MLEM/MLEM.Ui/Elements/TextField.cs

using System;
using System.Linq;
using System.Text;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;
using Microsoft.Xna.Framework.Input;
using MLEM.Extensions;
using MLEM.Font;
using MLEM.Textures;
using MLEM.Ui.Style;

namespace MLEM.Ui.Elements {
    public class TextField : Element {

        public static readonly Rule DefaultRule = (field, add) => !add.Any(char.IsControl);
        public static readonly Rule OnlyLetters = (field, add) => add.All(char.IsLetter);
        public static readonly Rule OnlyNumbers = (field, add) => add.All(char.IsNumber);
        public static readonly Rule LettersNumbers = (field, add) => add.All(c => char.IsLetter(c) || char.IsNumber(c));

        public NinePatch Texture;
        public NinePatch HoveredTexture;
        public Color HoveredColor;
        public float TextScale;
        private readonly StringBuilder text = new StringBuilder();
        public string Text => this.text.ToString();
        public string PlaceholderText;
        public TextChanged OnTextChange;
        public float TextOffsetX = 4;
        private IGenericFont font;
        private double caretBlinkTimer;
        private int textStartIndex;
        public Rule InputRule;

        public TextField(Anchor anchor, Vector2 size, Rule rule = null, IGenericFont font = null) : base(anchor, size) {
            this.InputRule = rule ?? DefaultRule;
            this.font = font;
            this.OnTextInput += (element, key, character) => {
                if (!this.IsSelected)
                    return;
                if (key == Keys.Back) {
                    if (this.text.Length > 0) {
                        this.RemoveText(this.text.Length - 1, 1);
                    }
                } else {
                    this.AppendText(character);
                }
            };
        }

        private void HandleTextChange() {
            // not initialized yet
            if (this.font == null)
                return;
            var length = this.font.MeasureString(this.text).X * this.TextScale;
            var maxWidth = this.DisplayArea.Width / this.Scale - this.TextOffsetX * 2;
            if (length > maxWidth) {
                for (var i = 0; i < this.text.Length; i++) {
                    var substring = this.text.ToString(i, this.text.Length - i);
                    if (this.font.MeasureString(substring).X * this.TextScale <= maxWidth) {
                        this.textStartIndex = i;
                        break;
                    }
                }
            } else {
                this.textStartIndex = 0;
            }

            this.OnTextChange?.Invoke(this, this.text.ToString());
        }

        public override void Update(GameTime time) {
            base.Update(time);

            this.caretBlinkTimer += time.ElapsedGameTime.TotalSeconds;
            if (this.caretBlinkTimer >= 1)
                this.caretBlinkTimer = 0;
        }

        public override void Draw(GameTime time, SpriteBatch batch, float alpha, Point offset) {
            var tex = this.Texture;
            var color = Color.White * alpha;
            if (this.IsMouseOver) {
                if (this.HoveredTexture != null)
                    tex = this.HoveredTexture;
                color = this.HoveredColor * alpha;
            }
            batch.Draw(tex, this.DisplayArea.OffsetCopy(offset), color, this.Scale);

            var textPos = this.DisplayArea.Location.ToVector2() + new Vector2(offset.X + this.TextOffsetX * this.Scale, offset.Y + this.DisplayArea.Height / 2);
            if (this.text.Length > 0 || this.IsSelected) {
                var caret = this.IsSelected && this.caretBlinkTimer >= 0.5F ? "|" : "";
                var display = this.text.ToString(this.textStartIndex, this.text.Length - this.textStartIndex) + caret;
                this.font.DrawCenteredString(batch, display, textPos, this.TextScale * this.Scale, Color.White * alpha, false, true);
            } else if (this.PlaceholderText != null) {
                this.font.DrawCenteredString(batch, this.PlaceholderText, textPos, this.TextScale * this.Scale, Color.Gray * alpha, false, true);
            }
            base.Draw(time, batch, alpha, offset);
        }

        public void SetText(object text) {
            if (!this.InputRule(this, text.ToString()))
                return;
            this.text.Clear();
            this.text.Append(text);
            this.HandleTextChange();
        }

        public void AppendText(object text) {
            if (!this.InputRule(this,  text.ToString()))
                return;
            this.text.Append(text);
            this.HandleTextChange();
        }

        public void RemoveText(int index, int length) {
            this.text.Remove(index, length);
            this.HandleTextChange();
        }

        protected override void InitStyle(UiStyle style) {
            base.InitStyle(style);
            this.TextScale = style.TextScale;
            this.font = style.Font;
            this.Texture = style.TextFieldTexture;
            this.HoveredTexture = style.TextFieldHoveredTexture;
            this.HoveredColor = style.TextFieldHoveredColor;
        }

        public delegate void TextChanged(TextField field, string text);

        public delegate bool Rule(TextField field, string textToAdd);

    }
}