using System.Collections.Generic;
using System.Linq;
using AcDream.App.UI;
using AcDream.App.UI.Layout;
using AcDream.Core.Items;
using AcDream.Core.Properties;

namespace AcDream.App.Tests.UI.Layout;

/// <summary>
/// Slice 5.4 — mirrors <see cref="ExternalContainerControllerTests"/>'s
/// harness shape (hand-built <see cref="ImportedLayout"/> over
/// <see cref="RetailWindowFrame.Mount"/>) for the behavioral suite, plus one
/// real-dat-fixture smoke test (mirroring
/// <c>AppraisalUiControllerTests</c>'s use of <see cref="FixtureLoader"/>)
/// that catches drift between the hardcoded ids in
/// <see cref="VendorUiController"/> and the actual LayoutDesc 0x21000012.
/// </summary>
public sealed class VendorUiControllerTests
{
    private const uint VendorGuid = 0x70000010u;
    private const uint ArmorItemGuid = 0x60000101u;
    private const uint FoodItemGuid = 0x60000102u;
    private const uint StackedItemGuid = 0x60000103u;

    private sealed class TestElement : UiElement { }

    [Fact]
    public void Bind_FromRealDatFixture_ResolvesAllRequiredControls()
    {
        ImportedLayout layout = FixtureLoader.LoadVendor();
        var screen = new UiRoot { Width = 1280f, Height = 800f };
        RetailWindowHandle window = RetailWindowFrame.Mount(
            screen,
            layout.Root,
            static _ => (0u, 0, 0),
            new RetailWindowFrame.Options
            {
                WindowName = "vendor-fixture-smoke",
                Chrome = RetailWindowChrome.Imported,
                Visible = false,
            });

        VendorUiController? controller = VendorUiController.Bind(
            layout,
            new VendorState(),
            window,
            static (_, _, _, _, _) => 0u,
            new ClientObjectTable(),
            static () => 0u,
            datFont: null,
            debugFont: null,
            static _ => (0u, 0, 0));

        Assert.NotNull(controller);
    }

    private sealed class Harness
    {
        // F2/F3: a deterministic non-zero player coin total so the cost-text
        // "(you have ...)" tail is assertable.
        public const int DefaultPlayerCoinValue = 1500;
        private const uint PlayerGuid = 0x50000001u;

        public readonly VendorState State = new();
        public readonly UiRoot Screen = new() { Width = 800f, Height = 600f };
        public readonly ClientObjectTable Objects = new();
        public readonly UiItemList ItemList = new();
        public readonly UiScrollbar ItemScrollbar = new();
        public readonly UiMenu TypeMenu = new();
        public readonly UiText ItemNameText = new();
        public readonly UiText ItemCostText = new();
        public readonly UiText ItemsTab = new();
        public readonly UiText BuyingTab = new();
        public readonly UiText SellingTab = new();
        public readonly UiElement ItemsPage = new TestElement();
        public readonly UiElement BuyingPage = new TestElement();
        public readonly UiElement SellingPage = new TestElement();
        public readonly UiButton CloseButton;
        public readonly UiButton BuyButton;
        public readonly UiButton AddButton;
        public readonly RetailWindowHandle Window;
        public readonly VendorUiController Controller;

        public Harness()
        {
            var bundle = new PropertyBundle();
            bundle.Ints[(uint)PropertyInt.CoinValue] = DefaultPlayerCoinValue;
            Objects.UpsertProperties(PlayerGuid, bundle);

            var root = new TestElement { Width = 800f, Height = 110f };
            CloseButton = new UiButton(
                new ElementInfo { Id = VendorUiController.CloseId, Type = 1 },
                static _ => (0u, 0, 0));
            BuyButton = new UiButton(
                new ElementInfo { Id = VendorUiController.BuyButtonId, Type = 1 },
                static _ => (0u, 0, 0));
            AddButton = new UiButton(
                new ElementInfo { Id = VendorUiController.AddButtonId, Type = 1 },
                static _ => (0u, 0, 0));

            root.AddChild(CloseButton);
            root.AddChild(ItemsTab);
            root.AddChild(BuyingTab);
            root.AddChild(SellingTab);
            root.AddChild(ItemsPage);
            root.AddChild(BuyingPage);
            root.AddChild(SellingPage);
            ItemsPage.AddChild(ItemList);
            ItemsPage.AddChild(ItemScrollbar);
            ItemsPage.AddChild(TypeMenu);
            ItemsPage.AddChild(ItemNameText);
            ItemsPage.AddChild(ItemCostText);
            ItemsPage.AddChild(BuyButton);
            ItemsPage.AddChild(AddButton);

            var layout = new ImportedLayout(root, new Dictionary<uint, UiElement>
            {
                [VendorUiController.CloseId] = CloseButton,
                [VendorUiController.ItemsTabId] = ItemsTab,
                [VendorUiController.BuyingTabId] = BuyingTab,
                [VendorUiController.SellingTabId] = SellingTab,
                [VendorUiController.ItemsPageId] = ItemsPage,
                [VendorUiController.BuyingPageId] = BuyingPage,
                [VendorUiController.SellingPageId] = SellingPage,
                [VendorUiController.ItemListId] = ItemList,
                [VendorUiController.ItemScrollbarId] = ItemScrollbar,
                [VendorUiController.TypeFilterMenuId] = TypeMenu,
                [VendorUiController.ItemNameTextId] = ItemNameText,
                [VendorUiController.ItemCostTextId] = ItemCostText,
                [VendorUiController.BuyButtonId] = BuyButton,
                [VendorUiController.AddButtonId] = AddButton,
            });

            Window = RetailWindowFrame.Mount(
                Screen,
                root,
                static _ => (0u, 0, 0),
                new RetailWindowFrame.Options
                {
                    WindowName = WindowNames.Vendor,
                    Chrome = RetailWindowChrome.Imported,
                    Visible = false,
                    Draggable = false,
                    Resizable = false,
                });

            Controller = VendorUiController.Bind(
                layout,
                State,
                Window,
                // F5: sum every argument so a test can prove underlay/overlay/
                // effects were actually forwarded (iconId-only would silently
                // regress to dropping the last three).
                static (_, iconId, underlay, overlay, effects) => iconId + underlay + overlay + effects,
                Objects,
                static () => PlayerGuid,
                datFont: null,
                debugFont: null,
                static _ => (0u, 0, 0))!;
            Screen.WindowManager.AttachController(WindowNames.Vendor, Controller);
        }
    }

    private static VendorShopProfile Profile(
        float sellRate = 1.5f, uint altCurrency = 0u, string altName = "", uint altAmount = 0u) =>
        new(0u, 0u, 0u, false, 1.0f, sellRate, altCurrency, altAmount, altName);

    private static string GetText(UiText text)
        => string.Concat(text.LinesProvider().Select(line => line.Text));

    [Fact]
    public void Bind_WiresTheScrollbarToTheItemListsScrollModel()
    {
        var h = new Harness();

        Assert.True(h.ItemScrollbar.Horizontal);
        Assert.Same(h.ItemList.Scroll, h.ItemScrollbar.Model);
    }

    [Fact]
    public void Opened_ShowsWindowAndPopulatesFirstPresentCategoryInTableOrder()
    {
        var h = new Harness();
        var items = new[]
        {
            // Food is table entry #5, Armor is #1 — retail's fixed table
            // order, not insertion order, decides the default selection.
            new VendorShopItem(FoodItemGuid, -1, 1u, "Bread", (uint)ItemType.Food, 100u, 5),
            new VendorShopItem(ArmorItemGuid, -1, 2u, "Chainmail", (uint)ItemType.Armor, 200u, 500),
        };

        h.State.Apply(VendorGuid, Profile(), items);

        Assert.True(h.Window.IsVisible);
        Assert.True(h.ItemsPage.Visible);
        Assert.False(h.BuyingPage.Visible);
        Assert.False(h.SellingPage.Visible);
        Assert.Equal(1, h.ItemList.GetNumUIItems());
        Assert.Equal(ArmorItemGuid, h.ItemList.GetItem(0)!.ItemId);
        Assert.Equal("Armor", h.TypeMenu.Items.Single(i => Equals(i.Payload, h.TypeMenu.Selected)).Label);
    }

    [Fact]
    public void Closed_HidesWindowAndClearsListAndText()
    {
        var h = new Harness();
        h.State.Apply(VendorGuid, Profile(), new[]
        {
            new VendorShopItem(ArmorItemGuid, -1, 2u, "Chainmail", (uint)ItemType.Armor, 200u, 500),
        });
        h.ItemList.GetItem(0)!.Clicked?.Invoke();
        Assert.True(h.Window.IsVisible);
        Assert.NotEqual(string.Empty, GetText(h.ItemNameText));

        h.State.Close();

        Assert.False(h.Window.IsVisible);
        Assert.Equal(0, h.ItemList.GetNumUIItems());
        Assert.Equal(string.Empty, GetText(h.ItemNameText));
        Assert.Equal(string.Empty, GetText(h.ItemCostText));
        Assert.Empty(h.TypeMenu.Items);
    }

    [Fact]
    public void Reset_HidesWindowAndClearsContent()
    {
        var h = new Harness();
        h.State.Apply(VendorGuid, Profile(), new[]
        {
            new VendorShopItem(ArmorItemGuid, -1, 2u, "Chainmail", (uint)ItemType.Armor, 200u, 500),
        });

        h.State.Reset();

        Assert.False(h.Window.IsVisible);
        Assert.Equal(0, h.ItemList.GetNumUIItems());
    }

    [Fact]
    public void SelectingItem_NotInSplitExemptMask_ShowsWholeStackPriceAndFallbackPluralName()
    {
        // F2/F3 (Slice 5.4 review): MissileWeapon (0x100) does NOT intersect
        // the 0xDC41CB0 split-exempt mask, so retail prices/names the WHOLE
        // stack, not one unit — the review flagged the OLD test (asserting a
        // per-unit price + bare "Arrows") as wrong.
        var h = new Harness();
        h.State.Apply(VendorGuid, Profile(sellRate: 2.0f), new[]
        {
            // Value=1000 is the STACK-TOTAL wire value for a 100-unit stack;
            // per-unit = 1000/100 = 10. quantity = DescStackSize = 100 (not
            // exempt). SellPrice = ceil(2.0*10*100 - 0.1) = 2000
            // (VendorPricing.SellPrice, ShopSystem::SellPrice pc:702107).
            new VendorShopItem(
                StackedItemGuid, -1, 3u, "Arrows", (uint)ItemType.MissileWeapon, 300u, 1000,
                DescStackSize: 100),
        });

        h.ItemList.GetItem(0)!.Clicked?.Invoke();

        // No authored PluralName -> ACCWeenieObject::GetObjectName falls back
        // to the singular name UNCHANGED (not an invented "Arrows" + "s").
        Assert.Equal("100 Arrows", GetText(h.ItemNameText));
        Assert.Equal(
            $"cost {2000:N0} (you have {Harness.DefaultPlayerCoinValue:N0})",
            GetText(h.ItemCostText));
    }

    [Fact]
    public void SelectingItem_InSplitExemptMask_ShowsPerUnitPriceAndSingularName()
    {
        // F2/F3: Food (0x20) DOES intersect the split-exempt mask, so
        // quantity is forced to 1 even though the item has a larger
        // authored stack — the mask-member case the review asked for.
        var h = new Harness();
        h.State.Apply(VendorGuid, Profile(sellRate: 2.0f), new[]
        {
            // perUnit = 500/50 = 10. quantity forced to 1 (Food is masked).
            // SellPrice = ceil(2.0*10*1 - 0.1) = 20.
            new VendorShopItem(
                FoodItemGuid, -1, 1u, "Bread", (uint)ItemType.Food, 100u, 500,
                DescStackSize: 50),
        });

        h.ItemList.GetItem(0)!.Clicked?.Invoke();

        Assert.Equal("Bread", GetText(h.ItemNameText));
        Assert.Equal(
            $"costs {20:N0} (you have {Harness.DefaultPlayerCoinValue:N0})",
            GetText(h.ItemCostText));
    }

    [Fact]
    public void SelectingItem_WithAuthoredPluralName_UsesItInsteadOfSingular()
    {
        var h = new Harness();
        h.State.Apply(VendorGuid, Profile(), new[]
        {
            new VendorShopItem(
                StackedItemGuid, -1, 3u, "Iron Key", (uint)ItemType.Key, 50u, 100,
                DescStackSize: 10, PluralName: "Iron Keys"),
        });

        h.ItemList.GetItem(0)!.Clicked?.Invoke();

        Assert.Equal("10 Iron Keys", GetText(h.ItemNameText));
    }

    [Fact]
    public void SelectingItem_WithAlternateCurrency_ShowsFullRetailCostSentence()
    {
        // F2/F3: the OLD implementation just appended the currency name after
        // a bare number ("50 Trade Notes"). Retail's actual alt-currency
        // sentence is a full two-clause sentence with a "you have" tail
        // (acclient_2013_pseudo_c.txt:991314), using RAW (non-comma-grouped)
        // integers — unlike the primary-currency branch.
        var h = new Harness();
        h.State.Apply(
            VendorGuid,
            Profile(sellRate: 1.0f, altCurrency: 0x12345678u, altName: "Trade Notes", altAmount: 12345u),
            new[]
            {
                new VendorShopItem(ArmorItemGuid, -1, 2u, "Chainmail", (uint)ItemType.Armor, 200u, 50),
            });

        h.ItemList.GetItem(0)!.Clicked?.Invoke();

        // Armor (not in the split-exempt mask) with DescStackSize null ->
        // PerUnitValue returns Value unchanged (50); quantity = 1 (no
        // authored stack) -> SellPrice(50, Armor, 1.0, 1) = ceil(50-0.1) = 50.
        Assert.Equal(
            "This item costs 50 Trade Notes. You have 12345 Trade Notes.",
            GetText(h.ItemCostText));
    }

    [Fact]
    public void NoSelection_DisablesBuyAndAddButtons_SelectionEnablesThem()
    {
        var h = new Harness();
        Assert.False(h.BuyButton.Enabled);
        Assert.False(h.AddButton.Enabled);

        h.State.Apply(VendorGuid, Profile(), new[]
        {
            new VendorShopItem(ArmorItemGuid, -1, 2u, "Chainmail", (uint)ItemType.Armor, 200u, 500),
        });

        // F4 auto-selects the sole item on open, so the buttons are already
        // enabled — SetState(1), pc:202784-202789.
        Assert.True(h.BuyButton.Enabled);
        Assert.True(h.AddButton.Enabled);

        // Closing clears the selection -> SetState(0xd), pc:202572-202577.
        h.State.Close();
        Assert.False(h.BuyButton.Enabled);
        Assert.False(h.AddButton.Enabled);
    }

    [Fact]
    public void ShopItem_WithIconUnderlayOverlayEffects_ForwardsThemToResolveIcon()
    {
        // F5: PublicWeenieDescBody already carries these three; the review
        // flagged VendorUiController hardcoding 0u/0u/0u instead of
        // forwarding item.IconUnderlayId/IconOverlayId/Effects.
        var h = new Harness();
        var item = new VendorShopItem(
            ArmorItemGuid, -1, 2u, "Chainmail", (uint)ItemType.Armor, IconId: 200u, Value: 500,
            IconUnderlayId: 10u, IconOverlayId: 100u, Effects: 1000u);
        h.State.Apply(VendorGuid, Profile(), new[] { item });

        // Harness's resolveIcon sums every argument (see its comment) — this
        // regresses to 200u alone if the three are dropped again.
        Assert.Equal(200u + 10u + 100u + 1000u, h.ItemList.GetItem(0)!.IconTexture);
    }

    [Fact]
    public void SelectingDifferentCategory_FiltersItemListToThatCategoryOnly()
    {
        var h = new Harness();
        var armor = new VendorShopItem(ArmorItemGuid, -1, 2u, "Chainmail", (uint)ItemType.Armor, 200u, 500);
        var food = new VendorShopItem(FoodItemGuid, -1, 1u, "Bread", (uint)ItemType.Food, 100u, 5);
        h.State.Apply(VendorGuid, Profile(), new[] { armor, food });
        Assert.Equal(ArmorItemGuid, h.ItemList.GetItem(0)!.ItemId); // default: Armor (table order)

        object? foodPayload = h.TypeMenu.Items.First(i => i.Label == "Food").Payload;
        h.TypeMenu.OnSelect!.Invoke(foodPayload);

        Assert.Equal(1, h.ItemList.GetNumUIItems());
        Assert.Equal(FoodItemGuid, h.ItemList.GetItem(0)!.ItemId);
    }

    [Fact]
    public void SelectingDifferentCategory_AutoSelectsFirstFilteredItem()
    {
        // F4: VendorItemsUI::UpdateItemsList's tail (pc:201180-201190) —
        // after a category switch the first item that passed the filter
        // becomes the display selection, not a cleared blank.
        var h = new Harness();
        var armor = new VendorShopItem(ArmorItemGuid, -1, 2u, "Chainmail", (uint)ItemType.Armor, 200u, 500);
        var food = new VendorShopItem(FoodItemGuid, -1, 1u, "Bread", (uint)ItemType.Food, 100u, 5);
        h.State.Apply(VendorGuid, Profile(), new[] { armor, food });

        object? foodPayload = h.TypeMenu.Items.First(i => i.Label == "Food").Payload;
        h.TypeMenu.OnSelect!.Invoke(foodPayload);

        Assert.Equal(FoodItemGuid, h.ItemList.GetItem(0)!.ItemId);
        Assert.True(h.ItemList.GetItem(0)!.Selected);
        Assert.NotEqual(string.Empty, GetText(h.ItemNameText));
        Assert.NotEqual(string.Empty, GetText(h.ItemCostText));
        Assert.True(h.BuyButton.Enabled);
    }

    [Fact]
    public void SelectingDifferentCategory_ResetsListScrollToStart()
    {
        // F7a: VendorItemsUI::UpdateItemsList's tail (pc:201186-201190) —
        // ScrollToShow(m_shopList, 0) fires unconditionally on every rebuild.
        var h = new Harness();
        var armor = new VendorShopItem(ArmorItemGuid, -1, 2u, "Chainmail", (uint)ItemType.Armor, 200u, 500);
        var food = new VendorShopItem(FoodItemGuid, -1, 1u, "Bread", (uint)ItemType.Food, 100u, 5);
        h.State.Apply(VendorGuid, Profile(), new[] { armor, food });

        object? foodPayload = h.TypeMenu.Items.First(i => i.Label == "Food").Payload;
        h.TypeMenu.OnSelect!.Invoke(foodPayload);

        Assert.Equal(0, h.ItemList.Scroll.ScrollY);
    }

    [Fact]
    public void ItemList_FillsVisibleEmptySlots()
    {
        // F7b: mirrors ExternalContainerController.ConfigureList's empty-slot
        // fill so the authored 22-slot strip doesn't show blank space.
        var h = new Harness();

        Assert.True(h.ItemList.FillVisibleEmptySlots);
        Assert.NotNull(h.ItemList.EmptySlotFactory);
    }

    [Fact]
    public void Opened_WithDifferentVendor_ResetsToFirstPresentCategory_NotThePreviousVendors()
    {
        // F6: gmVendorUI::OpenVendor flushes sub-UIs when sameVendor==0
        // (pc:203664-203667) — a different vendor must not inherit whatever
        // category index the LAST vendor happened to have selected.
        const uint OtherVendorGuid = 0x70000020u;
        const uint OtherArmorGuid = 0x60000201u;
        const uint OtherFoodGuid = 0x60000202u;

        var h = new Harness();
        h.State.Apply(VendorGuid, Profile(), new[]
        {
            new VendorShopItem(ArmorItemGuid, -1, 2u, "Chainmail", (uint)ItemType.Armor, 200u, 500),
            new VendorShopItem(FoodItemGuid, -1, 1u, "Bread", (uint)ItemType.Food, 100u, 5),
        });
        object? foodPayload = h.TypeMenu.Items.First(i => i.Label == "Food").Payload;
        h.TypeMenu.OnSelect!.Invoke(foodPayload);
        Assert.Equal("Food", h.TypeMenu.Items.Single(i => Equals(i.Payload, h.TypeMenu.Selected)).Label);

        // A DIFFERENT vendor, which ALSO has >=2 categories (Armor then
        // Food, table order) so a stale numeric index (1) would silently
        // "validate" without the fix and land on Food again by coincidence
        // rather than by the vendor's own contents.
        h.State.Apply(OtherVendorGuid, Profile(), new[]
        {
            new VendorShopItem(OtherArmorGuid, -1, 4u, "Buckler", (uint)ItemType.Armor, 900u, 40),
            new VendorShopItem(OtherFoodGuid, -1, 5u, "Ale", (uint)ItemType.Food, 100u, 3),
        });

        Assert.Equal("Armor", h.TypeMenu.Items.Single(i => Equals(i.Payload, h.TypeMenu.Selected)).Label);
        Assert.Equal(OtherArmorGuid, h.ItemList.GetItem(0)!.ItemId);
    }

    [Fact]
    public void Refreshed_SameVendor_PreservesCategorySelection()
    {
        // F6 counterpart: gmVendorUI::OpenVendor's sameVendor==1 path does
        // NOT flush sub-UIs, so a same-vendor refresh (Slice 6 post-buy/sell)
        // must keep the player's chosen category.
        var h = new Harness();
        var items = new[]
        {
            new VendorShopItem(ArmorItemGuid, -1, 2u, "Chainmail", (uint)ItemType.Armor, 200u, 500),
            new VendorShopItem(FoodItemGuid, -1, 1u, "Bread", (uint)ItemType.Food, 100u, 5),
        };
        h.State.Apply(VendorGuid, Profile(), items);
        object? foodPayload = h.TypeMenu.Items.First(i => i.Label == "Food").Payload;
        h.TypeMenu.OnSelect!.Invoke(foodPayload);

        // SAME vendor id re-approaches -> VendorStateTransitionKind.Refreshed.
        h.State.Apply(VendorGuid, Profile(), items);

        Assert.Equal("Food", h.TypeMenu.Items.Single(i => Equals(i.Payload, h.TypeMenu.Selected)).Label);
    }

    [Fact]
    public void CategoryMenu_OpensAndSelectsThroughRealHitPath_UsingAuthoredPopupGeometry()
    {
        // F1: the popup never rendered because SpriteResolve/fonts/sprites
        // were never wired, and the geometry was chat's own authored values
        // instead of the vendor dropdown's. This drives the SAME UiEvent
        // hit-test path UiMenuTests uses (not a direct OnSelect call), and
        // reads the geometry back off the live widget instead of hardcoding
        // pixel offsets tied to a specific constant set.
        var h = new Harness();
        h.State.Apply(VendorGuid, Profile(), new[]
        {
            new VendorShopItem(ArmorItemGuid, -1, 2u, "Chainmail", (uint)ItemType.Armor, 200u, 500),
            new VendorShopItem(FoodItemGuid, -1, 1u, "Bread", (uint)ItemType.Food, 100u, 5),
        });

        // Wiring: without these UiMenu.OnDrawOverlay early-returns (nothing
        // renders) and the button face never draws either.
        Assert.NotNull(h.TypeMenu.SpriteResolve);
        Assert.NotEqual(0u, h.TypeMenu.NormalSprite);
        Assert.NotEqual(0u, h.TypeMenu.ItemNormalSprite);
        Assert.NotEqual(0u, h.TypeMenu.ItemHighlightSprite);

        // Geometry from the authored template (LayoutDesc 0x21000043's row
        // element 0x10000352 and ListBox 0x10000350), NOT chat's 7/17/191.
        Assert.Equal(6, h.TypeMenu.RowsPerColumn);
        Assert.Equal(18f, h.TypeMenu.RowHeight);
        Assert.Equal(100f, h.TypeMenu.ColumnWidth);

        // Open via the real widget event path.
        Assert.True(h.TypeMenu.OnEvent(new UiEvent(0, h.TypeMenu, UiEventType.MouseDown, 0, 10, 5)));

        // "Food" is the 2nd present category in table order (Armor, then
        // Food) -> row index 1, column 0. Derive the click point from the
        // widget's own live geometry (mirrors UiMenu.OnEvent's own math)
        // rather than a hardcoded pixel constant.
        const int border = 5; // RetailChromeSprites.Border (UiMenu's private bevel thickness)
        float outerH = h.TypeMenu.RowsPerColumn * h.TypeMenu.RowHeight + 2 * border;
        const int targetRow = 1;
        float iy = targetRow * h.TypeMenu.RowHeight + h.TypeMenu.RowHeight / 2f;
        float ly = iy - outerH + border;

        Assert.True(h.TypeMenu.OnEvent(new UiEvent(0, h.TypeMenu, UiEventType.MouseDown, 0, 10, (int)ly)));

        Assert.Equal("Food", h.TypeMenu.Items.Single(i => Equals(i.Payload, h.TypeMenu.Selected)).Label);
        Assert.Equal(FoodItemGuid, h.ItemList.GetItem(0)!.ItemId);
    }

    [Fact]
    public void CloseButton_RoutesThroughVendorStateClose_NotADirectFieldWrite()
    {
        var h = new Harness();
        h.State.Apply(VendorGuid, Profile(), new[]
        {
            new VendorShopItem(ArmorItemGuid, -1, 2u, "Chainmail", (uint)ItemType.Armor, 200u, 500),
        });

        h.CloseButton.OnClick!.Invoke();

        // The panel never mutates VendorState directly — the ONLY path from
        // the close button to a cleared session is VendorState.Close()
        // itself, so VendorId reads back 0 through the owner's own public
        // surface, not a private field poke.
        Assert.Equal(0u, h.State.VendorId);
        Assert.False(h.Window.IsVisible);
    }

    [Fact]
    public void SellingTab_SwitchesPageButPopulatesNoSellContent()
    {
        var h = new Harness();
        h.State.Apply(VendorGuid, Profile(), new[]
        {
            new VendorShopItem(ArmorItemGuid, -1, 2u, "Chainmail", (uint)ItemType.Armor, 200u, 500),
        });

        h.SellingTab.OnClick!.Invoke();

        Assert.True(h.SellingPage.Visible);
        Assert.False(h.ItemsPage.Visible);
        Assert.False(h.BuyingPage.Visible);
        // Slice 6 fence: no sell-list/price/button wiring exists at all —
        // the page is exactly the authored-empty container it started as.
        Assert.Empty(h.SellingPage.Children);
    }

    [Fact]
    public void BuyingTab_SwitchesPageButPopulatesNoBuyContent()
    {
        var h = new Harness();
        h.State.Apply(VendorGuid, Profile(), new[]
        {
            new VendorShopItem(ArmorItemGuid, -1, 2u, "Chainmail", (uint)ItemType.Armor, 200u, 500),
        });

        h.BuyingTab.OnClick!.Invoke();

        Assert.True(h.BuyingPage.Visible);
        Assert.False(h.ItemsPage.Visible);
        Assert.Empty(h.BuyingPage.Children);
    }

    [Fact]
    public void ItemsTab_ReselectedAfterVisitingOtherTabs_ShowsBrowseListAgain()
    {
        var h = new Harness();
        h.State.Apply(VendorGuid, Profile(), new[]
        {
            new VendorShopItem(ArmorItemGuid, -1, 2u, "Chainmail", (uint)ItemType.Armor, 200u, 500),
        });
        h.SellingTab.OnClick!.Invoke();

        h.ItemsTab.OnClick!.Invoke();

        Assert.True(h.ItemsPage.Visible);
        Assert.False(h.SellingPage.Visible);
        Assert.Equal(1, h.ItemList.GetNumUIItems());
    }
}