using System.Collections.Generic;
using System.Linq;
using Microsoft.Xna.Framework.Input;

namespace StardewModdingAPI.Framework.Input
{
    /// <summary>Manages keyboard state.</summary>
    internal class KeyboardStateBuilder : IInputStateBuilder<KeyboardStateBuilder, KeyboardState>
    {
        /*********
        ** Fields
        *********/
        /// <summary>The underlying keyboard state.</summary>
        private KeyboardState? State;

        /// <summary>The pressed buttons.</summary>
        private readonly HashSet<Keys> PressedButtons = new HashSet<Keys>();


        /*********
        ** Public methods
        *********/
        /// <summary>Construct an instance.</summary>
        /// <param name="state">The initial state, or <c>null</c> to get the latest state.</param>
        public KeyboardStateBuilder(KeyboardState? state = null)
        {
            this.Reset(state);
        }

        /// <summary>Reset the tracked state.</summary>
        /// <param name="state">The state from which to reset, or <c>null</c> to get the latest state.</param>
        public KeyboardStateBuilder Reset(KeyboardState? state = null)
        {
            this.State = state ??= Keyboard.GetState();

            this.PressedButtons.Clear();
            foreach (var button in state.Value.GetPressedKeys())
                this.PressedButtons.Add(button);

            return this;
        }

        /// <summary>Override the states for a set of buttons.</summary>
        /// <param name="overrides">The button state overrides.</param>
        public KeyboardStateBuilder OverrideButtons(IDictionary<SButton, SButtonState> overrides)
        {
            foreach (var pair in overrides)
            {
                if (pair.Key.TryGetKeyboard(out Keys key))
                {
                    this.State = null;

                    if (pair.Value.IsDown())
                        this.PressedButtons.Add(key);
                    else
                        this.PressedButtons.Remove(key);
                }
            }

            return this;
        }

        /// <summary>Get the currently pressed buttons.</summary>
        public IEnumerable<SButton> GetPressedButtons()
        {
            foreach (Keys key in this.PressedButtons)
                yield return key.ToSButton();
        }

        /// <summary>Get the equivalent state.</summary>
        public KeyboardState GetState()
        {
            return
                this.State
                ?? (this.State = new KeyboardState(this.PressedButtons.ToArray())).Value;
        }
    }
}