using System.Globalization;
using System.IO;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.Options;
using StellaOps.Concelier.WebService.Diagnostics;
using StellaOps.Concelier.WebService.Options;
using StellaOps.Concelier.WebService.Services;
using StellaOps.Concelier.WebService.Results;
using HttpResults = Microsoft.AspNetCore.Http.Results;

namespace StellaOps.Concelier.WebService.Extensions;

internal static class MirrorEndpointExtensions
{
    private const string IndexScope = "index";
    private const string DownloadScope = "download";

    public static void MapConcelierMirrorEndpoints(this WebApplication app, bool authorityConfigured, bool enforceAuthority)
    {
        app.MapGet("/concelier/exports/index.json", async (
            MirrorFileLocator locator,
            MirrorRateLimiter limiter,
            IOptionsMonitor<ConcelierOptions> optionsMonitor,
            HttpContext context,
            CancellationToken cancellationToken) =>
        {
            var mirrorOptions = optionsMonitor.CurrentValue.Mirror ?? new ConcelierOptions.MirrorOptions();
            if (!mirrorOptions.Enabled)
            {
                return ConcelierProblemResultFactory.MirrorNotFound(context);
            }

            if (!TryAuthorize(mirrorOptions.RequireAuthentication, enforceAuthority, context, authorityConfigured, out var unauthorizedResult))
            {
                return unauthorizedResult;
            }

            if (!limiter.TryAcquire("__index__", IndexScope, mirrorOptions.MaxIndexRequestsPerHour, out var retryAfter))
            {
                ApplyRetryAfter(context.Response, retryAfter);
                return ConcelierProblemResultFactory.RateLimitExceeded(context, (int?)retryAfter?.TotalSeconds);
            }

            if (!locator.TryResolveIndex(out var path, out _))
            {
                return ConcelierProblemResultFactory.MirrorNotFound(context);
            }

            return await WriteFileAsync(context, path, "application/json").ConfigureAwait(false);
        });

        app.MapGet("/concelier/exports/{**relativePath}", async (
            string? relativePath,
            MirrorFileLocator locator,
            MirrorRateLimiter limiter,
            IOptionsMonitor<ConcelierOptions> optionsMonitor,
            HttpContext context,
            CancellationToken cancellationToken) =>
        {
            var mirrorOptions = optionsMonitor.CurrentValue.Mirror ?? new ConcelierOptions.MirrorOptions();
            if (!mirrorOptions.Enabled)
            {
                return ConcelierProblemResultFactory.MirrorNotFound(context);
            }

            if (string.IsNullOrWhiteSpace(relativePath))
            {
                return ConcelierProblemResultFactory.MirrorNotFound(context);
            }

            if (!locator.TryResolveRelativePath(relativePath, out var path, out _, out var domainId))
            {
                return ConcelierProblemResultFactory.MirrorNotFound(context, relativePath);
            }

            var domain = FindDomain(mirrorOptions, domainId);

            if (!TryAuthorize(domain?.RequireAuthentication ?? mirrorOptions.RequireAuthentication, enforceAuthority, context, authorityConfigured, out var unauthorizedResult))
            {
                return unauthorizedResult;
            }

            var limit = domain?.MaxDownloadRequestsPerHour ?? mirrorOptions.MaxIndexRequestsPerHour;
            if (!limiter.TryAcquire(domain?.Id ?? "__mirror__", DownloadScope, limit, out var retryAfter))
            {
                ApplyRetryAfter(context.Response, retryAfter);
                return ConcelierProblemResultFactory.RateLimitExceeded(context, (int?)retryAfter?.TotalSeconds);
            }

            var contentType = ResolveContentType(path);
            return await WriteFileAsync(context, path, contentType).ConfigureAwait(false);
        });
    }

    private static ConcelierOptions.MirrorDomainOptions? FindDomain(ConcelierOptions.MirrorOptions mirrorOptions, string? domainId)
    {
        if (domainId is null)
        {
            return null;
        }

        foreach (var candidate in mirrorOptions.Domains)
        {
            if (candidate is null)
            {
                continue;
            }

            if (string.Equals(candidate.Id, domainId, StringComparison.OrdinalIgnoreCase))
            {
                return candidate;
            }
        }

        return null;
    }

    private static bool TryAuthorize(bool requireAuthentication, bool enforceAuthority, HttpContext context, bool authorityConfigured, out IResult result)
    {
        result = HttpResults.Empty;
        if (!requireAuthentication)
        {
            return true;
        }

        if (!enforceAuthority || !authorityConfigured)
        {
            return true;
        }

        if (context.User?.Identity?.IsAuthenticated == true)
        {
            return true;
        }

        context.Response.Headers.WWWAuthenticate = "Bearer realm=\"StellaOps Concelier Mirror\"";
        result = HttpResults.StatusCode(StatusCodes.Status401Unauthorized);
        return false;
    }

    private static Task<IResult> WriteFileAsync(HttpContext context, string path, string contentType)
    {
        var fileInfo = new FileInfo(path);
        if (!fileInfo.Exists)
        {
            return Task.FromResult(ConcelierProblemResultFactory.MirrorNotFound(context, path));
        }

        var stream = new FileStream(
            path,
            FileMode.Open,
            FileAccess.Read,
            FileShare.Read | FileShare.Delete);

        context.Response.Headers.CacheControl = BuildCacheControlHeader(path);
        context.Response.Headers.LastModified = fileInfo.LastWriteTimeUtc.ToString("R", CultureInfo.InvariantCulture);
        context.Response.ContentLength = fileInfo.Length;
        return Task.FromResult(HttpResults.Stream(stream, contentType));
    }

    private static string ResolveContentType(string path)
    {
        if (path.EndsWith(".json", StringComparison.OrdinalIgnoreCase))
        {
            return "application/json";
        }

        if (path.EndsWith(".jws", StringComparison.OrdinalIgnoreCase))
        {
            return "application/jose+json";
        }

        return "application/octet-stream";
    }

    private static void ApplyRetryAfter(HttpResponse response, TimeSpan? retryAfter)
    {
        if (retryAfter is null)
        {
            return;
        }

        var seconds = Math.Max((int)Math.Ceiling(retryAfter.Value.TotalSeconds), 1);
        response.Headers.RetryAfter = seconds.ToString(CultureInfo.InvariantCulture);
    }

    private static string BuildCacheControlHeader(string path)
    {
        var fileName = Path.GetFileName(path);
        if (fileName is null)
        {
            return "public, max-age=60";
        }

        if (string.Equals(fileName, "index.json", StringComparison.OrdinalIgnoreCase))
        {
            return "public, max-age=60";
        }

        if (fileName.EndsWith(".json", StringComparison.OrdinalIgnoreCase) ||
            fileName.EndsWith(".jws", StringComparison.OrdinalIgnoreCase))
        {
            return "public, max-age=300, immutable";
        }

        return "public, max-age=300";
    }
}