// SPDX-License-Identifier: AGPL-3.0-or-later
// Sprint: SPRINT_4100_0004_0001 - Security State Delta & Verdict
// Task: T6 - Add Delta API endpoints

using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Caching.Memory;
using StellaOps.Auth.Abstractions;
using StellaOps.Auth.ServerIntegration;
using StellaOps.Policy.Deltas;
using StellaOps.Policy.Gateway.Contracts;

namespace StellaOps.Policy.Gateway.Endpoints;

/// <summary>
/// Delta API endpoints for Policy Gateway.
/// </summary>
public static class DeltasEndpoints
{
    private const string DeltaCachePrefix = "delta:";
    private static readonly TimeSpan DeltaCacheDuration = TimeSpan.FromMinutes(30);

    /// <summary>
    /// Maps delta endpoints to the application.
    /// </summary>
    public static void MapDeltasEndpoints(this WebApplication app)
    {
        var deltas = app.MapGroup("/api/policy/deltas")
            .WithTags("Deltas");

        // POST /api/policy/deltas/compute - Compute a security state delta
        deltas.MapPost("/compute", async Task<IResult>(
            ComputeDeltaRequest request,
            IDeltaComputer deltaComputer,
            IBaselineSelector baselineSelector,
            IMemoryCache cache,
            ILogger<DeltaComputer> logger,
            CancellationToken cancellationToken) =>
        {
            if (request is null)
            {
                return Results.BadRequest(new ProblemDetails
                {
                    Title = "Request body required",
                    Status = 400
                });
            }

            if (string.IsNullOrWhiteSpace(request.ArtifactDigest))
            {
                return Results.BadRequest(new ProblemDetails
                {
                    Title = "Artifact digest required",
                    Status = 400
                });
            }

            if (string.IsNullOrWhiteSpace(request.TargetSnapshotId))
            {
                return Results.BadRequest(new ProblemDetails
                {
                    Title = "Target snapshot ID required",
                    Status = 400
                });
            }

            try
            {
                // Select baseline
                BaselineSelectionResult baselineResult;
                if (!string.IsNullOrWhiteSpace(request.BaselineSnapshotId))
                {
                    baselineResult = await baselineSelector.SelectExplicitAsync(
                        request.BaselineSnapshotId,
                        cancellationToken);
                }
                else
                {
                    var strategy = ParseStrategy(request.BaselineStrategy);
                    baselineResult = await baselineSelector.SelectBaselineAsync(
                        request.ArtifactDigest,
                        strategy,
                        cancellationToken);
                }

                if (!baselineResult.IsFound)
                {
                    return Results.NotFound(new ProblemDetails
                    {
                        Title = "Baseline not found",
                        Status = 404,
                        Detail = baselineResult.Error
                    });
                }

                // Compute delta
                var delta = await deltaComputer.ComputeDeltaAsync(
                    baselineResult.Snapshot!.SnapshotId,
                    request.TargetSnapshotId,
                    new ArtifactRef(
                        request.ArtifactDigest,
                        request.ArtifactName,
                        request.ArtifactTag),
                    cancellationToken);

                // Cache the delta for subsequent retrieval
                cache.Set(
                    DeltaCachePrefix + delta.DeltaId,
                    delta,
                    DeltaCacheDuration);

                logger.LogInformation(
                    "Computed delta {DeltaId} between {Baseline} and {Target}",
                    delta.DeltaId, delta.BaselineSnapshotId, delta.TargetSnapshotId);

                return Results.Ok(new ComputeDeltaResponse
                {
                    DeltaId = delta.DeltaId,
                    BaselineSnapshotId = delta.BaselineSnapshotId,
                    TargetSnapshotId = delta.TargetSnapshotId,
                    ComputedAt = delta.ComputedAt,
                    Summary = DeltaSummaryDto.FromModel(delta.Summary),
                    DriverCount = delta.Drivers.Count
                });
            }
            catch (InvalidOperationException ex) when (ex.Message.Contains("not found"))
            {
                return Results.NotFound(new ProblemDetails
                {
                    Title = "Snapshot not found",
                    Status = 404,
                    Detail = ex.Message
                });
            }
        })
        .RequireAuthorization(policy => policy.RequireStellaOpsScopes(StellaOpsScopes.PolicyRun));

        // GET /api/policy/deltas/{deltaId} - Get a delta by ID
        deltas.MapGet("/{deltaId}", async Task<IResult>(
            string deltaId,
            IMemoryCache cache,
            CancellationToken cancellationToken) =>
        {
            if (string.IsNullOrWhiteSpace(deltaId))
            {
                return Results.BadRequest(new ProblemDetails
                {
                    Title = "Delta ID required",
                    Status = 400
                });
            }

            // Try to retrieve from cache
            if (!cache.TryGetValue(DeltaCachePrefix + deltaId, out SecurityStateDelta? delta) || delta is null)
            {
                return Results.NotFound(new ProblemDetails
                {
                    Title = "Delta not found",
                    Status = 404,
                    Detail = $"No delta found with ID: {deltaId}. Deltas are cached for {DeltaCacheDuration.TotalMinutes} minutes after computation."
                });
            }

            return Results.Ok(DeltaResponse.FromModel(delta));
        })
        .RequireAuthorization(policy => policy.RequireStellaOpsScopes(StellaOpsScopes.PolicyRead));

        // POST /api/policy/deltas/{deltaId}/evaluate - Evaluate delta and get verdict
        deltas.MapPost("/{deltaId}/evaluate", async Task<IResult>(
            string deltaId,
            EvaluateDeltaRequest? request,
            IMemoryCache cache,
            ILogger<DeltaComputer> logger,
            CancellationToken cancellationToken) =>
        {
            if (string.IsNullOrWhiteSpace(deltaId))
            {
                return Results.BadRequest(new ProblemDetails
                {
                    Title = "Delta ID required",
                    Status = 400
                });
            }

            // Try to retrieve delta from cache
            if (!cache.TryGetValue(DeltaCachePrefix + deltaId, out SecurityStateDelta? delta) || delta is null)
            {
                return Results.NotFound(new ProblemDetails
                {
                    Title = "Delta not found",
                    Status = 404,
                    Detail = $"No delta found with ID: {deltaId}"
                });
            }

            // Build verdict from delta drivers
            var builder = new DeltaVerdictBuilder();

            // Apply risk points based on summary
            builder.WithRiskPoints((int)delta.Summary.RiskScore);

            // Categorize drivers as blocking or warning
            foreach (var driver in delta.Drivers)
            {
                if (IsBlockingDriver(driver))
                {
                    builder.AddBlockingDriver(driver);
                }
                else if (driver.Severity >= DeltaDriverSeverity.Medium)
                {
                    builder.AddWarningDriver(driver);
                }
            }

            // Apply exceptions if provided
            if (request?.Exceptions is not null)
            {
                foreach (var exceptionId in request.Exceptions)
                {
                    builder.AddException(exceptionId);
                }
            }

            // Add recommendations based on drivers
            AddRecommendations(builder, delta.Drivers);

            var verdict = builder.Build(deltaId);

            // Cache the verdict
            cache.Set(
                DeltaCachePrefix + deltaId + ":verdict",
                verdict,
                DeltaCacheDuration);

            logger.LogInformation(
                "Evaluated delta {DeltaId}: status={Status}, gate={Gate}",
                deltaId, verdict.Status, verdict.RecommendedGate);

            return Results.Ok(DeltaVerdictResponse.FromModel(verdict));
        })
        .RequireAuthorization(policy => policy.RequireStellaOpsScopes(StellaOpsScopes.PolicyRun));

        // GET /api/policy/deltas/{deltaId}/attestation - Get signed attestation
        deltas.MapGet("/{deltaId}/attestation", async Task<IResult>(
            string deltaId,
            IMemoryCache cache,
            IDeltaVerdictAttestor? attestor,
            ILogger<DeltaComputer> logger,
            CancellationToken cancellationToken) =>
        {
            if (string.IsNullOrWhiteSpace(deltaId))
            {
                return Results.BadRequest(new ProblemDetails
                {
                    Title = "Delta ID required",
                    Status = 400
                });
            }

            // Try to retrieve delta from cache
            if (!cache.TryGetValue(DeltaCachePrefix + deltaId, out SecurityStateDelta? delta) || delta is null)
            {
                return Results.NotFound(new ProblemDetails
                {
                    Title = "Delta not found",
                    Status = 404,
                    Detail = $"No delta found with ID: {deltaId}"
                });
            }

            // Try to retrieve verdict from cache
            if (!cache.TryGetValue(DeltaCachePrefix + deltaId + ":verdict", out DeltaVerdict? verdict) || verdict is null)
            {
                return Results.NotFound(new ProblemDetails
                {
                    Title = "Verdict not found",
                    Status = 404,
                    Detail = "Delta must be evaluated before attestation can be generated. Call POST /evaluate first."
                });
            }

            if (attestor is null)
            {
                return Results.Problem(new ProblemDetails
                {
                    Title = "Attestor not configured",
                    Status = 501,
                    Detail = "Delta verdict attestation requires a signer to be configured"
                });
            }

            try
            {
                var envelope = await attestor.AttestAsync(delta, verdict, cancellationToken);

                logger.LogInformation(
                    "Created attestation for delta {DeltaId} verdict {VerdictId}",
                    deltaId, verdict.VerdictId);

                return Results.Ok(envelope);
            }
            catch (Exception ex)
            {
                logger.LogError(ex, "Failed to create attestation for delta {DeltaId}", deltaId);
                return Results.Problem(new ProblemDetails
                {
                    Title = "Attestation failed",
                    Status = 500,
                    Detail = "Failed to create signed attestation"
                });
            }
        })
        .RequireAuthorization(policy => policy.RequireStellaOpsScopes(StellaOpsScopes.PolicyRead));
    }

    private static BaselineSelectionStrategy ParseStrategy(string? strategy)
    {
        if (string.IsNullOrWhiteSpace(strategy))
            return BaselineSelectionStrategy.LastApproved;

        return strategy.ToLowerInvariant() switch
        {
            "previousbuild" or "previous_build" or "previous-build" => BaselineSelectionStrategy.PreviousBuild,
            "lastapproved" or "last_approved" or "last-approved" => BaselineSelectionStrategy.LastApproved,
            "productiondeployed" or "production_deployed" or "production-deployed" or "production" => BaselineSelectionStrategy.ProductionDeployed,
            "branchbase" or "branch_base" or "branch-base" => BaselineSelectionStrategy.BranchBase,
            _ => BaselineSelectionStrategy.LastApproved
        };
    }

    private static bool IsBlockingDriver(DeltaDriver driver)
    {
        // Block on critical/high severity negative drivers
        if (driver.Severity is DeltaDriverSeverity.Critical or DeltaDriverSeverity.High)
        {
            // These types indicate risk increase
            return driver.Type is
                "new-reachable-cve" or
                "lost-vex-coverage" or
                "vex-status-downgrade" or
                "new-policy-violation";
        }

        return false;
    }

    private static void AddRecommendations(DeltaVerdictBuilder builder, IReadOnlyList<DeltaDriver> drivers)
    {
        var hasReachableCve = drivers.Any(d => d.Type == "new-reachable-cve");
        var hasLostVex = drivers.Any(d => d.Type == "lost-vex-coverage");
        var hasNewViolation = drivers.Any(d => d.Type == "new-policy-violation");
        var hasNewUnknowns = drivers.Any(d => d.Type == "new-unknowns");

        if (hasReachableCve)
        {
            builder.AddRecommendation("Review new reachable CVEs and apply VEX statements or patches");
        }

        if (hasLostVex)
        {
            builder.AddRecommendation("Investigate lost VEX coverage - statements may have expired or been revoked");
        }

        if (hasNewViolation)
        {
            builder.AddRecommendation("Address policy violations or request exceptions");
        }

        if (hasNewUnknowns)
        {
            builder.AddRecommendation("Investigate new unknown packages - consider adding SBOM metadata");
        }
    }
}