#version 300 es
precision mediump float;

in vec3 vertPosition;
in vec2 vertTexCoord;
in mat3 vertTBNMatrix;
in vec4 vertColor;

uniform vec3 light0Position;
uniform vec3 light1Position;
uniform vec3 light2Direction;
uniform vec3 light0Color;
uniform vec3 light1Color;
uniform vec3 light2Color;
uniform vec3 ambientColor;
uniform vec3 specularColor;
uniform float specularExponent;
uniform vec3 emissiveColor;
uniform vec3 cameraPosition;
uniform sampler2D colorTexture;
uniform sampler2D normalTexture;

out vec4 fragColor;

vec3 applyDirectionalLight(vec3 lightToSurface, vec3 lightColor, vec3 surfaceColor, vec3 normal, vec3 surfacePosition, vec3 surfaceToCamera) {
	float diffuseStrength = max(dot(normal, -lightToSurface), 0.0);
	vec3 diffuseOutput = diffuseStrength * lightColor;
	float specularStrength = pow(max(0.0, dot(surfaceToCamera, reflect(lightToSurface, normal))), shininess);
	vec3 specularOutput = specularColor * specularStrength * lightColor;
	return (diffuseOutput + specularOutput) * surfaceColor;
}

vec3 applyPointLight(vec3 lightPosition, vec3 lightColor, vec3 surfaceColor, vec3 normal, vec3 surfacePosition, vec3 surfaceToCamera) {
	return applyDirectionalLight(normalize(surfacePosition - lightPosition), lightColor, surfaceColor, normal, surfacePosition, surfaceToCamera);
}

void main() {
	vec4 textureColor = texture(colorTexture, vertTexCoord) * vertColor;
	vec3 surfaceToCamera = normalize(cameraPosition - vertPosition);
	vec3 normal = texture(normalTexture, vertTexCoord).rgb;
	normal = normal * 2.0 - 1.0;
	normal = normalize(vertTBNMatrix * normal);
	vec3 litColor = applyPointLight(light0Position, light0Color, textureColor.rgb, normal, vertPosition, surfaceToCamera);
	litColor += applyPointLight(light1Position, light1Color, textureColor.rgb, normal, vertPosition, surfaceToCamera);
	litColor += applyDirectionalLight(light2Direction, light2Color, textureColor.rgb, normal, vertPosition, surfaceToCamera);
	litColor += ambientColor * textureColor.rgb;
	fragColor = vec4(emissiveColor * vec3(textureColor) + (vec3(1.0, 1.0, 1.0) - emissiveColor) * litColor, textureColor.a);
}