/*
The MIT License (MIT)

Copyright (c) 2022 Sascha Willems

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
*/

#version 450

layout (binding = 1) uniform sampler2D samplerposition;
layout (binding = 2) uniform sampler2D samplerNormal;
layout (binding = 3) uniform sampler2D samplerAlbedo;
layout (binding = 5) uniform sampler2DArray samplerShadowMap;

layout (location = 0) in vec2 inUV;

layout (location = 0) out vec4 outFragColor;

#define LIGHT_COUNT 3
#define SHADOW_FACTOR 0.25
#define AMBIENT_LIGHT 0.1
#define USE_PCF

struct Light 
{
	vec4 position;
	vec4 target;
	vec4 color;
	mat4 viewMatrix;
};

layout (binding = 4) uniform UBO 
{
	vec4 viewPos;
	Light lights[LIGHT_COUNT];
	int useShadows;
	int debugDisplayTarget;
} ubo;

float textureProj(vec4 P, float layer, vec2 offset)
{
	float shadow = 1.0;
	vec4 shadowCoord = P / P.w;
	shadowCoord.st = shadowCoord.st * 0.5 + 0.5;
	
	if (shadowCoord.z > -1.0 && shadowCoord.z < 1.0) 
	{
		float dist = texture(samplerShadowMap, vec3(shadowCoord.st + offset, layer)).r;
		if (shadowCoord.w > 0.0 && dist < shadowCoord.z) 
		{
			shadow = SHADOW_FACTOR;
		}
	}
	return shadow;
}

float filterPCF(vec4 sc, float layer)
{
	ivec2 texDim = textureSize(samplerShadowMap, 0).xy;
	float scale = 1.5;
	float dx = scale * 1.0 / float(texDim.x);
	float dy = scale * 1.0 / float(texDim.y);

	float shadowFactor = 0.0;
	int count = 0;
	int range = 1;
	
	for (int x = -range; x <= range; x++)
	{
		for (int y = -range; y <= range; y++)
		{
			shadowFactor += textureProj(sc, layer, vec2(dx*x, dy*y));
			count++;
		}
	
	}
	return shadowFactor / count;
}

vec3 shadow(vec3 fragcolor, vec3 fragpos) {
	for(int i = 0; i < LIGHT_COUNT; ++i)
	{
		vec4 shadowClip	= ubo.lights[i].viewMatrix * vec4(fragpos, 1.0);

		float shadowFactor;
		#ifdef USE_PCF
			shadowFactor= filterPCF(shadowClip, i);
		#else
			shadowFactor = textureProj(shadowClip, i, vec2(0.0));
		#endif

		fragcolor *= shadowFactor;
	}
	return fragcolor;
}

void main() 
{
	// Get G-Buffer values
	vec3 fragPos = texture(samplerposition, inUV).rgb;
	vec3 normal = texture(samplerNormal, inUV).rgb;
	vec4 albedo = texture(samplerAlbedo, inUV);

	// Debug display
	if (ubo.debugDisplayTarget > 0) {
		switch (ubo.debugDisplayTarget) {
			case 1: 
				outFragColor.rgb = shadow(vec3(1.0), fragPos).rgb;
				break;
			case 2: 
				outFragColor.rgb = fragPos;
				break;
			case 3: 
				outFragColor.rgb = normal;
				break;
			case 4: 
				outFragColor.rgb = albedo.rgb;
				break;
			case 5: 
				outFragColor.rgb = albedo.aaa;
				break;
		}		
		outFragColor.a = 1.0;
		return;
	}

	// Ambient part
	vec3 fragcolor  = albedo.rgb * AMBIENT_LIGHT;

	vec3 N = normalize(normal);
		
	for(int i = 0; i < LIGHT_COUNT; ++i)
	{
		// Vector to light
		vec3 L = ubo.lights[i].position.xyz - fragPos;
		// Distance from light to fragment position
		float dist = length(L);
		L = normalize(L);

		// Viewer to fragment
		vec3 V = ubo.viewPos.xyz - fragPos;
		V = normalize(V);

		float lightCosInnerAngle = cos(radians(15.0));
		float lightCosOuterAngle = cos(radians(25.0));
		float lightRange = 100.0;

		// Direction vector from source to target
		vec3 dir = normalize(ubo.lights[i].position.xyz - ubo.lights[i].target.xyz);

		// Dual cone spot light with smooth transition between inner and outer angle
		float cosDir = dot(L, dir);
		float spotEffect = smoothstep(lightCosOuterAngle, lightCosInnerAngle, cosDir);
		float heightAttenuation = smoothstep(lightRange, 0.0f, dist);

		// Diffuse lighting
		float NdotL = max(0.0, dot(N, L));
		vec3 diff = vec3(NdotL);

		// Specular lighting
		vec3 R = reflect(-L, N);
		float NdotR = max(0.0, dot(R, V));
		vec3 spec = vec3(pow(NdotR, 16.0) * albedo.a * 2.5);

		fragcolor += vec3((diff + spec) * spotEffect * heightAttenuation) * ubo.lights[i].color.rgb * albedo.rgb;
	}    	

	// Shadow calculations in a separate pass
	if (ubo.useShadows > 0)
	{
		fragcolor = shadow(fragcolor, fragPos);
	}

	outFragColor = vec4(fragcolor, 1.0);
}