using System;
using System.ComponentModel;
using System.Text;
using System.Windows.Input;

namespace ICSharpCode.Core.Presentation
{
    /// <summary>
    /// Describes full key gesture or part of a key gesture
    /// 
    /// This class is is designed to react to key events even it descibes only part of them
    /// For example if event argument holds modifiers Ctrl, Shift and key C then partial template
    /// with single modifier Ctrl and a key C will match this event
    /// </summary>
    [TypeConverter(typeof(PartialKeyGestureConverter))]
    public class PartialKeyGesture : KeyGesture
    {
        private readonly Key _key;
        private readonly ModifierKeys _modifiers;

        /// <summary>
        /// Key associated with partial key gesture
        /// </summary>
        public new Key Key
        {
            get
            {
                return _key;
            }
        }

        /// <summary>
        /// Modifier keys associated with partial key gesture
        /// </summary>
        public new ModifierKeys Modifiers
        {
            get
            {
                return _modifiers;
            }
        }

        /// <summary>
        /// Create new instance of <see cref="PartialKeyGesture"/> from <see cref="KeyEventArgs"/>
        /// </summary>
        /// <param name="keyEventArgs">Arguments generated by key event</param>
        public PartialKeyGesture(KeyEventArgs keyEventArgs)
            : base(Key.None, ModifierKeys.None)
        {
            var keyboardDevice = (KeyboardDevice)keyEventArgs.Device;
            
            var enteredKey = keyEventArgs.Key == Key.System ? keyEventArgs.SystemKey : keyEventArgs.Key;
            var enteredModifiers = keyboardDevice.Modifiers;

            if(Array.IndexOf(new[] {  Key.LeftAlt, Key.RightAlt, 
                           Key.LeftShift, Key.RightShift,
                           Key.LeftCtrl, Key.RightCtrl,
                           Key.LWin, Key.RWin}, enteredKey) >= 0) {
            	_key = Key.None;
            	_modifiers = enteredModifiers;
            } else {
            	_key = enteredKey;
            	_modifiers = enteredModifiers;
            }
        }

        /// <summary>
        /// Create new instance of <see cref="PartialKeyGesture"/> from <see cref="KeyGesture"/> 
        /// </summary>
        /// <param name="gesture">Key gesture</param>
        public PartialKeyGesture(KeyGesture gesture)
            : base(Key.None, ModifierKeys.None)
        {
            var partialKeyGesture = gesture as PartialKeyGesture;

            if (partialKeyGesture != null) {
                _key = partialKeyGesture.Key;
                _modifiers = partialKeyGesture.Modifiers;
            } else if (gesture is MultiKeyGesture) {
                throw new ArgumentException("Can not create partial key gesture from multi-key gesture");
            } else {
                _key = gesture.Key;
                _modifiers = gesture.Modifiers;
            }
        }

        /// <summary>
        /// Create new instance of <see cref="PartialKeyGesture"/> having key and modifiers
        /// </summary>
        /// <param name="key">The key associated with partial key gesture</param>
        /// <param name="modifiers">Modifier keys associated with partial key gesture</param>
        public PartialKeyGesture(Key key, ModifierKeys modifiers)
            : base(Key.None, ModifierKeys.None)
        {
            _key = key;
            _modifiers = modifiers;
        }

        /// <summary>
        /// Create new instance of<see cref="PartialKeyGesture"/> having only key and no modifiers
        /// </summary>
        /// <param name="key">The key associated with partial key gesture</param>
        public PartialKeyGesture(Key key)
            : base(Key.None, ModifierKeys.None)
        {
            _key = key;
            _modifiers = ModifierKeys.None;
        }


        /// <summary>
        /// Create new instance of<see cref="PartialKeyGesture"/> having only key and no modifiers
        /// </summary>
        /// <param name="modifiers">Modifier keys associated with partial key gesture</param>
        public PartialKeyGesture(ModifierKeys modifiers)
            : base(Key.None, ModifierKeys.None)
        {
            _key = Key.None;
            _modifiers = modifiers;
        }
        

        /// <summary>
        /// Determines whether key gesture strictly matches this key gesture template
        /// (That is key and modifier both match key event arguments)
        /// </summary>
        /// <param name="targetElement">The target</param>
        /// <param name="args">Input event arguments</param>
        /// <returns>True if the event data matches this <see cref="PartialKeyGesture"/>; otherwise, false. </returns>
        public bool StrictlyMatches(object targetElement, InputEventArgs args)
        {
            var keyEventArgs = args as KeyEventArgs;
            if(keyEventArgs == null)
            {
                return false;
            }

            var keyboard = (KeyboardDevice)keyEventArgs.Device;

            // If system key is pressed
            if (keyEventArgs.Key == Key.System)
            {
                return keyboard.Modifiers == Modifiers && keyEventArgs.SystemKey == Key;
            }

            return keyboard.Modifiers == Modifiers && keyEventArgs.Key == Key;
        }

        /// <summary>
        /// Determines whether key event arguments matches this instance of <see cref="PartialKeyGesture"/>
        /// </summary>
        /// <param name="targetElement">The target</param>
        /// <param name="inputEventArgs">Input event arguments</param>
        /// <returns>True if event data matches parial event arguments otherwise false</returns>
        public override bool Matches(object targetElement, InputEventArgs inputEventArgs)
        {
            var keyEventArgs = inputEventArgs as KeyEventArgs;
            if(keyEventArgs == null)
            {
                return false;
            }

            var keyboard = (KeyboardDevice)keyEventArgs.Device;

            // When system key (Alt) is pressed real key is moved to SystemKey property
            var enteredKey = keyEventArgs.Key == Key.System ? keyEventArgs.SystemKey : keyEventArgs.Key;
            
            var keyMatches = Key == enteredKey;

            // Determine whether template contains only part of modifier keys contained in
            // gesture. For example if template contains Control modifier, but gesture contains
            // Control and Alt true will be returned
            var modifierMatches = keyboard.Modifiers - (keyboard.Modifiers ^ Modifiers) >= 0;

            // Template contains no modifiers compare only keys
            if (Modifiers == ModifierKeys.None)
            {
                return keyMatches;
            }

            // If template has modifiers but key is one of modifier keys return true if
            // modifiers match. This is used because when user presses modifier key it is 
            // presented in Key property and Modifiers property
            if (Array.IndexOf(new[] {  Key.LeftAlt, Key.RightAlt, 
                                       Key.LeftShift, Key.RightShift,
                                       Key.LeftCtrl, Key.RightCtrl,
                                       Key.LWin, Key.RWin,
                                       Key.System}, enteredKey) >= 0)
            {
                return modifierMatches;
            }

            return modifierMatches && keyMatches;
        }

        /// <summary>
        /// Returns string that represents <see cref="PartialKeyGesture"/>
        /// </summary>
        /// <returns>String</returns>
        public override string ToString()
        {
            var pressedButton = new StringBuilder();

            if (Modifiers != ModifierKeys.None)
            {
                pressedButton.AppendFormat("{0}+", new ModifierKeysConverter().ConvertToInvariantString(Modifiers));
            }

            // Filter modifier keys from being displayed twice (example: Ctrl + LeftCtrl)
            if (Array.IndexOf(new[] { Key.LeftAlt, Key.RightAlt, 
                                       Key.LeftShift, Key.RightShift,
                                       Key.LeftCtrl, Key.RightCtrl,
                                       Key.LWin, Key.RWin,
                                       Key.System}, Key) < 0)
            {
                pressedButton.Append(new KeyConverter().ConvertToInvariantString(Key));
            }

            return pressedButton.ToString();
        }
    }
}