using System.Text.Json;

namespace VideoDownloader.Mobile;

public sealed record OfflineItem(string Id, string FileName, long SizeBytes);

/// <summary>
/// 폰 오프라인 저장(U4): 라이브러리 항목을 앱 전용 폴더에 저장·목록·삭제.
/// manifest.json(id→파일명)으로 서버 항목과 매핑한다.
/// </summary>
public sealed class OfflineStore
{
    public static OfflineStore Default { get; } = new();

    private readonly string _dir;
    private readonly string _manifestPath;
    private readonly object _gate = new();
    private Dictionary<string, string> _manifest;

    public OfflineStore()
    {
        _dir = Path.Combine(FileSystem.AppDataDirectory, "offline");
        _manifestPath = Path.Combine(_dir, "manifest.json");
        try
        {
            if (File.Exists(_manifestPath))
                _manifest = JsonSerializer.Deserialize<Dictionary<string, string>>(File.ReadAllText(_manifestPath)) ?? new();
        }
        catch { }
        _manifest ??= new Dictionary<string, string>();
    }

    public string Directory => _dir;

    public string PathFor(string id) => Path.Combine(_dir, id + Path.GetExtension(_manifest.GetValueOrDefault(id, ".mp4")));

    public bool Exists(string id) { lock (_gate) { var p = PathFor(id); return File.Exists(p) && _manifest.ContainsKey(id); } }

    /// <summary>다운로드 완료 후 등록.</summary>
    public void Record(string id, string fileName)
    {
        lock (_gate)
        {
            System.IO.Directory.CreateDirectory(_dir);
            _manifest[id] = fileName;
            Save();
        }
    }

    public void Delete(string id)
    {
        lock (_gate)
        {
            try { if (File.Exists(PathFor(id))) File.Delete(PathFor(id)); } catch { }
            _manifest.Remove(id);
            Save();
        }
    }

    public List<OfflineItem> List()
    {
        lock (_gate)
            return _manifest.Select(kv =>
            {
                var p = PathFor(kv.Key);
                return new OfflineItem(kv.Key, kv.Value, File.Exists(p) ? new FileInfo(p).Length : 0);
            }).Where(i => i.SizeBytes > 0).ToList();
    }

    private void Save()
    {
        try { System.IO.Directory.CreateDirectory(_dir); File.WriteAllText(_manifestPath, JsonSerializer.Serialize(_manifest)); } catch { }
    }}