//*PIXEL*
#version 460 core

#extension GL_ARB_bindless_texture : require


uint INVALID_HYDRA_ID = 4294967295;
uint DEPTH_TEXTURE_ID = 0;
uint DIFFUSE_TEXTURE_ID = 1;
uint METAL_ROUGH_TEXTURE_ID = 2;
uint NORMAL_TEXTURE_ID = 3;
uint POSITION_TEXTIURE_ID = 4;


uint HYDRA_LIGHT_DIRECTIONAL = 1;
uint HYDRA_LIGHT_POINT = 2;
uint HYDRA_LIGHT_SPOT = 3;

struct LightStructure
{
	vec4 ambient;
	vec4 diffuse;
	vec4 specular;
	float intensity;
	float constant;
	float linear;
	float quadratic;
    float cutoff;
	float cutoff_outer;
	uint entity_id;
    uint light_type;
	uint shadow_map_id;
	uint shadow_caster;
	uint padding0;
	uint padding1;
};

struct ShadowMapSet
{
    uint entity_id;
    uint cascade_count;
    uint shadow_texture_id;
    uint frame_buffer_id;
    float near_plane[8];
    float far_plane[8];
    mat4 light_space_proj[6];
    mat4 light_space_view[6];
};


layout(binding = 0) uniform uniform_per_frame
{
	mat4 view;
	mat4 proj;
	vec3 viewer_pos;
	uint light_count;
} ubo_per_frame;


layout(binding = 1) uniform uniform_output_textures
{
	uint texture_ids[16];
};

layout(std430, binding = 1) readonly buffer positions_buffer
{
	mat4 model_matrix[];
};

layout( std430, binding = 3) readonly buffer texture_buffer {
    uvec2 textures[1000];
};

layout (std430, binding = 4) readonly buffer light_buffer
{
	LightStructure lights[500];
};

layout (std430, binding = 5) readonly buffer shadow_map_sets
{
	ShadowMapSet shadows[10];
};


layout (location=0) in VS_OUT
{
	vec2 vsUV;
}vs_out;

layout (location=0) out vec4 uFragColor;

const float PI = 3.14159265358979323846;
const float M_INV_PI = 0.31830988618379067153776752674503;
float sqr(float x) { return x*x; }

// ----------------------------------------------------------------------------
float DistributionGGX(vec3 N, vec3 H, float roughness)
{
    float a = roughness*roughness;
    float a2 = a*a;
    float NdotH = max(dot(N, H), 0.0);
    float NdotH2 = NdotH*NdotH;

    float nom   = a2;
    float denom = (NdotH2 * (a2 - 1.0) + 1.0);
    denom = PI * denom * denom;

    return nom / denom;
}
// ----------------------------------------------------------------------------
float GeometrySchlickGGX(float NdotV, float roughness)
{
    float r = (roughness + 1.0);
    float k = (r*r) / 8.0;

    float nom   = NdotV;
    float denom = NdotV * (1.0 - k) + k;

    return nom / denom;
}
// ----------------------------------------------------------------------------
float GeometrySmith(vec3 N, vec3 V, vec3 L, float roughness)
{
    float NdotV = max(dot(N, V), 0.0);
    float NdotL = max(dot(N, L), 0.0);
    float ggx2 = GeometrySchlickGGX(NdotV, roughness);
    float ggx1 = GeometrySchlickGGX(NdotL, roughness);

    return ggx1 * ggx2;
}
// ----------------------------------------------------------------------------
vec3 fresnelSchlick(float cosTheta, vec3 F0)
{
    return F0 + (1.0 - F0) * pow(clamp(1.0 - cosTheta, 0.0, 1.0), 5.0);
}

vec3 CalculatePBR(vec3 normal, vec3 view_pos, vec3 world_pos,vec3 light_dir, vec3 diffuse, vec3 radiance, float roughness, float metallic )
{
	vec3 N = normalize(normal);
    vec3 V = normalize(view_pos - world_pos);

    // calculate reflectance at normal incidence; if dia-electric (like plastic) use F0
    // of 0.04 and if it's a metal, use the albedo color as F0 (metallic workflow)
    vec3 F0 = vec3(0.04);
    F0 = mix(F0, diffuse, metallic);


	// calculate per-light radiance
	vec3 L = normalize(light_dir);
	vec3 H = normalize(V + L);

	// Cook-Torrance BRDF
	float NDF = DistributionGGX(N, H, roughness);
	float G   = GeometrySmith(N, V, L, roughness);
	vec3 F    = fresnelSchlick(clamp(dot(H, V), 0.0, 1.0), F0);

	vec3 numerator    = NDF * G * F;
	float denominator = 4.0 * max(dot(N, V), 0.0) * max(dot(N, L), 0.0) + 0.0001; // + 0.0001 to prevent divide by zero
	vec3 specular = numerator / denominator;

	// kS is equal to Fresnel
	vec3 kS = F;
	// for energy conservation, the diffuse and specular light can't
	// be above 1.0 (unless the surface emits light); to preserve this
	// relationship the diffuse component (kD) should equal 1.0 - kS.
	vec3 kD = vec3(1.0) - kS;
	// multiply kD by the inverse metalness such that only non-metals
	// have diffuse lighting, or a linear blend if partly metal (pure metals
	// have no diffuse light).
	kD *= 1.0 - metallic;

	// scale light by NdotL
	float NdotL = max(dot(N, L), 0.0);

	// add to outgoing radiance Lo
	vec3 Lo = (kD * diffuse / PI + specular) * radiance * NdotL;  // note that we already multiplied the BRDF by the Fresnel (kS) so we won't multiply by kS again

	return Lo;
}

vec3 DirectionalShading(vec3 normal,
						vec3 diffuse,
						float roughness,
						float metallic,
						float light_intensity,
						vec3 light_dir,
						vec3 light_pos,
						vec3 world_pos,
						vec3 view_pos)
{

	float distance = length(light_pos - world_pos);
	float attenuation = 1.0;

	vec3 radiance = diffuse * attenuation;

	vec3 Lo = CalculatePBR(normal, view_pos, world_pos, light_dir, diffuse,  radiance, roughness, metallic);

	return Lo;
}


vec3 PointShading(vec3 normal,
					vec3 diffuse,
					float roughness,
					float metallic,
					float light_intensity,
					vec3 light_pos,
					float light_constant,
					float light_linear,
					float light_quadratic,
					vec3 world_pos,
					vec3 view_pos)
{
	float distance = length(light_pos - world_pos);
	float attenuation = 1.0;

	attenuation = light_intensity / (light_constant + (light_linear * distance) + (light_quadratic * distance * distance));
	vec3 radiance = diffuse * attenuation;
	 vec3 light_dir = normalize(light_pos - world_pos);
	vec3 Lo = CalculatePBR(normal, view_pos, world_pos, light_dir, diffuse,  radiance, roughness, metallic);

	return Lo;
}
vec3 SpotShading(vec3 normal,
					vec3 diffuse,
					float roughness,
					float metallic,
					float light_intensity,
					vec3 light_dir,
					vec3 light_pos,
					float cutoff,
					float cutoff_outer,
					float light_constant,
					float light_linear,
					float light_quadratic,
					vec3 world_pos,
					vec3 view_pos)
{

	vec3 direction_to_light = normalize(light_pos - world_pos);
	float theta = dot(direction_to_light, light_dir);
	float falloff = 0.0f;
	// if(theta > cutoff)
	// {
		float epsilon   = cutoff - cutoff_outer;
	 	falloff = clamp((theta - cutoff_outer) / epsilon, 0.0, 1.0);

	//}

	float distance = length(light_pos - world_pos);
	float attenuation = 1.0;

	attenuation = light_intensity / (light_constant + (light_linear * distance) + (light_quadratic * distance * distance));
	vec3 radiance = diffuse * attenuation * falloff;

	vec3 Lo = CalculatePBR(normal, view_pos, world_pos, direction_to_light, diffuse,  radiance, roughness, metallic);

	return Lo;
}

mat3 GetRotationOnlyMatrix(mat4 model_mat)
{
	mat3 rot_mat;
	rot_mat[0] = model_mat[0].xyz;
	rot_mat[1] = model_mat[1].xyz;
	rot_mat[2] = model_mat[2].xyz;
	return rot_mat;
}

float SimpleSampleShadow(vec4 frag_clip_space, sampler2DArray sampler_shadow_map, uint shadow_trans_idx)
{
	vec3 frag_light_space = frag_clip_space.xyz / frag_clip_space.w;
	frag_light_space = (frag_light_space * 0.5) + 0.5;

	float shadow_map_depth = texture(sampler_shadow_map, vec3(frag_light_space.xy, shadow_trans_idx)).r;
	// return frag_light_space.z - shadow_map_depth;
	//  return shadow_map_depth ;
	if(frag_light_space.z > shadow_map_depth)
	{
		return 0;
	}
	return 1;
}

float SampleShadow(vec4 frag_clip_space, sampler2DArray sampler_shadow_map, uint shadow_trans_idx, vec3 normal, vec3 light_dir)
{
	vec3 frag_light_space = frag_clip_space.xyz / frag_clip_space.w;
	frag_light_space = (frag_light_space * 0.5) + 0.5;

	float shadow_map_depth = texture(sampler_shadow_map, vec3(frag_light_space.xy, shadow_trans_idx)).r;
    // calculate bias (based on depth map resolution and slope)
    
    
    float bias = max(0.005 * (1.0 - dot(normal, light_dir)), 0.0005);
	
	
    // check whether current frag pos is in shadow
    // float shadow = currentDepth - bias > closestDepth  ? 1.0 : 0.0;
    // PCF
    float shadow = 0.0;
    vec2 texel_size = 1.0 / textureSize(sampler_shadow_map, 0).xy;

    for(int x = -1; x <= 1; ++x)
    {
        for(int y = -1; y <= 1; ++y)
        {			
            shadow_map_depth = texture(sampler_shadow_map, vec3(frag_light_space.xy + vec2(x, y) * texel_size, shadow_trans_idx)).r;
            shadow += frag_light_space.z - bias > shadow_map_depth  ? 1.0 : 0.0;
        }
    }
    shadow /= 9.0;

    // keep the shadow at 0.0 when outside the far_plane region of the light's frustum.
    if(frag_light_space.z > 1.0)
        shadow = 0.0;
	
    return shadow;
}

float CalculateDirectionalShadow(vec4 world_pos, uint shadow_idx, vec3 normal, vec3 light_dir)
{
		float shadow = 0;
		//Move the fragment to light space
		vec4 frag_in_light_space = shadows[shadow_idx].light_space_view[5] * world_pos;
		//measure the distance of the fragment from the light
		float frag_distance = length(frag_in_light_space.xyz);

		uint shadow_trans_idx = 0;
		uint ignore_shadow = 0;

		shadow_idx = 0;
		//Work out which shadowmap is appropriate for this distance
		for(uint i = 0; i < 6; i++)
		{
			if(frag_distance <= shadows[shadow_idx].far_plane[i])
			{
				//record the shadow map level
				shadow_trans_idx = i;
				//and indicate that this has a level
				ignore_shadow = 1;
				break;
			}
		}


		if(ignore_shadow == 1)
		{
			
			vec4 translated_pixel = shadows[shadow_idx].light_space_proj[shadow_trans_idx] *
								shadows[shadow_idx].light_space_view[shadow_trans_idx] *
								world_pos;

			
			uvec2 shadow_handle = textures[shadows[shadow_idx].shadow_texture_id];
			
			
			shadow = SampleShadow(translated_pixel, sampler2DArray(shadow_handle), shadow_trans_idx, normal, light_dir );

		}

	return shadow;
}


void main()
{
	uvec2 diffuse_handle = textures[texture_ids[DIFFUSE_TEXTURE_ID]];
	uvec2 normal_handle = textures[texture_ids[NORMAL_TEXTURE_ID]];
	uvec2 metal_rough_handle = textures[texture_ids[METAL_ROUGH_TEXTURE_ID]];
	uvec2 world_pos_handle = textures[texture_ids[POSITION_TEXTIURE_ID]];
	vec4 diffuse = texture(sampler2D(diffuse_handle), vs_out.vsUV.xy);

	if(diffuse[3] <= 0.1)
	{
		discard;
	}

	vec3 normal = texture(sampler2D(normal_handle), vs_out.vsUV.xy).xyz;
	vec3 metal_rough = texture(sampler2D(metal_rough_handle), vs_out.vsUV.xy).xyz;
	vec3 world_pos = texture(sampler2D(world_pos_handle), vs_out.vsUV.xy).xyz;
	float rough = metal_rough[1];
	float metal = metal_rough[2];
	float ao = 1;
    vec3 ambient = vec3(0.05) * diffuse.xyz * ao;
	vec3 Lo = ambient;
	for(int i = 0; i < ubo_per_frame.light_count; i ++)
	{
		mat4 model = model_matrix[lights[i].entity_id];
		mat3 rot_mat = GetRotationOnlyMatrix(model);
		vec3 light_direction = normalize(rot_mat * vec3(0,0,1));

		vec3 light_pos = model[3].xyz;
		if(lights[i].light_type == HYDRA_LIGHT_DIRECTIONAL)
		{
			Lo += DirectionalShading(normal, diffuse.xyz, rough, metal, lights[i].intensity, light_direction, light_pos, world_pos, ubo_per_frame.viewer_pos);
			if(lights[i].shadow_caster == 1)
			{
				float shadow = CalculateDirectionalShadow(vec4(world_pos, 1.0), lights[i].shadow_map_id, normal, light_direction);
				Lo = Lo * vec3(1-shadow);
			}
		}
		else if(lights[i].light_type == HYDRA_LIGHT_POINT)
		{

			Lo += PointShading(normal,
							diffuse.xyz,
							rough,
							metal,
							lights[i].intensity,
							light_pos,
							lights[i].constant,
							lights[i].linear,
							lights[i].quadratic,
							world_pos,
							ubo_per_frame.viewer_pos);
		}
		else if(lights[i].light_type == HYDRA_LIGHT_SPOT)
		{
			Lo += SpotShading(normal,
							diffuse.xyz,
							rough,
							metal,
							lights[i].intensity,
							light_direction,
							light_pos,
							lights[i].cutoff,
							lights[i].cutoff_outer,
							lights[i].constant,
							lights[i].linear,
							lights[i].quadratic,
							world_pos,
							ubo_per_frame.viewer_pos);
		}

	}

	float lighting = 0;
 // ambient lighting (note that the next IBL tutorial will replace
    // this ambient lighting with environment lighting).
	

    vec3 output_color = Lo;

    // HDR tonemapping
    output_color = output_color / (output_color + vec3(1.0));
    // gamma correct
    output_color = pow(output_color, vec3(1.0/2.1));

    uFragColor = vec4(output_color, 1.0);
	// float light = dot(lights[0].light_direction, normal);

	// uFragColor = vec4(diffuse.xyz * light,1);

	// uFragColor = vec4(normal, 1);
}