import * as THREE from 'three';

/**
 * END OF SHIFT: first light. A fixed low sun straight down the road throws a
 * warm rim on the terrain, the district facades and the asphalt as the dawn
 * rises. Shared uniform (one set for every generation), like the headlight
 * beam: the environment writes one float per frame, and 0 skips the term.
 */
export const dawnLightUniforms = {
  uDawnLight: { value: 0 },
};

/** Toward the sun: low over the horizon, down the road (-z). */
const SUN_DIRECTION = new THREE.Vector3(0, 0.2, -1).normalize();

/** GLSL: dawnRim(normal, toCamera) -> warm light to add (0 when uDawnLight is 0). */
export const DAWN_PARS = /* glsl */ `
  uniform float uDawnLight;
  vec3 dawnRim(vec3 n, vec3 toCamera) {
    if (uDawnLight <= 0.0) return vec3(0.0);
    vec3 sunDir = vec3(${SUN_DIRECTION.x.toFixed(4)}, ${SUN_DIRECTION.y.toFixed(4)}, ${SUN_DIRECTION.z.toFixed(4)});
    float facing = abs(dot(n, sunDir));
    float rim = pow(1.0 - abs(dot(n, toCamera)), 2.0);
    float against = max(0.0, dot(-toCamera, sunDir));
    return vec3(1.0, 0.6, 0.36) * uDawnLight * (facing * 0.09 + rim * against * 0.24);
  }
`;