// <copyright file="EvidenceResolver.cs" company="StellaOps">
// Copyright (c) StellaOps. Licensed under the BUSL-1.1.
// </copyright>

using System.Collections.Immutable;
using System.Security.Cryptography;
using System.Text;
using System.Text.Json;
using Microsoft.Extensions.Logging;
using StellaOps.Evidence.Pack.Models;

namespace StellaOps.Evidence.Pack;

/// <summary>
/// Implementation of <see cref="IEvidenceResolver"/> with pluggable type resolvers.
/// Sprint: SPRINT_20260109_011_005 Task: EVPK-004
/// </summary>
internal sealed class EvidenceResolver : IEvidenceResolver
{
    private readonly ImmutableDictionary<string, ITypeResolver> _resolvers;
    private readonly ILogger<EvidenceResolver> _logger;

    /// <summary>
    /// Creates a new EvidenceResolver.
    /// </summary>
    public EvidenceResolver(
        IEnumerable<ITypeResolver> resolvers,
        ILogger<EvidenceResolver> logger)
    {
        _logger = logger ?? throw new ArgumentNullException(nameof(logger));

        var builder = ImmutableDictionary.CreateBuilder<string, ITypeResolver>(
            StringComparer.OrdinalIgnoreCase);

        foreach (var resolver in resolvers)
        {
            foreach (var type in resolver.SupportedTypes)
            {
                builder[type] = resolver;
            }
        }

        _resolvers = builder.ToImmutable();
        _logger.LogDebug("Initialized EvidenceResolver with {Count} type resolvers", _resolvers.Count);
    }

    /// <inheritdoc/>
    public async Task<ResolvedEvidence> ResolveAndSnapshotAsync(
        string type,
        string path,
        CancellationToken cancellationToken)
    {
        _logger.LogDebug("Resolving evidence: type={Type}, path={Path}", type, path);

        if (!_resolvers.TryGetValue(type, out var resolver))
        {
            throw new UnsupportedEvidenceTypeException(type, _resolvers.Keys);
        }

        var snapshot = await resolver.ResolveAsync(type, path, cancellationToken)
            .ConfigureAwait(false);

        var digest = ComputeSnapshotDigest(snapshot);

        _logger.LogDebug("Resolved evidence: type={Type}, digest={Digest}", type, digest);

        return new ResolvedEvidence
        {
            Snapshot = snapshot,
            Digest = digest,
            ResolvedAt = DateTimeOffset.UtcNow
        };
    }

    /// <inheritdoc/>
    public async Task<EvidenceResolutionResult> VerifyEvidenceAsync(
        EvidenceItem evidence,
        CancellationToken cancellationToken)
    {
        _logger.LogDebug("Verifying evidence: {EvidenceId}", evidence.EvidenceId);

        try
        {
            // Parse the URI to get type and path
            var (type, path) = ParseStellaUri(evidence.Uri);

            if (!_resolvers.TryGetValue(type, out var resolver))
            {
                return new EvidenceResolutionResult
                {
                    EvidenceId = evidence.EvidenceId,
                    Uri = evidence.Uri,
                    Resolved = false,
                    DigestMatches = false,
                    Error = $"Unsupported evidence type: {type}"
                };
            }

            // Resolve current state
            var currentSnapshot = await resolver.ResolveAsync(type, path, cancellationToken)
                .ConfigureAwait(false);

            var currentDigest = ComputeSnapshotDigest(currentSnapshot);
            var digestMatches = string.Equals(
                evidence.Digest,
                currentDigest,
                StringComparison.OrdinalIgnoreCase);

            _logger.LogDebug(
                "Evidence {EvidenceId} verification: digestMatches={DigestMatches}",
                evidence.EvidenceId, digestMatches);

            return new EvidenceResolutionResult
            {
                EvidenceId = evidence.EvidenceId,
                Uri = evidence.Uri,
                Resolved = true,
                DigestMatches = digestMatches,
                Error = digestMatches ? null : "Digest mismatch - evidence has changed since collection"
            };
        }
        catch (EvidenceNotFoundException ex)
        {
            _logger.LogWarning(ex, "Evidence not found: {EvidenceId}", evidence.EvidenceId);
            return new EvidenceResolutionResult
            {
                EvidenceId = evidence.EvidenceId,
                Uri = evidence.Uri,
                Resolved = false,
                DigestMatches = false,
                Error = ex.Message
            };
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Failed to verify evidence: {EvidenceId}", evidence.EvidenceId);
            return new EvidenceResolutionResult
            {
                EvidenceId = evidence.EvidenceId,
                Uri = evidence.Uri,
                Resolved = false,
                DigestMatches = false,
                Error = $"Verification failed: {ex.Message}"
            };
        }
    }

    /// <inheritdoc/>
    public bool SupportsType(string type)
    {
        return _resolvers.ContainsKey(type);
    }

    private static (string type, string path) ParseStellaUri(string uri)
    {
        // Expected format: stella://type/path
        if (!uri.StartsWith("stella://", StringComparison.OrdinalIgnoreCase))
        {
            throw new ArgumentException($"Invalid evidence URI format: {uri}. Expected stella://type/path");
        }

        var withoutScheme = uri[9..]; // Remove "stella://"
        var slashIndex = withoutScheme.IndexOf('/', StringComparison.Ordinal);

        if (slashIndex <= 0)
        {
            throw new ArgumentException($"Invalid evidence URI format: {uri}. Missing path.");
        }

        var type = withoutScheme[..slashIndex];
        var path = withoutScheme[(slashIndex + 1)..];

        return (type, path);
    }

    private static string ComputeSnapshotDigest(EvidenceSnapshot snapshot)
    {
        // Canonical JSON for digest computation
        var json = JsonSerializer.Serialize(new
        {
            type = snapshot.Type,
            data = snapshot.Data.OrderBy(kvp => kvp.Key, StringComparer.Ordinal)
                .ToDictionary(kvp => kvp.Key, kvp => kvp.Value)
        }, new JsonSerializerOptions
        {
            PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
            WriteIndented = false
        });

        var hash = SHA256.HashData(Encoding.UTF8.GetBytes(json));
        return $"sha256:{Convert.ToHexStringLower(hash)}";
    }
}

/// <summary>
/// Interface for type-specific evidence resolvers.
/// </summary>
public interface ITypeResolver
{
    /// <summary>
    /// Gets the evidence types this resolver can handle.
    /// </summary>
    IEnumerable<string> SupportedTypes { get; }

    /// <summary>
    /// Resolves evidence and creates a snapshot.
    /// </summary>
    Task<EvidenceSnapshot> ResolveAsync(
        string type,
        string path,
        CancellationToken cancellationToken);
}

/// <summary>
/// Exception thrown when an evidence type is not supported.
/// </summary>
public sealed class UnsupportedEvidenceTypeException : Exception
{
    /// <summary>
    /// Creates a new UnsupportedEvidenceTypeException.
    /// </summary>
    public UnsupportedEvidenceTypeException(string type, IEnumerable<string> supportedTypes)
        : base($"Unsupported evidence type: {type}. Supported types: {string.Join(", ", supportedTypes)}")
    {
        Type = type;
        SupportedTypes = supportedTypes.ToImmutableArray();
    }

    /// <summary>Gets the unsupported type.</summary>
    public string Type { get; }

    /// <summary>Gets the supported types.</summary>
    public ImmutableArray<string> SupportedTypes { get; }
}

/// <summary>
/// Exception thrown when evidence cannot be found.
/// </summary>
public sealed class EvidenceNotFoundException : Exception
{
    /// <summary>
    /// Creates a new EvidenceNotFoundException.
    /// </summary>
    public EvidenceNotFoundException(string type, string path)
        : base($"Evidence not found: {type}/{path}")
    {
        Type = type;
        Path = path;
    }

    /// <summary>Gets the evidence type.</summary>
    public string Type { get; }

    /// <summary>Gets the evidence path.</summary>
    public string Path { get; }
}