using System;
using OpenTK;
using OpenTK.Graphics.ES20;
using GL1 = OpenTK.Graphics.ES11.GL;
using All1 = OpenTK.Graphics.ES11.All;
using OpenTK.Platform.iPhoneOS;
using Foundation;
using CoreAnimation;
using ObjCRuntime;
using OpenGLES;
using UIKit;

namespace ES11
{

    [Register("EAGLView")]
    public class EAGLView : iPhoneOSGameView
    {
        [Export("initWithCoder:")]
        public EAGLView(NSCoder coder) : base(coder)
        {
            LayerRetainsBacking = true;
            LayerColorFormat = EAGLColorFormat.RGBA8;
        }

        [Export("layerClass")]
        public static new Class GetLayerClass()
        {
            return iPhoneOSGameView.GetLayerClass();
        }

        protected override void ConfigureLayer(CAEAGLLayer eaglLayer)
        {
            eaglLayer.Opaque = true;
        }

        protected override void CreateFrameBuffer()
        {
            try
            {
                ContextRenderingApi = EAGLRenderingAPI.OpenGLES2;
                base.CreateFrameBuffer();
            }
            catch (Exception e)
            {
                System.Diagnostics.Debug.Print(e.ToString());
                ContextRenderingApi = EAGLRenderingAPI.OpenGLES1;
                base.CreateFrameBuffer();
            }
            
            if (ContextRenderingApi == EAGLRenderingAPI.OpenGLES2)
                LoadShaders();
        }

        protected override void DestroyFrameBuffer()
        {
            base.DestroyFrameBuffer();
            DestroyShaders();
        }

        #region DisplayLink support

        int frameInterval;
        CADisplayLink displayLink;

        public bool IsAnimating { get; private set; }
        // How many display frames must pass between each time the display link fires.
        public int FrameInterval
        {
            get
            {
                return frameInterval;
            }
            set
            {
                if (value <= 0)
                    throw new ArgumentException();
                frameInterval = value;
                if (IsAnimating)
                {
                    StopAnimating();
                    StartAnimating();
                }
            }
        }

        public void StartAnimating()
        {
            if (IsAnimating)
                return;
            
            CreateFrameBuffer();
            displayLink = UIScreen.MainScreen.CreateDisplayLink(this, new Selector("drawFrame"));
            displayLink.FrameInterval = frameInterval;
            displayLink.AddToRunLoop(NSRunLoop.Current, NSRunLoop.NSDefaultRunLoopMode);
            
            IsAnimating = true;
        }

        public void StopAnimating()
        {
            if (!IsAnimating)
                return;

            displayLink.Invalidate();
            displayLink = null;
            DestroyFrameBuffer();
            IsAnimating = false;
        }

        [Export("drawFrame")]
        void DrawFrame()
        {
            OnRenderFrame(new FrameEventArgs());
        }

        #endregion

        static readonly float[] squareVertices =
        {
            -0.5f, -0.33f,
            0.5f, -0.33f,
            -0.5f,  0.33f,
            0.5f,  0.33f,
        };
        static readonly byte[] squareColors =
        {
            255, 255,   0, 255,
            0,   255, 255, 255,
            0,     0,   0,   0,
            255,   0, 255, 255,
        };
        static float transY = 0.0f;
        const int UNIFORM_TRANSLATE = 0;
        const int UNIFORM_COUNT = 1;
        readonly int[] uniforms = new int [UNIFORM_COUNT];
        const int ATTRIB_VERTEX = 0;
        const int ATTRIB_COLOR = 1;
        const int ATTRIB_COUNT = 2;
        int program;

        protected override void OnRenderFrame(FrameEventArgs e)
        {
            base.OnRenderFrame(e);
            
            MakeCurrent();
            
            // Replace the implementation of this method to do your own custom drawing.
            GL.ClearColor(0.5f, 0.5f, 0.5f, 1.0f);
            GL.Clear(ClearBufferMask.ColorBufferBit);
            
            if (ContextRenderingApi == EAGLRenderingAPI.OpenGLES2)
            {
                // Use shader program.
                GL.UseProgram(program);
                
                // Update uniform value.
                GL.Uniform1(uniforms[UNIFORM_TRANSLATE], transY);
                transY += 0.075f;
                
                // Update attribute values.
                GL.VertexAttribPointer(ATTRIB_VERTEX, 2, VertexAttribPointerType.Float, false, 0, squareVertices);
                GL.EnableVertexAttribArray(ATTRIB_VERTEX);
                GL.VertexAttribPointer(ATTRIB_COLOR, 4, VertexAttribPointerType.UnsignedByte, true, 0, squareColors);
                GL.EnableVertexAttribArray(ATTRIB_COLOR);
                
                // Validate program before drawing. This is a good check, but only really necessary in a debug build.
#if DEBUG
                if (!ValidateProgram (program)) {
                    Console.WriteLine ("Failed to validate program {0:x}", program);
                    return;
                }
#endif
            }
            else
            {
                GL1.MatrixMode(All1.Projection);
                GL1.LoadIdentity();
                GL1.MatrixMode(All1.Modelview);
                GL1.LoadIdentity();
                GL1.Translate(0.0f, (float)Math.Sin(transY) / 2.0f, 0.0f);
                transY += 0.075f;
                
                GL1.VertexPointer(2, All1.Float, 0, squareVertices);
                GL1.EnableClientState(All1.VertexArray);
                GL1.ColorPointer(4, All1.UnsignedByte, 0, squareColors);
                GL1.EnableClientState(All1.ColorArray);
            }

            GL.DrawArrays(BeginMode.TriangleStrip, 0, 4);
            
            SwapBuffers();
        }

        bool LoadShaders()
        {
            int vertShader, fragShader;
            
            // Create shader program.
            program = GL.CreateProgram();
            
            // Create and compile vertex shader.
            var vertShaderPathname = NSBundle.MainBundle.PathForResource("Shader", "vsh");
            if (!CompileShader(ShaderType.VertexShader, vertShaderPathname, out vertShader))
            {
                Console.WriteLine("Failed to compile vertex shader");
                return false;
            }
            
            // Create and compile fragment shader.
            var fragShaderPathname = NSBundle.MainBundle.PathForResource("Shader", "fsh");
            if (!CompileShader(ShaderType.FragmentShader, fragShaderPathname, out fragShader))
            {
                Console.WriteLine("Failed to compile fragment shader");
                return false;
            }

            // Attach vertex shader to program.
            GL.AttachShader(program, vertShader);
            
            // Attach fragment shader to program.
            GL.AttachShader(program, fragShader);
            
            // Bind attribute locations.
            // This needs to be done prior to linking.
            GL.BindAttribLocation(program, ATTRIB_VERTEX, "position");
            GL.BindAttribLocation(program, ATTRIB_COLOR, "color");
            
            // Link program.
            if (!LinkProgram(program))
            {
                Console.WriteLine("Failed to link program: {0:x}", program);
                
                if (vertShader != 0)
                    GL.DeleteShader(vertShader);
                
                if (fragShader != 0)
                    GL.DeleteShader(fragShader);
                
                if (program != 0)
                {
                    GL.DeleteProgram(program);
                    program = 0;
                }

                return false;
            }
            
            // Get uniform locations.
            uniforms[UNIFORM_TRANSLATE] = GL.GetUniformLocation(program, "translate");
            
            // Release vertex and fragment shaders.
            if (vertShader != 0)
            {
                GL.DetachShader(program, vertShader);
                GL.DeleteShader(vertShader);
            }
                
            if (fragShader != 0)
            {
                GL.DetachShader(program, fragShader);
                GL.DeleteShader(fragShader);
            }
            
            return true;
        }

        void DestroyShaders()
        {
            if (program != 0)
            {
                GL.DeleteProgram(program);
                program = 0;
            }
        }

        #region Shader utilities

        static bool CompileShader(ShaderType type, string file, out int shader)
        {
            string src = System.IO.File.ReadAllText(file);

            shader = GL.CreateShader(type);
            GL.ShaderSource(shader, 1, new string[] { src }, (int[])null);
            GL.CompileShader(shader);
            
#if DEBUG
            int logLength;
            GL.GetShader (shader, ShaderParameter.InfoLogLength, out logLength);
            if (logLength > 0) {
                var infoLog = new System.Text.StringBuilder ();
                GL.GetShaderInfoLog (shader, logLength, out logLength, infoLog);
                Console.WriteLine ("Shader compile log:\n{0}", infoLog);
            }
#endif
            int status;
            GL.GetShader(shader, ShaderParameter.CompileStatus, out status);
            if (status == 0)
            {
                GL.DeleteShader(shader);
                return false;
            }
            
            return true;
        }

        static bool LinkProgram(int program)
        {
            GL.LinkProgram(program);
            
#if DEBUG
            int logLength;
            GL.GetProgram (program, ProgramParameter.InfoLogLength, out logLength);
            if (logLength > 0) {
                var infoLog = new System.Text.StringBuilder ();
                GL.GetProgramInfoLog (program, logLength, out logLength, infoLog);
                Console.WriteLine ("Program link log:\n{0}", infoLog);
            }
#endif
            int status;
            GL.GetProgram(program, ProgramParameter.LinkStatus, out status);
            if (status == 0)
                return false;
            
            return true;
        }

        static bool ValidateProgram(int program)
        {
            GL.ValidateProgram(program);
            
            int logLength;
            GL.GetProgram(program, ProgramParameter.InfoLogLength, out logLength);
            if (logLength > 0)
            {
                var infoLog = new System.Text.StringBuilder();
                GL.GetProgramInfoLog(program, logLength, out logLength, infoLog);
                Console.WriteLine("Program validate log:\n{0}", infoLog);
            }
            
            int status;
            GL.GetProgram(program, ProgramParameter.LinkStatus, out status);
            if (status == 0)
                return false;
            
            return true;
        }

        #endregion
    }
}