using System.Collections.Generic;
using System.Linq;
using UnityEngine;
using UnityEngine.UIElements;

namespace Ironspore
{
    public sealed partial class GameHud
    {
        string selectedUid;
        Hold selectedHold;
        int selectedSlot = -1;
        bool rotated;
        int quantity;
        const int CellWidth = 103, CellHeight = 55;

        sealed class GridCell
        {
            public Hold hold;
            public int x, y;
            public CargoStack occupant;
        }

        CargoStack dragItem;
        Hold dragHold;
        int dragSlot, dragPointer;
        Vector2 dragStart;
        VisualElement dragPreview;

        CargoStack Selection => selectedSlot >= 0 ? game.Run.installed.Find(i => i.uid == selectedUid) :
            Contents(selectedHold).Find(i => i.uid == selectedUid);

        List<CargoStack> Contents(Hold hold) => hold == Hold.Cargo ? game.Run.cargo : game.Run.safeCase;

        void SelectInventoryItem(CargoStack item, Hold hold, int slot = -1)
        {
            selectedUid = item?.uid;
            selectedSlot = slot;
            selectedHold = hold;
            rotated = item?.rotated ?? false;
            quantity = item?.count ?? 0;
            ShowCargo();
        }

        void RotateSelection()
        {
            rotated = !rotated;
            if (dragPreview == null) ShowCargo();
            else SizePreview();
        }

        public void ShowCargo()
        {
            var panel = Overlay(L("ui.cargo.title"), L(game.Run.podUsed ? "ui.cargo.used" : "ui.cargo.help"));
            view = View.Cargo;
            var installed = Element(panel, "row");
            foreach (var part in game.Run.installed)
            {
                int slot = InventoryGrid.Slot(part.itemId);
                var button = Button(installed, part.Name, () => SelectInventoryItem(part, Hold.Cargo, slot),
                    part.uid == selectedUid ? "loadout selected" : "loadout");
                EnableDrag(button, part, Hold.Cargo, slot);
            }
            var grids = Element(panel, "row");
            DrawHold(grids, Hold.Cargo, InventoryGrid.CargoSize);
            DrawHold(grids, Hold.SafeCase, InventoryGrid.CaseSize);
            Text(panel, L("ui.cargo.capacity", game.Run.cargo.Sum(InventoryGrid.Area),
                game.Run.cargo.Where(i => game.SelectedCargo.Contains(i.uid)).Sum(InventoryGrid.Area)), "budget");
            var item = Selection;
            if (item != null)
            {
                InventoryGrid.Size(item.itemId, rotated, out int w, out int h);
                Text(panel, L("ui.cargo.selection", item.Name, w, h, quantity), "body");
                var actions = Element(panel, "row");
                Button(actions, L("ui.cargo.rotate"), RotateSelection);
                if (item.count > 1)
                {
                    Button(actions, "−", () => { quantity--; ShowCargo(); }).SetEnabled(quantity > 1);
                    Button(actions, "+", () => { quantity++; ShowCargo(); }).SetEnabled(quantity < item.count);
                }
                if (selectedSlot < 0)
                {
                    if (selectedHold == Hold.Cargo && !game.Run.podUsed)
                        Button(actions, L(game.SelectedCargo.Contains(item.uid) ? "ui.cargo.unmark" : "ui.cargo.mark"), () => game.ToggleCargo(item.uid));
                    if (InventoryGrid.Slot(item.itemId) >= 0)
                        Button(actions, L("ui.cargo.install"), () =>
                        {
                            if (game.InstallItem(item, selectedHold)) selectedUid = null;
                            ShowCargo();
                        });
                }
                Button(actions, L("ui.cargo.cancel"), () => SelectInventoryItem(null, Hold.Cargo));
            }
            Text(panel, game.Notice, "warning");
            Button(panel, L("ui.return"), game.CloseMenu, "primary");
        }

        void DrawHold(VisualElement parent, Hold hold, int size)
        {
            var column = Element(parent, "inventory-column");
            Text(column, L(hold == Hold.Cargo ? "ui.cargo.hold" : "ui.cargo.case"), "section");
            var grid = new VisualElement();
            column.Add(grid);
            grid.style.width = size * CellWidth;
            grid.style.height = size * CellHeight;
            var items = Contents(hold);
            for (int y = 0; y < size; y++)
                for (int x = 0; x < size; x++)
                {
                    int cx = x, cy = y;
                    var occupant = items.Find(i =>
                    {
                        InventoryGrid.Size(i.itemId, i.rotated, out int w, out int h);
                        return cx >= i.x && cy >= i.y && cx < i.x + w && cy < i.y + h;
                    });
                    var cell = Button(grid, "", () => InventoryClick(hold, cx, cy, occupant), "inventory-cell");
                    cell.name = hold + "-" + x + "-" + y;
                    cell.tooltip = occupant?.Name ?? "";
                    cell.userData = new GridCell { hold = hold, x = x, y = y, occupant = occupant };
                    if (occupant != null) EnableDrag(cell, occupant, hold, -1);
                    PositionInGrid(cell, x, y, 1, 1);
                }
            foreach (var item in items)
            {
                InventoryGrid.Size(item.itemId, item.rotated, out int w, out int h);
                string prefix = game.SelectedCargo.Contains(item.uid) ? "✓ " : "";
                var label = Text(grid, prefix + item.Name + (item.count > 1 ? " ×" + item.count : ""), "inventory-item");
                label.pickingMode = PickingMode.Ignore;
                if (item.uid == selectedUid) label.AddToClassList("selected");
                PositionInGrid(label, item.x, item.y, w, h);
            }
        }

        void EnableDrag(Button button, CargoStack item, Hold hold, int slot)
        {
            // Captured pointer events can be dispatched directly to the pressed button.
            button.RegisterCallback<PointerMoveEvent>(DragMove, TrickleDown.TrickleDown);
            button.RegisterCallback<PointerUpEvent>(DragEnd, TrickleDown.TrickleDown);
            button.RegisterCallback<PointerDownEvent>(evt =>
            {
                if (evt.button != 0) return;
                dragItem = item;
                dragHold = hold;
                dragSlot = slot;
                dragStart = evt.position;
                dragPointer = evt.pointerId;
            }, TrickleDown.TrickleDown);
        }

        void DragMove(PointerMoveEvent evt)
        {
            if (dragItem == null || evt.pointerId != dragPointer) return;
            Vector2 pos = evt.position;
            if (dragPreview == null)
            {
                if ((pos - dragStart).sqrMagnitude < 36) return;
                if (selectedUid != dragItem.uid)
                {
                    quantity = dragItem.count;
                    rotated = dragItem.rotated;
                }
                selectedUid = dragItem.uid;
                selectedSlot = dragSlot;
                selectedHold = dragHold;
                dragPreview = Text(root, dragItem.Name, "inventory-item selected");
                dragPreview.pickingMode = PickingMode.Ignore;
                dragPreview.style.position = UnityEngine.UIElements.Position.Absolute;
                SizePreview();
            }
            var target = root.panel.Pick(pos);
            Vector2 anchor = target?.userData is GridCell ? target.worldBound.min : pos;
            Vector2 local = root.WorldToLocal(anchor);
            dragPreview.style.left = local.x;
            dragPreview.style.top = local.y;
        }

        void SizePreview()
        {
            InventoryGrid.Size(dragItem.itemId, rotated, out int w, out int h);
            dragPreview.style.width = CellWidth * w - 2;
            dragPreview.style.height = CellHeight * h - 2;
        }

        void DragEnd(PointerUpEvent evt)
        {
            if (dragItem == null || evt.pointerId != dragPointer) return;
            bool dragged = dragPreview != null;
            ResetDrag();
            if (!dragged) return;
            evt.StopImmediatePropagation();
            var owner = root.panel.GetCapturingElement(evt.pointerId) as VisualElement;
            owner?.ReleasePointer(evt.pointerId);
            var target = root.panel.Pick(evt.position)?.userData as GridCell;
            if (target != null) InventoryClick(target.hold, target.x, target.y, target.occupant);
            else ShowCargo();
        }

        void ResetDrag()
        {
            dragPreview?.RemoveFromHierarchy();
            dragPreview = null;
            dragItem = null;
        }

        static void PositionInGrid(VisualElement element, int x, int y, int w, int h)
        {
            element.style.position = UnityEngine.UIElements.Position.Absolute;
            element.style.left = x * CellWidth;
            element.style.top = y * CellHeight;
            element.style.width = w * CellWidth - 2;
            element.style.height = h * CellHeight - 2;
        }

        void InventoryClick(Hold hold, int x, int y, CargoStack occupant)
        {
            var item = Selection;
            if (item == null)
            {
                SelectInventoryItem(occupant, hold);
                return;
            }
            bool ok;
            if (selectedSlot >= 0)
                ok = game.Store.Uninstall(selectedSlot, hold, x, y, rotated);
            else if (occupant == null || item.uid == occupant.uid)
                ok = game.Store.MoveItem(item.uid, selectedHold, hold, x, y, rotated, quantity);
            else if (item.itemId == occupant.itemId && InventoryGrid.IsMaterial(item.itemId))
                ok = game.Store.MergeMaterial(item.uid, selectedHold, occupant.uid, hold, quantity);
            else
                ok = quantity == item.count && game.Store.SwapItems(item.uid, selectedHold, occupant.uid, hold, rotated);
            if (ok)
            {
                selectedUid = null;
                game.SelectedCargo.RemoveAll(uid => !game.Run.cargo.Exists(i => i.uid == uid));
                game.Pilot.ApplyLoadout();
            }
            else game.Notify(string.IsNullOrEmpty(game.Store.Error) ? "notice.placement" : "notice.saveFailed");
            ShowCargo();
        }
    }
}