Add DISCORDCHATEXPORTER_SETTINGS_PATH env var override for settings file path (#1500)

Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>
Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>

DiscordChatExporter.Gui/Services/SettingsService.cs

@@ -1,6 +1,4 @@
-using System;
-using System.IO;
-using System.Text.Json.Serialization;
+using System.Text.Json.Serialization;
 using Cogwheel;
 using CommunityToolkit.Mvvm.ComponentModel;
 using DiscordChatExporter.Core.Discord;
@@ -13,10 +11,7 @@ namespace DiscordChatExporter.Gui.Services;
 
 [ObservableObject]
 public partial class SettingsService()
-    : SettingsBase(
-        Path.Combine(AppContext.BaseDirectory, "Settings.dat"),
-        SerializerContext.Default
-    )
+    : SettingsBase(StartOptions.Current.SettingsPath, SerializerContext.Default)
 {
     [ObservableProperty]
     public partial bool IsUkraineSupportMessageEnabled { get; set; } = true;

DiscordChatExporter.Gui/StartOptions.cs

@@ -0,0 +1,24 @@
+using System;
+using System.IO;
+
+namespace DiscordChatExporter.Gui;
+
+public partial class StartOptions
+{
+    public required string SettingsPath { get; init; }
+}
+
+public partial class StartOptions
+{
+    public static StartOptions Current { get; } =
+        new()
+        {
+            SettingsPath =
+                Environment.GetEnvironmentVariable("DISCORDCHATEXPORTER_SETTINGS_PATH") is { } path
+                && !string.IsNullOrWhiteSpace(path)
+                    ? Path.EndsInDirectorySeparator(path) || Directory.Exists(path)
+                        ? Path.Combine(path, "Settings.dat")
+                        : path
+                    : Path.Combine(AppContext.BaseDirectory, "Settings.dat"),
+        };
+}