fix: handle empty blueprint exports from shopping list

Yafc.Model.Tests/Blueprints/BlueprintUtilitiesTests.cs

@@ -0,0 +1,53 @@
+using System;
+using System.IO;
+using System.IO.Compression;
+using System.Text;
+using System.Text.Json;
+using Xunit;
+using Yafc.Blueprints;
+
+namespace Yafc.Model.Tests.Blueprints;
+
+public class BlueprintUtilitiesTests {
+    [Fact]
+    public void ExportConstantCombinators_WithEmptyGoods_ReturnsEmptyBlueprint() {
+        string blueprintString = BlueprintUtilities.ExportConstantCombinators(
+            "empty",
+            Array.Empty<(IObjectWithQuality<Goods> item, int amount)>());
+
+        AssertEmptyBlueprint(blueprintString, "empty");
+    }
+
+    [Fact]
+    public void ExportRequesterChests_WithEmptyGoods_ReturnsEmptyBlueprint() {
+        EntityContainer chest = new() {
+            logisticSlotsCount = 10,
+        };
+
+        string blueprintString = BlueprintUtilities.ExportRequesterChests(
+            "empty",
+            Array.Empty<(IObjectWithQuality<Item> item, int amount)>(),
+            chest);
+
+        AssertEmptyBlueprint(blueprintString, "empty");
+    }
+
+    private static void AssertEmptyBlueprint(string blueprintString, string name) {
+        Assert.StartsWith("0", blueprintString);
+        using JsonDocument document = JsonDocument.Parse(DecodeBlueprintString(blueprintString));
+        JsonElement blueprint = document.RootElement.GetProperty("blueprint");
+
+        Assert.Equal("blueprint", blueprint.GetProperty("item").GetString());
+        Assert.Equal(name, blueprint.GetProperty("label").GetString());
+        Assert.Empty(blueprint.GetProperty("entities").EnumerateArray());
+    }
+
+    private static string DecodeBlueprintString(string blueprintString) {
+        byte[] compressed = Convert.FromBase64String(blueprintString[1..]);
+        using MemoryStream input = new MemoryStream(compressed);
+        using ZLibStream zlib = new ZLibStream(input, CompressionMode.Decompress);
+        using MemoryStream output = new MemoryStream();
+        zlib.CopyTo(output);
+        return Encoding.UTF8.GetString(output.ToArray());
+    }
+}

Yafc.Model/Blueprints/BlueprintUtilities.cs

@@ -8,6 +8,10 @@ namespace Yafc.Blueprints;
 
 public static class BlueprintUtilities {
     public static string ExportConstantCombinators(string name, IReadOnlyList<(IObjectWithQuality<Goods> item, int amount)> goods) {
+        if (goods.Count == 0) {
+            return ExportEmptyBlueprint(name);
+        }
+
         int combinatorCount = ((goods.Count - 1) / Database.constantCombinatorCapacity) + 1;
         int offset = -combinatorCount / 2;
         BlueprintString blueprint = new BlueprintString(name);
@@ -45,6 +49,10 @@ public static string ExportRequesterChests(string name, IReadOnlyList<(IObjectWi
             throw new ArgumentException("Chest does not have logistic slots");
         }
 
+        if (goods.Count == 0) {
+            return ExportEmptyBlueprint(name);
+        }
+
         int combinatorCount = ((goods.Count - 1) / chest.logisticSlotsCount) + 1;
         int offset = -chest.size * combinatorCount / 2;
         BlueprintString blueprint = new BlueprintString(name);
@@ -76,6 +84,9 @@ public static string ExportRequesterChests(string name, IReadOnlyList<(IObjectWi
         return blueprint.ToBpString();
     }
 
+    private static string ExportEmptyBlueprint(string name)
+        => new BlueprintString(name).ToBpString();
+
     private class PlacedEntity {
         public RecipeRow Recipe { get; }
         public int X { get; } // Top-left X coordinate

Yafc/Windows/ShoppingListScreen.cs

@@ -175,7 +175,7 @@ public override void Build(ImGui gui) {
                 Decompose();
             }
 
-            if (gui.BuildButton(LSs.ShoppingListExportBlueprint, SchemeColor.Grey)) {
+            if (gui.BuildButton(LSs.ShoppingListExportBlueprint, SchemeColor.Grey, active: list.data.Count > 0)) {
                 gui.ShowDropDown(ExportBlueprintDropdown);
             }
         }