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

public interface IMonoObjectPool<T> where T : MonoBehaviour
{
    IReadOnlyCollection<T> Instances { get; }

    void Initialize(Func<T> creator, Action<T> disposer, Action<T> onEnterPool, Action<T> onExitPool, int count);
    T Get();
    void Return(T obj);
    void Dispose();
}

public class FixedMonoObjectPool<T> : IMonoObjectPool<T> where T : MonoBehaviour
{
    Action<T> disposer;

    HashSet<T> instances = new();
    Queue<T> pool = new();

    Action<T> onEnterPool;
    Action<T> onExitPool;

    public IReadOnlyCollection<T> Instances => instances;

    public void Initialize(Func<T> creator, Action<T> disposer, Action<T> onEnterPool, Action<T> onExitPool, int count)
    {
        this.disposer = disposer;
        this.onEnterPool = onEnterPool;
        this.onExitPool = onExitPool;

        for (int i = 0; i < count; ++i)
        {
            T obj = creator.Invoke();
            onEnterPool.Invoke(obj);

            instances.Add(obj);
            pool.Enqueue(obj);
        }
    }

    public T Get()
    {
        Debug.Assert(pool.Count > 0, "pool is empty");

        var result = pool.Dequeue();
        onExitPool.Invoke(result);

        return result;
    }

    public void Return(T obj)
    {
        if(instances.Contains(obj))
        {
            onEnterPool.Invoke(obj);
            pool.Enqueue(obj);
        }
    }

    public void Dispose()
    {
        pool.Clear();

        foreach (var obj in instances)
        {
            disposer.Invoke(obj);
        }

        instances.Clear();
    }
}

public class DynamicMonoObjectPool<T> : IMonoObjectPool<T> where T : MonoBehaviour
{
    Func<T> creator;    
    Action<T> disposer;

    HashSet<T> instances = new();
    Queue<T> pool = new();

    Action<T> onEnterPool;
    Action<T> onExitPool;

    public IReadOnlyCollection<T> Instances => instances;

    public void Initialize(Func<T> creator, Action<T> disposer, Action<T> onEnterPool, Action<T> onExitPool, int count = 0)
    {
        this.creator = creator;
        this.disposer = disposer;
        this.onEnterPool = onEnterPool;
        this.onExitPool = onExitPool;

        for (int i = 0; i < count; ++i)
        {
            T obj = creator.Invoke();
            onEnterPool.Invoke(obj);

            instances.Add(obj);
            pool.Enqueue(obj);
        }
    }

    public T Get()
    {
        if (pool.Count == 0)
        {
            T obj = creator.Invoke();
            instances.Add(obj);
            pool.Enqueue(obj);
        }

        var result = pool.Dequeue();
        onExitPool.Invoke(result);

        return result;
    }

    public void Return(T obj)
    {
        if(instances.Contains(obj))
        {
            onEnterPool.Invoke(obj);
            pool.Enqueue(obj);
        }
    }

    public void Dispose()
    {
        pool.Clear();

        foreach (var obj in instances)
        {
            disposer.Invoke(obj);
        }

        instances.Clear();
    }
}