using System;
using Framework.Support;
using UnityEngine;
using UnityEditor;

namespace Framework.Dialogue {

  /// <summary>
  ///   Assists the user in editing ground definitions for the navigation system
  /// </summary>
  [CustomEditor(typeof(DialogueOwner), true)]
  public class DialogueOwnerEditor : Editor {

    /// <summary>Called when Unity wants to layout or draw the inspector</summary>
    public override void OnInspectorGUI() {
      base.OnInspectorGUI();

      if(!Application.isPlaying) {
        var dialoguePlacement = target as DialogueOwner;
        if (dialoguePlacement != null) {
          doPreviewGui(dialoguePlacement);

          EditorGUILayout.HelpBox(
            "NOTE: Do not leave dialogue UI previews open. " +
            "These would remain open when the game starts",
            MessageType.Info
          );

          updateSelection(dialoguePlacement);
        }
      }
    }

    /// <summary>Called when the editor UI is created for a game object</summary>
    protected virtual void OnEnable() {

      // Destroy any preview UIs. If we destroyed them in OnDestroy(), the user
      // would be unable to actually use the previews to position the UI,
      // but leaving them active would mean the editor UI (which is recreated
      // each time the object gets selected) would create ever more preview UIs.
      var dialogueOwner = target as DialogueOwner;
      if(dialogueOwner != null) {
        int placementCount = getPlacementCount(dialogueOwner);

        for(int index = 0; index < placementCount; ++index) {
          Transform placement = dialogueOwner.StaticPlacements[index];
          destroyPreviewPlacement(placement);
        }
      }

    }

    /// <summary>Shows the UI controls for the dialogue placement preview</summary>
    /// <param name="dialogueOwner">Dialogue placement the GUI will be shown for</param>
    private void doPreviewGui(DialogueOwner dialogueOwner) {
      int placementCount = getPlacementCount(dialogueOwner);

      if(this.selectedPreviewIndex > placementCount) {
        this.selectedPreviewIndex = -1;
      }

      // If there are placement slots present, allow the user to select
      // between them to display an in-editor preview.
      if(placementCount > 0) {
        var previews = new string[placementCount];
        for(int index = 0; index < placementCount; ++index) {
          previews[index] = (index + 1).ToString();
        }

        using(var horizontalScope = new EditorGUILayout.HorizontalScope()) {
          EditorGUILayout.PrefixLabel("Preview");
          this.selectedPreviewIndex = GUILayout.SelectionGrid(
            this.selectedPreviewIndex, previews, placementCount
          );
        }
      }

      // Also provide a button for the user to hide all previews
      using(var horizontalScope = new EditorGUILayout.HorizontalScope()) {
        if(placementCount == 0) {
          EditorGUILayout.PrefixLabel("Preview");
        } else {
          EditorGUILayout.PrefixLabel(" ");
        }

        bool hidePreviewClicked = GUILayout.Button("Hide Preview");
        if(hidePreviewClicked) {
          this.selectedPreviewIndex = -1;
        }
      }
    }

    /// <summary>Activates the currently selected preview</summary>
    /// <param name="dialogueOwner">Dialogue placement </param>
    private void updateSelection(DialogueOwner dialogueOwner) {
      int placementCount = getPlacementCount(dialogueOwner);

      if(this.selectedPreviewIndex != this.activePreviewIndex) {
        if((this.activePreviewIndex != -1) && (this.activePreviewIndex < placementCount)) {
          Transform placement = dialogueOwner.StaticPlacements[this.activePreviewIndex];
          if(placement != null) {
            destroyPreviewPlacement(placement);
          }
        }
        if((this.selectedPreviewIndex != -1) && (this.selectedPreviewIndex < placementCount)) {
          Transform placement = dialogueOwner.StaticPlacements[this.selectedPreviewIndex];
          if(placement == null) {
            Debug.LogWarning("Showing no preview because the placement is set to null.");
          } else {
            createPreviewPlacement(placement, dialogueOwner.PreviewPrefab);
          }
        }

        this.activePreviewIndex = this.selectedPreviewIndex;
      }
    }

    /// <summary>Creates a preview placement in the editor</summary>
    /// <param name="placement">Position at which a preview placement will be created</param>
    /// <param name="prefab">Prefab to instantiate for the preview</param>
    private void createPreviewPlacement(Transform placement, DialogueCanvas prefab) {
      DialogueCanvas canvas = GameObject.Instantiate<DialogueCanvas>(prefab);
      GameObjectHelper.SetAsChild(placement.gameObject, canvas.gameObject);
    }

    /// <summary>Destroys a preview placement in the editor</summary>
    /// <param name="placement">Parent in which hte preview placement will be destroyed</param>
    private void destroyPreviewPlacement(Transform placement) {
      DialogueCanvas canvas = placement.GetComponentInChildren<DialogueCanvas>();
      if(canvas != null) {
        GameObject.DestroyImmediate(canvas.gameObject);
      }
    }

    /// <summary>Returns the number of dialogue placements set up</summary>
    /// <param name="dialogueOwner">
    ///   Dialogue placement container whose placement count will be checked
    /// </param>
    /// <returns>The number of placements set up in the placement container</returns>
    private static int getPlacementCount(DialogueOwner dialogueOwner) {
      if(dialogueOwner.StaticPlacements == null) {
        return 0;
      } else {
        return dialogueOwner.StaticPlacements.Length;
      }
    }

    /// <summary>Index of the placement that is being previewed currently</summary>
    private int selectedPreviewIndex = -1;
    /// <summary>Index of the placement that is being previewed currently</summary>
    private int activePreviewIndex = -1;

  }

} // namespace Framework.Dialogue