using System.IO;
using System.IO.Compression;
using System.Text.Json;

namespace DeskCore;

/// <summary>Export/Import aller Kategorien samt Einstellungen als ZIP – mit Fortschritt und Abbrechen.</summary>
public static class Backup
{
    private const string CategoriesPrefix = "Kategorien/";
    private const string SettingsEntry = "einstellungen.json";
    private const int Chunk = 1 << 20;

    public static long StorageSize() => StorageSize(Storage.Root);

    public static long StorageSize(string root)
    {
        try
        {
            return Directory.EnumerateFiles(root, "*", SearchOption.AllDirectories)
                .Sum(f => { try { return new FileInfo(f).Length; } catch { return 0L; } });
        }
        catch { return 0; }
    }

    public static string FormatSize(long bytes) => bytes switch
    {
        < 1024 * 1024 => $"{Math.Max(1, bytes / 1024)} KB",
        < 1024L * 1024 * 1024 => $"{bytes / 1024.0 / 1024:0.#} MB",
        _ => $"{bytes / 1024.0 / 1024 / 1024:0.##} GB",
    };

    /// <summary>Sichert alle Kategorien. Gibt die Anzahl gesicherter Dateien zurück.</summary>
    public static int Export(string zipPath, Action<long>? onBytes = null, CancellationToken ct = default) =>
        Export(zipPath, Storage.Root, Storage.Categories(), JsonSerializer.Serialize(AppSettings.Current, AppSettings.Json), onBytes, ct);

    public static int Export(string zipPath, string root, IEnumerable<string> categories, string settingsJson,
        Action<long>? onBytes = null, CancellationToken ct = default)
    {
        var tmp = zipPath + ".teil";
        int count = 0;
        try
        {
            if (File.Exists(tmp)) File.Delete(tmp);
            // große Sicherungen bestehen meist aus Videos/Bildern → stärkere Kompression bringt kaum etwas
            var level = StorageSize(root) > 1L << 30 ? CompressionLevel.Fastest : CompressionLevel.Optimal;
            using (var zip = ZipFile.Open(tmp, ZipArchiveMode.Create))
            {
                foreach (var cat in categories)
                {
                    var dir = Path.Combine(root, cat);
                    zip.CreateEntry(CategoriesPrefix + cat + "/"); // auch leere Kategorien sichern
                    foreach (var f in Directory.EnumerateFiles(dir, "*", SearchOption.AllDirectories))
                    {
                        ct.ThrowIfCancellationRequested();
                        var rel = Path.GetRelativePath(root, f).Replace('\\', '/');
                        var entry = zip.CreateEntry(CategoriesPrefix + rel, level);
                        entry.LastWriteTime = File.GetLastWriteTime(f);
                        using (var input = new FileStream(f, FileMode.Open, FileAccess.Read, FileShare.ReadWrite, Chunk, FileOptions.SequentialScan))
                        using (var output = entry.Open())
                            CopyWithProgress(input, output, onBytes, ct);
                        count++;
                    }
                    foreach (var d in Directory.EnumerateDirectories(dir, "*", SearchOption.AllDirectories))
                        if (!Directory.EnumerateFileSystemEntries(d).Any())
                            zip.CreateEntry(CategoriesPrefix + Path.GetRelativePath(root, d).Replace('\\', '/') + "/");
                }
                var se = zip.CreateEntry(SettingsEntry);
                using (var w = new StreamWriter(se.Open()))
                    w.Write(settingsJson);
            }
            // erst am Ende an den richtigen Namen – so bleibt nie eine halbe Sicherung mit gültigem Namen liegen
            if (File.Exists(zipPath)) File.Delete(zipPath);
            File.Move(tmp, zipPath);
            return count;
        }
        catch
        {
            try { if (File.Exists(tmp)) File.Delete(tmp); } catch { }
            throw;
        }
    }

    /// <summary>Summe der unkomprimierten Größen (für die Fortschrittsanzeige beim Wiederherstellen).</summary>
    public static long ArchiveSize(string zipPath)
    {
        using var zip = ZipFile.OpenRead(zipPath);
        return zip.Entries.Sum(e => e.Length);
    }

    /// <summary>Führt eine Sicherung mit dem Bestand zusammen. Vorhandenes wird nicht überschrieben.</summary>
    public static (int Added, int Skipped) Import(string zipPath, Action<long>? onBytes = null, CancellationToken ct = default)
    {
        var (added, skipped, settings) = Import(zipPath, Storage.Root, onBytes, ct);
        if (settings is not null) Merge(settings);
        return (added, skipped);
    }

    public static (int Added, int Skipped, AppSettings? Settings) Import(string zipPath, string root,
        Action<long>? onBytes = null, CancellationToken ct = default)
    {
        int added = 0, skipped = 0;
        AppSettings? settings = null;
        using var zip = ZipFile.OpenRead(zipPath);
        root = Path.GetFullPath(root);

        foreach (var e in zip.Entries)
        {
            ct.ThrowIfCancellationRequested();
            if (e.FullName.Equals(SettingsEntry, StringComparison.OrdinalIgnoreCase))
            {
                try
                {
                    using var r = new StreamReader(e.Open());
                    settings = JsonSerializer.Deserialize<AppSettings>(r.ReadToEnd(), AppSettings.Json);
                }
                catch { }
                continue;
            }
            if (!e.FullName.StartsWith(CategoriesPrefix, StringComparison.OrdinalIgnoreCase)) continue;
            var rel = e.FullName[CategoriesPrefix.Length..];
            if (rel.Length == 0) continue;
            var target = Path.GetFullPath(Path.Combine(root, rel));
            if (!Storage.IsUnder(target, root)) continue; // Schutz vor manipulierten ZIPs

            if (e.FullName.EndsWith('/'))
            {
                Directory.CreateDirectory(target);
                continue;
            }
            if (File.Exists(target)) { skipped++; onBytes?.Invoke(e.Length); continue; }
            Directory.CreateDirectory(Path.GetDirectoryName(target)!);
            try
            {
                using (var input = e.Open())
                using (var output = new FileStream(target, FileMode.CreateNew, FileAccess.Write, FileShare.None, Chunk))
                    CopyWithProgress(input, output, onBytes, ct);
                File.SetLastWriteTime(target, e.LastWriteTime.DateTime);
            }
            catch (OperationCanceledException)
            {
                try { File.Delete(target); } catch { } // halbe Datei nicht liegen lassen
                throw;
            }
            added++;
        }
        return (added, skipped, settings);
    }

    private static void CopyWithProgress(Stream input, Stream output, Action<long>? onBytes, CancellationToken ct)
    {
        var buffer = new byte[Chunk];
        int read;
        while ((read = input.Read(buffer, 0, buffer.Length)) > 0)
        {
            ct.ThrowIfCancellationRequested();
            output.Write(buffer, 0, read);
            onBytes?.Invoke(read);
        }
    }

    private static void Merge(AppSettings from)
    {
        var s = AppSettings.Current;
        foreach (var (name, meta) in from.Categories ?? [])
            if (!s.Categories.ContainsKey(name)) s.Categories[name] = meta;
        foreach (var n in from.CategoryOrder ?? [])
            if (!s.CategoryOrder.Contains(n, StringComparer.OrdinalIgnoreCase)) s.CategoryOrder.Add(n);
        foreach (var r in from.Rules ?? [])
            if (!s.Rules.Any(x => string.Equals(x.Contains, r.Contains, StringComparison.OrdinalIgnoreCase) &&
                                  string.Equals(x.Category, r.Category, StringComparison.OrdinalIgnoreCase)))
                s.Rules.Add(r);
        s.Save();
    }
}