How do I move and flip my character in Unity2D?

Question

I am new to Unity. I am playing around with a 2D sidescroller. Here are the features of the script I am trying to write:

• Move left and right
• Flip character when changing direction
• Increase speed to a cap while continuously moving

Currently, the only thing working is Animation transitions. I am not sure what is wrong. Here is the code:

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

public class Avatar_Manager : MonoBehaviour {
    private Animator anim;
    private Rigidbody2D rigidbody2D;
    private Transform trans;
    private int direction;
    private bool moving;
    public const float acceleration = 1.0f / 180;
    public float horizontal_speed;
    public float vertical_speed;
    // Use this for initialization
    void Start () {
        anim = GetComponent<Animator>();
        rigidbody2D = GetComponent<Rigidbody2D>();
        trans = GetComponent<Transform>();
        //Default facing right
        direction = 1;
        moving = false;
        vertical_speed = 0;
    }

    // Update is called once per frame
    void Update () {
        //Check direction
        if (rigidbody2D.velocity.x < 0)
        {
            direction = -1;
        }
        else if (rigidbody2D.velocity.x > 0)
        {
            direction = 1;
        }
        // Move right
        if (Input.GetKeyDown(KeyCode.D))
        {
            //Flip Avatar if facing left
            if (direction == -1)
            {
                direction = 1;
                trans.rotation.Set(trans.rotation.x, trans.rotation.y + 180, trans.rotation.z, trans.rotation.w);
            }
            //Start moving
            if (!moving)
            {
                moving = true;
                horizontal_speed = 10;
                rigidbody2D.velocity = new Vector2(horizontal_speed, vertical_speed);
                anim.SetInteger("State", 1);
            }
            //Update speed
            else
            {
                if(horizontal_speed < 20)
                {
                    horizontal_speed += acceleration;
                    rigidbody2D.velocity.Set(horizontal_speed, vertical_speed);
                }
            }
        }
        //Stop moving right
        if (Input.GetKeyUp(KeyCode.D))
        {
            moving = false;
            horizontal_speed = 0;
            rigidbody2D.velocity.Set(horizontal_speed, vertical_speed);
            anim.SetInteger("State", 0);
        }

        // Move left
        if (Input.GetKeyDown(KeyCode.A))
        {
            //Flip Avatar if facing right
            if (direction == 1)
            {
                direction = -1;
                trans.rotation.Set(trans.rotation.x, trans.rotation.y - 180, trans.rotation.z, trans.rotation.w);
            }
            //Start moving
            if (!moving)
            {
                moving = true;
                horizontal_speed = -10;
                rigidbody2D.velocity = new Vector2(horizontal_speed, vertical_speed);
                anim.SetInteger("State", 1);
            }
            //Update speed
            else
            {
                if (horizontal_speed > -20)
                {
                    horizontal_speed -= acceleration;
                    rigidbody2D.velocity.Set(horizontal_speed, vertical_speed);
                }
            }
        }
        //Stop moving right
        if (Input.GetKeyUp(KeyCode.A))
        {
            moving = false;
            horizontal_speed = 0;
            rigidbody2D.velocity.Set(horizontal_speed, vertical_speed);
            anim.SetInteger("State", 0);
        }
    }
}

Answer 1

change this

if (rigidbody2D.velocity.x < 0)
        {
            direction = -1;
        }
else if (rigidbody2D.velocity.x > 0)
        {
            direction = 1;
        }

to this

if (rigidbody2D.velocity.x < 0)
        {
             transform.localscale = new Vector3 (-1,1,1);
        }
else if (rigidbody2D.velocity.x > 0)
        {
             transform.localscale = new Vector3 (1,1,1);
        }