using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;

// Require the rect transform to be on the same object as this navigation behaviour
[RequireComponent(typeof(RectTransform))]
public class GridNavigation : MonoBehaviour {

    // The layout
    public GridLayoutGroup layout;

    // Default starting position (top left)
    public Vector2Int position = new Vector2Int(0, 0);

    // Child elements of the transform
    private List<RectTransform> children;

    // The rect transform of the object
    private RectTransform rectTransform;

    public Vector2Int Position {
        get {
            return position;
        }
        set {
            bool update = false;
            if (position != value) {
                update = true;
            }
            position = value;
            if (update) {
                UpdateUI();
            }
        }
    }

    // Use this for initialization
    void Start() {
        rectTransform = GetComponent<RectTransform>();
        children = new List<RectTransform>();
        for (int i = 0; i < rectTransform.childCount; i++) {
            children.Add(rectTransform.GetChild(i).GetComponent<RectTransform>());
        }
        Debug.Log("Width: " + GetWidth());
        Debug.Log("Height: " + GetHeight());
        // Position = new Vector2Int(1, 1);
    }

    RectTransform GetTile(int x, int y) {
        return children[Get1DPosition(x, y)];
    }

    RectTransform GetTile(Vector2Int pos) {
        return children[Get1DPosition(pos.x, pos.y)];
    }

    Vector2Int Get2DPosition(int index) {
        return new Vector2Int(
            index % GetWidth(),     // % is the "modulo operator", the remainder of i / width;
            index / GetWidth());    // where "/" is an integer division
    }

    int Get1DPosition(int x, int y) {
        return (GetWidth() * y) + x;
    }

    void SelectTile(RectTransform tile) {
        if (tile != null) {
            tile.GetComponent<Button>().Select();
        }
        else {
            Debug.LogError("Can't select null tile.");
        }
    }

    // Update is called once per frame
    void Update() {
        int v = 0, h = 0;
        if (Input.GetKeyDown(KeyCode.W)) { v = -1; h = 0; }
        else if (Input.GetKeyDown(KeyCode.A)) { v = 0; h = -1; }
        else if (Input.GetKeyDown(KeyCode.S)) { v = 1; h = 0; }
        else if (Input.GetKeyDown(KeyCode.D)) { v = 0; h = 1; }
        if (h != 0 || v != 0) {
            if (InBounds(h, v)) {
                Move(h, v);
            }
            else {
                Debug.LogError(string.Format("Invalid grid navigation move: ({0}, {1})", h, v));
            }
        }
    }

    void UpdateUI() {
        SelectTile(GetTile(Position.x, Position.y));
    }

    // Check if the move is valid, within the bounds of the grid
    bool InBounds(int h, int v) {
        bool valid = false;
        if (Position.y + v < GetHeight() && Position.y + v >= 0) {
            if (Position.x + h < GetWidth() && Position.x + h >= 0) {
                valid = true;
            }
        }
        return valid;
    }

    void Move(int h, int v) {
        Position += new Vector2Int(h, v);
    }

    public int ChildCount() {
        return transform.childCount;
    }

    public int GetWidth() {
        int width = 0;
        switch (layout.constraint) {
            case GridLayoutGroup.Constraint.Flexible:
                width = Mathf.FloorToInt(rectTransform.rect.width / (layout.cellSize.x + layout.spacing.x));
                break;
            case GridLayoutGroup.Constraint.FixedColumnCount:
                width = layout.constraintCount;
                break;
            case GridLayoutGroup.Constraint.FixedRowCount:
                width = (ChildCount() / layout.constraintCount);
                break;
            default:
                break;
        }
        return width;
    }

    public int GetHeight() {
        return 2;
    }
}