using System.Text.Json;
using LehrerApp.Sync;

namespace LehrerApp.Api;

/// <summary>
/// Stoppt veraltete Sync-Clients vor Authentifizierung und insbesondere vor jedem Store-Zugriff.
/// Die Prüfung gilt auch für Anhänge, Plain-Sync und Device-Pairing-Snapshots.
/// </summary>
public sealed class SyncProtocolVersionMiddleware(RequestDelegate next)
{
    public async Task InvokeAsync(HttpContext context)
    {
        if (!IsProtectedSyncPath(context.Request.Path))
        {
            await next(context);
            return;
        }

        context.Response.Headers[SyncProtocol.VersionHeaderName] = SyncProtocol.CurrentVersion;
        var clientVersion = context.Request.Headers[SyncProtocol.VersionHeaderName].ToString();
        if (string.Equals(clientVersion, SyncProtocol.CurrentVersion, StringComparison.Ordinal))
        {
            await next(context);
            return;
        }

        context.Response.StatusCode = StatusCodes.Status426UpgradeRequired;
        context.Response.ContentType = "application/problem+json";
        await JsonSerializer.SerializeAsync(context.Response.Body, new
        {
            type = "https://lehrerapp.local/problems/sync-version-mismatch",
            title = "Inkompatible Sync-Version",
            status = StatusCodes.Status426UpgradeRequired,
            detail = $"Der Server erwartet Sync-Version {SyncProtocol.CurrentVersion}.",
            expectedVersion = SyncProtocol.CurrentVersion,
            receivedVersion = string.IsNullOrEmpty(clientVersion) ? null : clientVersion,
        });
    }

    private static bool IsProtectedSyncPath(PathString path) =>
        path.StartsWithSegments("/api/sync", StringComparison.OrdinalIgnoreCase) ||
        path.StartsWithSegments("/api/snapshot", StringComparison.OrdinalIgnoreCase);
}