using System;
using System.Collections.Generic;
using System.Text;

using UnityEngine;

namespace Framework.Input {

  /// <summary>Provides helper methods for the input system</summary>
  public static class InputHelper {

    /// <summary>
    ///   Text that is used to indicate that an action has no buttons or axes assigned
    /// </summary>
    private const string UnassignedText = "<no keys assigned>";

    /// <summary>
    ///   Retrieves the human-readable name of the first key or axis assigned to an action
    /// </summary>
    /// <param name="inputMapper">Input mapper that holds the key bindings</param>
    /// <param name="actionName">Name of the action whose bindings will be looked up</param>
    /// <returns>The human-readable name of the key or axis assigned to the action</returns>
    public static string GetAssignedKeyName(InputMapper inputMapper, string actionName) {
      IAction action;
      if(inputMapper.Actions.TryGet(actionName, out action)) {
        if(action.BoundJoystickAxes.Count > 0) {
          return getBoundJoystickAxisName(action.BoundJoystickAxes);
        } else if(action.BoundKeys.Count > 0) {
          return getBoundKeyName(action.BoundKeys);
        }
      }

      return UnassignedText;
    }

    /// <summary>
    ///   Replaces any action names in a string with the keys assigned to the action
    /// </summary>
    /// <param name="textWithPlaceholders">
    ///   Text in which the action names will be replaced with their bound keys
    /// </param>
    /// <returns>The input string with all action names replaced by their bound keys</returns>
    /// <remarks>
    ///   <para>
    ///     This replaces any action names in the format %action% with the keys bound to
    ///     the action. This is useful if you want to display instructions to the player,
    ///     for example &quot;Press %jump% to jump!&quot; or &quot;Move left and right
    ///     with %left% and %right%!&quot;.
    ///   </para>
    ///   <para>
    ///     If you want to use a percent character in your text, just write a double
    ///     percent character (eg. &quot;Press %fire% when the weapon is 100%% charged&quot;).
    ///   </para>
    ///   <para>
    ///     While this method is optimized fairly well, since text will be displayed for
    ///     multiple frames, it's a good idea to cache the result and display that instead
    ///     of expanding the actions over and over (at the very least it will feed
    ///     the garbage collector).
    ///   </para>
    ///   <para>
    ///     <example>
    ///       <code>
    ///         void Awake() {
    ///           this.tutorialMessage = InputHelper.ExpandActions(
    ///             this.myInputMapper,
    ///             "Press %jump% and then %crouch% to jump into the small gap"
    ///           );
    ///         }
    ///       </code>
    ///     </example>
    ///   </para>
    /// </remarks>
    public static string ExpandActions(InputMapper inputMapper, string textWithPlaceholders) {
      if(string.IsNullOrEmpty(textWithPlaceholders)) {
        return textWithPlaceholders;
      }

      var builder = new StringBuilder(textWithPlaceholders.Length);
      int actionStartIndex = -1;
      int textStartIndex = 0;

      // Append text outside '%' characters normally and replace text inside '%' characters
      for(int index = 0; index < textWithPlaceholders.Length; ++index) {
        if(textWithPlaceholders[index] == '%') {
          if(actionStartIndex == -1) { // First '%' character, append text until here
            builder.Append(textWithPlaceholders, textStartIndex, index - textStartIndex);
            textStartIndex = -1;
            actionStartIndex = index + 1;
          } else if(index == actionStartIndex) { // Double '%' character?
            builder.Append('%');
          } else { // Second '%' character with content inbetween, replace action name
            string actionName = textWithPlaceholders.Substring(
              actionStartIndex, index - actionStartIndex
            );
            builder.Append(GetAssignedKeyName(inputMapper, actionName));
            actionStartIndex = -1;
            textStartIndex = index + 1;
          }
        }
      }

      // Append the last chunk of text, if any
      if(textStartIndex < textWithPlaceholders.Length) {
        builder.Append(
          textWithPlaceholders, textStartIndex, textWithPlaceholders.Length - textStartIndex
        );
      }

      return builder.ToString();
    }

    /// <summary>Retrieves the name of a bound key</summary>
    /// <param name="boundKeys">Keys that have been bound to the action</param>
    /// <returns>The name of the first bound key in the collection</returns>
    private static string getBoundKeyName(ICollection<KeyCode> boundKeys) {
      foreach(KeyCode keyCode in boundKeys) {
        return keyCode.ToString();
      }

      return UnassignedText;
    }

    /// <summary>Retrieves the name of a bound axis</summary>
    /// <param name="boundAxes">Joystick axis that have been bound to the action</param>
    /// <returns>The name of the first bound joystick axis in the collection</returns>
    private static string getBoundJoystickAxisName(ICollection<JoystickAxis> boundAxes) {
      foreach(JoystickAxis axis in boundAxes) {

        // Check if this is a joystick's X axis
        int index = indexOfAxis(axis.AxisName, "X");
        if(index == -1) {
          index = axis.AxisName.IndexOf(
            "horizontal", StringComparison.InvariantCultureIgnoreCase
          );
        }
        if(index != -1) {
          string joystickName = axis.AxisName.Substring(0, index);
          return string.Concat(joystickName, " ", axis.IsNegative ? "left" : "right");
        }

        // Check if this is a joystick's Y axis
        index = indexOfAxis(axis.AxisName, "Y");
        if(index == -1) {
          index = axis.AxisName.IndexOf(
            "vertical", StringComparison.InvariantCultureIgnoreCase
          );
        }
        if(index != -1) {
          string joystickName = axis.AxisName.Substring(0, index);
          // TODO: Verify that 'up' and 'down' are not flipped here
          return string.Concat(joystickName, " ", axis.IsNegative ? "up" : "down");
        }

      }

      // It's probably not the X or Y axis, so use the axis name
      foreach(JoystickAxis axis in boundAxes) {
        return string.Concat(axis.AxisName, " ", axis.IsNegative ? "negative" : "positive");
      }

      return UnassignedText;
    }

    /// <summary>Looks for an axis in a joystick axis name</summary>
    /// <param name="axisName">Joystick axis name in which the axis part will be searched</param>
    /// <param name="axis">Axis to search the joystick axis name for</param>
    /// <returns>The index of the axis part in the joystick axis name</returns>
    private static int indexOfAxis(string axisName, string axis) {
      int index;

      index = axisName.IndexOf(axis + " axis", StringComparison.InvariantCultureIgnoreCase);
      if(index != -1) {
        return index;
      }

      index = axisName.IndexOf(axis + "axis", StringComparison.InvariantCultureIgnoreCase);
      if(index != -1) {
        return index;
      }

      index = axisName.IndexOf("axis " + axis, StringComparison.InvariantCultureIgnoreCase);
      if(index != -1) {
        return index;
      }

      return axisName.IndexOf("axis" + axis, StringComparison.InvariantCultureIgnoreCase);
    }

  }

} // namespace Framework.Input