#version 330

// Input from vertex shader
in vec3 fragPosition;
in vec3 fragNormal;
in vec2 fragTexCoord;

// Uniforms
uniform sampler2D texture0;
uniform vec3 viewPos;
uniform vec3 lightDir;
uniform vec3 lightColor;
uniform float lightIntensity;
uniform float ambientIntensity;
uniform vec3 terrainColor;

// Output
out vec4 finalColor;

// Simplex noise for AO calculation
float hash(float n) {
    return fract(sin(n) * 43758.5453123);
}

float noise(vec3 p) {
    vec3 i = floor(p);
    vec3 f = fract(p);
    f = f * f * (3.0 - 2.0 * f);
    
    float n = i.x + i.y * 157.0 + i.z * 113.0;
    return mix(
        mix(mix(hash(n), hash(n + 1.0), f.x),
            mix(hash(n + 157.0), hash(n + 158.0), f.x), f.y),
        mix(mix(hash(n + 113.0), hash(n + 114.0), f.x),
            mix(hash(n + 270.0), hash(n + 271.0), f.x), f.y),
        f.z
    );
}

// Calculate ambient occlusion with more contrast
float calculateAO(vec3 position, vec3 normal) {
    // Sample 8 directions around the surface
    float ao = 0.0;
    float radius = 2.5;
    int samples = 8;
    
    for (int i = 0; i < samples; i++) {
        float angle = 6.28318530718 * float(i) / float(samples);
        vec3 offset = vec3(cos(angle) * radius, noise(position * 0.5 + float(i)), sin(angle) * radius);
        
        // Sample height variation (approximated via noise)
        float heightVariation = noise((position + offset) * 0.3);
        
        // Calculate occlusion based on height and normal
        float dotProduct = max(0.0, dot(normal, normalize(offset)));
        ao += mix(0.0, dotProduct * heightVariation, 0.7);
    }
    
    // Increased contrast: 0.8 multiplier instead of 0.6
    ao = 1.0 - (ao / float(samples)) * 0.8;
    // Min 0.1 (darker shadows) instead of 0.2
    return max(0.1, ao);
}

void main()
{
    // Normalize interpolated normal
    vec3 norm = normalize(fragNormal);

    // Use normal Y component to create geometry-revealing green shading
    // Higher Y normal (upward-facing) = brighter green (peaks/flat areas)
    // Lower Y normal (sloped) = darker green (slopes/valleys)
    float brightness = (norm.y + 1.0) * 0.5;  // Map -1..1 to 0..1

    // Increase contrast: darker minimum, brighter maximum
    // Old range: 0.4 to 1.0 (0.6 total range)
    // New range: 0.2 to 1.2 (1.0 total range) - much more contrast
    float contrastMultiplier = 0.2 + brightness * 1.0;

    // Create base terrain color modulated by geometry
    vec3 baseColor = terrainColor;
    vec3 finalColorRGB = baseColor * contrastMultiplier;

    finalColor = vec4(finalColorRGB, 1.0);
}