#version 330 core

// Fragment shader for basic lighting with texture mapping

out vec4 outputColor; // The final output color of the fragment

// --- INPUTS ---
// These come from the Vertex Shader
in vec3 FragPos;
in vec3 Normal;
in vec2 TexCoord;

struct MaterialProperty {
    vec3 ambientColour;
    vec3 diffuseColour;
    vec3 specularColour;
    float shininess;
};

struct LightProperty {
    vec3 position;
    vec3 ambientColour;
    vec3 diffuseColour;
    vec3 specularColour;
};

// --- UNIFORMS ---
uniform sampler2D uTexture; // Image Texture
uniform vec3 uViewPos; // Camera Position
uniform MaterialProperty uMaterial; // Material Properties
uniform LightProperty uPointLight; // Light Properties


void main()
{
    // --- LIGHTING CALCULATIONS ---
    // Lighting Setup (hardcoded for simplicity)
    vec3 lightPos = vec3(1.2f, 1.0f, 2.0f);
    vec3 lightColor = vec3(1.0f, 1.0f, 1.0f);

    // 1. Get Texture Color
    // Sample the texture at the given texture coordinates
    vec4 objColor = texture(uTexture, TexCoord);

    // 2. Ambient strength
    // A constant, dim light that ensure s object are not completely dark
    // It simply multiplies the light color by a small factor
    float ambientStrength = 0.1f;
    vec3 ambient = uMaterial.ambientColour * uPointLight.ambientColour;

    // 3. Diffuse
    // Creates the "matte" effect by calculating the angle between the light direction and the surface normal
    
    // Normalize the normal vector and calculate the light direction
    vec3 norm = normalize(Normal);
    vec3 lightDir = normalize(uPointLight.position - FragPos);
    
    // The dot product gives us the cosine of the angle between the two vectors
    // The max function ensures we don't get negative values (light coming from behind the surface)
    float diff = max(dot(norm, lightDir), 0.0f);
    vec3 diffuse = (uPointLight.diffuseColour * diff) * uMaterial.diffuseColour;

    // 4. Specular
    // Creates the shiny highlights on the surface
    float shininess = 32.0f;
    // Calculate the view direction and the reflection direction
    vec3 viewDirection = normalize(uViewPos - FragPos);
    // If the light is coming from the light direction, we need to negate it for reflection
    vec3 reflectDirection = reflect(-lightDir, normalize(Normal));
    
    // Calculate the specular component using the dot product and shininess factor
    float spec = pow(max(dot(viewDirection, reflectDirection), 0.0f), shininess);
    vec3 specular = uMaterial.specularColour * spec * uPointLight.specularColour;

    // 5. Combine
    // We multiply (Ambient + Diffuse) by the Texture Color.
    // We ADD Specular afterwards so the highlights look bright white (like plastic/metal).
    vec3 result = (ambient + diffuse) * objColor.rgb + specular;

    outputColor = vec4(result, objColor.a);
}