Save/load settings, Move about window to dialog

Models/ReportFile.cs

@@ -1,5 +1,6 @@
 using System;
 using System.IO;
+using System.Text.Json.Serialization;
 using ReceiptPDFBuilder.Helpers;
 
 namespace ReceiptPDFBuilder.Models;
@@ -44,6 +45,7 @@ class ReportFile : ChangeNotifier
         }
     }
 
+    [JsonIgnore]
     public DateOnly ReceiptDate
     {
         get => DateOnly.FromDateTime(_receiptDateTime);
@@ -61,6 +63,7 @@ class ReportFile : ChangeNotifier
         set { _filePath = value; NotifyPropertyChanged(); }
     }
 
+    [JsonIgnore]
     public string FileName
     {
         get => Path.GetFileName(_filePath);

Models/Settings.cs

@@ -0,0 +1,86 @@
+using System;
+using System.IO;
+using System.Text;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using System.Threading.Tasks;
+using ReceiptPDFBuilder.Helpers;
+
+namespace ReceiptPDFBuilder.Models;
+
+class Settings : ChangeNotifier
+{
+    private string _lastUsedPath;
+
+    public Settings()
+    {
+        _lastUsedPath = "";
+    }
+
+    [JsonInclude]
+    public string LastUsedPath
+    {
+        get => _lastUsedPath;
+        set { _lastUsedPath = value; NotifyPropertyChanged(); }
+    }
+
+    public static string GetSettingsFileName()
+    {
+        return "settings.json";
+    }
+
+    public static string GetSettingsPath()
+    {
+        var path = Path.Combine(
+            Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData),
+            "ReceiptPDFBuilder"
+        );
+        if (!Directory.Exists(path))
+        {
+            Directory.CreateDirectory(path);
+        }
+        return Path.Combine(path, GetSettingsFileName());
+    }
+
+    private static JsonSerializerOptions GetSerializerOptions()
+    {
+        var opts = new JsonSerializerOptions 
+        { 
+            WriteIndented = false,
+            DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
+        };
+        return opts;
+    }
+
+    public async Task<string> SaveSettingsAsync()
+    {
+        var jsonContext = new SourceGenerationContext(GetSerializerOptions());
+        using MemoryStream memoryStream = new MemoryStream();
+        await JsonSerializer.SerializeAsync(memoryStream, this, jsonContext.Settings);
+        memoryStream.Position = 0;
+        using var reader = new StreamReader(memoryStream);
+        var json = await reader.ReadToEndAsync();
+        await File.WriteAllTextAsync(GetSettingsPath(), json);
+        return json;
+    }
+
+    public static Settings LoadSettings()
+    {
+        var path = GetSettingsPath();
+        if (!File.Exists(path))
+        {
+            return new Settings();
+        }
+        var json = File.ReadAllText(GetSettingsPath());
+        var jsonContext = new SourceGenerationContext(GetSerializerOptions());
+        return JsonSerializer.Deserialize<Settings>(json, jsonContext.Settings) ?? new Settings();
+    }
+
+    public static async Task<Settings> LoadSettingsAsync()
+    {
+        using FileStream fileStream = File.OpenRead(GetSettingsPath());
+        var jsonContext = new SourceGenerationContext(GetSerializerOptions());
+        var output = await JsonSerializer.DeserializeAsync<Settings>(fileStream, jsonContext.Settings) ?? new Settings();
+        return output;
+    }
+}