// ----------------------------------------------------------------
// From Game Programming in C++ by Sanjay Madhav
// Copyright (C) 2017 Sanjay Madhav. All rights reserved.
// 
// Released under the BSD License
// See LICENSE.txt for full details.
// ----------------------------------------------------------------

#include "Renderer.h"
#include "Texture.h"
#include "Mesh.h"
#include <algorithm>
#include "Shader.h"
#include "VertexArray.h"
#include "SpriteComponent.h"
#include "MeshComponent.h"
#include "UIScreen.h"
#include "Game.h"
#include <GL/glew.h>
#include "SkeletalMeshComponent.h"
#include "GBuffer.h"
#include "PointLightComponent.h"

Renderer::Renderer(Game* game)
	:mGame(game)
	,mSpriteShader(nullptr)
	,mMeshShader(nullptr)
	,mSkinnedShader(nullptr)
	,mMirrorBuffer(0)
	,mMirrorTexture(nullptr)
	,mGBuffer(nullptr)
	,mGGlobalShader(nullptr)
	,mGPointLightShader(nullptr)
{
}

Renderer::~Renderer()
{
}

bool Renderer::Initialize(float screenWidth, float screenHeight)
{
	mScreenWidth = screenWidth;
	mScreenHeight = screenHeight;

	// Set OpenGL attributes
	// Use the core OpenGL profile
	SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
	// Specify version 3.3
	SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
	SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 3);
	// Request a color buffer with 8-bits per RGBA channel
	SDL_GL_SetAttribute(SDL_GL_RED_SIZE, 8);
	SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE, 8);
	SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 8);
	SDL_GL_SetAttribute(SDL_GL_ALPHA_SIZE, 8);
	SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);
	// Enable double buffering
	SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
	// Force OpenGL to use hardware acceleration
	SDL_GL_SetAttribute(SDL_GL_ACCELERATED_VISUAL, 1);

	mWindow = SDL_CreateWindow("Game Programming in C++ (Chapter 13)", 100, 100,
		static_cast<int>(mScreenWidth), static_cast<int>(mScreenHeight), SDL_WINDOW_OPENGL);
	if (!mWindow)
	{
		SDL_Log("Failed to create window: %s", SDL_GetError());
		return false;
	}

	// Create an OpenGL context
	mContext = SDL_GL_CreateContext(mWindow);

	// Initialize GLEW
	glewExperimental = GL_TRUE;
	if (glewInit() != GLEW_OK)
	{
		SDL_Log("Failed to initialize GLEW.");
		return false;
	}

	// On some platforms, GLEW will emit a benign error code,
	// so clear it
	glGetError();

	// Make sure we can create/compile shaders
	if (!LoadShaders())
	{
		SDL_Log("Failed to load shaders.");
		return false;
	}

	// Create quad for drawing sprites
	CreateSpriteVerts();

	// Create render target for mirror
	if (!CreateMirrorTarget())
	{
		SDL_Log("Failed to create render target for mirror.");
		return false;
	}
	
	// Create G-buffer
	mGBuffer = new GBuffer();
	int width = static_cast<int>(mScreenWidth);
	int height = static_cast<int>(mScreenHeight);
	if (!mGBuffer->Create(width, height))
	{
		SDL_Log("Failed to create G-buffer.");
		return false;
	}

	// Load point light mesh
	mPointLightMesh = GetMesh("Assets/PointLight.gpmesh");

	return true;
}

void Renderer::Shutdown()
{
	// Get rid of any render target textures, if they exist
	if (mMirrorTexture != nullptr)
	{
		glDeleteFramebuffers(1, &mMirrorBuffer);
		mMirrorTexture->Unload();
		delete mMirrorTexture;
	}
	// Get rid of G-buffer
	if (mGBuffer != nullptr)
	{
		mGBuffer->Destroy();
		delete mGBuffer;
	}
	// Delete point lights
	while (!mPointLights.empty())
	{
		delete mPointLights.back();
	}
	delete mSpriteVerts;
	mSpriteShader->Unload();
	delete mSpriteShader;
	mMeshShader->Unload();
	delete mMeshShader;
	SDL_GL_DeleteContext(mContext);
	SDL_DestroyWindow(mWindow);
}

void Renderer::UnloadData()
{
	// Destroy textures
	for (auto i : mTextures)
	{
		i.second->Unload();
		delete i.second;
	}
	mTextures.clear();

	// Destroy meshes
	for (auto i : mMeshes)
	{
		i.second->Unload();
		delete i.second;
	}
	mMeshes.clear();
}

void Renderer::Draw()
{
	// Draw to the mirror texture first
	Draw3DScene(mMirrorBuffer, mMirrorView, mProjection, 0.25f);
	// Draw the 3D scene to the G-buffer
	Draw3DScene(mGBuffer->GetBufferID(), mView, mProjection, 1.0f, false);
	// Set the frame buffer back to zero (screen's frame buffer)
	glBindFramebuffer(GL_FRAMEBUFFER, 0);
	// Draw from the GBuffer
	DrawFromGBuffer();
	
	// Draw all sprite components
	// Disable depth buffering
	glDisable(GL_DEPTH_TEST);
	// Enable alpha blending on the color buffer
	glEnable(GL_BLEND);
	glBlendEquationSeparate(GL_FUNC_ADD, GL_FUNC_ADD);
	glBlendFuncSeparate(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA, GL_ONE, GL_ZERO);

	// Set shader/vao as active
	mSpriteShader->SetActive();
	mSpriteVerts->SetActive();
	for (auto sprite : mSprites)
	{
		if (sprite->GetVisible())
		{
			sprite->Draw(mSpriteShader);
		}
	}
	
	// Draw any UI screens
	for (auto ui : mGame->GetUIStack())
	{
		ui->Draw(mSpriteShader);
	}

	// Swap the buffers
	SDL_GL_SwapWindow(mWindow);
}

void Renderer::AddSprite(SpriteComponent* sprite)
{
	// Find the insertion point in the sorted vector
	// (The first element with a higher draw order than me)
	int myDrawOrder = sprite->GetDrawOrder();
	auto iter = mSprites.begin();
	for (;
		iter != mSprites.end();
		++iter)
	{
		if (myDrawOrder < (*iter)->GetDrawOrder())
		{
			break;
		}
	}

	// Inserts element before position of iterator
	mSprites.insert(iter, sprite);
}

void Renderer::RemoveSprite(SpriteComponent* sprite)
{
	auto iter = std::find(mSprites.begin(), mSprites.end(), sprite);
	mSprites.erase(iter);
}

void Renderer::AddMeshComp(MeshComponent* mesh)
{
	if (mesh->GetIsSkeletal())
	{
		SkeletalMeshComponent* sk = static_cast<SkeletalMeshComponent*>(mesh);
		mSkeletalMeshes.emplace_back(sk);
	}
	else
	{
		mMeshComps.emplace_back(mesh);
	}
}

void Renderer::RemoveMeshComp(MeshComponent* mesh)
{
	if (mesh->GetIsSkeletal())
	{
		SkeletalMeshComponent* sk = static_cast<SkeletalMeshComponent*>(mesh);
		auto iter = std::find(mSkeletalMeshes.begin(), mSkeletalMeshes.end(), sk);
		mSkeletalMeshes.erase(iter);
	}
	else
	{
		auto iter = std::find(mMeshComps.begin(), mMeshComps.end(), mesh);
		mMeshComps.erase(iter);
	}
}

void Renderer::AddPointLight(PointLightComponent* light)
{
	mPointLights.emplace_back(light);
}

void Renderer::RemovePointLight(PointLightComponent* light)
{
	auto iter = std::find(mPointLights.begin(), mPointLights.end(), light);
	mPointLights.erase(iter);
}

Texture* Renderer::GetTexture(const std::string& fileName)
{
	Texture* tex = nullptr;
	auto iter = mTextures.find(fileName);
	if (iter != mTextures.end())
	{
		tex = iter->second;
	}
	else
	{
		tex = new Texture();
		if (tex->Load(fileName))
		{
			mTextures.emplace(fileName, tex);
		}
		else
		{
			delete tex;
			tex = nullptr;
		}
	}
	return tex;
}

Mesh* Renderer::GetMesh(const std::string & fileName)
{
	Mesh* m = nullptr;
	auto iter = mMeshes.find(fileName);
	if (iter != mMeshes.end())
	{
		m = iter->second;
	}
	else
	{
		m = new Mesh();
		if (m->Load(fileName, this))
		{
			mMeshes.emplace(fileName, m);
		}
		else
		{
			delete m;
			m = nullptr;
		}
	}
	return m;
}

void Renderer::Draw3DScene(unsigned int framebuffer, const Matrix4& view, const Matrix4& proj, 
	float viewPortScale, bool lit)
{
	// Set the current frame buffer
	glBindFramebuffer(GL_FRAMEBUFFER, framebuffer);

	// Set viewport size based on scale
	glViewport(0, 0,
		static_cast<int>(mScreenWidth * viewPortScale),
		static_cast<int>(mScreenHeight * viewPortScale)
	);

	// Clear color buffer/depth buffer
	glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
	glDepthMask(GL_TRUE);
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

	// Draw mesh components
	// Enable depth buffering/disable alpha blend
	glEnable(GL_DEPTH_TEST);
	glDisable(GL_BLEND);
	// Set the mesh shader active
	mMeshShader->SetActive();
	// Update view-projection matrix
	mMeshShader->SetMatrixUniform("uViewProj", view * proj);
	// Update lighting uniforms
	if (lit)
	{
		SetLightUniforms(mMeshShader, view);
	}
	for (auto mc : mMeshComps)
	{
		if (mc->GetVisible())
		{
			mc->Draw(mMeshShader);
		}
	}

	// Draw any skinned meshes now
	mSkinnedShader->SetActive();
	// Update view-projection matrix
	mSkinnedShader->SetMatrixUniform("uViewProj", view * proj);
	// Update lighting uniforms
	if (lit)
	{
		SetLightUniforms(mSkinnedShader, view);
	}
	for (auto sk : mSkeletalMeshes)
	{
		if (sk->GetVisible())
		{
			sk->Draw(mSkinnedShader);
		}
	}
}

bool Renderer::CreateMirrorTarget()
{
	int width = static_cast<int>(mScreenWidth) / 4;
	int height = static_cast<int>(mScreenHeight) / 4;

	// Generate a frame buffer for the mirror texture
	glGenFramebuffers(1, &mMirrorBuffer);
	glBindFramebuffer(GL_FRAMEBUFFER, mMirrorBuffer);

	// Create the texture we'll use for rendering
	mMirrorTexture = new Texture();
	mMirrorTexture->CreateForRendering(width, height, GL_RGB);

	// Add a depth buffer to this target
	GLuint depthBuffer;
	glGenRenderbuffers(1, &depthBuffer);
	glBindRenderbuffer(GL_RENDERBUFFER, depthBuffer);
	glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT, width, height);
	glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depthBuffer);

	// Attach mirror texture as the output target for the frame buffer
	glFramebufferTexture(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, mMirrorTexture->GetTextureID(), 0);

	// Set the list of buffers to draw to for this frame buffer
	GLenum drawBuffers[] = { GL_COLOR_ATTACHMENT0 };
	glDrawBuffers(1, drawBuffers);

	// Make sure everything worked
	if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
	{
		// If it didn't work, delete the framebuffer,
		// unload/delete the texture and return false
		glDeleteFramebuffers(1, &mMirrorBuffer);
		mMirrorTexture->Unload();
		delete mMirrorTexture;
		mMirrorTexture = nullptr;
		return false;
	}
	return true;
}

void Renderer::DrawFromGBuffer()
{
	// Disable depth testing for the global lighting pass
	glDisable(GL_DEPTH_TEST);
	// Activate global G-buffer shader
	mGGlobalShader->SetActive();
	// Activate sprite verts quad
	mSpriteVerts->SetActive();
	// Set the G-buffer textures to sample
	mGBuffer->SetTexturesActive();
	// Set the lighting uniforms
	SetLightUniforms(mGGlobalShader, mView);
	// Draw the triangles
	glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, nullptr);

	// Copy depth buffer from G-buffer to default frame buffer
	glBindFramebuffer(GL_READ_FRAMEBUFFER, mGBuffer->GetBufferID());
	int width = static_cast<int>(mScreenWidth);
	int height = static_cast<int>(mScreenHeight);
	glBlitFramebuffer(0, 0, width, height,
		0, 0, width, height,
		GL_DEPTH_BUFFER_BIT, GL_NEAREST);

	// Enable depth test, but disable writes to depth buffer
	glEnable(GL_DEPTH_TEST);
	glDepthMask(GL_FALSE);

	// Set the point light shader and mesh as active
	mGPointLightShader->SetActive();
	mPointLightMesh->GetVertexArray()->SetActive();
	// Set the view-projection matrix
	mGPointLightShader->SetMatrixUniform("uViewProj",
		mView * mProjection);
	// Set the G-buffer textures for sampling
	mGBuffer->SetTexturesActive();

	// The point light color should add to existing color
	glEnable(GL_BLEND);
	glBlendFunc(GL_ONE, GL_ONE);

	// Draw the point lights
	for (PointLightComponent* p : mPointLights)
	{
		p->Draw(mGPointLightShader, mPointLightMesh);
	}
}

bool Renderer::LoadShaders()
{
	// Create sprite shader
	mSpriteShader = new Shader();
	if (!mSpriteShader->Load("Shaders/Sprite.vert", "Shaders/Sprite.frag"))
	{
		return false;
	}

	mSpriteShader->SetActive();
	// Set the view-projection matrix
	Matrix4 spriteViewProj = Matrix4::CreateSimpleViewProj(mScreenWidth, mScreenHeight);
	mSpriteShader->SetMatrixUniform("uViewProj", spriteViewProj);

	// Create basic mesh shader
	mMeshShader = new Shader();
	if (!mMeshShader->Load("Shaders/Phong.vert", "Shaders/GBufferWrite.frag"))
	{
		return false;
	}

	mMeshShader->SetActive();
	// Set the view-projection matrix
	mView = Matrix4::CreateLookAt(Vector3::Zero, Vector3::UnitX, Vector3::UnitZ);
	mProjection = Matrix4::CreatePerspectiveFOV(Math::ToRadians(70.0f),
		mScreenWidth, mScreenHeight, 10.0f, 10000.0f);
	mMeshShader->SetMatrixUniform("uViewProj", mView * mProjection);

	// Create skinned shader
	mSkinnedShader = new Shader();
	if (!mSkinnedShader->Load("Shaders/Skinned.vert", "Shaders/GBufferWrite.frag"))
	{
		return false;
	}

	mSkinnedShader->SetActive();
	mSkinnedShader->SetMatrixUniform("uViewProj", mView * mProjection);
	
	// Create shader for drawing from GBuffer (global lighting)
	mGGlobalShader = new Shader();
	if (!mGGlobalShader->Load("Shaders/GBufferGlobal.vert", "Shaders/GBufferGlobal.frag"))
	{
		return false;
	}
	// For the GBuffer, we need to associate each sampler with an index
	mGGlobalShader->SetActive();
	mGGlobalShader->SetIntUniform("uGDiffuse", 0);
	mGGlobalShader->SetIntUniform("uGNormal", 1);
	mGGlobalShader->SetIntUniform("uGWorldPos", 2);
	// The view projection is just the sprite one
	mGGlobalShader->SetMatrixUniform("uViewProj", spriteViewProj);
	// The world transform scales to the screen and flips y
	Matrix4 gbufferWorld = Matrix4::CreateScale(mScreenWidth, -mScreenHeight,
												1.0f);
	mGGlobalShader->SetMatrixUniform("uWorldTransform", gbufferWorld);
	
	// Create a shader for point lights from GBuffer
	mGPointLightShader = new Shader();
	if (!mGPointLightShader->Load("Shaders/BasicMesh.vert",
								  "Shaders/GBufferPointLight.frag"))
	{
		return false;
	}
	// Set sampler indices
	mGPointLightShader->SetActive();
	mGPointLightShader->SetIntUniform("uGDiffuse", 0);
	mGPointLightShader->SetIntUniform("uGNormal", 1);
	mGPointLightShader->SetIntUniform("uGWorldPos", 2);
	mGPointLightShader->SetVector2Uniform("uScreenDimensions",
		Vector2(mScreenWidth, mScreenHeight));
	return true;
}

void Renderer::CreateSpriteVerts()
{
	float vertices[] = {
		-0.5f, 0.5f, 0.f, 0.f, 0.f, 0.0f, 0.f, 0.f, // top left
		0.5f, 0.5f, 0.f, 0.f, 0.f, 0.0f, 1.f, 0.f, // top right
		0.5f,-0.5f, 0.f, 0.f, 0.f, 0.0f, 1.f, 1.f, // bottom right
		-0.5f,-0.5f, 0.f, 0.f, 0.f, 0.0f, 0.f, 1.f  // bottom left
	};

	unsigned int indices[] = {
		0, 1, 2,
		2, 3, 0
	};

	mSpriteVerts = new VertexArray(vertices, 4, VertexArray::PosNormTex, indices, 6);
}

void Renderer::SetLightUniforms(Shader* shader, const Matrix4& view)
{
	// Camera position is from inverted view
	Matrix4 invView = view;
	invView.Invert();
	shader->SetVectorUniform("uCameraPos", invView.GetTranslation());
	// Ambient light
	shader->SetVectorUniform("uAmbientLight", mAmbientLight);
	// Directional light
	shader->SetVectorUniform("uDirLight.mDirection",
		mDirLight.mDirection);
	shader->SetVectorUniform("uDirLight.mDiffuseColor",
		mDirLight.mDiffuseColor);
	shader->SetVectorUniform("uDirLight.mSpecColor",
		mDirLight.mSpecColor);
}

Vector3 Renderer::Unproject(const Vector3& screenPoint) const
{
	// Convert screenPoint to device coordinates (between -1 and +1)
	Vector3 deviceCoord = screenPoint;
	deviceCoord.x /= (mScreenWidth) * 0.5f;
	deviceCoord.y /= (mScreenHeight) * 0.5f;

	// Transform vector by unprojection matrix
	Matrix4 unprojection = mView * mProjection;
	unprojection.Invert();
	return Vector3::TransformWithPerspDiv(deviceCoord, unprojection);
}

void Renderer::GetScreenDirection(Vector3& outStart, Vector3& outDir) const
{
	// Get start point (in center of screen on near plane)
	Vector3 screenPoint(0.0f, 0.0f, 0.0f);
	outStart = Unproject(screenPoint);
	// Get end point (in center of screen, between near and far)
	screenPoint.z = 0.9f;
	Vector3 end = Unproject(screenPoint);
	// Get direction vector
	outDir = end - outStart;
	outDir.Normalize();
}