using System.Diagnostics;
using System.Linq;
using Microsoft.AspNetCore.Http.HttpResults;
using Microsoft.AspNetCore.Mvc;
using StellaOps.Auth.Abstractions;
using StellaOps.Policy.Engine.BatchEvaluation;
using StellaOps.Policy.Engine.Services;

namespace StellaOps.Policy.Engine.Endpoints;

internal static class BatchEvaluationEndpoint
{
    public static IEndpointRouteBuilder MapBatchEvaluation(this IEndpointRouteBuilder routes)
    {
        var group = routes.MapGroup("/policy/eval")
            .RequireAuthorization()
            .WithTags("Policy Evaluation");

        group.MapPost("/batch", EvaluateBatchAsync)
            .WithName("PolicyEngine.BatchEvaluate")
            .WithSummary("Batch-evaluate policy packs against advisory/VEX/SBOM tuples with deterministic ordering and cache-aware responses.")
            .Produces<BatchEvaluationResponseDto>(StatusCodes.Status200OK)
            .Produces<ProblemHttpResult>(StatusCodes.Status400BadRequest);

        return routes;
    }

    private static async Task<IResult> EvaluateBatchAsync(
        HttpContext httpContext,
        [FromBody] BatchEvaluationRequestDto request,
        IRuntimeEvaluationExecutor evaluator,
        TimeProvider timeProvider,
        CancellationToken cancellationToken)
    {
        var scopeResult = ScopeAuthorization.RequireScope(httpContext, StellaOpsScopes.PolicyRead);
        if (scopeResult is not null)
        {
            return scopeResult;
        }

        if (!BatchEvaluationValidator.TryValidate(request, out var error))
        {
            return Results.BadRequest(new ProblemDetails
            {
                Title = "Invalid request",
                Detail = error,
                Status = StatusCodes.Status400BadRequest
            });
        }

        if (!TryParseOffset(request.PageToken, out var offset))
        {
            return Results.BadRequest(new ProblemDetails
            {
                Title = "Invalid pageToken",
                Detail = "pageToken must be a non-negative integer offset.",
                Status = StatusCodes.Status400BadRequest
            });
        }

        var pageSize = Math.Clamp(request.PageSize ?? 100, 1, 500);
        var budgetMs = request.BudgetMs;
        var sw = Stopwatch.StartNew();

        var pageItems = request.Items
            .Skip(offset)
            .Take(pageSize)
            .ToList();

        var runtimeRequests = BatchEvaluationMapper.ToRuntimeRequests(request.TenantId, pageItems);

        var results = new List<BatchEvaluationResultDto>(runtimeRequests.Count);
        var cacheHits = 0;
        var cacheMisses = 0;
        var processed = 0;

        foreach (var runtimeRequest in runtimeRequests)
        {
            if (budgetMs is int budget && sw.ElapsedMilliseconds >= budget)
            {
                break;
            }

            var response = await evaluator.EvaluateAsync(runtimeRequest, cancellationToken).ConfigureAwait(false);
            processed++;

            if (response.Cached)
            {
                cacheHits++;
            }
            else
            {
                cacheMisses++;
            }

            results.Add(new BatchEvaluationResultDto(
                response.PackId,
                response.Version,
                response.PolicyDigest,
                response.Status,
                response.Severity,
                response.RuleName,
                response.Priority,
                response.Annotations,
                response.Warnings,
                response.AppliedException,
                response.CorrelationId,
                response.Cached,
                response.CacheSource,
                response.EvaluationDurationMs));
        }

        var nextOffset = offset + processed;
        string? nextPageToken = null;
        if (nextOffset < request.Items.Count)
        {
            nextPageToken = nextOffset.ToString();
        }

        var budgetRemaining = budgetMs is int budgetValue
            ? Math.Max(0, budgetValue - sw.ElapsedMilliseconds)
            : (long?)null;

        var responsePayload = new BatchEvaluationResponseDto(
            Results: results,
            NextPageToken: nextPageToken,
            Total: request.Items.Count,
            Returned: processed,
            CacheHits: cacheHits,
            CacheMisses: cacheMisses,
            DurationMs: sw.ElapsedMilliseconds,
            BudgetRemainingMs: budgetRemaining);

        return Results.Ok(responsePayload);
    }

    private static bool TryParseOffset(string? token, out int offset)
    {
        if (string.IsNullOrWhiteSpace(token))
        {
            offset = 0;
            return true;
        }

        return int.TryParse(token, out offset) && offset >= 0;
    }
}