportResult
                {
                    Success = true,
                    BundlePath = outputPath,
                    BundleDigest = $"sha256:{bundleDigest}",
                    Metrics = manifest.Metrics
                };
            }
            finally
            {
                // Cleanup temp directory
                try { Directory.Delete(tempDir, true); } catch { /* Ignore cleanup errors */ }
            }
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Failed to export policy pack bundle");
            return new PolicyPackBundleExportResult
            {
                Success = false,
                Error = ex.Message
            };
        }
    }

    /// <summary>
    /// Imports a policy pack from an offline bundle.
    /// </summary>
    public async Task<PolicyPackBundleImportResult> ImportAsync(
        string bundlePath,
        bool verifyIntegrity = true,
        CancellationToken cancellationToken = default)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(bundlePath);

        if (!File.Exists(bundlePath))
        {
            return new PolicyPackBundleImportResult
            {
                Success = false,
                Error = $"Bundle not found: {bundlePath}"
            };
        }

        try
        {
            _logger.LogInformation("Importing policy pack bundle from {BundlePath}", bundlePath);

            // Extract to temp directory
            var tempDir = Path.Combine(Path.GetTempPath(), $"stellaops-policy-import-{Guid.NewGuid():N}");
            Directory.CreateDirectory(tempDir);

            try
            {
                // Extract tar.gz
                await using (var fs = File.OpenRead(bundlePath))
                await using (var gzip = new GZipStream(fs, CompressionMode.Decompress))
                {
                    await ExtractTarAsync(gzip, tempDir, cancellationToken).ConfigureAwait(false);
                }

                // Read manifest
                var manifestPath = Path.Combine(tempDir, ManifestFile);
                if (!File.Exists(manifestPath))
                {
                    return new PolicyPackBundleImportResult
                    {
                        Success = false,
                        Error = "Bundle manifest not found"
                    };
                }

                var manifestJson = await File.ReadAllTextAsync(manifestPath, cancellationToken).ConfigureAwait(false);
                var manifest = JsonSerializer.Deserialize<PolicyPackBundleManifest>(manifestJson, JsonOptions);

                if (manifest is null)
                {
                    return new PolicyPackBundleImportResult
                    {
                        Success = false,
                        Error = "Failed to parse bundle manifest"
                    };
                }

                // Verify integrity if requested
                bool integrityVerified = false;
                if (verifyIntegrity)
                {
                    integrityVerified = await VerifyBundleIntegrityAsync(tempDir, manifest, cancellationToken)
                        .ConfigureAwait(false);

                    if (!integrityVerified)
                    {
                        return new PolicyPackBundleImportResult
                        {
                            Success = false,
                            Error = "Bundle integrity verification failed"
                        };
                    }
                }

                // Read artifacts
                byte[]? packContent = null;
                var overrides = new Dictionary<string, byte[]>();
                byte[]? attestation = null;

                foreach (var artifact in manifest.Artifacts)
                {
                    var artifactPath = Path.Combine(tempDir, artifact.Path);
                    if (!File.Exists(artifactPath))
                    {
                        _logger.LogWarning("Artifact not found in bundle: {Path}", artifact.Path);
                        continue;
                    }

                    var content = await File.ReadAllBytesAsync(artifactPath, cancellationToken).ConfigureAwait(false);

                    if (artifact.MediaType.Contains("policy-pack.yaml"))
                    {
                        packContent = content;
                    }
                    else if (artifact.MediaType.Contains("override"))
                    {
                        var env = artifact.Annotations?.GetValueOrDefault("stellaops.policy.pack.override.env");
                        if (!string.IsNullOrEmpty(env))
                        {
                            overrides[env] = content;
                        }
                    }
                    else if (artifact.MediaType.Contains("attestation"))
                    {
                        attestation = content;
                    }
                }

                if (packContent is null)
                {
                    return new PolicyPackBundleImportResult
                    {
                        Success = false,
                        Error = "No policy pack content found in bundle"
                    };
                }

                _logger.LogInformation(
                    "Bundle imported: {PackName}:{PackVersion}, {OverrideCount} overrides",
                    manifest.PackName, manifest.PackVersion, overrides.Count);

                return new PolicyPackBundleImportResult
                {
                    Success = true,
                    PackName = manifest.PackName,
                    PackVersion = manifest.PackVersion,
                    PackContent = packContent,
                    Overrides = overrides.Count > 0 ? overrides : null,
                    Attestation = attestation,
                    IntegrityVerified = integrityVerified
                };
            }
            finally
            {
                // Cleanup temp directory
                try { Directory.Delete(tempDir, true); } catch { /* Ignore cleanup errors */ }
            }
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Failed to import policy pack bundle from {BundlePath}", bundlePath);
            return new PolicyPackBundleImportResult
            {
                Success = false,
                Error = ex.Message
            };
        }
    }

    private async Task<bool> VerifyBundleIntegrityAsync(
        string tempDir,
        PolicyPackBundleManifest manifest,
        CancellationToken cancellationToken)
    {
        foreach (var artifact in manifest.Artifacts)
        {
            var artifactPath = Path.Combine(tempDir, artifact.Path);
            if (!File.Exists(artifactPath))
            {
                _logger.LogWarning("Missing artifact: {Path}", artifact.Path);
                return false;
            }

            var data = await File.ReadAllBytesAsync(artifactPath, cancellationToken).ConfigureAwait(false);
            var actualDigest = $"sha256:{ComputeDigest(data)}";

            if (!string.Equals(actualDigest, artifact.Digest, StringComparison.OrdinalIgnoreCase))
            {
                _logger.LogWarning(
                    "Digest mismatch for {Path}: expected {Expected}, got {Actual}",
                    artifact.Path, artifact.Digest, actualDigest);
                return false;
            }
        }

        return true;
    }

    private static string ComputeDigest(byte[] data)
    {
        var hash = SHA256.HashData(data);
        return Convert.ToHexString(hash).ToLowerInvariant();
    }

    private static string ComputeFileDigest(string path)
    {
        using var fs = File.OpenRead(path);
        var hash = SHA256.HashData(fs);
        return Convert.ToHexString(hash).ToLowerInvariant();
    }

    private static async Task CreateTarAsync(string sourceDir, Stream output, CancellationToken cancellationToken)
    {
        // Simplified tar creation - in production, use a proper tar library
        var files = Directory.GetFiles(sourceDir, "*", SearchOption.AllDirectories);
        using var writer = new BinaryWriter(output, Encoding.UTF8, leaveOpen: true);

        foreach (var file in files)
        {
            var relativePath = Path.GetRelativePath(sourceDir, file).Replace('\\', '/');
            var content = await File.ReadAllBytesAsync(file, cancellationToken).ConfigureAwait(false);

            // Write simple header
            var header = Encoding.UTF8.GetBytes($"FILE:{relativePath}:{content.Length}\n");
            writer.Write(header);
            writer.Write(content);
        }
    }

    private static async Task ExtractTarAsync(Stream input, string targetDir, CancellationToken cancellationToken)
    {
        // Simplified tar extraction - in production, use a proper tar library
        using var memoryStream = new MemoryStream();
        await input.CopyToAsync(memoryStream, cancellationToken).ConfigureAwait(false);
        memoryStream.Position = 0;

        var textReader = new StreamReader(memoryStream, Encoding.UTF8, leaveOpen: true);

        while (memoryStream.Position < memoryStream.Length)
        {
            var headerLine = textReader.ReadLine();
            if (string.IsNullOrEmpty(headerLine) || !headerLine.StartsWith("FILE:"))
                break;

            var parts = headerLine[5..].Split(':');
            if (parts.Length != 2 || !int.TryParse(parts[1], out var size))
                break;

            var relativePath = parts[0];
            var fullPath = Path.Combine(targetDir, relativePath);
            Directory.CreateDirectory(Path.GetDirectoryName(fullPath)!);

            var content = new byte[size];
            _ = memoryStream.Read(content, 0, size);
            await File.WriteAllBytesAsync(fullPath, content, cancellationToken).ConfigureAwait(false);
        }
    }
}

/// <summary>
/// Request to export a policy pack to offline bundle.
/// </summary>
public sealed record PolicyPackBundleExportRequest
{
    public required string PackName { get; init; }
    public required string PackVersion { get; init; }
    public required byte[] PackContent { get; init; }
    public IReadOnlyDictionary<string, byte[]>? Overrides { get; init; }
    public byte[]? Attestation { get; init; }
}

/// <summary>
/// Result of policy pack bundle export.
/// </summary>
public sealed record PolicyPackBundleExportResult
{
    public required bool Success { get; init; }
    public string? BundlePath { get; init; }
    public string? BundleDigest { get; init; }
    public PolicyPackBundleMetrics? Metrics { get; init; }
    public string? Error { get; init; }
}

/// <summary>
/// Result of policy pack bundle import.
/// </summary>
public sealed record PolicyPackBundleImportResult
{
    public required bool Success { get; init; }
    public string? PackName { get; init; }
    public string? PackVersion { get; init; }
    public byte[]? PackContent { get; init; }
    public IReadOnlyDictionary<string, byte[]>? Overrides { get; init; }
    public byte[]? Attestation { get; init; }
    public bool IntegrityVerified { get; init; }
    public string? Error { get; init; }
}

/// <summary>
/// Bundle manifest for policy pack.
/// </summary>
public sealed record PolicyPackBundleManifest
{
    public required string SchemaVersion { get; init; }
    public required DateTimeOffset CreatedAt { get; init; }
    public required string PackName { get; init; }
    public required string PackVersion { get; init; }
    public required ImmutableArray<PolicyPackBundleArtifact> Artifacts { get; init; }
    public required PolicyPackBundleMetrics Metrics { get; init; }
    public required string ManifestDigest { get; init; }
}

/// <summary>
/// Artifact entry in bundle manifest.
/// </summary>
public sealed record PolicyPackBundleArtifact
{
    public required string Digest { get; init; }
    public required string MediaType { get; init; }
    public required long Size { get; init; }
    public required string Path { get; init; }
    public ImmutableDictionary<string, string>? Annotations { get; init; }
}

/// <summary>
/// Metrics about bundle contents.
/// </summary>
public sealed record PolicyPackBundleMetrics
{
    public int ArtifactCount { get; init; }
    public int OverrideCount { get; init; }
    public bool HasAttestation { get; init; }
    public long TotalSize { get; init; }
}