using System.Text;
using System.Text.Json;
using SharepointToolbox.Web.Core.Models;

namespace SharepointToolbox.Web.Infrastructure.Persistence;

/// <summary>
/// JSON-file index of produced report files (reports-index.json). The files
/// themselves live under {ExportsFolder}/{ProfileId}/; this is the catalogue the
/// per-client "Reports" list and the id-based download endpoint read.
/// </summary>
public class GeneratedReportRepository
{
    private readonly string _filePath;
    private readonly SemaphoreSlim _writeLock = new(1, 1);

    private static readonly JsonSerializerOptions ReadOpts = new() { PropertyNameCaseInsensitive = true };
    private static readonly JsonSerializerOptions WriteOpts = new()
    {
        WriteIndented = true,
        PropertyNamingPolicy = JsonNamingPolicy.CamelCase
    };

    public GeneratedReportRepository(string filePath) { _filePath = filePath; }

    public async Task<IReadOnlyList<GeneratedReport>> LoadAsync()
    {
        if (!File.Exists(_filePath)) return Array.Empty<GeneratedReport>();
        string json;
        try { json = await File.ReadAllTextAsync(_filePath, Encoding.UTF8); }
        catch (IOException ex) { throw new InvalidDataException($"Failed to read report index: {_filePath}", ex); }

        Root? root;
        try { root = JsonSerializer.Deserialize<Root>(json, ReadOpts); }
        catch (JsonException ex) { throw new InvalidDataException($"Invalid JSON in report index: {_filePath}", ex); }

        return (IReadOnlyList<GeneratedReport>?)root?.Reports ?? Array.Empty<GeneratedReport>();
    }

    public async Task<GeneratedReport?> GetAsync(string id)
        => (await LoadAsync()).FirstOrDefault(r => r.Id == id);

    public async Task<IReadOnlyList<GeneratedReport>> LoadForProfileAsync(string profileId)
    {
        var all = await LoadAsync();
        return all.Where(r => r.ProfileId == profileId)
                  .OrderByDescending(r => r.GeneratedUtc)
                  .ToList();
    }

    public async Task AddAsync(GeneratedReport report)
    {
        await _writeLock.WaitAsync();
        try
        {
            var list = (await LoadAsync()).ToList();
            list.Add(report);
            await WriteUnlockedAsync(list);
        }
        finally { _writeLock.Release(); }
    }

    public async Task DeleteAsync(string id)
    {
        await _writeLock.WaitAsync();
        try
        {
            var list = (await LoadAsync()).ToList();
            list.RemoveAll(r => r.Id == id);
            await WriteUnlockedAsync(list);
        }
        finally { _writeLock.Release(); }
    }

    private async Task WriteUnlockedAsync(IReadOnlyList<GeneratedReport> reports)
    {
        var json = JsonSerializer.Serialize(new Root { Reports = reports.ToList() }, WriteOpts);
        var tmpPath = _filePath + ".tmp";
        var dir = Path.GetDirectoryName(_filePath);
        if (!string.IsNullOrEmpty(dir)) Directory.CreateDirectory(dir);
        await File.WriteAllTextAsync(tmpPath, json, Encoding.UTF8);
        JsonDocument.Parse(await File.ReadAllTextAsync(tmpPath, Encoding.UTF8)).Dispose();
        File.Move(tmpPath, _filePath, overwrite: true);
    }

    private sealed class Root { public List<GeneratedReport> Reports { get; set; } = new(); }
}