package eu.tankernn.gameEngine.renderEngine.shadows;

import org.lwjgl.opengl.Display;
import org.lwjgl.opengl.GL11;
import org.lwjgl.opengl.GL30;

import eu.tankernn.gameEngine.loader.textures.Texture;
import eu.tankernn.gameEngine.loader.textures.TextureUtils;

/**
 * The frame buffer for the shadow pass. This class sets up the depth texture
 * which can be rendered to during the shadow render pass, producing a shadow
 * map.
 * 
 * @author Karl
 *
 */
public class ShadowFrameBuffer {

	private final int WIDTH;
	private final int HEIGHT;
	private int fbo;
	private Texture shadowMap;

	/**
	 * Initialises the frame buffer and shadow map of a certain size.
	 * 
	 * @param width
	 *            - the width of the shadow map in pixels.
	 * @param height
	 *            - the height of the shadow map in pixels.
	 */
	protected ShadowFrameBuffer(int width, int height) {
		this.WIDTH = width;
		this.HEIGHT = height;
		initialiseFrameBuffer();
	}

	/**
	 * Deletes the frame buffer and shadow map texture when the game closes.
	 */
	protected void finalize() {
		GL30.glDeleteFramebuffers(fbo);
		shadowMap.delete();
	}

	/**
	 * Binds the frame buffer, setting it as the current render target.
	 */
	protected void bindFrameBuffer() {
		bindFrameBuffer(fbo, WIDTH, HEIGHT);
	}

	/**
	 * Unbinds the frame buffer, setting the default frame buffer as the current
	 * render target.
	 */
	protected void unbindFrameBuffer() {
		GL30.glBindFramebuffer(GL30.GL_FRAMEBUFFER, 0);
		GL11.glViewport(0, 0, Display.getWidth(), Display.getHeight());
	}

	/**
	 * @return The ID of the shadow map texture.
	 */
	protected Texture getShadowMap() {
		return shadowMap;
	}

	/**
	 * Creates the frame buffer and adds its depth attachment texture.
	 */
	private void initialiseFrameBuffer() {
		fbo = createFrameBuffer();
		shadowMap = TextureUtils.createDepthTextureAttachment(WIDTH, HEIGHT);
		unbindFrameBuffer();
	}

	/**
	 * Binds the frame buffer as the current render target.
	 * 
	 * @param frameBuffer
	 *            - the frame buffer.
	 * @param width
	 *            - the width of the frame buffer.
	 * @param height
	 *            - the height of the frame buffer.
	 */
	private static void bindFrameBuffer(int frameBuffer, int width, int height) {
		GL11.glBindTexture(GL11.GL_TEXTURE_2D, 0);
		GL30.glBindFramebuffer(GL30.GL_DRAW_FRAMEBUFFER, frameBuffer);
		GL11.glViewport(0, 0, width, height);
	}

	/**
	 * Creates a frame buffer and binds it so that attachments can be added to
	 * it. The draw buffer is set to none, indicating that there's no colour
	 * buffer to be rendered to.
	 * 
	 * @return The newly created frame buffer's ID.
	 */
	private static int createFrameBuffer() {
		int frameBuffer = GL30.glGenFramebuffers();
		GL30.glBindFramebuffer(GL30.GL_FRAMEBUFFER, frameBuffer);
		GL11.glDrawBuffer(GL11.GL_NONE);
		return frameBuffer;
	}
}