using System;
using System.Collections.Generic;
using System.Diagnostics;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;
using Microsoft.Xna.Framework.Input;
using MLEM.Extensions;
using MLEM.Input;
using MLEM.Ui.Style;

namespace MLEM.Ui.Elements {
    public abstract class Element {

        protected readonly List<Element> Children = new List<Element>();
        private readonly List<Element> sortedChildren = new List<Element>();
        protected List<Element> SortedChildren {
            get {
                this.UpdateSortedChildrenIfDirty();
                return this.sortedChildren;
            }
        }
        private Anchor anchor;
        private Vector2 size;
        private Vector2 offset;
        public Point Padding;
        public Point ScaledPadding => this.Padding.Multiply(this.Scale);
        private Point childPadding;
        public Anchor Anchor {
            get => this.anchor;
            set {
                if (this.anchor == value)
                    return;
                this.anchor = value;
                this.SetAreaDirty();
            }
        }
        public Vector2 Size {
            get => this.size;
            set {
                if (this.size == value)
                    return;
                this.size = value;
                this.SetAreaDirty();
            }
        }
        public Vector2 ScaledSize => this.size * this.Scale;
        public Vector2 PositionOffset {
            get => this.offset;
            set {
                if (this.offset == value)
                    return;
                this.offset = value;
                this.SetAreaDirty();
            }
        }
        public Point ScaledOffset => (this.offset * this.Scale).ToPoint();
        public Point ChildPadding {
            get => this.childPadding;
            set {
                if (this.childPadding == value)
                    return;
                this.childPadding = value;
                this.SetAreaDirty();
            }
        }
        public Rectangle ChildPaddedArea {
            get {
                var padded = this.Area;
                padded.Location += this.ScaledChildPadding;
                padded.Width -= this.ScaledChildPadding.X * 2;
                padded.Height -= this.ScaledChildPadding.Y * 2;
                return padded;
            }
        }
        public Point ScaledChildPadding => this.childPadding.Multiply(this.Scale);

        public MouseClickCallback OnClicked;
        public GenericCallback OnSelected;
        public GenericCallback OnDeselected;
        public MouseCallback OnMouseEnter;
        public MouseCallback OnMouseExit;
        public TextInputCallback OnTextInput;

        private UiSystem system;
        public UiSystem System {
            get => this.system;
            private set {
                this.system = value;
                if (this.system != null && !this.HasCustomStyle)
                    this.InitStyle(this.system.Style);
            }
        }
        protected InputHandler Input => this.System.InputHandler;
        public RootElement Root { get; private set; }
        public float Scale => this.Root.ActualScale;
        public Point MousePos => this.Input.MousePosition;
        public Element Parent { get; private set; }
        public bool IsMouseOver { get; private set; }
        public bool IsSelected { get; private set; }
        private bool isHidden;
        public bool IsHidden {
            get => this.isHidden;
            set {
                if (this.isHidden == value)
                    return;
                this.isHidden = value;
                this.SetAreaDirty();
            }
        }
        public bool IgnoresMouse;
        public float DrawAlpha = 1;
        public bool HasCustomStyle;
        public bool SetHeightBasedOnChildren;

        private Rectangle area;
        public Rectangle Area {
            get {
                this.UpdateAreaIfDirty();
                return this.area;
            }
        }
        public Rectangle DisplayArea {
            get {
                var padded = this.Area;
                padded.Location += this.ScaledPadding;
                padded.Width -= this.ScaledPadding.X * 2;
                padded.Height -= this.ScaledPadding.Y * 2;
                return padded;
            }
        }
        private int priority;
        public int Priority {
            get => this.priority;
            set {
                this.priority = value;
                if (this.Parent != null)
                    this.Parent.SetSortedChildrenDirty();
            }
        }
        private bool areaDirty;
        private bool sortedChildrenDirty;

        public Element(Anchor anchor, Vector2 size) {
            this.anchor = anchor;
            this.size = size;

            this.OnMouseEnter += element => this.IsMouseOver = true;
            this.OnMouseExit += element => this.IsMouseOver = false;
            this.OnSelected += element => this.IsSelected = true;
            this.OnDeselected += element => this.IsSelected = false;

            this.SetAreaDirty();
        }

        public T AddChild<T>(T element, int index = -1, bool propagateInfo = true) where T : Element {
            if (index < 0 || index > this.Children.Count)
                index = this.Children.Count;
            this.Children.Insert(index, element);
            if (propagateInfo) {
                element.Parent = this;
                element.PropagateRoot(this.Root);
                element.PropagateUiSystem(this.System);
            }
            this.SetSortedChildrenDirty();
            this.SetAreaDirty();
            return element;
        }

        public void RemoveChild(Element element, bool propagateInfo = true) {
            this.Children.Remove(element);
            if (propagateInfo) {
                element.Parent = null;
                element.PropagateRoot(null);
                element.PropagateUiSystem(null);
            }
            this.SetSortedChildrenDirty();
            this.SetAreaDirty();
        }

        public void MoveToFront() {
            if (this.Parent != null) {
                this.Parent.RemoveChild(this, false);
                this.Parent.AddChild(this, -1, false);
            }
        }

        public void MoveToBack() {
            if (this.Parent != null) {
                this.Parent.RemoveChild(this, false);
                this.Parent.AddChild(this, 0, false);
            }
        }

        public void SetAreaDirty() {
            this.areaDirty = true;
            if (this.Anchor >= Anchor.AutoLeft && this.Parent != null)
                this.Parent.SetAreaDirty();
        }

        public void SetSortedChildrenDirty() {
            this.sortedChildrenDirty = true;
        }

        public void UpdateSortedChildrenIfDirty() {
            if (this.sortedChildrenDirty) {
                this.sortedChildrenDirty = false;

                this.sortedChildren.Clear();
                this.sortedChildren.AddRange(this.Children);
                this.sortedChildren.Sort((e1, e2) => e1.Priority.CompareTo(e1.Priority));
            }
        }

        public void UpdateAreaIfDirty() {
            if (this.areaDirty)
                this.ForceUpdateArea();
        }

        public virtual void ForceUpdateArea() {
            this.areaDirty = false;
            if (this.IsHidden)
                return;

            var parentArea = this.Parent != null ? this.Parent.ChildPaddedArea : this.system.Viewport;
            var parentCenterX = parentArea.X + parentArea.Width / 2;
            var parentCenterY = parentArea.Y + parentArea.Height / 2;

            var actualSize = this.CalcActualSize(parentArea);
            var pos = new Point();

            switch (this.anchor) {
                case Anchor.TopLeft:
                case Anchor.AutoLeft:
                case Anchor.AutoInline:
                case Anchor.AutoInlineIgnoreOverflow:
                    pos.X = parentArea.X + this.ScaledOffset.X;
                    pos.Y = parentArea.Y + this.ScaledOffset.Y;
                    break;
                case Anchor.TopCenter:
                case Anchor.AutoCenter:
                    pos.X = parentCenterX - actualSize.X / 2 + this.ScaledOffset.X;
                    pos.Y = parentArea.Y + this.ScaledOffset.Y;
                    break;
                case Anchor.TopRight:
                case Anchor.AutoRight:
                    pos.X = parentArea.Right - actualSize.X - this.ScaledOffset.X;
                    pos.Y = parentArea.Y + this.ScaledOffset.Y;
                    break;
                case Anchor.CenterLeft:
                    pos.X = parentArea.X + this.ScaledOffset.X;
                    pos.Y = parentCenterY - actualSize.Y / 2 + this.ScaledOffset.Y;
                    break;
                case Anchor.Center:
                    pos.X = parentCenterX - actualSize.X / 2 + this.ScaledOffset.X;
                    pos.Y = parentCenterY - actualSize.Y / 2 + this.ScaledOffset.Y;
                    break;
                case Anchor.CenterRight:
                    pos.X = parentArea.Right - actualSize.X - this.ScaledOffset.X;
                    pos.Y = parentCenterY - actualSize.Y / 2 + this.ScaledOffset.Y;
                    break;
                case Anchor.BottomLeft:
                    pos.X = parentArea.X + this.ScaledOffset.X;
                    pos.Y = parentArea.Bottom - actualSize.Y - this.ScaledOffset.Y;
                    break;
                case Anchor.BottomCenter:
                    pos.X = parentCenterX - actualSize.X / 2 + this.ScaledOffset.X;
                    pos.Y = parentArea.Bottom - actualSize.Y - this.ScaledOffset.Y;
                    break;
                case Anchor.BottomRight:
                    pos.X = parentArea.Right - actualSize.X - this.ScaledOffset.X;
                    pos.Y = parentArea.Bottom - actualSize.Y - this.ScaledOffset.Y;
                    break;
            }

            if (this.Anchor >= Anchor.AutoLeft) {
                var previousChild = this.GetPreviousChild(false);
                if (previousChild != null) {
                    var prevArea = previousChild.Area;
                    switch (this.Anchor) {
                        case Anchor.AutoLeft:
                        case Anchor.AutoCenter:
                        case Anchor.AutoRight:
                            pos.Y = prevArea.Bottom + this.ScaledOffset.Y;
                            break;
                        case Anchor.AutoInline:
                            var newX = prevArea.Right + this.ScaledOffset.X;
                            if (newX + actualSize.X <= parentArea.Right) {
                                pos.X = newX;
                                pos.Y = prevArea.Y;
                            } else {
                                pos.Y = prevArea.Bottom + this.ScaledOffset.Y;
                            }
                            break;
                        case Anchor.AutoInlineIgnoreOverflow:
                            pos.X = prevArea.Right + this.ScaledOffset.X;
                            pos.Y = prevArea.Y;
                            break;
                    }
                }
            }

            this.area = new Rectangle(pos, actualSize);
            foreach (var child in this.Children)
                child.ForceUpdateArea();

            if (this.SetHeightBasedOnChildren) {
                var height = 0;
                foreach (var child in this.Children) {
                    if (!child.isHidden && (child.Anchor <= Anchor.TopRight || child.Anchor >= Anchor.AutoLeft) && child.area.Bottom > height)
                        height = child.area.Bottom;
                }

                var newHeight = (height - pos.Y + this.ScaledChildPadding.Y) / this.Scale;
                if (newHeight != this.size.Y) {
                    this.size.Y = newHeight;
                    if (this.Anchor > Anchor.TopRight)
                        this.ForceUpdateArea();
                }
            }
        }

        protected virtual Point CalcActualSize(Rectangle parentArea) {
            return new Point(
                (this.size.X > 1 ? this.ScaledSize.X : parentArea.Width * this.size.X).Floor(),
                (this.size.Y > 1 ? this.ScaledSize.Y : parentArea.Height * this.size.Y).Floor());
        }

        protected Element GetPreviousChild(bool hiddenAlso) {
            if (this.Parent == null)
                return null;

            Element lastChild = null;
            foreach (var child in this.Parent.Children) {
                if (!hiddenAlso && child.IsHidden)
                    continue;
                if (child == this)
                    break;
                lastChild = child;
            }
            return lastChild;
        }

        protected IEnumerable<Element> GetSiblings(bool hiddenAlso) {
            if (this.Parent == null)
                yield break;
            foreach (var child in this.Parent.Children) {
                if (!hiddenAlso && child.IsHidden)
                    continue;
                if (child != this)
                    yield return child;
            }
        }

        public virtual void Update(GameTime time) {
            foreach (var child in this.SortedChildren)
                child.Update(time);
        }

        public virtual void Draw(GameTime time, SpriteBatch batch, float alpha, Point offset) {
            foreach (var child in this.SortedChildren) {
                if (!child.IsHidden)
                    child.Draw(time, batch, alpha * child.DrawAlpha, offset);
            }
        }

        public virtual void DrawEarly(GameTime time, SpriteBatch batch, float alpha, BlendState blendState = null, SamplerState samplerState = null) {
            foreach (var child in this.SortedChildren) {
                if (!child.IsHidden)
                    child.DrawEarly(time, batch, alpha * child.DrawAlpha, blendState, samplerState);
            }
        }

        public Element GetMousedElement() {
            if (this.IsHidden || this.IgnoresMouse)
                return null;
            if (!this.Area.Contains(this.MousePos))
                return null;
            for (var i = this.SortedChildren.Count - 1; i >= 0; i--) {
                var element = this.SortedChildren[i].GetMousedElement();
                if (element != null)
                    return element;
            }
            return this;
        }

        protected virtual void InitStyle(UiStyle style) {
        }

        public delegate void MouseClickCallback(Element element, MouseButton button);

        public delegate void MouseCallback(Element element);

        public delegate void TextInputCallback(Element element, Keys key, char character);

        public delegate void GenericCallback(Element element);

        internal void PropagateUiSystem(UiSystem system) {
            this.System = system;
            foreach (var child in this.Children)
                child.PropagateUiSystem(system);
        }

        internal void PropagateRoot(RootElement root) {
            this.Root = root;
            foreach (var child in this.Children)
                child.PropagateRoot(root);
        }

        internal void PropagateInput(Keys key, char character) {
            this.OnTextInput?.Invoke(this, key, character);
            foreach (var child in this.Children)
                child.PropagateInput(key, character);
        }

    }
}