package space.engine;

import org.lwjgl.opengl.ARBShaderObjects;
import org.lwjgl.opengl.GL11;
import org.lwjgl.opengl.GL20;
import org.lwjgl.opengl.GL32;
import org.newdawn.slick.SlickException;
import org.newdawn.slick.util.Log;

public class Shader {

    public static final int VERTEX_SHADER = GL20.GL_VERTEX_SHADER;
    public static final int FRAGMENT_SHADER = GL20.GL_FRAGMENT_SHADER;
    public static final int GEOMETRY_SHADER = GL32.GL_GEOMETRY_SHADER;

    protected String source;
    protected int type;
    protected int id;
    protected String log = "";

    public Shader(int type, String source) throws SlickException {
        if (source==null)
            throw new IllegalArgumentException("shader source code must not be null");
        this.source = source;
        this.type = type;
        id = compileShader(type, source);
    }

    /**
     * Implementations may wish to override Shader for specific functionality; e.g. creating
     * a tesselation shader or creating a single vertex shader made up of multiple
     * mix-and-matched Shader objects.
     */
    protected Shader() { }

    public boolean valid() {
        return id!=0;
    }

    void attach(ShaderProgram program) {
        ARBShaderObjects.glAttachObjectARB(program.getID(), getID());
    }

    void detach(ShaderProgram program) {
        ARBShaderObjects.glDetachObjectARB(program.getID(), getID());
    }

    private String shaderTypeString(int type) {
        if (type==FRAGMENT_SHADER) return "FRAGMENT_SHADER";
        if (type==GEOMETRY_SHADER) return "GEOMETRY_SHADER";
        else if (type==VERTEX_SHADER) return "VERTEX_SHADER";
        else return "shader";
    }

    protected int compileShader(int type, String source) throws SlickException {
        int shader = ARBShaderObjects.glCreateShaderObjectARB(type);
        if (shader==0)
            throw new SlickException("could not create shader object; check ShaderProgram.isSupported()");
        ARBShaderObjects.glShaderSourceARB(shader, source);
        ARBShaderObjects.glCompileShaderARB(shader);
        int comp = ARBShaderObjects.glGetObjectParameteriARB(shader, GL20.GL_COMPILE_STATUS);
        int len = ARBShaderObjects.glGetObjectParameteriARB(shader, GL20.GL_INFO_LOG_LENGTH);
        log = ARBShaderObjects.glGetInfoLogARB(shader, len);
        if (comp==GL11.GL_FALSE)
            throw new SlickException("ERROR: Compiler error in "+shaderTypeString(type)+"\n"+log);
        else if (log!=null&&log.length()!=0)
            Log.warn("GLSL shader compile warning: "+log);
        return shader;
    }

    public String getCompileLog() {
        return log;
    }

    public void release() {
        if (id!=0) {
            ARBShaderObjects.glDeleteObjectARB(id);
            id = 0;
        }
    }

    public int getID() {
        return id;
    }

    public int getType() {
        return type;
    }

    public String getSource() {
        return source;
    }
}