using System.Collections.Concurrent;
using System.Text;
using System.Text.Json;
using System.Text.Json.Serialization;
using StellaOps.Canonical.Json;

namespace StellaOps.Testing.Determinism;

/// <summary>
/// Stores and retrieves determinism baselines for artifact comparison.
/// Baselines are SHA-256 hashes of canonical artifact representations used to detect drift.
/// </summary>
public sealed class DeterminismBaselineStore
{
    private readonly string _baselineDirectory;
    private readonly ConcurrentDictionary<string, DeterminismBaseline> _cache = new();

    private static readonly JsonSerializerOptions JsonOptions = new()
    {
        WriteIndented = true,
        PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
        DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
        Converters = { new JsonStringEnumConverter(JsonNamingPolicy.CamelCase) }
    };

    /// <summary>
    /// Creates a baseline store with the specified directory.
    /// </summary>
    /// <param name="baselineDirectory">Directory path for storing baselines.</param>
    public DeterminismBaselineStore(string baselineDirectory)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(baselineDirectory);
        _baselineDirectory = baselineDirectory;
    }

    /// <summary>
    /// Creates a baseline store using the default baseline directory.
    /// Default: tests/baselines/determinism relative to repository root.
    /// </summary>
    /// <param name="repositoryRoot">Repository root directory.</param>
    /// <returns>Configured baseline store.</returns>
    public static DeterminismBaselineStore CreateDefault(string repositoryRoot)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(repositoryRoot);
        var baselineDir = Path.Combine(repositoryRoot, "tests", "baselines", "determinism");
        return new DeterminismBaselineStore(baselineDir);
    }

    /// <summary>
    /// Stores a baseline for an artifact.
    /// </summary>
    /// <param name="artifactType">Type of artifact (e.g., "sbom", "vex", "policy-verdict").</param>
    /// <param name="artifactName">Name of the artifact (e.g., "alpine-3.18-spdx").</param>
    /// <param name="baseline">The baseline to store.</param>
    /// <param name="cancellationToken">Cancellation token.</param>
    public async Task StoreBaselineAsync(
        string artifactType,
        string artifactName,
        DeterminismBaseline baseline,
        CancellationToken cancellationToken = default)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(artifactType);
        ArgumentException.ThrowIfNullOrWhiteSpace(artifactName);
        ArgumentNullException.ThrowIfNull(baseline);

        var key = GetBaselineKey(artifactType, artifactName);
        var filePath = GetBaselineFilePath(artifactType, artifactName);

        // Ensure directory exists
        var directory = Path.GetDirectoryName(filePath);
        if (!string.IsNullOrEmpty(directory))
        {
            Directory.CreateDirectory(directory);
        }

        // Serialize and write
        var json = JsonSerializer.Serialize(baseline, JsonOptions);
        await File.WriteAllTextAsync(filePath, json, Encoding.UTF8, cancellationToken).ConfigureAwait(false);

        // Update cache
        _cache[key] = baseline;
    }

    /// <summary>
    /// Retrieves a baseline for an artifact.
    /// </summary>
    /// <param name="artifactType">Type of artifact.</param>
    /// <param name="artifactName">Name of the artifact.</param>
    /// <param name="cancellationToken">Cancellation token.</param>
    /// <returns>The baseline if found, null otherwise.</returns>
    public async Task<DeterminismBaseline?> GetBaselineAsync(
        string artifactType,
        string artifactName,
        CancellationToken cancellationToken = default)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(artifactType);
        ArgumentException.ThrowIfNullOrWhiteSpace(artifactName);

        var key = GetBaselineKey(artifactType, artifactName);

        // Check cache first
        if (_cache.TryGetValue(key, out var cached))
        {
            return cached;
        }

        // Load from file
        var filePath = GetBaselineFilePath(artifactType, artifactName);
        if (!File.Exists(filePath))
        {
            return null;
        }

        var json = await File.ReadAllTextAsync(filePath, Encoding.UTF8, cancellationToken).ConfigureAwait(false);
        var baseline = JsonSerializer.Deserialize<DeterminismBaseline>(json, JsonOptions);

        if (baseline is not null)
        {
            _cache[key] = baseline;
        }

        return baseline;
    }

    /// <summary>
    /// Compares an artifact against its stored baseline.
    /// </summary>
    /// <param name="artifactType">Type of artifact.</param>
    /// <param name="artifactName">Name of the artifact.</param>
    /// <param name="currentHash">Current SHA-256 hash of the artifact.</param>
    /// <param name="cancellationToken">Cancellation token.</param>
    /// <returns>Comparison result indicating match, drift, or missing baseline.</returns>
    public async Task<BaselineComparisonResult> CompareAsync(
        string artifactType,
        string artifactName,
        string currentHash,
        CancellationToken cancellationToken = default)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(artifactType);
        ArgumentException.ThrowIfNullOrWhiteSpace(artifactName);
        ArgumentException.ThrowIfNullOrWhiteSpace(currentHash);

        var baseline = await GetBaselineAsync(artifactType, artifactName, cancellationToken).ConfigureAwait(false);

        if (baseline is null)
        {
            return new BaselineComparisonResult
            {
                ArtifactType = artifactType,
                ArtifactName = artifactName,
                Status = BaselineStatus.Missing,
                CurrentHash = currentHash,
                BaselineHash = null,
                Message = $"No baseline found for {artifactType}/{artifactName}. Run with UPDATE_BASELINES=true to create."
            };
        }

        var isMatch = string.Equals(baseline.CanonicalHash, currentHash, StringComparison.OrdinalIgnoreCase);

        return new BaselineComparisonResult
        {
            ArtifactType = artifactType,
            ArtifactName = artifactName,
            Status = isMatch ? BaselineStatus.Match : BaselineStatus.Drift,
            CurrentHash = currentHash,
            BaselineHash = baseline.CanonicalHash,
            BaselineVersion = baseline.Version,
            Message = isMatch
                ? $"Artifact {artifactType}/{artifactName} matches baseline."
                : $"DRIFT DETECTED: {artifactType}/{artifactName} hash changed from {baseline.CanonicalHash} to {currentHash}."
        };
    }

    /// <summary>
    /// Lists all baselines in the store.
    /// </summary>
    /// <param name="cancellationToken">Cancellation token.</param>
    /// <returns>Collection of baseline entries.</returns>
    public async Task<IReadOnlyList<BaselineEntry>> ListBaselinesAsync(
        CancellationToken cancellationToken = default)
    {
        var entries = new List<BaselineEntry>();

        if (!Directory.Exists(_baselineDirectory))
        {
            return entries;
        }

        var files = Directory.GetFiles(_baselineDirectory, "*.baseline.json", SearchOption.AllDirectories);

        foreach (var file in files)
        {
            try
            {
                var json = await File.ReadAllTextAsync(file, Encoding.UTF8, cancellationToken).ConfigureAwait(false);
                var baseline = JsonSerializer.Deserialize<DeterminismBaseline>(json, JsonOptions);

                if (baseline is not null)
                {
                    var relativePath = Path.GetRelativePath(_baselineDirectory, file);
                    var parts = relativePath.Split(Path.DirectorySeparatorChar, Path.AltDirectorySeparatorChar);

                    entries.Add(new BaselineEntry
                    {
                        ArtifactType = parts.Length > 1 ? parts[0] : "unknown",
                        ArtifactName = Path.GetFileNameWithoutExtension(Path.GetFileNameWithoutExtension(file)),
                        CanonicalHash = baseline.CanonicalHash,
                        Version = baseline.Version,
                        UpdatedAt = baseline.UpdatedAt,
                        FilePath = file
                    });
                }
            }
            catch
            {
                // Skip invalid baseline files
            }
        }

        return entries.OrderBy(e => e.ArtifactType).ThenBy(e => e.ArtifactName).ToList();
    }

    /// <summary>
    /// Creates a baseline from an artifact.
    /// </summary>
    /// <param name="artifactBytes">The artifact bytes to hash.</param>
    /// <param name="version">Version identifier for this baseline.</param>
    /// <param name="metadata">Optional metadata about the baseline.</param>
    /// <returns>Created baseline.</returns>
    public static DeterminismBaseline CreateBaseline(
        ReadOnlySpan<byte> artifactBytes,
        string version,
        IReadOnlyDictionary<string, string>? metadata = null)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(version);

        var hash = CanonJson.Sha256Hex(artifactBytes);

        return new DeterminismBaseline
        {
            CanonicalHash = hash,
            Algorithm = "SHA-256",
            Version = version,
            UpdatedAt = DateTimeOffset.UtcNow,
            Metadata = metadata
        };
    }

    /// <summary>
    /// Creates a baseline from a JSON artifact with canonical serialization.
    /// </summary>
    /// <typeparam name="T">The artifact type.</typeparam>
    /// <param name="artifact">The artifact to serialize and hash.</param>
    /// <param name="version">Version identifier for this baseline.</param>
    /// <param name="metadata">Optional metadata about the baseline.</param>
    /// <returns>Created baseline.</returns>
    public static DeterminismBaseline CreateBaselineFromJson<T>(
        T artifact,
        string version,
        IReadOnlyDictionary<string, string>? metadata = null)
    {
        ArgumentNullException.ThrowIfNull(artifact);
        ArgumentException.ThrowIfNullOrWhiteSpace(version);

        var canonicalBytes = CanonJson.Canonicalize(artifact);
        var hash = CanonJson.Sha256Hex(canonicalBytes);

        return new DeterminismBaseline
        {
            CanonicalHash = hash,
            Algorithm = "SHA-256",
            Version = version,
            UpdatedAt = DateTimeOffset.UtcNow,
            Metadata = metadata
        };
    }

    /// <summary>
    /// Gets the baseline directory path.
    /// </summary>
    public string BaselineDirectory => _baselineDirectory;

    private string GetBaselineFilePath(string artifactType, string artifactName)
    {
        var safeType = SanitizePathComponent(artifactType);
        var safeName = SanitizePathComponent(artifactName);
        return Path.Combine(_baselineDirectory, safeType, $"{safeName}.baseline.json");
    }

    private static string GetBaselineKey(string artifactType, string artifactName)
    {
        return $"{artifactType}/{artifactName}".ToLowerInvariant();
    }

    private static string SanitizePathComponent(string component)
    {
        var invalid = Path.GetInvalidFileNameChars();
        var sanitized = new StringBuilder(component.Length);

        foreach (var c in component)
        {
            sanitized.Append(invalid.Contains(c) ? '_' : c);
        }

        return sanitized.ToString();
    }
}

/// <summary>
/// A stored baseline for determinism comparison.
/// </summary>
public sealed record DeterminismBaseline
{
    /// <summary>
    /// SHA-256 hash of the canonical artifact representation (hex-encoded).
    /// </summary>
    [JsonPropertyName("canonicalHash")]
    public required string CanonicalHash { get; init; }

    /// <summary>
    /// Hash algorithm used (always "SHA-256").
    /// </summary>
    [JsonPropertyName("algorithm")]
    public required string Algorithm { get; init; }

    /// <summary>
    /// Version identifier for this baseline (e.g., "1.0.0", git SHA, or timestamp).
    /// </summary>
    [JsonPropertyName("version")]
    public required string Version { get; init; }

    /// <summary>
    /// UTC timestamp when this baseline was created or updated.
    /// </summary>
    [JsonPropertyName("updatedAt")]
    public required DateTimeOffset UpdatedAt { get; init; }

    /// <summary>
    /// Optional metadata about the baseline.
    /// </summary>
    [JsonPropertyName("metadata")]
    public IReadOnlyDictionary<string, string>? Metadata { get; init; }
}

/// <summary>
/// Result of comparing an artifact against its baseline.
/// </summary>
public sealed record BaselineComparisonResult
{
    /// <summary>
    /// Type of artifact compared.
    /// </summary>
    [JsonPropertyName("artifactType")]
    public required string ArtifactType { get; init; }

    /// <summary>
    /// Name of artifact compared.
    /// </summary>
    [JsonPropertyName("artifactName")]
    public required string ArtifactName { get; init; }

    /// <summary>
    /// Comparison status.
    /// </summary>
    [JsonPropertyName("status")]
    public required BaselineStatus Status { get; init; }

    /// <summary>
    /// Current hash of the artifact.
    /// </summary>
    [JsonPropertyName("currentHash")]
    public required string CurrentHash { get; init; }

    /// <summary>
    /// Baseline hash (null if missing).
    /// </summary>
    [JsonPropertyName("baselineHash")]
    public string? BaselineHash { get; init; }

    /// <summary>
    /// Baseline version (null if missing).
    /// </summary>
    [JsonPropertyName("baselineVersion")]
    public string? BaselineVersion { get; init; }

    /// <summary>
    /// Human-readable message describing the result.
    /// </summary>
    [JsonPropertyName("message")]
    public required string Message { get; init; }
}

/// <summary>
/// Status of a baseline comparison.
/// </summary>
public enum BaselineStatus
{
    /// <summary>
    /// Artifact matches baseline hash.
    /// </summary>
    Match,

    /// <summary>
    /// Artifact hash differs from baseline (drift detected).
    /// </summary>
    Drift,

    /// <summary>
    /// No baseline exists for this artifact.
    /// </summary>
    Missing
}

/// <summary>
/// Entry in the baseline registry.
/// </summary>
public sealed record BaselineEntry
{
    /// <summary>
    /// Type of artifact.
    /// </summary>
    [JsonPropertyName("artifactType")]
    public required string ArtifactType { get; init; }

    /// <summary>
    /// Name of artifact.
    /// </summary>
    [JsonPropertyName("artifactName")]
    public required string ArtifactName { get; init; }

    /// <summary>
    /// Canonical hash of the baseline.
    /// </summary>
    [JsonPropertyName("canonicalHash")]
    public required string CanonicalHash { get; init; }

    /// <summary>
    /// Version identifier.
    /// </summary>
    [JsonPropertyName("version")]
    public required string Version { get; init; }

    /// <summary>
    /// When baseline was last updated.
    /// </summary>
    [JsonPropertyName("updatedAt")]
    public required DateTimeOffset UpdatedAt { get; init; }

    /// <summary>
    /// File path of the baseline.
    /// </summary>
    [JsonPropertyName("filePath")]
    public required string FilePath { get; init; }
}