#version 330 core

in vec3 pos;

out vec4 fragColor;

uniform sampler2DArray textureAtlas;
uniform float DayTime;
uniform vec4 sunTexture;
uniform float sunTextureLayer;
uniform vec4 moonTexture;
uniform float moonTextureLayer;

const vec4 DaySkyColor = vec4(0.49, 0.66, 1, 1);

const vec3 SunPos = vec3(0, 0.1, 0.5);

const vec3 MoonPos = vec3(0, 0.1, -0.5);

vec3 TransformTextureCoord(vec4 TextureAtlasCoords, vec2 UvCoords, float Layer) {
    float x = TextureAtlasCoords.x;
    float y = TextureAtlasCoords.y;
    float w = TextureAtlasCoords.z;
    float h = TextureAtlasCoords.w;
    vec2 A = vec2(x, 1 - y - h);
    vec2 B = vec2(x + w, 1 - y);
    vec2 transformed = A + UvCoords * (B - A);
    return vec3(transformed.x, transformed.y, Layer);
}

vec4 Sun() {
    vec3 sunDelta = (pos - SunPos) * 3.0f;
    float distanceToSun = length(sunDelta);
    vec4 sunColor = texture(textureAtlas, TransformTextureCoord(sunTexture, (vec2(sunDelta.xy) + 0.5f), sunTextureLayer));
    vec4 sun = mix(vec4(0, 0, 0, 1), sunColor, clamp(1 - distanceToSun * 2.0f, 0, 1));
    return sun;
}

vec4 Moon() {
    vec3 moonDelta = (pos - MoonPos) * 4.5f;
    float distanceToMoon = length(moonDelta);
    vec4 moonColor = texture(textureAtlas, TransformTextureCoord(moonTexture, (vec2(moonDelta.xy) + 0.5f), moonTextureLayer));
    vec4 moon = mix(vec4(0, 0, 0, 1),moonColor, clamp(1 - distanceToMoon * 2.0f, 0, 1));
    return moon;
}

void main() {
    vec4 starColor = vec4(0.0f, 0.04f, 0.06f, 1.0f);
    fragColor = mix(starColor, DaySkyColor, DayTime);
    fragColor += Sun();
    fragColor += Moon();
}