#version 460 core

layout(location = 0) out vec4 color;
in vec4 vColor;
in vec3 vNormal;
in vec3 vPosition;

void main() {
    vec3 lightDirection = normalize(vec3(0.8, -0.5, 0.6));
    // ambient component
    float ambientStrength = 0.1;
    vec3 ambient = ambientStrength * vColor.rgb;
    // terrain bump mapping with multi‐octave noise based on world position
    float bumpStrength = 0.4;
    float n1 = fract(sin(dot(vPosition.xz, vec2(12.9898, 78.233))) * 43758.5453);
    float n2 = fract(sin(dot(vPosition.xz * 0.5, vec2(93.9898, 67.345))) * 24634.6345);
    float noiseVal = mix(n1, n2, 0.5);
    vec3 bumpNormal = normalize(vNormal + bumpStrength * (noiseVal - 0.5) * vec3(1.0));
    // diffuse component (Lambert) with bump
    float lambert = max(0.0, dot(normalize(bumpNormal), -lightDirection));
    vec3 diffuse = vColor.rgb * lambert;
    // combine ambient and diffuse
    vec3 result = ambient + diffuse;
    // specular component (Phong)
    float shininess = 32.0;
    vec3 viewDir     = vec3(0.0, 0.0, 1.0);
    vec3 reflectDir  = reflect(-lightDirection, bumpNormal);
    float spec       = pow(max(dot(reflectDir, viewDir), 0.0), shininess);
    float specStrength = 0.5;
    vec3 specular    = specStrength * spec * vec3(1.0);
    result += specular;
    color = vec4(result, vColor.a);
}