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

/// <summary>
/// 对 Unity 的扩展方法。
/// </summary>
public static class UnityExtension
{
    private static readonly List<Transform> s_CachedTransforms = new List<Transform>();

    /// <summary>
    /// 获取或增加组件。
    /// </summary>
    /// <typeparam name="T">要获取或增加的组件。</typeparam>
    /// <param name="gameObject">目标对象。</param>
    /// <returns>获取或增加的组件。</returns>
    public static T GetOrAddComponent<T>(this GameObject gameObject) where T : Component
    {
        T component = gameObject.GetComponent<T>();
        if (component == null)
        {
            component = gameObject.AddComponent<T>();
        }

        return component;
    }

    /// <summary>
    /// 获取或增加组件。
    /// </summary>
    /// <param name="gameObject">目标对象。</param>
    /// <param name="type">要获取或增加的组件类型。</param>
    /// <returns>获取或增加的组件。</returns>
    public static Component GetOrAddComponent(this GameObject gameObject, Type type)
    {
        Component component = gameObject.GetComponent(type);
        if (component == null)
        {
            component = gameObject.AddComponent(type);
        }

        return component;
    }

    /// <summary>
    /// 获取 GameObject 是否在场景中。
    /// </summary>
    /// <param name="gameObject">目标对象。</param>
    /// <returns>GameObject 是否在场景中。</returns>
    /// <remarks>若返回 true，表明此 GameObject 是一个场景中的实例对象；若返回 false，表明此 GameObject 是一个 Prefab。</remarks>
    public static bool InScene(this GameObject gameObject)
    {
        return gameObject.scene.name != null;
    }

    /// <summary>
    /// 递归设置游戏对象的层次。
    /// </summary>
    /// <param name="gameObject"><see cref="GameObject" /> 对象。</param>
    /// <param name="layer">目标层次的编号。</param>
    public static void SetLayerRecursively(this GameObject gameObject, int layer)
    {
        gameObject.GetComponentsInChildren(true, s_CachedTransforms);
        for (int i = 0; i < s_CachedTransforms.Count; i++)
        {
            s_CachedTransforms[i].gameObject.layer = layer;
        }

        s_CachedTransforms.Clear();
    }

    /// <summary>
    /// 取 <see cref="Vector3" /> 的 (x, y, z) 转换为 <see cref="Vector2" /> 的 (x, z)。
    /// </summary>
    /// <param name="vector3">要转换的 Vector3。</param>
    /// <returns>转换后的 Vector2。</returns>
    public static Vector2 ToVector2(this Vector3 vector3)
    {
        return new Vector2(vector3.x, vector3.z);
    }

    /// <summary>
    /// 取 <see cref="Vector2" /> 的 (x, y) 转换为 <see cref="Vector3" /> 的 (x, 0, y)。
    /// </summary>
    /// <param name="vector2">要转换的 Vector2。</param>
    /// <returns>转换后的 Vector3。</returns>
    public static Vector3 ToVector3(this Vector2 vector2)
    {
        return new Vector3(vector2.x, 0f, vector2.y);
    }

    /// <summary>
    /// 取 <see cref="Vector2" /> 的 (x, y) 和给定参数 y 转换为 <see cref="Vector3" /> 的 (x, 参数 y, y)。
    /// </summary>
    /// <param name="vector2">要转换的 Vector2。</param>
    /// <param name="y">Vector3 的 y 值。</param>
    /// <returns>转换后的 Vector3。</returns>
    public static Vector3 ToVector3(this Vector2 vector2, float y)
    {
        return new Vector3(vector2.x, y, vector2.y);
    }

    #region Transform

    /// <summary>
    /// 设置绝对位置的 x 坐标。
    /// </summary>
    /// <param name="transform"><see cref="Transform" /> 对象。</param>
    /// <param name="newValue">x 坐标值。</param>
    public static void SetPositionX(this Transform transform, float newValue)
    {
        Vector3 v = transform.position;
        v.x = newValue;
        transform.position = v;
    }

    /// <summary>
    /// 设置绝对位置的 y 坐标。
    /// </summary>
    /// <param name="transform"><see cref="Transform" /> 对象。</param>
    /// <param name="newValue">y 坐标值。</param>
    public static void SetPositionY(this Transform transform, float newValue)
    {
        Vector3 v = transform.position;
        v.y = newValue;
        transform.position = v;
    }

    /// <summary>
    /// 设置绝对位置的 z 坐标。
    /// </summary>
    /// <param name="transform"><see cref="Transform" /> 对象。</param>
    /// <param name="newValue">z 坐标值。</param>
    public static void SetPositionZ(this Transform transform, float newValue)
    {
        Vector3 v = transform.position;
        v.z = newValue;
        transform.position = v;
    }

    /// <summary>
    /// 增加绝对位置的 x 坐标。
    /// </summary>
    /// <param name="transform"><see cref="Transform" /> 对象。</param>
    /// <param name="deltaValue">x 坐标值增量。</param>
    public static void AddPositionX(this Transform transform, float deltaValue)
    {
        Vector3 v = transform.position;
        v.x += deltaValue;
        transform.position = v;
    }

    /// <summary>
    /// 增加绝对位置的 y 坐标。
    /// </summary>
    /// <param name="transform"><see cref="Transform" /> 对象。</param>
    /// <param name="deltaValue">y 坐标值增量。</param>
    public static void AddPositionY(this Transform transform, float deltaValue)
    {
        Vector3 v = transform.position;
        v.y += deltaValue;
        transform.position = v;
    }

    /// <summary>
    /// 增加绝对位置的 z 坐标。
    /// </summary>
    /// <param name="transform"><see cref="Transform" /> 对象。</param>
    /// <param name="deltaValue">z 坐标值增量。</param>
    public static void AddPositionZ(this Transform transform, float deltaValue)
    {
        Vector3 v = transform.position;
        v.z += deltaValue;
        transform.position = v;
    }

    /// <summary>
    /// 设置相对位置的 x 坐标。
    /// </summary>
    /// <param name="transform"><see cref="Transform" /> 对象。</param>
    /// <param name="newValue">x 坐标值。</param>
    public static void SetLocalPositionX(this Transform transform, float newValue)
    {
        Vector3 v = transform.localPosition;
        v.x = newValue;
        transform.localPosition = v;
    }

    /// <summary>
    /// 设置相对位置的 y 坐标。
    /// </summary>
    /// <param name="transform"><see cref="Transform" /> 对象。</param>
    /// <param name="newValue">y 坐标值。</param>
    public static void SetLocalPositionY(this Transform transform, float newValue)
    {
        Vector3 v = transform.localPosition;
        v.y = newValue;
        transform.localPosition = v;
    }

    /// <summary>
    /// 设置相对位置的 z 坐标。
    /// </summary>
    /// <param name="transform"><see cref="Transform" /> 对象。</param>
    /// <param name="newValue">z 坐标值。</param>
    public static void SetLocalPositionZ(this Transform transform, float newValue)
    {
        Vector3 v = transform.localPosition;
        v.z = newValue;
        transform.localPosition = v;
    }

    /// <summary>
    /// 增加相对位置的 x 坐标。
    /// </summary>
    /// <param name="transform"><see cref="Transform" /> 对象。</param>
    /// <param name="deltaValue">x 坐标值。</param>
    public static void AddLocalPositionX(this Transform transform, float deltaValue)
    {
        Vector3 v = transform.localPosition;
        v.x += deltaValue;
        transform.localPosition = v;
    }

    /// <summary>
    /// 增加相对位置的 y 坐标。
    /// </summary>
    /// <param name="transform"><see cref="Transform" /> 对象。</param>
    /// <param name="deltaValue">y 坐标值。</param>
    public static void AddLocalPositionY(this Transform transform, float deltaValue)
    {
        Vector3 v = transform.localPosition;
        v.y += deltaValue;
        transform.localPosition = v;
    }

    /// <summary>
    /// 增加相对位置的 z 坐标。
    /// </summary>
    /// <param name="transform"><see cref="Transform" /> 对象。</param>
    /// <param name="deltaValue">z 坐标值。</param>
    public static void AddLocalPositionZ(this Transform transform, float deltaValue)
    {
        Vector3 v = transform.localPosition;
        v.z += deltaValue;
        transform.localPosition = v;
    }

    /// <summary>
    /// 设置相对尺寸的 x 分量。
    /// </summary>
    /// <param name="transform"><see cref="Transform" /> 对象。</param>
    /// <param name="newValue">x 分量值。</param>
    public static void SetLocalScaleX(this Transform transform, float newValue)
    {
        Vector3 v = transform.localScale;
        v.x = newValue;
        transform.localScale = v;
    }

    /// <summary>
    /// 设置相对尺寸的 y 分量。
    /// </summary>
    /// <param name="transform"><see cref="Transform" /> 对象。</param>
    /// <param name="newValue">y 分量值。</param>
    public static void SetLocalScaleY(this Transform transform, float newValue)
    {
        Vector3 v = transform.localScale;
        v.y = newValue;
        transform.localScale = v;
    }

    /// <summary>
    /// 设置相对尺寸的 z 分量。
    /// </summary>
    /// <param name="transform"><see cref="Transform" /> 对象。</param>
    /// <param name="newValue">z 分量值。</param>
    public static void SetLocalScaleZ(this Transform transform, float newValue)
    {
        Vector3 v = transform.localScale;
        v.z = newValue;
        transform.localScale = v;
    }

    /// <summary>
    /// 增加相对尺寸的 x 分量。
    /// </summary>
    /// <param name="transform"><see cref="Transform" /> 对象。</param>
    /// <param name="deltaValue">x 分量增量。</param>
    public static void AddLocalScaleX(this Transform transform, float deltaValue)
    {
        Vector3 v = transform.localScale;
        v.x += deltaValue;
        transform.localScale = v;
    }

    /// <summary>
    /// 增加相对尺寸的 y 分量。
    /// </summary>
    /// <param name="transform"><see cref="Transform" /> 对象。</param>
    /// <param name="deltaValue">y 分量增量。</param>
    public static void AddLocalScaleY(this Transform transform, float deltaValue)
    {
        Vector3 v = transform.localScale;
        v.y += deltaValue;
        transform.localScale = v;
    }

    /// <summary>
    /// 增加相对尺寸的 z 分量。
    /// </summary>
    /// <param name="transform"><see cref="Transform" /> 对象。</param>
    /// <param name="deltaValue">z 分量增量。</param>
    public static void AddLocalScaleZ(this Transform transform, float deltaValue)
    {
        Vector3 v = transform.localScale;
        v.z += deltaValue;
        transform.localScale = v;
    }

    /// <summary>
    /// 二维空间下使 <see cref="Transform" /> 指向指向目标点的算法，使用世界坐标。
    /// </summary>
    /// <param name="transform"><see cref="Transform" /> 对象。</param>
    /// <param name="lookAtPoint2D">要朝向的二维坐标点。</param>
    /// <remarks>假定其 forward 向量为 <see cref="Vector3.up" />。</remarks>
    public static void LookAt2D(this Transform transform, Vector2 lookAtPoint2D)
    {
        Vector3 vector = lookAtPoint2D.ToVector3() - transform.position;
        vector.y = 0f;

        if (vector.magnitude > 0f)
        {
            transform.rotation = Quaternion.LookRotation(vector.normalized, Vector3.up);
        }
    }

    #endregion Transform
}