using System;
using System.Collections.Generic;
using System.Collections.Immutable;
using System.Globalization;
using System.Linq;
using System.Text;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.Primitives;
using MongoDB.Bson;
using StellaOps.Excititor.Core;
using StellaOps.Excititor.Core.Aoc;
using StellaOps.Excititor.Storage.Mongo;
using StellaOps.Excititor.WebService.Contracts;
using StellaOps.Excititor.WebService.Services;
public partial class Program
{
    private const string TenantHeaderName = "X-Stella-Tenant";

    private static bool TryResolveTenant(HttpContext context, VexMongoStorageOptions options, bool requireHeader, out string tenant, out IResult? problem)
    {
        tenant = options.DefaultTenant;
        problem = null;

        if (context.Request.Headers.TryGetValue(TenantHeaderName, out var headerValues) && headerValues.Count > 0)
        {
            var requestedTenant = headerValues[0]?.Trim();
            if (string.IsNullOrEmpty(requestedTenant))
            {
                problem = Results.Problem(detail: "X-Stella-Tenant header must not be empty.", statusCode: StatusCodes.Status400BadRequest, title: "Validation error");
                return false;
            }

            if (!string.Equals(requestedTenant, options.DefaultTenant, StringComparison.OrdinalIgnoreCase))
            {
                var detail = string.Format(CultureInfo.InvariantCulture, "Tenant '{0}' is not allowed for this Excititor deployment.", requestedTenant);
                problem = Results.Problem(detail: detail, statusCode: StatusCodes.Status403Forbidden, title: "Forbidden");
                return false;
            }

            tenant = requestedTenant;
            return true;
        }

        if (requireHeader)
        {
            var detail = string.Format(CultureInfo.InvariantCulture, "{0} header is required.", TenantHeaderName);
            problem = Results.Problem(detail: detail, statusCode: StatusCodes.Status400BadRequest, title: "Validation error");
            return false;
        }

        return true;
    }

    private static IReadOnlyDictionary<string, string> ReadMetadata(BsonValue value)
    {
        if (value is not BsonDocument doc || doc.ElementCount == 0)
        {
            return new Dictionary<string, string>(StringComparer.Ordinal);
        }

        var result = new Dictionary<string, string>(StringComparer.Ordinal);
        foreach (var element in doc.Elements)
        {
            if (string.IsNullOrWhiteSpace(element.Name))
            {
                continue;
            }

            result[element.Name] = element.Value?.ToString() ?? string.Empty;
        }

        return result;
    }

    private static bool TryDecodeCursor(string? cursor, out DateTimeOffset timestamp, out string digest)
    {
        timestamp = default;
        digest = string.Empty;
        if (string.IsNullOrWhiteSpace(cursor))
        {
            return false;
        }

        try
        {
            var payload = Encoding.UTF8.GetString(Convert.FromBase64String(cursor));
            var parts = payload.Split('|');
            if (parts.Length != 2)
            {
                return false;
            }

            if (!DateTimeOffset.TryParse(parts[0], CultureInfo.InvariantCulture, DateTimeStyles.AssumeUniversal, out timestamp))
            {
                return false;
            }

            digest = parts[1];
            return true;
        }
        catch
        {
            return false;
        }
    }

    private static string EncodeCursor(DateTime timestamp, string digest)
    {
        var payload = string.Format(CultureInfo.InvariantCulture, "{0:O}|{1}", timestamp, digest);
        return Convert.ToBase64String(Encoding.UTF8.GetBytes(payload));
    }

    private static IResult ValidationProblem(string message)
        => Results.Problem(detail: message, statusCode: StatusCodes.Status400BadRequest, title: "Validation error");

    private static IResult MapGuardException(ExcititorAocGuardException exception)
    {
        var violations = exception.Violations.Select(violation => new
        {
            code = violation.ErrorCode,
            path = violation.Path,
            message = violation.Message
        });

        return Results.Problem(
            detail: "VEX document failed Aggregation-Only Contract validation.",
            statusCode: StatusCodes.Status400BadRequest,
            title: "AOC violation",
            extensions: new Dictionary<string, object?>
            {
                ["violations"] = violations.ToArray(),
                ["primaryCode"] = exception.PrimaryErrorCode,
            });
    }

    private static ImmutableHashSet<string> BuildStringFilterSet(StringValues values)
    {
        if (values.Count == 0)
        {
            return ImmutableHashSet<string>.Empty;
        }

        var builder = ImmutableHashSet.CreateBuilder<string>(StringComparer.OrdinalIgnoreCase);
        foreach (var value in values)
        {
            if (!string.IsNullOrWhiteSpace(value))
            {
                builder.Add(value.Trim());
            }
        }

        return builder.ToImmutable();
    }

    private static ImmutableHashSet<VexClaimStatus> BuildStatusFilter(StringValues values)
    {
        if (values.Count == 0)
        {
            return ImmutableHashSet<VexClaimStatus>.Empty;
        }

        var builder = ImmutableHashSet.CreateBuilder<VexClaimStatus>();
        foreach (var value in values)
        {
            if (Enum.TryParse<VexClaimStatus>(value, ignoreCase: true, out var status))
            {
                builder.Add(status);
            }
        }

        return builder.ToImmutable();
    }

    private static DateTimeOffset? ParseSinceTimestamp(StringValues values)
    {
        if (values.Count == 0)
        {
            return null;
        }

        var candidate = values[0];
        return DateTimeOffset.TryParse(candidate, CultureInfo.InvariantCulture, DateTimeStyles.AssumeUniversal | DateTimeStyles.AdjustToUniversal, out var parsed)
            ? parsed
            : null;
    }

    private static int ResolveLimit(StringValues values, int defaultValue, int min, int max)
    {
        if (values.Count == 0)
        {
            return defaultValue;
        }

        if (!int.TryParse(values[0], NumberStyles.Integer, CultureInfo.InvariantCulture, out var parsed))
        {
            return defaultValue;
        }

        return Math.Clamp(parsed, min, max);
    }

    private static IReadOnlyList<string> NormalizePurls(string[]? purls)
    {
        if (purls is null || purls.Length == 0)
        {
            return Array.Empty<string>();
        }

        var seen = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
        var ordered = new List<string>(purls.Length);
        foreach (var purl in purls)
        {
            var trimmed = purl?.Trim();
            if (string.IsNullOrWhiteSpace(trimmed))
            {
                continue;
            }

            var normalized = trimmed.ToLowerInvariant();
            if (seen.Add(normalized))
            {
                ordered.Add(normalized);
            }
        }

        return ordered;
    }

    private static VexObservationStatementResponse ToResponse(VexObservationStatementProjection projection)
    {
        var scope = projection.Scope;
        var document = projection.Document;
        var signature = projection.Signature;

        return new VexObservationStatementResponse(
            projection.ObservationId,
            projection.ProviderId,
            projection.Status.ToString().ToLowerInvariant(),
            projection.Justification?.ToString().ToLowerInvariant(),
            projection.Detail,
            projection.FirstSeen,
            projection.LastSeen,
            new VexObservationScopeResponse(
                scope.Key,
                scope.Name,
                scope.Version,
                scope.Purl,
                scope.Cpe,
                scope.ComponentIdentifiers),
            projection.Anchors,
            new VexObservationDocumentResponse(
                document.Digest,
                document.Format.ToString().ToLowerInvariant(),
                document.Revision,
                document.SourceUri.ToString()),
            signature is null
                ? null
                : new VexObservationSignatureResponse(
                    signature.Type,
                    signature.KeyId,
                    signature.Issuer,
                    signature.VerifiedAt));
    }

    private sealed record CachedGraphOverlay(
        IReadOnlyList<GraphOverlayItem> Items,
        DateTimeOffset CachedAt);
}