using System.Security.Cryptography;
using System.Text.Json;
using KronaStaffTerminal.Models;

namespace KronaStaffTerminal.Services;

public sealed class TerminalStore
{
    private static readonly byte[] Entropy = "Krona.Staff.Terminal.v1"u8.ToArray();
    private static readonly JsonSerializerOptions JsonOptions = new() { WriteIndented = true };
    private readonly SemaphoreSlim _saveGate = new(1, 1);
    private readonly string _filePath = Path.Combine(
        Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData),
        "Krona",
        "StaffTerminal",
        "terminal-state.dat");

    public async Task<TerminalState> LoadAsync()
    {
        var sourcePath = File.Exists(_filePath) ? _filePath : FindLegacyPackagedState();
        if (sourcePath is null) return new TerminalState();

        try
        {
            var state = await ReadStateAsync(sourcePath);
            var migrated = MigrateFingerprints(state);
            if (migrated || !string.Equals(sourcePath, _filePath, StringComparison.OrdinalIgnoreCase))
            {
                await SaveAsync(state);
            }
            return state;
        }
        catch (Exception primaryException) when (string.Equals(sourcePath, _filePath, StringComparison.OrdinalIgnoreCase))
        {
            var corruptPath = _filePath + $".corrupt-{DateTimeOffset.UtcNow:yyyyMMdd-HHmmss}";
            try
            {
                File.Move(_filePath, corruptPath, false);
            }
            catch (Exception moveException)
            {
                throw new InvalidDataException(
                    "Хранилище терминала повреждено и не может быть сохранено отдельно. Работа заблокирована, чтобы не потерять данные.",
                    new AggregateException(primaryException, moveException));
            }

            foreach (var backupPath in BackupPaths())
            {
                if (!File.Exists(backupPath)) continue;
                try
                {
                    var recovered = await ReadStateAsync(backupPath);
                    MigrateFingerprints(recovered);
                    await SaveAsync(recovered);
                    return recovered;
                }
                catch (Exception backupException)
                {
                    CrashLogService.Write(backupException);
                }
            }

            throw new InvalidDataException(
                $"Хранилище терминала повреждено. Исходный файл сохранён как {Path.GetFileName(corruptPath)}. Работа заблокирована до восстановления резервной копии.",
                primaryException);
        }
    }

    private static async Task<TerminalState> ReadStateAsync(string path)
    {
        var encrypted = await File.ReadAllBytesAsync(path);
        var clear = ProtectedData.Unprotect(encrypted, Entropy, DataProtectionScope.CurrentUser);
        return JsonSerializer.Deserialize<TerminalState>(clear, JsonOptions)
               ?? throw new InvalidDataException("Файл состояния не содержит данных.");
    }

    private static bool MigrateFingerprints(TerminalState state)
    {
        var changed = false;
        foreach (var employee in state.Employees)
        {
            employee.Fingerprints ??= [];
            if (employee.FingerprintId <= 0 || string.IsNullOrWhiteSpace(employee.FingerprintTemplate))
            {
                continue;
            }

            if (employee.Fingerprints.All(item => item.Id != employee.FingerprintId))
            {
                employee.Fingerprints.Add(new FingerprintRecord
                {
                    Id = employee.FingerprintId,
                    Template = employee.FingerprintTemplate,
                    Label = "Отпечаток 1"
                });
            }
            employee.FingerprintId = 0;
            employee.FingerprintTemplate = null;
            changed = true;
        }
        return changed;
    }

    public async Task SaveAsync(TerminalState state)
    {
        await _saveGate.WaitAsync();
        try
        {
            var directory = Path.GetDirectoryName(_filePath)!;
            Directory.CreateDirectory(directory);
            var clear = JsonSerializer.SerializeToUtf8Bytes(state, JsonOptions);
            var encrypted = ProtectedData.Protect(clear, Entropy, DataProtectionScope.CurrentUser);
            var temporaryPath = _filePath + ".tmp";
            await using (var stream = new FileStream(
                             temporaryPath,
                             FileMode.Create,
                             FileAccess.Write,
                             FileShare.None,
                             4096,
                             FileOptions.Asynchronous | FileOptions.WriteThrough))
            {
                await stream.WriteAsync(encrypted);
                await stream.FlushAsync();
                stream.Flush(true);
            }

            RotateBackups();
            File.Move(temporaryPath, _filePath, true);
        }
        finally
        {
            _saveGate.Release();
        }
    }

    private IEnumerable<string> BackupPaths()
    {
        for (var index = 1; index <= 3; index++) yield return _filePath + $".bak{index}";
    }

    private void RotateBackups()
    {
        var backups = BackupPaths().ToArray();
        for (var index = backups.Length - 1; index > 0; index--)
        {
            if (File.Exists(backups[index - 1])) File.Copy(backups[index - 1], backups[index], true);
        }
        if (File.Exists(_filePath)) File.Copy(_filePath, backups[0], true);
    }

    private static string? FindLegacyPackagedState()
    {
        var packagesPath = Path.Combine(
            Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData),
            "Packages");
        if (!Directory.Exists(packagesPath)) return null;
        return Directory.EnumerateDirectories(packagesPath, "223A9635-262B-4298-9F19-1D2FE0A6B5F7_*")
            .Select(directory => Path.Combine(directory, "LocalCache", "Local", "Krona", "StaffTerminal", "terminal-state.dat"))
            .FirstOrDefault(File.Exists);
    }
}