using UnityEngine;
using System.Collections;

[RequireComponent( typeof( ParticleSystem ) )]
public class CustomParticleSystem : MonoBehaviour 
{
    #region Properties
    public Mesh[] EmissionShapes;
    public float  EmissionShapeSwitchSpeed = 0.5f;
    public float  EmissionRate = 10f;
    #endregion

    float          _shapeIndex = 0f;
    float          _timeToEmission = 0f;
    ParticleSystem _particleSystem;

    float EmissionPeriod { get { return 1f / EmissionRate; } }

    void Awake () 
    {
        _particleSystem = GetComponent<ParticleSystem>();
        _particleSystem.emissionRate = 0f;
        _timeToEmission = EmissionPeriod;
    }

    void Start () 
    {   
    }

    void Update () 
    {
        _shapeIndex += EmissionShapeSwitchSpeed * Time.deltaTime;
        if( _shapeIndex > EmissionShapes.Length-1 ) _shapeIndex -= (EmissionShapes.Length-1);

        _timeToEmission -= Time.deltaTime;
        if( _timeToEmission <= 0f )
        {
            _timeToEmission = EmissionPeriod - _timeToEmission;

            Mesh currentShape = EmissionShapes[(int)_shapeIndex];

            int triangleIndex = Random.Range( 0, currentShape.triangles.Length/3 );

            int vertexIndex0 = currentShape.triangles[triangleIndex*3];
            int vertexIndex1 = currentShape.triangles[triangleIndex*3+1];
            int vertexIndex2 = currentShape.triangles[triangleIndex*3+2];

            Vector3 v0 = currentShape.vertices[vertexIndex0];
            Vector3 v1 = currentShape.vertices[vertexIndex1];
            Vector3 v2 = currentShape.vertices[vertexIndex2];

            Vector3 n0 = currentShape.normals[vertexIndex0];
            Vector3 n1 = currentShape.normals[vertexIndex1];
            Vector3 n2 = currentShape.normals[vertexIndex2];

            float u = Random.Range( 0f, 1f );
            float v = Random.Range( 0f, 1f );
            float w = Random.Range( 0f, 1f );
            float uvw = u+v+w;
            u /= uvw;
            v /= uvw;
            w /= uvw;

            Vector3 randomPosition = v0*u + v1*v + v2*w;
            Vector3 normalAtRandomPosition = n0*u + n1*v + n2*w;

            randomPosition = this.transform.localToWorldMatrix.MultiplyPoint( randomPosition );
            normalAtRandomPosition = this.transform.localToWorldMatrix.MultiplyVector( normalAtRandomPosition );

            _particleSystem.Emit( 
                randomPosition,
                normalAtRandomPosition * _particleSystem.startSpeed, 
                _particleSystem.startSize,
                _particleSystem.startLifetime,
                _particleSystem.startColor
            );
        }
    }
}