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

namespace DeskCore;

/// <summary>Export/Import aller Kategorien samt Einstellungen als ZIP.</summary>
public static class Backup
{
    private const string CategoriesPrefix = "Kategorien/";
    private const string SettingsEntry = "einstellungen.json";

    public static long StorageSize()
    {
        try
        {
            return Directory.EnumerateFiles(Storage.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>Gibt die Anzahl gesicherter Dateien zurück.</summary>
    public static int Export(string zipPath)
    {
        if (File.Exists(zipPath)) File.Delete(zipPath);
        int count = 0;
        using var zip = ZipFile.Open(zipPath, ZipArchiveMode.Create);
        foreach (var cat in Storage.Categories())
        {
            var dir = Storage.CategoryPath(cat);
            zip.CreateEntry(CategoriesPrefix + cat + "/"); // auch leere Kategorien sichern
            foreach (var f in Directory.EnumerateFiles(dir, "*", SearchOption.AllDirectories))
            {
                var rel = Path.GetRelativePath(Storage.Root, f).Replace('\\', '/');
                zip.CreateEntryFromFile(f, CategoriesPrefix + rel, CompressionLevel.Optimal);
                count++;
            }
            foreach (var d in Directory.EnumerateDirectories(dir, "*", SearchOption.AllDirectories))
                if (!Directory.EnumerateFileSystemEntries(d).Any())
                    zip.CreateEntry(CategoriesPrefix + Path.GetRelativePath(Storage.Root, d).Replace('\\', '/') + "/");
        }
        var entry = zip.CreateEntry(SettingsEntry);
        using (var w = new StreamWriter(entry.Open()))
            w.Write(JsonSerializer.Serialize(AppSettings.Current, AppSettings.Json));
        return count;
    }

    /// <summary>Führt eine Sicherung mit dem Bestand zusammen. Vorhandenes wird nicht überschrieben.</summary>
    public static (int Added, int Skipped) Import(string zipPath)
    {
        int added = 0, skipped = 0;
        using var zip = ZipFile.OpenRead(zipPath);
        var root = Path.GetFullPath(Storage.Root);

        foreach (var e in zip.Entries)
        {
            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++; continue; }
            Directory.CreateDirectory(Path.GetDirectoryName(target)!);
            e.ExtractToFile(target);
            added++;
        }

        if (zip.GetEntry(SettingsEntry) is { } se)
        {
            try
            {
                using var r = new StreamReader(se.Open());
                var imported = JsonSerializer.Deserialize<AppSettings>(r.ReadToEnd(), AppSettings.Json);
                if (imported is not null) Merge(imported);
            }
            catch { }
        }
        return (added, skipped);
    }

    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();
    }
}