using UnityEngine;
using System.Collections;

public class LevelPiece : MonoBehaviour {

  public Transform exitPoint;

}

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

public class LevelGenerator : MonoBehaviour {

  public static LevelGenerator instance;
  //all level pieces blueprints used to copy from
  public List<LevelPiece> levelPrefabs = new List<LevelPiece>();
  //starting point of the very first level piece
  public Transform levelStartPoint;
  //all level pieces that are currently in the level
  public List<LevelPiece> pieces = new List<LevelPiece>();
  
  void Awake() {
    instance = this;
  }

  void Start() {
    GenerateInitialPieces();
  }


  public void GenerateInitialPieces() {
    for (int i=0; i<2; i++) {
      AddPiece();
    }
  }
  
  public void AddPiece() {

    //pick the random number
    int randomIndex = Random.Range(0, levelPrefabs.Count-1);

    //Instantiate copy of random level prefab and store it in piece variable
    LevelPiece piece = (LevelPiece)Instantiate(levelPrefabs[randomIndex]);
    piece.transform.SetParent(this.transform, false);

    Vector3 spawnPosition = Vector3.zero;

    //position
    if (pieces.Count == 0) {
      //first piece
      spawnPosition = levelStartPoint.position;
    }
    else {
      //take exit point from last piece as a spawn point to new piece
      spawnPosition = pieces[pieces.Count-1].exitPoint.position;
    }
    
    piece.transform.position = spawnPosition;
    pieces.Add(piece);
  }




  public void RemoveOldestPiece() {
    
    LevelPiece oldestPiece = pieces[0];
    
    pieces.Remove(oldestPiece);
    Destroy(oldestPiece.gameObject);
  }

}

using UnityEngine;
using System.Collections;

public class LeaveTrigger : MonoBehaviour {


  void OnTriggerEnter2D(Collider2D other) {

    LevelGenerator.instance.AddPiece();
    LevelGenerator.instance.RemoveOldestPiece();
  }
  
}