using UnityEngine;

//this class holds movement functions for a rigidbody character such as player, enemy, npc..
//you can then call these functions from another script, in order to move the character
[RequireComponent(typeof(Rigidbody))]
public class CharacterMotor : MonoBehaviour 
{
    [HideInInspector]
    public Vector3 currentSpeed;
    [HideInInspector]
    public float DistanceToTarget;
    
    void Awake()
    {
        rigidbody.interpolation = RigidbodyInterpolation.Interpolate;//设置插值，对于主角等可以让运动平滑
        rigidbody.constraints = RigidbodyConstraints.FreezeRotation;//冻结旋转

        //如没有物理材质新建添加
        if(collider.material.name == "Default (Instance)")
        {
            PhysicMaterial pMat = new PhysicMaterial();
            pMat.name = "Frictionless";
            pMat.frictionCombine = PhysicMaterialCombine.Multiply;
            pMat.bounceCombine = PhysicMaterialCombine.Multiply;
            pMat.dynamicFriction = 0f;
            pMat.staticFriction = 0f;
            collider.material = pMat;
            Debug.LogWarning("No physics material found for CharacterMotor, a frictionless one has been created and assigned", transform);
        }
    }
    //move rigidbody to a target and return the bool "have we arrived?"
    public bool MoveTo(Vector3 destination, float acceleration, float stopDistance, bool ignoreY)
    {
        Vector3 relativePos = (destination - transform.position);
        if(ignoreY)
            relativePos.y = 0;

        //向量长度 到目标点距离
        DistanceToTarget = relativePos.magnitude;
        //运动参数
        if (DistanceToTarget <= stopDistance)
            return true;
        else
            rigidbody.AddForce(relativePos.normalized * acceleration * Time.deltaTime, ForceMode.VelocityChange);
            return false;
    }
    
    //rotates rigidbody to face its current velocity
    public void RotateToVelocity(float turnSpeed, bool ignoreY)
    {    
        Vector3 dir;
        if(ignoreY)
            dir = new Vector3(rigidbody.velocity.x, 0f, rigidbody.velocity.z);
        else
            dir = rigidbody.velocity; //刚体的速度向量
        
        if (dir.magnitude > 0.1)
        {
            Quaternion dirQ = Quaternion.LookRotation (dir);
            Quaternion slerp = Quaternion.Slerp (transform.rotation, dirQ, dir.magnitude * turnSpeed * Time.deltaTime);
            rigidbody.MoveRotation(slerp);
        }
    }
    
    //rotates rigidbody to a specific direction
    public void RotateToDirection(Vector3 lookDir, float turnSpeed, bool ignoreY)
    {
        Vector3 characterPos = transform.position;
        if(ignoreY)
        {
            characterPos.y = 0;
            lookDir.y = 0;
        }
        
        Vector3 newDir = lookDir - characterPos;
        Quaternion dirQ = Quaternion.LookRotation (newDir);
        Quaternion slerp = Quaternion.Slerp (transform.rotation, dirQ, turnSpeed * Time.deltaTime);
        rigidbody.MoveRotation (slerp);
    }
    
    // apply friction to rigidbody, and make sure it doesn‘t exceed its max speed
    public void ManageSpeed(float deceleration, float maxSpeed, bool ignoreY)
    {    
        currentSpeed = rigidbody.velocity;
        if (ignoreY)
            currentSpeed.y = 0;
        
        if (currentSpeed.magnitude > 0)
        {
            rigidbody.AddForce ((currentSpeed * -1) * deceleration * Time.deltaTime, ForceMode.VelocityChange);
            if (rigidbody.velocity.magnitude > maxSpeed)
                rigidbody.AddForce ((currentSpeed * -1) * deceleration * Time.deltaTime, ForceMode.VelocityChange);
        }
    }
}

/* NOTE: ManageSpeed does a similar job to simply increasing the friction property of a rigidbodies "physics material"
 * but this is unpredictable and can result in sluggish controls and things like gripping against walls as you walk/falls past them
 * it‘s not ideal for gameplay, and so we use 0 friction physics materials and control friction ourselves with the ManageSpeed function instead */

/* NOTE: when you use MoveTo, make sure the stopping distance is something like 0.3 and not 0
 * if it is 0, the object is likely to never truly reach the destination, and it will jitter on the spot as it
 * attempts to move toward the destination vector but overshoots it each frame
 */