import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.InputStreamReader;

import org.lwjgl.opengl.ARBFragmentShader;
import org.lwjgl.opengl.ARBShaderObjects;
import org.lwjgl.opengl.ARBVertexShader;
import org.lwjgl.opengl.GL11;

/**
* The vertex and fragment shaders are setup when the box object is
* constructed. They are applied to the GL state prior to the box
* being drawn, and released from that state after drawing.
* @author Stephen Jones
*/
public class Box {

    /*
    * if the shaders are setup ok we can use shaders, otherwise we just
    * use default settings
    */
    private boolean useShader;

    /*
    * program shader, to which is attached a vertex and fragment shaders.
    * They are set to 0 as a check because GL will assign unique int
    * values to each
    */
    private int program=0;

    public Box(){
        int vertShader = 0, fragShader = 0;

        try {
            vertShader = createShader("res/screen.vert",ARBVertexShader.GL_VERTEX_SHADER_ARB);
            fragShader = createShader("res/screen.frag",ARBFragmentShader.GL_FRAGMENT_SHADER_ARB);
        }
        catch(Exception exc) {
            exc.printStackTrace();
            return;
        }
        finally {
            if(vertShader == 0 || fragShader == 0)
                return;
        }

        program = ARBShaderObjects.glCreateProgramObjectARB();

        if(program == 0)
            return;

        /*
        * if the vertex and fragment shaders setup sucessfully,
        * attach them to the shader program, link the sahder program
        * (into the GL context I suppose), and validate
        */
        ARBShaderObjects.glAttachObjectARB(program, vertShader);
        ARBShaderObjects.glAttachObjectARB(program, fragShader);

        ARBShaderObjects.glLinkProgramARB(program);
        if (ARBShaderObjects.glGetObjectParameteriARB(program, ARBShaderObjects.GL_OBJECT_LINK_STATUS_ARB) == GL11.GL_FALSE) {
            System.err.println(getLogInfo(program));
            return;
        }

        ARBShaderObjects.glValidateProgramARB(program);
        if (ARBShaderObjects.glGetObjectParameteriARB(program, ARBShaderObjects.GL_OBJECT_VALIDATE_STATUS_ARB) == GL11.GL_FALSE) {
            System.err.println(getLogInfo(program));
            return;
        }

        useShader = true;
    }

    /*
    * If the shader was setup succesfully, we use the shader. Otherwise
    * we run normal drawing code.
    */
    public void draw(){
        if(useShader)
            ARBShaderObjects.glUseProgramObjectARB(program);

        GL11.glLoadIdentity();
        GL11.glTranslatef(0.0f, 0.0f, -10.0f);
        GL11.glColor3f(1.0f, 1.0f, 1.0f);//white

        GL11.glBegin(GL11.GL_QUADS);
        GL11.glVertex3f(-1.0f, 1.0f, 0.0f);
        GL11.glVertex3f(1.0f, 1.0f, 0.0f);
        GL11.glVertex3f(1.0f, -1.0f, 0.0f);
        GL11.glVertex3f(-1.0f, -1.0f, 0.0f);
        GL11.glEnd();

        //release the shader
        if(useShader)
            ARBShaderObjects.glUseProgramObjectARB(0);

    }

    /*
    * With the exception of syntax, setting up vertex and fragment shaders
    * is the same.
    * @param the name and path to the vertex shader
    */
    private int createShader(String filename, int shaderType) throws Exception {
        int shader = 0;
        try {
            shader = ARBShaderObjects.glCreateShaderObjectARB(shaderType);

            if(shader == 0)
                return 0;

            ARBShaderObjects.glShaderSourceARB(shader, readFileAsString(filename));
            ARBShaderObjects.glCompileShaderARB(shader);

            if (ARBShaderObjects.glGetObjectParameteriARB(shader, ARBShaderObjects.GL_OBJECT_COMPILE_STATUS_ARB) == GL11.GL_FALSE)
                throw new RuntimeException("Error creating shader: " + getLogInfo(shader));

            return shader;
        }
        catch(Exception exc) {
            ARBShaderObjects.glDeleteObjectARB(shader);
            throw exc;
        }
    }

    private static String getLogInfo(int obj) {
        return ARBShaderObjects.glGetInfoLogARB(obj, ARBShaderObjects.glGetObjectParameteriARB(obj, ARBShaderObjects.GL_OBJECT_INFO_LOG_LENGTH_ARB));
    }

    private String readFileAsString(String filename) throws Exception {
        StringBuilder source = new StringBuilder();

        FileInputStream in = new FileInputStream(filename);

        Exception exception = null;

        BufferedReader reader;
        try{
            reader = new BufferedReader(new InputStreamReader(in,"UTF-8"));

            Exception innerExc= null;
            try {
                String line;
                while((line = reader.readLine()) != null)
                    source.append(line).append('\n');
            }
            catch(Exception exc) {
                exception = exc;
            }
            finally {
                try {
                    reader.close();
                }
                catch(Exception exc) {
                    if(innerExc == null)
                        innerExc = exc;
                    else
                        exc.printStackTrace();
                }
            }

            if(innerExc != null)
                throw innerExc;
        }
        catch(Exception exc) {
            exception = exc;
        }
        finally {
            try {
                in.close();
            }
            catch(Exception exc) {
                if(exception == null)
                    exception = exc;
                else
                    exc.printStackTrace();
            }

            if(exception != null)
                throw exception;
        }

        return source.toString();
    }
}