using System.Collections.Generic;
using System.Linq;
using System.Security.Cryptography;
using System.Text;
using System.Text.Json;
using System.Text.Json.Serialization;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Routing;
using Microsoft.Extensions.Logging;
using StellaOps.Policy;
using StellaOps.Scanner.WebService.Constants;
using StellaOps.Scanner.WebService.Contracts;
using StellaOps.Scanner.WebService.Infrastructure;
using StellaOps.Scanner.WebService.Security;
using StellaOps.Scanner.WebService.Services;

namespace StellaOps.Scanner.WebService.Endpoints;

#pragma warning disable ASPDEPR002

internal static class ReportEndpoints
{
    private const string PayloadType = "application/vnd.stellaops.report+json";

    private static readonly JsonSerializerOptions SerializerOptions = new(JsonSerializerDefaults.Web)
    {
        DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
        Converters = { new JsonStringEnumConverter() }
    };

    public static void MapReportEndpoints(this RouteGroupBuilder apiGroup, string reportsSegment)
    {
        ArgumentNullException.ThrowIfNull(apiGroup);

        var reports = apiGroup
            .MapGroup(NormalizeSegment(reportsSegment))
            .WithTags("Reports");

        reports.MapPost("/", HandleCreateReportAsync)
            .WithName("scanner.reports.create")
            .Produces<ReportResponseDto>(StatusCodes.Status200OK)
            .Produces(StatusCodes.Status400BadRequest)
            .Produces(StatusCodes.Status503ServiceUnavailable)
            .RequireAuthorization(ScannerPolicies.Reports)
            .WithOpenApi(operation =>
            {
                operation.Summary = "Assemble a signed scan report.";
                operation.Description = "Aggregates latest findings with the active policy snapshot, returning verdicts plus an optional DSSE envelope.";
                return operation;
            });
    }

    private static async Task<IResult> HandleCreateReportAsync(
        ReportRequestDto request,
        PolicyPreviewService previewService,
        IReportSigner signer,
        TimeProvider timeProvider,
        IReportEventDispatcher eventDispatcher,
        ISurfacePointerService surfacePointerService,
        ILinksetResolver linksetResolver,
        ILoggerFactory loggerFactory,
        HttpContext context,
        CancellationToken cancellationToken)
    {
        ArgumentNullException.ThrowIfNull(request);
        ArgumentNullException.ThrowIfNull(previewService);
        ArgumentNullException.ThrowIfNull(signer);
        ArgumentNullException.ThrowIfNull(timeProvider);
        ArgumentNullException.ThrowIfNull(eventDispatcher);
        ArgumentNullException.ThrowIfNull(surfacePointerService);
        ArgumentNullException.ThrowIfNull(linksetResolver);
        ArgumentNullException.ThrowIfNull(loggerFactory);
        var logger = loggerFactory.CreateLogger("Scanner.WebService.Reports");

        if (string.IsNullOrWhiteSpace(request.ImageDigest))
        {
            return ProblemResultFactory.Create(
                context,
                ProblemTypes.Validation,
                "Invalid report request",
                StatusCodes.Status400BadRequest,
                detail: "imageDigest is required.");
        }

        if (!request.ImageDigest.Contains(':', StringComparison.Ordinal))
        {
            return ProblemResultFactory.Create(
                context,
                ProblemTypes.Validation,
                "Invalid report request",
                StatusCodes.Status400BadRequest,
                detail: "imageDigest must include algorithm prefix (e.g. sha256:...).");
        }

        if (request.Findings is not null && request.Findings.Any(f => string.IsNullOrWhiteSpace(f.Id)))
        {
            return ProblemResultFactory.Create(
                context,
                ProblemTypes.Validation,
                "Invalid report request",
                StatusCodes.Status400BadRequest,
                detail: "All findings must include an id value.");
        }

        var previewDto = new PolicyPreviewRequestDto
        {
            ImageDigest = request.ImageDigest,
            Findings = request.Findings,
            Baseline = request.Baseline,
            Policy = null
        };

        var domainRequest = PolicyDtoMapper.ToDomain(previewDto) with { ProposedPolicy = null };
        var preview = await previewService.PreviewAsync(domainRequest, cancellationToken).ConfigureAwait(false);

        if (!preview.Success)
        {
            var issues = preview.Issues.Select(PolicyDtoMapper.ToIssueDto).ToArray();
            var extensions = new Dictionary<string, object?>(StringComparer.Ordinal)
            {
                ["issues"] = issues
            };

            return ProblemResultFactory.Create(
                context,
                ProblemTypes.Validation,
                "Unable to assemble report",
                StatusCodes.Status503ServiceUnavailable,
                detail: "No policy snapshot is available or validation failed.",
                extensions: extensions);
        }

        var projectedVerdicts = preview.Diffs
            .Select(diff => PolicyDtoMapper.ToVerdictDto(diff.Projected))
            .ToArray();

        var issuesDto = preview.Issues.Select(PolicyDtoMapper.ToIssueDto).ToArray();
        var summary = BuildSummary(projectedVerdicts);
        var verdict = ComputeVerdict(projectedVerdicts);
        var reportId = CreateReportId(request.ImageDigest!, preview.PolicyDigest);
        var generatedAt = timeProvider.GetUtcNow();
        var linksets = await linksetResolver.ResolveAsync(request.Findings, cancellationToken).ConfigureAwait(false);
        SurfacePointersDto? surfacePointers = null;

        try
        {
            surfacePointers = await surfacePointerService
                .TryBuildAsync(request.ImageDigest!, context.RequestAborted)
                .ConfigureAwait(false);
        }
        catch (OperationCanceledException) when (context.RequestAborted.IsCancellationRequested)
        {
            throw;
        }
        catch (Exception ex)
        {
            if (!context.RequestAborted.IsCancellationRequested)
            {
                logger.LogDebug(ex, "Failed to build surface pointers for digest {Digest}.", request.ImageDigest);
            }
        }

        var document = new ReportDocumentDto
        {
            ReportId = reportId,
            ImageDigest = request.ImageDigest!,
            GeneratedAt = generatedAt,
            Verdict = verdict,
            Policy = new ReportPolicyDto
            {
                RevisionId = preview.RevisionId,
                Digest = preview.PolicyDigest
            },
            Summary = summary,
            Verdicts = projectedVerdicts,
            Issues = issuesDto,
            Surface = surfacePointers,
            Linksets = linksets.Count == 0 ? null : linksets
        };

        var payloadBytes = JsonSerializer.SerializeToUtf8Bytes(document, SerializerOptions);
        var signature = signer.Sign(payloadBytes);
        DsseEnvelopeDto? envelope = null;
        if (signature is not null)
        {
            envelope = new DsseEnvelopeDto
            {
                PayloadType = PayloadType,
                Payload = Convert.ToBase64String(payloadBytes),
                Signatures = new[]
                {
                    new DsseSignatureDto
                    {
                        KeyId = signature.KeyId,
                        Algorithm = signature.Algorithm,
                        Signature = signature.Signature
                    }
                }
            };
        }

        var response = new ReportResponseDto
        {
            Report = document,
            Dsse = envelope
        };

        await eventDispatcher
            .PublishAsync(request, preview, document, envelope, context, cancellationToken)
            .ConfigureAwait(false);

        return Json(response);
    }

    private static ReportSummaryDto BuildSummary(IReadOnlyList<PolicyPreviewVerdictDto> verdicts)
    {
        if (verdicts.Count == 0)
        {
            return new ReportSummaryDto { Total = 0 };
        }

        var blocked = verdicts.Count(v => string.Equals(v.Status, nameof(PolicyVerdictStatus.Blocked), StringComparison.OrdinalIgnoreCase));
        var warned = verdicts.Count(v =>
            string.Equals(v.Status, nameof(PolicyVerdictStatus.Warned), StringComparison.OrdinalIgnoreCase)
            || string.Equals(v.Status, nameof(PolicyVerdictStatus.Deferred), StringComparison.OrdinalIgnoreCase)
            || string.Equals(v.Status, nameof(PolicyVerdictStatus.RequiresVex), StringComparison.OrdinalIgnoreCase)
            || string.Equals(v.Status, nameof(PolicyVerdictStatus.Escalated), StringComparison.OrdinalIgnoreCase));
        var ignored = verdicts.Count(v => string.Equals(v.Status, nameof(PolicyVerdictStatus.Ignored), StringComparison.OrdinalIgnoreCase));
        var quieted = verdicts.Count(v => v.Quiet is true);

        return new ReportSummaryDto
        {
            Total = verdicts.Count,
            Blocked = blocked,
            Warned = warned,
            Ignored = ignored,
            Quieted = quieted
        };
    }

    private static string ComputeVerdict(IReadOnlyList<PolicyPreviewVerdictDto> verdicts)
    {
        if (verdicts.Count == 0)
        {
            return "unknown";
        }

        if (verdicts.Any(v => string.Equals(v.Status, nameof(PolicyVerdictStatus.Blocked), StringComparison.OrdinalIgnoreCase)))
        {
            return "blocked";
        }

        if (verdicts.Any(v => string.Equals(v.Status, nameof(PolicyVerdictStatus.Escalated), StringComparison.OrdinalIgnoreCase)))
        {
            return "escalated";
        }

        if (verdicts.Any(v =>
            string.Equals(v.Status, nameof(PolicyVerdictStatus.Warned), StringComparison.OrdinalIgnoreCase)
            || string.Equals(v.Status, nameof(PolicyVerdictStatus.Deferred), StringComparison.OrdinalIgnoreCase)
            || string.Equals(v.Status, nameof(PolicyVerdictStatus.RequiresVex), StringComparison.OrdinalIgnoreCase)))
        {
            return "warn";
        }

        return "pass";
    }

    private static string CreateReportId(string imageDigest, string policyDigest)
    {
        var builder = new StringBuilder();
        builder.Append(imageDigest.Trim());
        builder.Append('|');
        builder.Append(policyDigest ?? string.Empty);

        using var sha256 = SHA256.Create();
        var hash = sha256.ComputeHash(Encoding.UTF8.GetBytes(builder.ToString()));
        var hex = Convert.ToHexString(hash.AsSpan(0, 10)).ToLowerInvariant();
        return $"report-{hex}";
    }

    private static string NormalizeSegment(string segment)
    {
        if (string.IsNullOrWhiteSpace(segment))
        {
            return "/reports";
        }

        var trimmed = segment.Trim('/');
        return "/" + trimmed;
    }

    private static IResult Json<T>(T value)
    {
        var payload = JsonSerializer.Serialize(value, SerializerOptions);
        return Results.Content(payload, "application/json", Encoding.UTF8);
    }
}

#pragma warning restore ASPDEPR002