using Duempelkas.App.Services.Models;
using System.Diagnostics;
using System.Runtime.InteropServices;
using Duempelkas.App.Services;
using Microsoft.Data.Sqlite;

namespace Duempelkas.Infrastructure.Services;

public class BackupService : IBackupService
{
    private readonly DatabaseLocation location;

    private readonly IFileDialogService dialogs;
    public BackupService(DatabaseLocation location, IFileDialogService? dialogs = null)
    {
        this.location = location;
        this.dialogs = dialogs ?? new FileDialogService();
    }

    public async Task<FileOperationResult> CreateBackupAsync()
    {
        try
        {
            var path = await dialogs.SaveAsync($"duempelkas-backup-{DateTime.Now:yyyyMMdd-HHmmss}.bak");
            if (string.IsNullOrWhiteSpace(path)) return FileOperationResult.Cancelled();
            await CreateBackupToAsync(path);
            return new(FileOperationStatus.Success, "Sicherung gespeichert.", path);
        }
        catch (Exception ex) { return FileOperationResult.Error(ex); }
    }

    public async Task<FileOperationResult> RestoreBackupAsync()
    {
        try
        {
            var path = await dialogs.OpenBackupAsync();
            if (string.IsNullOrWhiteSpace(path)) return FileOperationResult.Cancelled();
            var fallback = await RestoreFromAsync(path);
            return new(FileOperationStatus.Success, "Sicherung zurückgespielt. Die bisherigen Daten liegen in der Rückfallsicherung:", fallback);
        }
        catch (Exception ex) { return FileOperationResult.Error(ex); }
    }

    public async Task CreateBackupToAsync(string path)
    {
        using var lease = await DatabaseLease.AcquireAsync(location);
        RejectActivePath(path);
        await Task.Run(() =>
        {
            var staged = System.IO.Path.GetFullPath(path) + $".{Guid.NewGuid():N}.tmp";
            try
            {
                Snapshot(location.Path, staged);
                File.Move(staged, path, overwrite: true);
            }
            finally { if (File.Exists(staged)) File.Delete(staged); }
        });
    }

    public async Task<string> RestoreFromAsync(string path)
    {
        using var lease = await DatabaseLease.AcquireAsync(location);
        return await Task.Run(() =>
        {
            RejectActivePath(path);
            // Stage the selected database first, so a changing/removable source cannot
            // change between validation and restore. BackupDatabase includes WAL data.
            var staged = System.IO.Path.Combine(System.IO.Path.GetTempPath(), $"duempelkas-{Guid.NewGuid():N}.db");
            try
            {
                Snapshot(path, staged);
                Validate(staged);
                var fallback = location.Path + $".before-restore-{DateTime.Now:yyyyMMdd-HHmmss}-{Guid.NewGuid():N}.bak";
                Snapshot(location.Path, fallback);
                // SQLite's online backup atomically replaces database contents, retaining
                // the active file/handles and coordinating locks. Never copy over an open DB.
                Snapshot(staged, location.Path);
                return fallback;
            }
            finally { if (File.Exists(staged)) File.Delete(staged); }
        });
    }

    private void RejectActivePath(string path)
    {
        if (new[] { location.Path, location.Path + "-wal", location.Path + "-shm", location.Path + "-journal" }
            .Contains(System.IO.Path.GetFullPath(path), StringComparer.OrdinalIgnoreCase))
            throw new InvalidOperationException("Bitte eine andere Datei als die aktive Datenbank wählen.");
    }

    private static SqliteConnection Open(string path, SqliteOpenMode mode)
    {
        var connection = new SqliteConnection(new SqliteConnectionStringBuilder
        {
            DataSource = System.IO.Path.GetFullPath(path), Mode = mode, Pooling = false
        }.ToString());
        try { connection.Open(); return connection; }
        catch { connection.Dispose(); throw; }
    }

    private static void Snapshot(string source, string destination)
    {
        if (string.Equals(System.IO.Path.GetFullPath(source), System.IO.Path.GetFullPath(destination), StringComparison.OrdinalIgnoreCase))
            throw new InvalidOperationException("Quelle und Ziel müssen verschiedene Dateien sein.");
        using var input = Open(source, SqliteOpenMode.ReadOnly);
        using var output = Open(destination, SqliteOpenMode.ReadWriteCreate);
        input.BackupDatabase(output);
    }

    private static void Validate(string path)
    {
        using var connection = Open(path, SqliteOpenMode.ReadOnly);
        using var check = connection.CreateCommand();
        check.CommandText = "PRAGMA integrity_check";
        if (!string.Equals(check.ExecuteScalar()?.ToString(), "ok", StringComparison.Ordinal))
            throw new InvalidOperationException("Die Sicherung ist beschädigt.");
        check.CommandText = "PRAGMA foreign_key_check";
        using (var reader = check.ExecuteReader())
            if (reader.Read()) throw new InvalidOperationException("Die Sicherung enthält ungültige Verknüpfungen.");
        var options = new Microsoft.EntityFrameworkCore.DbContextOptionsBuilder<Duempelkas.Infrastructure.Persistence.FinanceDbContext>();
        Microsoft.EntityFrameworkCore.SqliteDbContextOptionsBuilderExtensions.UseSqlite(options, connection);
        using var db = new Duempelkas.Infrastructure.Persistence.FinanceDbContext(options.Options);
        var expected = Microsoft.EntityFrameworkCore.RelationalDatabaseFacadeExtensions.GetMigrations(db.Database).ToArray();
        var applied = Microsoft.EntityFrameworkCore.RelationalDatabaseFacadeExtensions.GetAppliedMigrations(db.Database).ToArray();
        if (!expected.SequenceEqual(applied))
            throw new InvalidOperationException("Diese Sicherung passt nicht zu dieser Programmversion.");
        // Materialize every mapped column to reject a forged/missing schema before touching active data.
        _ = db.Accounts.ToArray();
        _ = db.Entries.ToArray();
        _ = db.TransferLinks.ToArray();
    }

}