#version 330 core
out vec4 FragColor;

in vec3 FragPos;
in vec3 Normal;
in vec2 TexCoords;
in vec4 FragPosLightSpace;

uniform vec3 lightPos;
uniform vec3 viewPos;
uniform sampler2D shadowMap;
uniform sampler2D texture_diffuse1;
uniform sampler2D texture_specular1;

float ShadowCalculation(vec4 fragPosLightSpace, float bias)
{
    // perform perspective divide
    vec3 projCoords = fragPosLightSpace.xyz / fragPosLightSpace.w;

    // transform to [0,1] range
    projCoords = projCoords * 0.5 + 0.5;

    // avoid the frustrum
    if(projCoords.z > 1.0) return 0.0;

    // get closest depth value from light's perspective (using [0,1] range fragPosLight as coords)
    float closestDepth = texture(shadowMap, projCoords.xy).r;

    // get depth of current fragment from light's perspective
    float currentDepth = projCoords.z;

    // check whether current frag pos is in shadow
    // PCF
    float shadow = 0.0;
    vec2 texelSize = 1.0 / textureSize(shadowMap, 0);
    for(int x = -1; x <= 1; ++x) {
      for(int y = -1; y <= 1; ++y) {
        float pcfDepth = texture(shadowMap, projCoords.xy + vec2(x, y) * texelSize).r;
        shadow += currentDepth - bias > pcfDepth  ? 1.0 : 0.0;
      }
    }

    return shadow / 9.0;
}

void main()
{
  vec3 color = texture(texture_diffuse1, TexCoords).rgb;
  vec3 normal = normalize(Normal);
  vec3 lightColor = vec3(0.7);
  // ambient
  vec3 ambient = 0.3 * lightColor;
  // diffuse
  vec3 lightDir = normalize(lightPos - FragPos);
  float diff = max(dot(lightDir, normal), 0.0);
  vec3 diffuse = diff * lightColor;
  // specular
  vec3 viewDir = normalize(viewPos - FragPos);
  vec3 reflectDir = reflect(-lightDir, normal);
  float spec = 0.0;
  vec3 halfwayDir = normalize(lightDir + viewDir);
  spec = pow(max(dot(normal, halfwayDir), 0.0), 64.0);
  vec3 specular = spec * lightColor;
  // calculate shadow

  float bias = max(0.05 * (1.0 - dot(normal, lightDir)), 0.005);
  float shadow = ShadowCalculation(FragPosLightSpace, bias);

  vec3 lighting = (ambient + (1.0 - shadow) * (diffuse + specular)) * color;

  FragColor = vec4(lighting, 1.0);
}