using System;
using System.IO;
using System.Security.Cryptography;
using System.Text;
using System.Text.Json;
using System.Threading;
using System.Threading.Tasks;
using StellaOps.Scanner.Cache.Abstractions;

namespace StellaOps.Scanner.Reachability;

/// <summary>
/// Options for edge-bundle DSSE publishing.
/// </summary>
public sealed record EdgeBundlePublisherOptions
{
    /// <summary>
    /// Whether to publish DSSE envelopes for edge bundles.
    /// Default: true.
    /// </summary>
    public bool Enabled { get; init; } = true;

    /// <summary>
    /// Maximum number of edge-bundle DSSEs to publish to Rekor per graph.
    /// Default: 5 (capped to prevent volume spikes).
    /// </summary>
    public int MaxRekorPublishesPerGraph { get; init; } = 5;

    /// <summary>
    /// Whether to publish runtime-hit bundles.
    /// </summary>
    public bool PublishRuntimeHits { get; init; } = true;

    /// <summary>
    /// Whether to publish init-array/static-init bundles.
    /// </summary>
    public bool PublishInitArray { get; init; } = true;

    /// <summary>
    /// Whether to publish third-party edge bundles.
    /// </summary>
    public bool PublishThirdParty { get; init; } = false;

    /// <summary>
    /// Whether to publish contested (low-confidence) edge bundles.
    /// </summary>
    public bool PublishContested { get; init; } = false;

    /// <summary>
    /// Whether to publish revoked edge bundles.
    /// </summary>
    public bool PublishRevoked { get; init; } = true;

    /// <summary>
    /// Confidence threshold below which edges are considered contested.
    /// </summary>
    public double ContestedConfidenceThreshold { get; init; } = 0.5;
}

/// <summary>
/// Result of publishing an edge bundle.
/// </summary>
public sealed record EdgeBundlePublishResult(
    string BundleId,
    string GraphHash,
    EdgeBundleReason BundleReason,
    string ContentHash,
    string RelativePath,
    string CasUri,
    string DsseRelativePath,
    string DsseCasUri,
    string DsseDigest,
    int EdgeCount);

/// <summary>
/// Interface for edge-bundle DSSE publishing.
/// </summary>
public interface IEdgeBundlePublisher
{
    Task<EdgeBundlePublishResult> PublishAsync(
        EdgeBundle bundle,
        IFileContentAddressableStore cas,
        CancellationToken cancellationToken = default);
}

/// <summary>
/// Publishes edge bundles to CAS with deterministic DSSE envelopes.
/// CAS paths follow: cas://reachability/edges/{graph_hash}/{bundle_id}[.dsse]
/// </summary>
public sealed class EdgeBundlePublisher : IEdgeBundlePublisher
{
    private static readonly JsonSerializerOptions JsonOptions = new(JsonSerializerDefaults.Web)
    {
        WriteIndented = false,
        PropertyNamingPolicy = JsonNamingPolicy.CamelCase
    };

    public async Task<EdgeBundlePublishResult> PublishAsync(
        EdgeBundle bundle,
        IFileContentAddressableStore cas,
        CancellationToken cancellationToken = default)
    {
        ArgumentNullException.ThrowIfNull(bundle);
        ArgumentNullException.ThrowIfNull(cas);

        var canonical = bundle.Canonical();
        var contentHash = canonical.ComputeContentHash();
        var hashDigest = ExtractHashDigest(contentHash);
        var graphHashDigest = ExtractHashDigest(canonical.GraphHash);

        // Build the bundle JSON
        var bundleJson = SerializeBundle(canonical);

        // Store bundle JSON in CAS
        // Path: cas://reachability/edges/{graph_hash}/{bundle_id}
        var bundleKey = $"edges/{graphHashDigest}/{canonical.BundleId}";
        await using var bundleStream = new MemoryStream(bundleJson, writable: false);
        var bundleEntry = await cas.PutAsync(new FileCasPutRequest(bundleKey, bundleStream, leaveOpen: false), cancellationToken).ConfigureAwait(false);
        var casUri = $"cas://reachability/edges/{graphHashDigest}/{canonical.BundleId}";

        // Build and store DSSE envelope
        var dsse = BuildDeterministicEdgeBundleDsse(canonical, casUri, contentHash);
        await using var dsseStream = new MemoryStream(dsse.EnvelopeJson, writable: false);
        var dsseKey = $"edges/{graphHashDigest}/{canonical.BundleId}.dsse";
        var dsseEntry = await cas.PutAsync(new FileCasPutRequest(dsseKey, dsseStream, leaveOpen: false), cancellationToken).ConfigureAwait(false);
        var dsseCasUri = $"cas://reachability/edges/{graphHashDigest}/{canonical.BundleId}.dsse";

        return new EdgeBundlePublishResult(
            BundleId: canonical.BundleId,
            GraphHash: canonical.GraphHash,
            BundleReason: canonical.BundleReason,
            ContentHash: contentHash,
            RelativePath: bundleEntry.RelativePath,
            CasUri: casUri,
            DsseRelativePath: dsseEntry.RelativePath,
            DsseCasUri: dsseCasUri,
            DsseDigest: dsse.Digest,
            EdgeCount: canonical.Edges.Count);
    }

    private static byte[] SerializeBundle(EdgeBundle bundle)
    {
        var payload = new
        {
            schema = "edge-bundle-v1",
            bundleId = bundle.BundleId,
            graphHash = bundle.GraphHash,
            bundleReason = bundle.BundleReason.ToString(),
            customReason = bundle.CustomReason,
            generatedAt = bundle.GeneratedAt.ToString("O"),
            edges = bundle.Edges.Select(e => new
            {
                from = e.From,
                to = e.To,
                kind = e.Kind,
                reason = e.Reason.ToString(),
                revoked = e.Revoked,
                confidence = e.Confidence,
                purl = e.Purl,
                symbolDigest = e.SymbolDigest,
                evidence = e.Evidence
            }).ToArray()
        };

        return Encoding.UTF8.GetBytes(JsonSerializer.Serialize(payload, JsonOptions));
    }

    private static EdgeBundleDsse BuildDeterministicEdgeBundleDsse(EdgeBundle bundle, string casUri, string contentHash)
    {
        var predicate = new
        {
            version = "1.0",
            schema = "edge-bundle-v1",
            bundleId = bundle.BundleId,
            graphHash = bundle.GraphHash,
            bundleReason = bundle.BundleReason.ToString(),
            hashes = new
            {
                contentHash
            },
            cas = new
            {
                location = casUri
            },
            edges = new
            {
                total = bundle.Edges.Count,
                revoked = bundle.Edges.Count(e => e.Revoked),
                reasons = bundle.Edges
                    .GroupBy(e => e.Reason)
                    .OrderBy(g => (int)g.Key)
                    .ToDictionary(g => g.Key.ToString(), g => g.Count())
            }
        };

        var payloadType = "application/vnd.stellaops.edgebundle.predicate+json";
        var payloadBytes = Encoding.UTF8.GetBytes(JsonSerializer.Serialize(predicate, JsonOptions));

        var signatureHex = ComputeSha256Hex(payloadBytes);
        var envelope = new
        {
            payloadType,
            payload = Base64UrlEncode(payloadBytes),
            signatures = new[]
            {
                new { keyid = "scanner-deterministic", sig = Base64UrlEncode(Encoding.UTF8.GetBytes(signatureHex)) }
            }
        };

        var envelopeJson = Encoding.UTF8.GetBytes(JsonSerializer.Serialize(envelope, JsonOptions));

        return new EdgeBundleDsse(envelopeJson, $"sha256:{signatureHex}");
    }

    private static string ComputeSha256Hex(ReadOnlySpan<byte> data)
    {
        Span<byte> hash = stackalloc byte[32];
        SHA256.HashData(data, hash);
        return Convert.ToHexString(hash).ToLowerInvariant();
    }

    private static string Base64UrlEncode(ReadOnlySpan<byte> data)
    {
        var base64 = Convert.ToBase64String(data);
        return base64.Replace("+", "-").Replace("/", "_").TrimEnd('=');
    }

    private static string ExtractHashDigest(string prefixedHash)
    {
        var colonIndex = prefixedHash.IndexOf(':');
        return colonIndex >= 0 ? prefixedHash[(colonIndex + 1)..] : prefixedHash;
    }
}

internal sealed record EdgeBundleDsse(byte[] EnvelopeJson, string Digest);