using System.Security.Cryptography;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Logging.Abstractions;
using StellaOps.Policy.Snapshots;

namespace StellaOps.Policy.Replay;

/// <summary>
/// Resolves knowledge sources from snapshot descriptors.
/// </summary>
public sealed class KnowledgeSourceResolver : IKnowledgeSourceResolver
{
    private readonly ISnapshotStore _snapshotStore;
    private readonly ILogger<KnowledgeSourceResolver> _logger;

    public KnowledgeSourceResolver(
        ISnapshotStore snapshotStore,
        ILogger<KnowledgeSourceResolver>? logger = null)
    {
        _snapshotStore = snapshotStore ?? throw new ArgumentNullException(nameof(snapshotStore));
        _logger = logger ?? NullLogger<KnowledgeSourceResolver>.Instance;
    }

    /// <summary>
    /// Resolves a knowledge source to its actual content.
    /// </summary>
    public async Task<ResolvedSource?> ResolveAsync(
        KnowledgeSourceDescriptor descriptor,
        bool allowNetworkFetch,
        CancellationToken ct = default)
    {
        _logger.LogDebug("Resolving source {Name} ({Type})", descriptor.Name, descriptor.Type);

        // Try bundled content first
        if (descriptor.InclusionMode != SourceInclusionMode.Referenced &&
            descriptor.BundlePath is not null)
        {
            var bundled = await ResolveBundledAsync(descriptor, ct).ConfigureAwait(false);
            if (bundled is not null)
                return bundled;
        }

        // Try local store by digest
        var local = await ResolveFromLocalStoreAsync(descriptor, ct).ConfigureAwait(false);
        if (local is not null)
            return local;

        // Network fetch not implemented yet (air-gap safe default)
        if (allowNetworkFetch && descriptor.Origin is not null)
        {
            _logger.LogWarning("Network fetch not implemented for {Name}", descriptor.Name);
        }

        _logger.LogWarning("Failed to resolve source {Name} with digest {Digest}",
            descriptor.Name, descriptor.Digest);

        return null;
    }

    private async Task<ResolvedSource?> ResolveBundledAsync(
        KnowledgeSourceDescriptor descriptor,
        CancellationToken ct)
    {
        try
        {
            var content = await _snapshotStore.GetBundledContentAsync(descriptor.BundlePath!, ct)
                .ConfigureAwait(false);

            if (content is null)
                return null;

            // Verify digest
            var actualDigest = ComputeDigest(content);
            if (actualDigest != descriptor.Digest)
            {
                _logger.LogWarning(
                    "Bundled source {Name} digest mismatch: expected {Expected}, got {Actual}",
                    descriptor.Name, descriptor.Digest, actualDigest);
                return null;
            }

            return new ResolvedSource(
                descriptor.Name,
                descriptor.Type,
                content,
                SourceResolutionMethod.Bundled);
        }
        catch (Exception ex)
        {
            _logger.LogWarning(ex, "Failed to resolve bundled source {Name}", descriptor.Name);
            return null;
        }
    }

    private async Task<ResolvedSource?> ResolveFromLocalStoreAsync(
        KnowledgeSourceDescriptor descriptor,
        CancellationToken ct)
    {
        try
        {
            var content = await _snapshotStore.GetByDigestAsync(descriptor.Digest, ct)
                .ConfigureAwait(false);

            if (content is null)
                return null;

            return new ResolvedSource(
                descriptor.Name,
                descriptor.Type,
                content,
                SourceResolutionMethod.LocalStore);
        }
        catch (Exception ex)
        {
            _logger.LogWarning(ex, "Failed to resolve source {Name} from local store", descriptor.Name);
            return null;
        }
    }

    private static string ComputeDigest(byte[] content)
    {
        var hash = SHA256.HashData(content);
        return $"sha256:{Convert.ToHexString(hash).ToLowerInvariant()}";
    }
}

/// <summary>
/// Resolved knowledge source with content.
/// </summary>
public sealed record ResolvedSource(
    string Name,
    string Type,
    byte[] Content,
    SourceResolutionMethod Method);

/// <summary>
/// Method used to resolve a source.
/// </summary>
public enum SourceResolutionMethod
{
    Bundled,
    LocalStore,
    NetworkFetch
}

/// <summary>
/// Interface for source resolution.
/// </summary>
public interface IKnowledgeSourceResolver
{
    Task<ResolvedSource?> ResolveAsync(
        KnowledgeSourceDescriptor descriptor,
        bool allowNetworkFetch,
        CancellationToken ct = default);
}

/// <summary>
/// Frozen inputs for replay.
/// </summary>
public sealed class FrozenInputs
{
    public Dictionary<string, ResolvedSource> ResolvedSources { get; } = new();
    public IReadOnlyList<string> MissingSources { get; init; } = [];
    public bool IsComplete => MissingSources.Count == 0;
}

/// <summary>
/// Builder for frozen inputs.
/// </summary>
public sealed class FrozenInputsBuilder
{
    private readonly Dictionary<string, ResolvedSource> _sources = new();

    public FrozenInputsBuilder AddSource(string name, ResolvedSource source)
    {
        _sources[name] = source;
        return this;
    }

    public FrozenInputs Build(IReadOnlyList<string> missingSources)
    {
        var inputs = new FrozenInputs
        {
            MissingSources = missingSources
        };

        // Copy resolved sources
        foreach (var kvp in _sources)
        {
            inputs.ResolvedSources[kvp.Key] = kvp.Value;
        }

        return inputs;
    }
}