#version 460 core

in vec3 FragPos;
in vec2 TexCoords;
in vec3 Normal;

out vec4 FragColor;

uniform vec3 cameraPos;
uniform vec3 lightPos;

// Material constants
const vec3 waterShallowColor = vec3(0.0, 0.6, 0.7);
const vec3 waterDeepColor    = vec3(0.05, 0.15, 0.3);
const vec3 sunColor          = vec3(1.0, 0.95, 0.8);

void main() {
    // Normalize vectors
    vec3 n = normalize(Normal);
    vec3 viewDir = normalize(cameraPos - FragPos);
    vec3 lightDir = normalize(lightPos - FragPos);

    // 1. Ambient Lighting
    vec3 ambient = 0.3 * waterShallowColor;

    // 2. Diffuse Shading
    float diff = max(dot(n, lightDir), 0.0);
    vec3 diffuse = diff * sunColor * 0.4;

    // 3. Specular Highlights (Blinn-Phong)
    vec3 halfwayDir = normalize(lightDir + viewDir);
    float spec = pow(max(dot(n, halfwayDir), 0.0), 64.0); // High shininess for water glaze
    vec3 specular = spec * sunColor * 0.8;

    // 4. Fresnel Approximation (Schlick's approximation)
    // Water has a base reflectivity of roughly 0.02 at a perpendicular view angle
    float F0 = 0.02;
    float fresnel = F0 + (1.0 - F0) * pow(1.0 - max(dot(n, viewDir), 0.0), 5.0);

    // Mix deep and shallow water colors based on the normal angle
    vec3 baseWaterColor = mix(waterShallowColor, waterDeepColor, max(dot(n, vec3(0.0, 1.0, 0.0)), 0.0));

    // Combine lighting results
    vec3 lightingResult = ambient + diffuse + specular;

    // Blend final look with Fresnel reflection dominance
    vec3 finalColor = mix(baseWaterColor + specular, lightingResult + vec3(fresnel * 0.5), fresnel);

    // Output final color with subtle translucency opacity
    FragColor = vec4(finalColor, 0.85);
}