using System;
using System.Collections;
using UnityEngine;

public class WorldSwitcher : MonoBehaviour {
	[Range(0, 5)]
	[SerializeField] float transitionDuration;
	[SerializeField] AnimationCurve transitionCurve;
	[SerializeField] Camera[] cameras;
	[SerializeField] Transform renderQuad;
	[SerializeField] float quadOffset;
	int lastWorldIndex;
	int currentWorldIndex;
	Coroutine transition;
	RenderTexture renderTexture;
	Material renderMaterial;

	void Awake() {
		if (cameras.Length <= 1)
			Debug.LogWarning("WorldSwitcher should have multiple cameras");

		currentWorldIndex = 0;
		lastWorldIndex = 0;

		renderMaterial = renderQuad.GetComponent<Renderer>().material;
		GenerateRenderTexture();
	}

	public void SwitchWorld(int index) {
		if (index == currentWorldIndex)
			return;

		if (index < 0 || index >= cameras.Length)
			throw new IndexOutOfRangeException($"{index} is not an available world.");

		lastWorldIndex = currentWorldIndex;
		currentWorldIndex = index;

		Camera currCam = cameras[currentWorldIndex]; 
		currCam.enabled = true;

		//TODO Block window resize during transition?
		if (Screen.width != renderTexture.width || Screen.height != renderTexture.height)
			GenerateRenderTexture();
		
		currCam.targetTexture = renderTexture;

		renderQuad.localScale = new Vector3(cameras[lastWorldIndex].aspect, 1f, 1f);
		
		transition = StartCoroutine(TransitionCamera());
	}

	void OnGUI() {
		for (int i = 0; i < cameras.Length; ++i) {
			if (i == currentWorldIndex)
				continue;
			
			if (GUILayout.Button($"World {i}"))
				SwitchWorld(i);
		}
	}

	IEnumerator TransitionCamera() {
		float startTime = Time.time;
		Transform lastCam = cameras[lastWorldIndex].transform;

		while (Time.time < startTime + transitionDuration) {
			float t = transitionCurve.Evaluate((Time.time - startTime) / transitionDuration);

			renderQuad.position = lastCam.position + Vector3.forward * quadOffset + Vector3.right * (2f * t - 2f);

			yield return null;
		}

		cameras[currentWorldIndex].targetTexture = null;
		cameras[lastWorldIndex].enabled = false;
		transition = null;
	}

	void GenerateRenderTexture() {
		renderTexture = new RenderTexture(Screen.width, Screen.height, 32);
		renderMaterial.mainTexture = renderTexture;
	}
}