package atmos;

import com.badlogic.gdx.ApplicationListener;
import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.Input.Keys;
import com.badlogic.gdx.InputAdapter;
import com.badlogic.gdx.backends.lwjgl.LwjglApplication;
import com.badlogic.gdx.backends.lwjgl.LwjglApplicationConfiguration;
import com.badlogic.gdx.graphics.GL10;
import com.badlogic.gdx.graphics.OrthographicCamera;
import com.badlogic.gdx.graphics.Texture;
import com.badlogic.gdx.graphics.g2d.SpriteBatch;
import com.badlogic.gdx.graphics.g2d.TextureRegion;
import com.badlogic.gdx.graphics.glutils.ShaderProgram;
import com.badlogic.gdx.math.Matrix4;
import com.badlogic.gdx.math.Vector2;
import com.badlogic.gdx.math.Vector3;

/**
 * Simple illumination model with shaders in LibGDX.
 * @author davedes / mattdesl
 */
public class Illumination2D implements ApplicationListener {

    Texture texture, texture_n;
    OrthographicCamera cam;
    SpriteBatch fxBatch, batch;
    TextureRegion sprite, spriteNormals;
    Matrix4 transform = new Matrix4();

    // the color of our light
    Vector3 lightColor = new Vector3(1f, 1f, 1f);
    // the position of our light in 3D space
    Vector3 lightPos = new Vector3(0f, 0f, 2f);
    // the ambient color (color to use when unlit)
    Vector3 ambientColor = new Vector3(1f, 1f, 1f);
    // the resolution of our game/graphics
    Vector2 resolution = new Vector2();
    // the attenuation factor: x=constant, y=linear, z=quadratic
    Vector3 attenuation = new Vector3(0.75f, 0.0f, 0.00001f);
    // the ambient intensity (brightness to use when unlit)
    float ambientIntensity = 0.1f;

    // whether to use attenuation/shadows
    boolean useShadow = true;

    // whether to use lambert shading (with our normal map)
    boolean useNormals = true;

    ShaderProgram program;

    public void create() {
        // load our textures
        texture = new Texture(Gdx.files.internal("data/rock.png"));
        texture_n = new Texture(Gdx.files.internal("data/rock_n.png"));

        // we'll use texture regions instead of Stage2D/Actors for simplicity's sake
        sprite = new TextureRegion(texture);
        sprite.flip(false, true);
        spriteNormals = new TextureRegion(texture_n);
        spriteNormals.flip(false, true);

        // a simple 2D orthographic camera
        cam = new OrthographicCamera(Gdx.graphics.getWidth(),
                Gdx.graphics.getHeight());
        cam.setToOrtho(true);

        // create our shader program...
        program = createShader();

        // now we create our sprite batch for our shader
        fxBatch = new SpriteBatch(100, program);
        // setShader is needed; perhaps this is a LibGDX bug?
        fxBatch.setShader(program);
        fxBatch.setProjectionMatrix(cam.combined);
        fxBatch.setTransformMatrix(transform);

        // usually we would just use a single batch for our application,
        // but for demonstration let's also show the un-affected image
        batch = new SpriteBatch(100);
        batch.setProjectionMatrix(cam.combined);
        batch.setTransformMatrix(transform);

        // quick little input for debugging -- press S to toggle shadows, N to
        // toggle normals
        Gdx.input.setInputProcessor(new InputAdapter() {
            public boolean keyDown(int key) {
                if (key == Keys.S) {
                    useShadow = !useShadow;
                    return true;
                } else if (key == Keys.N) {
                    useNormals = !useNormals;
                    return true;
                }
                return false;
            }
        });
    }

    private ShaderProgram createShader() {
        // see the code here: http://pastebin.com/7fkh1ax8
        // simple illumination model using ambient, diffuse (lambert) and attenuation
        // see here: http://nccastaff.bournemouth.ac.uk/jmacey/CGF/slides/IlluminationModels4up.pdf
        String vert = "attribute vec4 " + ShaderProgram.POSITION_ATTRIBUTE + ";\n" //
                + "attribute vec4 " + ShaderProgram.COLOR_ATTRIBUTE + ";\n" //
                + "attribute vec2 " + ShaderProgram.TEXCOORD_ATTRIBUTE + "0;\n" //
                + "uniform mat4 u_proj;\n" //
                + "uniform mat4 u_trans;\n" //
                + "uniform mat4 u_projTrans;\n" //
                + "varying vec4 v_color;\n" //
                + "varying vec2 v_texCoords;\n" //
                + "\n" //
                + "void main()\n" //
                + "{\n" //
                + "   v_color = " + ShaderProgram.COLOR_ATTRIBUTE + ";\n" //
                + "   v_texCoords = " + ShaderProgram.TEXCOORD_ATTRIBUTE + "0;\n" //
                + "   gl_Position =  u_projTrans * " + ShaderProgram.POSITION_ATTRIBUTE + ";\n" //
                + "}\n";

        String frag = "#ifdef GL_ES\n" +
                "precision mediump float;\n" +
                "#endif\n" +
                "varying vec4 v_color;\n" +
                "varying vec2 v_texCoords;\n" +

                "uniform sampler2D u_texture;\n" +
                "uniform sampler2D u_normals;\n" +
                "uniform vec3 light;\n" +
                "uniform vec3 ambientColor;\n" +
                "uniform float ambientIntensity; \n" +
                "uniform vec2 resolution;\n" +
                "uniform vec3 lightColor;\n" +
                "uniform bool useNormals;\n" +
                "uniform bool useShadow;\n" +
                "uniform vec3 attenuation;\n" +
                "\n" +
                "void main() {\n" +
                "   vec4 color = texture2D(u_texture, v_texCoords.st);\n" +
                "   vec3 normal = normalize(texture2D(u_normals, v_texCoords.st).rgb * 2.0 - 1.0);\n" +
                "   vec3 light_pos = normalize(light);\n" +
                "   float lambert = useNormals ? max(dot(normal, light_pos), 0.0) : 1.0;\n" +
                "   \n" +
                "   //now let's get a nice little falloff\n" +
                "   float d = distance(gl_FragCoord.xy, light.xy * resolution);\n" +
                "   d *= light.z;\n" +
                "   \n" +
                "   float att = useShadow ? 1.0 / ( attenuation.x + (attenuation.y*d) + (attenuation.z*d*d) ) : 1.0;\n" +
                "   \n" +
                "   vec3 result = (ambientColor * ambientIntensity) + (lightColor.rgb * lambert) * att;\n" +
                "   result *= color.rgb;\n" +
                "   \n" +
                "   gl_FragColor = v_color * vec4(result, color.a);\n" +
                "}";

        ShaderProgram program = new ShaderProgram(vert, frag);
        // u_proj and u_trans will not be active but SpriteBatch will still try to set them...
        program.pedantic = false;
        if (program.isCompiled() == false)
            throw new IllegalArgumentException("couldn't compile shader: "
                    + program.getLog());

        // set resolution vector
        resolution.set(Gdx.graphics.getWidth(), Gdx.graphics.getHeight());

        // we are only using this many uniforms for testing purposes...!!
        program.begin();
        program.setUniformi("u_texture", 0);
        program.setUniformi("u_normals", 1);
        program.setUniformf("light", lightPos);
        program.setUniformf("ambientIntensity", ambientIntensity);
        program.setUniformf("ambientColor", ambientColor);
        program.setUniformf("resolution", resolution);
        program.setUniformf("lightColor", lightColor);
        program.setUniformf("attenuation", attenuation);
        program.setUniformi("useShadow", useShadow ? 1 : 0);
        program.setUniformi("useNormals", useNormals ? 1 : 0);
        program.end();

        return program;
    }

    public void dispose() {
        fxBatch.dispose();
        batch.dispose();
        texture.dispose();
        texture_n.dispose();
    }

    public void render() {
        Gdx.gl.glClear(GL10.GL_COLOR_BUFFER_BIT);
        cam.update();

        // draw our sprites without any effects
        batch.begin();
        batch.draw(sprite, 0, 0);
        batch.draw(spriteNormals, sprite.getRegionWidth() + 10, 0);
        batch.end();

        // start our FX batch, which will bind our shader program
        fxBatch.begin();

        // get y-down light position based on mouse/touch
        lightPos.x = Gdx.input.getX() / (float) Gdx.graphics.getWidth();
        lightPos.y = (resolution.y - Gdx.input.getY() - 1)
                / (float) Gdx.graphics.getHeight();

        // update our uniforms
        program.setUniformf("light", lightPos);
        program.setUniformi("useNormals", useNormals ? 1 : 0);
        program.setUniformi("useShadow", useShadow ? 1 : 0);

        // bind the normal first at texture1
        texture_n.bind(1);

        // bind the actual texture at texture0
        texture.bind(0);

        // we bind texture0 second since draw(sprite) will end up binding it at
        // texture0...
        fxBatch.draw(sprite, 0, sprite.getRegionHeight() + 10);
        fxBatch.end();
    }

    public void resize(int width, int height) {
        cam.setToOrtho(true, width, height);
        resolution.set(width, height);
        program.setUniformf("resolution", resolution);
    }

    public void pause() {
    }

    public void resume() {
    }

    public static void main(String[] args) {
        LwjglApplicationConfiguration cfg = new LwjglApplicationConfiguration();
        cfg.title = "lighting";
        cfg.useGL20 = true;
        cfg.width = 1024;
        cfg.height = 768;

        new LwjglApplication(new Illumination2D(), cfg);
    }
}