using System.Linq;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;
using MLEM.Font;
using MLEM.Formatting;
using MLEM.Formatting.Codes;
using MLEM.Misc;
using MLEM.Ui.Style;

namespace MLEM.Ui.Elements {
    /// <summary>
    /// A paragraph element for use inside of a <see cref="UiSystem"/>.
    /// A paragraph is an element that contains text.
    /// A paragraph's text can be formatted using the ui system's <see cref="UiSystem.TextFormatter"/>.
    /// </summary>
    public class Paragraph : Element {

        private string text;
        /// <summary>
        /// The font that this paragraph draws text with.
        /// To set its bold and italic font, use <see cref="GenericFont.Bold"/> and <see cref="GenericFont.Italic"/>.
        /// </summary>
        public StyleProp<GenericFont> RegularFont;
        /// <summary>
        /// The tokenized version of the <see cref="Text"/>
        /// </summary>
        public TokenizedString TokenizedText { get; private set; }

        /// <summary>
        /// The color that the text will be rendered with
        /// </summary>
        public StyleProp<Color> TextColor;
        /// <summary>
        /// The scale that the text will be rendered with
        /// </summary>
        public StyleProp<float> TextScale;
        /// <summary>
        /// The text to render inside of this paragraph.
        /// Use <see cref="GetTextCallback"/> if the text changes frequently.
        /// </summary>
        public string Text {
            get {
                this.QueryTextCallback();
                return this.text;
            }
            set {
                if (this.text != value) {
                    this.text = value;
                    this.IsHidden = string.IsNullOrWhiteSpace(this.text);
                    this.SetAreaDirty();
                    // force text to be re-tokenized
                    this.TokenizedText = null;
                }
            }
        }
        /// <summary>
        /// If this paragraph should automatically adjust its width based on the width of the text within it
        /// </summary>
        public bool AutoAdjustWidth;
        /// <summary>
        /// An event that gets called when this paragraph's <see cref="Text"/> is queried.
        /// Use this event for setting this paragraph's text if it changes frequently.
        /// </summary>
        public TextCallback GetTextCallback;

        /// <summary>
        /// Creates a new paragraph with the given settings.
        /// </summary>
        /// <param name="anchor">The paragraph's anchor</param>
        /// <param name="width">The paragraph's width. Note that its height is automatically calculated.</param>
        /// <param name="textCallback">The paragraph's text</param>
        /// <param name="centerText">Whether the paragraph's width should automatically be calculated based on the text within it.</param>
        public Paragraph(Anchor anchor, float width, TextCallback textCallback, bool centerText = false)
            : this(anchor, width, "", centerText) {
            this.GetTextCallback = textCallback;
            this.Text = textCallback(this);
            if (this.Text == null)
                this.IsHidden = true;
        }

        /// <inheritdoc cref="Paragraph(Anchor,float,TextCallback,bool)"/>
        public Paragraph(Anchor anchor, float width, string text, bool centerText = false) : base(anchor, new Vector2(width, 0)) {
            this.Text = text;
            if (this.Text == null)
                this.IsHidden = true;
            this.AutoAdjustWidth = centerText;
            this.CanBeSelected = false;
            this.CanBeMoused = false;
        }

        /// <inheritdoc />
        protected override Vector2 CalcActualSize(RectangleF parentArea) {
            var size = base.CalcActualSize(parentArea);
            this.ParseText(size);
            var dims = this.TokenizedText.Measure(this.RegularFont) * this.TextScale * this.Scale;
            return new Vector2(this.AutoAdjustWidth ? dims.X + this.ScaledPadding.Width : size.X, dims.Y + this.ScaledPadding.Height);
        }

        /// <inheritdoc />
        public override void Update(GameTime time) {
            this.QueryTextCallback();
            base.Update(time);
            if (this.TokenizedText != null)
                this.TokenizedText.Update(time);
        }

        /// <inheritdoc />
        public override void Draw(GameTime time, SpriteBatch batch, float alpha, BlendState blendState, SamplerState samplerState, Matrix matrix) {
            var pos = this.DisplayArea.Location;
            var sc = this.TextScale * this.Scale;
            var color = this.TextColor.OrDefault(Color.White) * alpha;
            this.TokenizedText.Draw(time, batch, pos, this.RegularFont, color, sc, 0);
            base.Draw(time, batch, alpha, blendState, samplerState, matrix);
        }

        /// <inheritdoc />
        protected override void InitStyle(UiStyle style) {
            base.InitStyle(style);
            this.TextScale.SetFromStyle(style.TextScale);
            this.RegularFont.SetFromStyle(style.Font); 
        }

        /// <summary>
        /// Parses this paragraph's <see cref="Text"/> into <see cref="TokenizedText"/>.
        /// Additionally, this method adds any <see cref="Link"/> elements for tokenized links in the text.
        /// </summary>
        /// <param name="size">The paragraph's default size</param>
        protected virtual void ParseText(Vector2 size) {
            if (this.TokenizedText == null)
                this.TokenizedText = this.System.TextFormatter.Tokenize(this.RegularFont, this.Text);

            this.TokenizedText.Split(this.RegularFont, size.X - this.ScaledPadding.Width, this.TextScale * this.Scale);
            var linkTokens = this.TokenizedText.Tokens.Where(t => t.AppliedCodes.Any(c => c is LinkCode)).ToArray();
            // this basically checks if there are any tokens that have an area that doesn't have a link element associated with it
            if (linkTokens.Any(t => !t.GetArea(Vector2.Zero, this.TextScale).All(a => this.GetChildren<Link>(c => c.PositionOffset == a.Location && c.Size == a.Size).Any()))) {
                this.RemoveChildren(c => c is Link);
                foreach (var link in linkTokens) {
                    var areas = link.GetArea(Vector2.Zero, this.TextScale).ToArray();
                    var cluster = new Link[areas.Length];
                    for (var i = 0; i < areas.Length; i++) {
                        var area = areas[i];
                        cluster[i] = this.AddChild(new Link(Anchor.TopLeft, link, area.Size, cluster) {
                            PositionOffset = area.Location,
                            // only allow selecting the first part of a link
                            CanBeSelected = i == 0
                        });
                    }
                }
            }
        }

        private void QueryTextCallback() {
            if (this.GetTextCallback != null)
                this.Text = this.GetTextCallback(this);
        }

        /// <summary>
        /// A delegate method used for <see cref="Paragraph.GetTextCallback"/>
        /// </summary>
        /// <param name="paragraph">The current paragraph</param>
        public delegate string TextCallback(Paragraph paragraph);

        /// <summary>
        /// A link is a sub-element of the <see cref="Paragraph"/> that is added onto it as a child for any tokens that contain <see cref="LinkCode"/>, to make them selectable and clickable.
        /// </summary>
        public class Link : Element {

            /// <summary>
            /// The token that this link represents
            /// </summary>
            public readonly Token Token;
            /// <summary>
            /// The links that form a cluster for the given token.
            /// This only contains more than one element if the tokenized string has previously been <see cref="TokenizedString.Split"/>.
            /// </summary>
            public readonly Link[] LinkCluster;

            /// <summary>
            /// Creates a new link element with the given settings
            /// </summary>
            /// <param name="anchor">The link's anchor</param>
            /// <param name="token">The token that this link represents</param>
            /// <param name="size">The size of the token</param>
            /// <param name="linkCluster">The links that form a cluster for the given token. This only contains more than one element if the tokenized string has previously been split.</param>
            public Link(Anchor anchor, Token token, Vector2 size, Link[] linkCluster) : base(anchor, size) {
                this.Token = token;
                this.LinkCluster = linkCluster;
                this.OnSelected += e => {
                    foreach (var link in this.LinkCluster)
                        link.IsSelected = true;
                };
                this.OnDeselected += e => {
                    foreach (var link in this.LinkCluster)
                        link.IsSelected = false;
                };
                this.OnPressed += e => {
                    foreach (var code in token.AppliedCodes.OfType<LinkCode>())
                        this.System?.LinkBehavior?.Invoke(code);
                };
            }

        }

    }
}