#version 300 es
precision highp float;

uniform float iTime;
uniform vec2  iResolution;
out vec4 fragColor;

float noise(vec2 p) {
    return fract(sin(dot(p, vec2(127.1, 311.7))) * 43758.5453123);
}

float smoothNoise(vec2 p) {
    vec2 i = floor(p);
    vec2 f = fract(p);
    float a = noise(i + vec2(0.0,0.0));
    float b = noise(i + vec2(1.0,0.0));
    float c = noise(i + vec2(0.0,1.0));
    float d = noise(i + vec2(1.0,1.0));
    vec2 u = f*f*(3.0-2.0*f);
    return mix(a, b, u.x) +
           (c - a)* u.y * (1.0 - u.x) +
           (d - b)* u.x *        u.y;
}

void main() {
    vec2 uv = gl_FragCoord.xy / iResolution.xy;
    uv = (uv - 0.5) * vec2(iResolution.x / iResolution.y, 1.0);
    uv *= 32.0;

    float time = iTime * 0.6; // faster light movement

    // Height map
    float h = smoothNoise(uv + vec2(0.0, time * 0.2));

    // Approximate normal
    float eps = 0.01;
    float hx = smoothNoise(uv + vec2(eps, 0.0) + vec2(0.0, time * 0.2));
    float hy = smoothNoise(uv + vec2(0.0, eps) + vec2(0.0, time * 0.2));
    vec3 n = normalize(vec3(h - hx, h - hy, eps));

    // Light and view directions
    vec3 lightDir = normalize(vec3(sin(time * 2.0) * 1.0, cos(time * 1.7) * 1.0, 1.5)); // faster swing
    vec3 viewDir = normalize(vec3(0.0, 0.0, 1.0)); // viewing from above

    // Diffuse lighting
    float diff = max(dot(n, lightDir), 0.0);

    // Specular (Blinn-Phong)
    vec3 halfDir = normalize(lightDir + viewDir);
    float spec = pow(max(dot(n, halfDir), 0.0), 50.0); // higher exponent = sharper highlight

    // Base color
    vec3 baseColor = mix(vec3(0.2, 0.2, 0.3), vec3(0.9, 0.85, 0.7), h);

    // Combine lighting
    vec3 color = baseColor * diff + vec3(1.0) * spec * 0.8;

    fragColor = vec4(color, 1.0);
}