// Licensed to StellaOps under the BUSL-1.1 license.


using Blake3;
using StellaOps.ReachGraph.Schema;
using StellaOps.ReachGraph.Serialization;

namespace StellaOps.ReachGraph.Hashing;

/// <summary>
/// Computes BLAKE3-256 digests for reachability graphs using canonical serialization.
/// </summary>
public sealed partial class ReachGraphDigestComputer
{
    private readonly CanonicalReachGraphSerializer _serializer;

    public ReachGraphDigestComputer()
        : this(new CanonicalReachGraphSerializer())
    {
    }

    public ReachGraphDigestComputer(CanonicalReachGraphSerializer serializer)
    {
        _serializer = serializer ?? throw new ArgumentNullException(nameof(serializer));
    }

    /// <summary>
    /// Compute BLAKE3-256 digest of canonical JSON (excluding signatures).
    /// </summary>
    /// <param name="graph">The reachability graph to hash.</param>
    /// <returns>Digest in format "blake3:{hex}".</returns>
    public string ComputeDigest(ReachGraphMinimal graph)
    {
        ArgumentNullException.ThrowIfNull(graph);

        // Remove signatures before hashing (avoid circular dependency)
        var unsigned = graph with { Signatures = null };
        var canonical = _serializer.SerializeMinimal(unsigned);

        using var hasher = Hasher.New();
        hasher.Update(canonical);
        var hash = hasher.Finalize();

        return $"blake3:{Convert.ToHexString(hash.AsSpan()).ToLowerInvariant()}";
    }

    /// <summary>
    /// Compute BLAKE3-256 digest from raw canonical JSON bytes.
    /// </summary>
    /// <param name="canonicalJson">The canonical JSON bytes to hash.</param>
    /// <returns>Digest in format "blake3:{hex}".</returns>
    public static string ComputeDigest(ReadOnlySpan<byte> canonicalJson)
    {
        using var hasher = Hasher.New();
        hasher.Update(canonicalJson);
        var hash = hasher.Finalize();

        return $"blake3:{Convert.ToHexString(hash.AsSpan()).ToLowerInvariant()}";
    }

    /// <summary>
    /// Verify digest matches graph content.
    /// </summary>
    /// <param name="graph">The reachability graph to verify.</param>
    /// <param name="expectedDigest">The expected digest.</param>
    /// <returns>True if digest matches, false otherwise.</returns>
    public bool VerifyDigest(ReachGraphMinimal graph, string expectedDigest)
    {
        ArgumentNullException.ThrowIfNull(graph);
        ArgumentException.ThrowIfNullOrEmpty(expectedDigest);

        var computed = ComputeDigest(graph);
        return string.Equals(computed, expectedDigest, StringComparison.Ordinal);
    }

}