using System.Text.Json;
using System.Text.Json.Serialization;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Routing;
using StellaOps.Scanner.WebService.Constants;
using StellaOps.Scanner.WebService.Contracts;
using StellaOps.Scanner.WebService.Domain;
using StellaOps.Scanner.WebService.Infrastructure;
using StellaOps.Scanner.WebService.Security;
using StellaOps.Scanner.WebService.Services;

namespace StellaOps.Scanner.WebService.Endpoints;

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

    private static readonly HashSet<string> SupportedLanguages = new(StringComparer.OrdinalIgnoreCase)
    {
        "dotnet", "java", "node", "python", "go", "rust", "binary", "ruby", "php"
    };

    public static void MapCallGraphEndpoints(this RouteGroupBuilder scansGroup)
    {
        ArgumentNullException.ThrowIfNull(scansGroup);

        // POST /scans/{scanId}/callgraphs
        scansGroup.MapPost("/{scanId}/callgraphs", HandleSubmitCallGraphAsync)
            .WithName("scanner.scans.callgraphs.submit")
            .WithTags("CallGraphs")
            .Produces<CallGraphAcceptedResponseDto>(StatusCodes.Status202Accepted)
            .Produces(StatusCodes.Status400BadRequest)
            .Produces(StatusCodes.Status404NotFound)
            .Produces(StatusCodes.Status409Conflict)
            .Produces(StatusCodes.Status413PayloadTooLarge)
            .RequireAuthorization(ScannerPolicies.CallGraphIngest);
    }

    private static async Task<IResult> HandleSubmitCallGraphAsync(
        string scanId,
        CallGraphV1Dto request,
        IScanCoordinator coordinator,
        ICallGraphIngestionService ingestionService,
        HttpContext context,
        CancellationToken cancellationToken)
    {
        ArgumentNullException.ThrowIfNull(coordinator);
        ArgumentNullException.ThrowIfNull(ingestionService);
        ArgumentNullException.ThrowIfNull(request);

        if (!ScanId.TryParse(scanId, out var parsed))
        {
            return ProblemResultFactory.Create(
                context,
                ProblemTypes.Validation,
                "Invalid scan identifier",
                StatusCodes.Status400BadRequest,
                detail: "Scan identifier is required.");
        }

        // Validate Content-Digest header for idempotency
        var contentDigest = context.Request.Headers["Content-Digest"].FirstOrDefault();
        if (string.IsNullOrWhiteSpace(contentDigest))
        {
            return ProblemResultFactory.Create(
                context,
                ProblemTypes.Validation,
                "Missing Content-Digest header",
                StatusCodes.Status400BadRequest,
                detail: "Content-Digest header is required for idempotent call graph submission.");
        }

        // Verify scan exists
        var snapshot = await coordinator.GetAsync(parsed, cancellationToken).ConfigureAwait(false);
        if (snapshot is null)
        {
            return ProblemResultFactory.Create(
                context,
                ProblemTypes.NotFound,
                "Scan not found",
                StatusCodes.Status404NotFound,
                detail: "Requested scan could not be located.");
        }

        // Validate call graph schema
        var validationResult = ValidateCallGraph(request);
        if (!validationResult.IsValid)
        {
            var extensions = new Dictionary<string, object?>
            {
                ["errors"] = validationResult.Errors
            };

            return ProblemResultFactory.Create(
                context,
                ProblemTypes.Validation,
                "Invalid call graph",
                StatusCodes.Status400BadRequest,
                detail: "Call graph validation failed.",
                extensions: extensions);
        }

        // Check for duplicate submission (idempotency)
        var existing = await ingestionService.FindByDigestAsync(parsed, contentDigest, cancellationToken)
            .ConfigureAwait(false);

        if (existing is not null)
        {
            var conflictExtensions = new Dictionary<string, object?>
            {
                ["callgraphId"] = existing.Id,
                ["digest"] = existing.Digest
            };

            return ProblemResultFactory.Create(
                context,
                ProblemTypes.Conflict,
                "Duplicate call graph",
                StatusCodes.Status409Conflict,
                detail: "Call graph with this Content-Digest already submitted.",
                extensions: conflictExtensions);
        }

        // Ingest the call graph
        var result = await ingestionService.IngestAsync(parsed, request, contentDigest, cancellationToken)
            .ConfigureAwait(false);

        var response = new CallGraphAcceptedResponseDto(
            CallgraphId: result.CallgraphId,
            NodeCount: result.NodeCount,
            EdgeCount: result.EdgeCount,
            Digest: result.Digest);

        context.Response.Headers.Location = $"/api/scans/{scanId}/callgraphs/{result.CallgraphId}";
        return Json(response, StatusCodes.Status202Accepted);
    }

    private static CallGraphValidationResult ValidateCallGraph(CallGraphV1Dto callGraph)
    {
        var errors = new List<string>();

        // Validate schema version
        if (string.IsNullOrWhiteSpace(callGraph.Schema))
        {
            errors.Add("Schema version is required.");
        }
        else if (!string.Equals(callGraph.Schema, "stella.callgraph.v1", StringComparison.Ordinal))
        {
            errors.Add($"Unsupported schema '{callGraph.Schema}'. Expected 'stella.callgraph.v1'.");
        }

        // Validate scan key
        if (string.IsNullOrWhiteSpace(callGraph.ScanKey))
        {
            errors.Add("ScanKey is required.");
        }

        // Validate language
        if (string.IsNullOrWhiteSpace(callGraph.Language))
        {
            errors.Add("Language is required.");
        }
        else if (!SupportedLanguages.Contains(callGraph.Language))
        {
            errors.Add($"Unsupported language '{callGraph.Language}'. Supported: {string.Join(", ", SupportedLanguages)}.");
        }

        // Validate nodes
        if (callGraph.Nodes is null || callGraph.Nodes.Count == 0)
        {
            errors.Add("At least one node is required.");
        }
        else
        {
            var nodeIds = new HashSet<string>(StringComparer.Ordinal);
            for (var i = 0; i < callGraph.Nodes.Count; i++)
            {
                var node = callGraph.Nodes[i];
                if (string.IsNullOrWhiteSpace(node.NodeId))
                {
                    errors.Add($"nodes[{i}].nodeId is required.");
                }
                else if (!nodeIds.Add(node.NodeId))
                {
                    errors.Add($"Duplicate nodeId '{node.NodeId}'.");
                }

                if (string.IsNullOrWhiteSpace(node.SymbolKey))
                {
                    errors.Add($"nodes[{i}].symbolKey is required.");
                }
            }
        }

        // Validate edges
        if (callGraph.Edges is null || callGraph.Edges.Count == 0)
        {
            errors.Add("At least one edge is required.");
        }
        else
        {
            var nodeIds = callGraph.Nodes?
                .Where(n => !string.IsNullOrWhiteSpace(n.NodeId))
                .Select(n => n.NodeId)
                .ToHashSet(StringComparer.Ordinal) ?? new HashSet<string>();

            for (var i = 0; i < callGraph.Edges.Count; i++)
            {
                var edge = callGraph.Edges[i];
                if (string.IsNullOrWhiteSpace(edge.From))
                {
                    errors.Add($"edges[{i}].from is required.");
                }
                else if (nodeIds.Count > 0 && !nodeIds.Contains(edge.From))
                {
                    errors.Add($"edges[{i}].from references unknown node '{edge.From}'.");
                }

                if (string.IsNullOrWhiteSpace(edge.To))
                {
                    errors.Add($"edges[{i}].to is required.");
                }
                else if (nodeIds.Count > 0 && !nodeIds.Contains(edge.To))
                {
                    errors.Add($"edges[{i}].to references unknown node '{edge.To}'.");
                }
            }
        }

        return errors.Count > 0
            ? CallGraphValidationResult.Failure(errors.ToArray())
            : CallGraphValidationResult.Success();
    }

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