EnemyAI.cs

using UnityEngine;
using System.Collections;

public class EnemyAI : MonoBehaviour {

    // Debugging
    public bool loggingEnabled = false;

    // A.I.
    public string playerTag = "Player";

    private GameObject player;

    // Stats
    public float acceleration = 10;
    public float jumpForce = 200;
    public float maxSpeed = 10;

    public float damage = 1;

    // Physics
    private Vector2 moveDir = Vector2.zero;
    // By doing this, isGrounded becomes read-only outside of this script
    [HideInInspector] public bool isGrounded { get; private set; }

    // Initialization
    void Start ()
    {
        isGrounded = false;

        player = GameObject.FindWithTag ("Player");
    }

    void FixedUpdate ()
    {
        moveDir = Vector2.zero;

        // Get player position in local space
        Vector2 playerPos = transform.InverseTransformPoint (player.transform.position);

        // Determine what direction to go in
        if (playerPos.x > 0.5f)
            moveDir.x += acceleration;
        else if (playerPos.x < -0.5f)
            moveDir.x -= acceleration;

        if (playerPos.y > 0.2f && isGrounded)
            moveDir.y += jumpForce;

        rigidbody2D.AddForce (moveDir);

        Vector2 velocity = rigidbody2D.velocity;
        velocity.x = Mathf.Clamp (velocity.x, -maxSpeed, maxSpeed);
        rigidbody2D.velocity = velocity;

        if (loggingEnabled)
            Debug.Log (isGrounded + " " + playerPos + " | " + transform.position + " | " + moveDir);
    }

    void OnTriggerStay2D (Collider2D other)
    {
        if (other.tag == "Ground" && isGrounded == false)
            isGrounded = true;
        else if (other.tag == "Player")
            other.GetComponent<HealthLogic> ().Damage (damage);
    }

    void OnTriggerExit2D (Collider2D other)
    {
        if (other.tag == "Ground")
            isGrounded = false;
    }
}