#version 330 core

in  vec3 v_normal;
in  vec2 v_tex;
in  vec3 v_position;

out vec4 frag_color;

uniform vec3 u_light;      // direction TO the light (normalized)
uniform sampler2D tex;
uniform vec3 color;        // base colour factor (acts as solid colour when no texture)

void main() {
    // Combine base texture (or constant white) with colour factor supplied by CPU.
    vec3 base_col = texture(tex, v_tex).rgb * color;

    vec3 N = normalize(v_normal);
    vec3 L = normalize(u_light);

    // Classic Blinn-Phong lighting
    // Ambient: always present
    vec3 ambient = base_col * 0.15;

    // Diffuse: N dot L, clamped
    float NdotL = max(dot(N, L), 0.0);
    vec3 diffuse = base_col * NdotL * 0.7;

    // Specular: only on surfaces facing the light (NdotL > 0)
    float specular = 0.0;
    if (NdotL > 0.0) {
        vec3 V = normalize(-v_position);         // view direction (camera at origin in view space)
        vec3 H = normalize(L + V);               // half-vector
        float NdotH = max(dot(N, H), 0.0);
        specular = pow(NdotH, 32.0) * 0.5;       // tighter highlight, moderated intensity
    }

    vec3 result = ambient + diffuse + vec3(specular);

    // Convert from linear to sRGB for display (approximate gamma correction)
    result = pow(result, vec3(1.0 / 2.2));

    frag_color = vec4(result, 1.0);
}