using System;
using System.IO;

namespace Notify.Ipc;

/// <summary>
/// Host 侧：监视 spool 目录，新文件出现即消费并回调
/// </summary>
public sealed class SpoolWatcher
{
    private readonly Action<NotifyMessage> _onMessage;
    private FileSystemWatcher? _watcher;

    public SpoolWatcher(Action<NotifyMessage> onMessage) => _onMessage = onMessage;

    public void Start()
    {
        Directory.CreateDirectory(NotificationSpool.Dir);

        // 先补弹启动前堆积的请求
        NotificationSpool.DrainExisting(_onMessage);

        _watcher = new FileSystemWatcher(NotificationSpool.Dir, "*.json")
        {
            NotifyFilter = NotifyFilters.FileName,
            EnableRaisingEvents = true,
        };
        _watcher.Created += OnCreated;
        _watcher.Renamed += OnRenamed;
    }

    private void OnCreated(object sender, FileSystemEventArgs e) => Handle(e.FullPath);

    private void OnRenamed(object sender, RenamedEventArgs e) => Handle(e.FullPath);

    private void Handle(string path)
    {
        if (NotificationSpool.ReadAndRemove(path) is { } msg)
        {
            _onMessage(msg);
        }
    }
}