using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;

/* TODO:
 * * apply
 *   * HOW????
 *   * OnApply: protecteed internal :(
 *   * INTERNAL_applyEffect: internal...
 *     + calls mojoshader! --> hijack?!!
 *       -> glEffect{Begin,End}: state mgmt | unbind shader!
 *       -> glEffect{Begin,End}Pass: bind shader! | state mgmt
 *   * GD draw calls: ok
 *     * EXCEPT mojoshader: glProgramReady, glProgramViewportInfo
 *       -> set up uniforms and vertex arrays!
 *       --> circumvent? --> HOW??
 *       --> just go with it?? --> glProgramReady ok, glProgramViewportInfo might segfault!
 *
 * * uniforms
 * * samplers, textures
 *   -> https://www.khronos.org/opengl/wiki/Program_Introspection
 *   -> https://stackoverflow.com/questions/440144/in-opengl-is-there-a-way-to-get-a-list-of-all-uniforms-attribs-used-by-a-shade#442819
 * * vertex format verification!
 */

namespace PoroCYon.FNAGLSL {
	public class GLSLEffect : Effect {
		public struct ActiveEffect : IDisposable {
			internal uint oldprgm;
			bool disposed;

			internal ActiveEffect(uint old) {
				oldprgm = old; disposed = false;
			}

			public void Dispose() {
				if (disposed) return;

				GL.UseProgram(oldprgm);
				oldprgm = 0;

				disposed = true;
			}
		}

		uint[] glshdrs;
		uint glprgm;

		EffectTechnique fakeTech;

		//readonly static List<EffectTechnique> emptyEffTechList = new List<EffectTechnique>();
		public unsafe GLSLEffect(GraphicsDevice gd,
					IDictionary<GLSLPurpose, string> shaders)
				: base(/*UGLY hack*/new BasicEffect(gd)) {
			fakeTech = Techniques[0];

			// cause NullRefExns when dumb code would try to access the techns
			this.SetTechniques(null/*ReflUtil.CreateTechColl(emptyEffTechList)*/);

			GL.Init(gd);
			GL.GetError(); // ignore errors from FNA/mojoshader

			// this basically makes FNA think this effect is a noop, so binding
			// this effect will do the same as binding the 0 program in OpenGL,
			// so the BasicEffect used won't do much anymore
			/*gd.DeleteEffect(this);
			this.SetGLEffectData(IntPtr.Zero);
			this.SetEffectData  (IntPtr.Zero);*/
			// turns out we can't do this, or libmojoshader will segfault
			// because it lacks some null checking in
			// glEffectEnd, glEffectBeginPass, glProgramViewportInfo :/ ...
			// so we basically have to make sure the usual route of Apply()ing
			// the shader happens (unless we can circumvent this *somehow*),
			// and then apply the shader manually.

			var shdrs = new uint[shaders.Count];
			bool ok = false;
			uint prgm = 0;

			try {
				prgm = GL.CreateProgram();
				if (prgm == 0) GL.Throw();

				int i = 0;
				foreach (var kvp in shaders) {
					uint sh = GL.CreateShader(kvp.Key);
					if (sh == 0) GL.Throw();

					byte[] utf8src = Encoding.UTF8.GetBytes(kvp.Value);
					fixed (byte* sbuf = utf8src) {
						sbyte** uurgh = stackalloc sbyte*[1];
						*uurgh = (sbyte*)sbuf;
						int* uurgh2 = stackalloc int[1];
						*uurgh2 = utf8src.Length;
						GL.ShaderSource(sh, 1, uurgh, uurgh2);
					}
					GL.Throw();

					GL.CompileShader(sh);

					if (GL.GetError() != 0 || GL.GetShaderiv(sh, GL.COMPILE_STATUS) == 0) {
						int len = GL.GetShaderiv(sh, GL.INFO_LOG_LENGTH);
						var msg = GL.GetShaderInfoLog(sh, len);
						throw new GLSLCompileException("Failed to compile "
								+ kvp.Key + ": " + msg);
					}

					GL.AttachShader(prgm, sh);
					GL.Throw();

					shdrs[i++] = sh;
				}

				GL.LinkProgram(prgm);
				if (GL.GetError() != 0 || GL.GetProgramiv(prgm, GL.LINK_STATUS) == 0) {
					int len = GL.GetProgramiv(prgm, GL.INFO_LOG_LENGTH);
					var msg = GL.GetProgramInfoLog(prgm, len);
					throw new GLSLLinkException("Failed to link shader: " + msg);
				}

				glshdrs = shdrs;
				glprgm  = prgm ;

				ParseAttribUnif();

				ok = true;
			}
			finally {
				if (!ok) {
					DelShdrPrgm();
				} else {
					glshdrs = shdrs;
					glprgm  = prgm ;
				}
			}
		}

		void ParseAttribUnif() {
			// TODO: build EffectParameter stuff
			int attrs = GL.GetProgramiv(glprgm, GL.ACTIVE_ATTRIBUTES);
			GL.Throw();
			Console.WriteLine("#attrs = " + attrs);
			for (int i = 0; i < attrs; ++i) {
				int size; GLSLType type; string name;
				GL.GetActiveAttrib(glprgm, unchecked((uint)i), out size,
						out type, out name);
				GL.Throw();
				int loc = GL.GetAttribLocation(glprgm, name);
				GL.Throw();

				Console.WriteLine("attrs["+i+"] = {size=" + size + ", type="
						+ type + ", name=" + name + ", loc="+loc+"}");
			}

			int unifs = GL.GetProgramiv(glprgm, GL.ACTIVE_UNIFORMS);
			GL.Throw();
			Console.WriteLine("#unifs = " + unifs);
			for (int i = 0; i < unifs; ++i) {
				int size; GLSLType type; string name;
				GL.GetActiveUniform(glprgm, unchecked((uint)i), out size,
						out type, out name);
				GL.Throw();
				int loc = GL.GetUniformLocation(glprgm, name);
				GL.Throw();

				Console.WriteLine("unifs["+i+"] = {size=" + size + ", type="
						+ type + ", name=" + name + ", loc="+loc+"}");
			}

			/* #attrs = 1
			 * attrs[0] = {size=1, type=FLOAT_VEC3, name=in_pos, loc=0}
			 * #unifs = 2
			 * unifs[0] = {size=1, type=FLOAT, name=fGlobalTime, loc=0}
			 * unifs[1] = {size=1, type=FLOAT_VEC2, name=v2Resolution, loc=1}
			 */
		}

		// TODO: find out a better (i.e. more API-conform) way to do this!
		///<summary>
		///USAGE: using (var eff &eq; glslEffect.Bind()) { ... gd.DrawPrimitives(...); ... }
		///</summary>
		public ActiveEffect Bind() { // TODO: how to warn on discarding the retval?
			GL.GetError(); // ignore errors from FNA/mojoshader

			// workaround FNA crap
			CurrentTechnique = fakeTech;
			fakeTech.Passes[0].Apply();

			uint oldprgm = unchecked((uint)GL.GetIntegerv(GL.CURRENT_PROGRAM));
			GL.Throw();

			GL.UseProgram(glprgm);
			GL.Throw();

			// TODO: apply uniforms and samplers! (XNA API -> OpenGL state)

			return new ActiveEffect(oldprgm);
		}
		[Obsolete("Please use Bind() instead")]
		public ActiveEffect Apply() { return Bind(); }

		void DelShdrPrgm() {
			for (int i = 0; glshdrs != null && i < glshdrs.Length; ++i)
				if (glshdrs[i] != 0)
					GL.DeleteShader(glshdrs[i]);
			glshdrs = null;

			if (glprgm != 0)
				GL.DeleteProgram(glprgm);
		}

		protected override void Dispose(bool disposing) {
			if (!IsDisposed) {
				DelShdrPrgm();

				this.SetTechniques(ReflUtil.CreateTechColl(new[]{fakeTech}.ToList()));
				fakeTech = null;
			}

			base.Dispose(disposing);
		}
	}
}