using System.Text.Json;
using foodmarket.Application.Notifications;
using foodmarket.Infrastructure.Persistence;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Logging;
using WebPush;

namespace foodmarket.Infrastructure.Notifications;

/// <summary>Реальная отправка Web Push (VAPID) через web-push-csharp. Ключи VAPID
/// хранятся в PlatformSettings (singleton) — генерируются один раз при первом
/// обращении. Payload — JSON {title, body, url}, который разбирает service worker.
///
/// Best-effort: любая ошибка доставки логируется и не валит вызывающего; подписки,
/// на которые push-сервис ответил 404/410 (устройство отписалось), удаляются.</summary>
public sealed class WebPushSender : IWebPushSender
{
    private readonly AppDbContext _db;
    private readonly ILogger<WebPushSender> _log;
    private static readonly WebPushClient _client = new();

    public WebPushSender(AppDbContext db, ILogger<WebPushSender> log) { _db = db; _log = log; }

    // Ключи в БД → всегда можно сгенерировать, поэтому включён всегда.
    public bool IsEnabled => true;

    public async Task<string> GetPublicKeyAsync(CancellationToken ct = default)
    {
        var (pub, _, _) = await EnsureKeysAsync(ct);
        return pub;
    }

    private async Task<(string Public, string Private, string Subject)> EnsureKeysAsync(CancellationToken ct)
    {
        var ps = await _db.PlatformSettings.FirstOrDefaultAsync(ct);
        if (ps is null)
        {
            ps = new Domain.Platform.PlatformSettings();
            _db.PlatformSettings.Add(ps);
        }
        if (string.IsNullOrWhiteSpace(ps.WebPushVapidPublicKey) || string.IsNullOrWhiteSpace(ps.WebPushVapidPrivateKey))
        {
            var keys = VapidHelper.GenerateVapidKeys();
            ps.WebPushVapidPublicKey = keys.PublicKey;
            ps.WebPushVapidPrivateKey = keys.PrivateKey;
            await _db.SaveChangesAsync(ct);
            _log.LogInformation("Сгенерирована пара VAPID-ключей для Web Push");
        }
        var subject = string.IsNullOrWhiteSpace(ps.WebPushVapidSubject) ? "mailto:admin@food-market.kz" : ps.WebPushVapidSubject!;
        return (ps.WebPushVapidPublicKey!, ps.WebPushVapidPrivateKey!, subject);
    }

    public async Task SendToUsersAsync(IReadOnlyCollection<Guid> userIds, string title, string body,
        string? link = null, IReadOnlyDictionary<string, string>? data = null, CancellationToken ct = default)
    {
        if (userIds.Count == 0) return;
        var subs = await _db.WebPushSubscriptions.Where(s => userIds.Contains(s.UserId)).ToListAsync(ct);
        if (subs.Count == 0) return;

        var (pub, priv, subject) = await EnsureKeysAsync(ct);
        var vapid = new VapidDetails(subject, pub, priv);
        var payload = JsonSerializer.Serialize(new
        {
            title, body, url = link ?? "/",
            data = data ?? new Dictionary<string, string>(),
        });

        var dead = new List<Domain.Notifications.WebPushSubscription>();
        foreach (var s in subs)
        {
            try
            {
                var pushSub = new PushSubscription(s.Endpoint, s.P256dh, s.Auth);
                await _client.SendNotificationAsync(pushSub, payload, vapid, ct);
            }
            catch (WebPushException ex) when ((int)ex.StatusCode is 404 or 410)
            {
                dead.Add(s); // устройство отписалось — удаляем подписку
            }
            catch (Exception ex)
            {
                _log.LogWarning(ex, "Web push не доставлен на подписку {Id}", s.Id);
            }
        }
        if (dead.Count > 0)
        {
            _db.WebPushSubscriptions.RemoveRange(dead);
            await _db.SaveChangesAsync(ct);
        }
    }
}