using System.Collections.Generic;
using System.Drawing;

namespace System.Windows.Forms
{
    internal class LayoutEngine
    {
        private Control control;
        private List<LayoutTransaction> transactions = new();
        private bool suspended;
        private bool updatingLayout;

        public void SuspendLayout()
        {
            suspended = true;
        }

        public void AddTransaction(int deltaX, int deltaY)
        {
            if (updatingLayout)
                return;
            int width = control.DisplayRectangle.Width;
            int height = control.DisplayRectangle.Height;

            if (suspended)
                transactions.Add(new LayoutTransaction(deltaX, deltaY, width, height));
            else
                UpdateLayout(deltaX, deltaY, width, height);
        }

        public void AddTransaction() => AddTransaction(0, 0);

        public void ResumeLayout(bool resume)
        {
            if (resume)
            {
                foreach (LayoutTransaction tr in transactions)
                {
                    UpdateLayout(tr.DeltaX, tr.DeltaY, tr.Width, tr.Height);
                }
            }
            transactions.Clear();
            suspended = false;
        }

        private Rectangle Bounds(int left, int top, int width, int height)
        {
            if (left < 0)
                left = 0;
            if (top < 0)
                top = 0;
            if (width < 0)
                width = 0;
            if (height < 0)
                height = 0;
            return new Rectangle(left, top, width, height);
        }

        private void UpdateLayout(int dx, int dy, int width, int height)
        {
            if (updatingLayout)
                return;
            updatingLayout = true;
            try
            {
                Rectangle remainingBounds = new Rectangle(control.Padding.Left + control.DefaultPadding.Left,
                    control.Padding.Top + control.DefaultPadding.Top,
                    width - control.Padding.Horizontal - control.DefaultPadding.Horizontal,
                    height - control.Padding.Vertical - control.DefaultPadding.Vertical);
                remainingBounds.Width += dx;
                remainingBounds.Height += dy;

                // phase 1: everything except Dock = Fill
                for (int i = control.Controls.Count - 1; i >= 0; i--)
                {
                    var c = control.Controls[i];

                    if ((c.Anchor & AnchorStyles.Right) != 0)
                    {
                        if ((c.Anchor & AnchorStyles.Left) != 0)
                            c.Width += dx;
                        else
                            c.Left += dx;
                    }
                    else if ((c.Anchor & AnchorStyles.Left) == 0)
                    {
                        c.Left += dx / 2;
                    }
                    if ((c.Anchor & AnchorStyles.Bottom) != 0)
                    {
                        if ((c.Anchor & AnchorStyles.Top) != 0)
                            c.Height += dy;
                        else
                            c.Top += dy;
                    }
                    else if ((c.Anchor & AnchorStyles.Top) == 0)
                    {
                        c.Top += dy / 2;
                    }

                    if (!c.Visible)
                        continue;
                    switch (c.Dock)
                    {
                        case DockStyle.Left:
                            c.Bounds = Bounds(remainingBounds.Left, remainingBounds.Top, c.Width, remainingBounds.Height);
                            remainingBounds.X += c.Width;
                            remainingBounds.Width -= c.Width;
                            break;

                        case DockStyle.Top:
                            c.Bounds = Bounds(remainingBounds.Left, remainingBounds.Top, remainingBounds.Width, c.Height);
                            remainingBounds.Y += c.Height;
                            remainingBounds.Height -= c.Height;
                            break;

                        case DockStyle.Right:
                            c.Bounds = Bounds(remainingBounds.Right - c.Width, remainingBounds.Top, c.Width, remainingBounds.Height);
                            remainingBounds.Width -= c.Width;
                            break;

                        case DockStyle.Bottom:
                            c.Bounds = Bounds(remainingBounds.Left, remainingBounds.Bottom - c.Height, remainingBounds.Width, c.Height);
                            remainingBounds.Height -= c.Height;
                            break;
                    }
                }

                // phase 2: Dock = Fill
                for (int i = control.Controls.Count - 1; i >= 0; i--)
                {
                    var c = control.Controls[i];
                    if (!c.Visible)
                        continue;

                    switch (c.Dock)
                    {
                        case DockStyle.Fill:
                            c.Bounds = Bounds(remainingBounds.Left, remainingBounds.Top, remainingBounds.Width, remainingBounds.Height);
                            break;
                    }
                }
            }
            finally
            {
                updatingLayout = false;
                control.OnLayout();
            }
        }

        public LayoutEngine(Control control) => this.control = control;

        private struct LayoutTransaction
        {
            public int DeltaX { get; }
            public int DeltaY { get; }
            public int Width { get; }
            public int Height { get; }

            public LayoutTransaction(int deltaX, int deltaY, int width, int height)
            {
                DeltaX = deltaX;
                DeltaY = deltaY;
                Width = width;
                Height = height;
            }
        }
    }

}