#version 330 core
out vec4 FragColor;

in vec3 normal;
in vec2 texCoord;
in vec3 FragPos;
in vec4 fragposlightspace;

struct DirLight {
    vec3 direction;
    vec3 color;
    float intensity;
};

uniform DirLight dirLight;
uniform vec3 viewPos;

uniform sampler2DShadow shadowMap;
uniform sampler2D tex;
uniform samplerCube environmentMap;
uniform vec4 colorOverride = vec4(0.0);
uniform int useTexture = 0;
uniform float metallic = 0.0;
uniform float roughness = 0.7;
uniform float ao = 1.0;
uniform float envIntensity = 0.8;

const float PI = 3.14159265359;

float DistributionGGX(vec3 N, vec3 H, float rough)
{
    float a = rough * rough;
    float a2 = a * a;
    float NdotH = max(dot(N, H), 0.0);
    float NdotH2 = NdotH * NdotH;
    float denom = NdotH2 * (a2 - 1.0) + 1.0;
    return a2 / max(PI * denom * denom, 1e-5);
}

float GeometrySchlickGGX(float NdotV, float rough)
{
    float r = rough + 1.0;
    float k = (r * r) / 8.0;
    return NdotV / (NdotV * (1.0 - k) + k);
}

float GeometrySmith(vec3 N, vec3 V, vec3 L, float rough)
{
    float NdotV = max(dot(N, V), 0.0);
    float NdotL = max(dot(N, L), 0.0);
    return GeometrySchlickGGX(NdotV, rough) * GeometrySchlickGGX(NdotL, rough);
}

vec3 FresnelSchlick(float cosTheta, vec3 F0)
{
    return F0 + (1.0 - F0) * pow(clamp(1.0 - cosTheta, 0.0, 1.0), 5.0);
}

vec3 FresnelSchlickRoughness(float cosTheta, vec3 F0, float rough)
{
    vec3 f = max(vec3(1.0 - rough), F0);
    return F0 + (f - F0) * pow(clamp(1.0 - cosTheta, 0.0, 1.0), 5.0);
}

vec3 EnvironmentBRDF(vec3 F0, float rough, float NdotV)
{
    const vec4 c0 = vec4(-1.0, -0.0275, -0.572, 0.022);
    const vec4 c1 = vec4(1.0, 0.0425, 1.04, -0.04);
    vec4 r = rough * c0 + c1;
    float a004 = min(r.x * r.x, exp2(-9.28 * NdotV)) * r.x + r.y;
    vec2 AB = vec2(-1.04, 1.04) * a004 + r.zw;
    return F0 * AB.x + AB.y;
}

float ShadowCalculation(vec4 fragPosLightSpace, vec3 N, vec3 L)
{
    vec3 projCoords = fragPosLightSpace.xyz / fragPosLightSpace.w;
    projCoords = projCoords * 0.5 + 0.5;

    if (projCoords.z > 1.0 || any(lessThan(projCoords, vec3(0.0))) ||
        any(greaterThan(projCoords, vec3(1.0))))
        return 1.0;

    float bias = max(0.004 * (1.0 - dot(N, L)), 0.001);
    vec2 texelSize = 1.0 / vec2(textureSize(shadowMap, 0));
    float shadow = 0.0;

    for (int x = -1; x <= 1; x++) {
        for (int y = -1; y <= 1; y++) {
            vec2 offset = vec2(x, y) * texelSize;
            shadow += texture(shadowMap, vec3(projCoords.xy + offset, projCoords.z - bias));
        }
    }
    return shadow / 9.0;
}

void main()
{
    vec4 albedoSample = vec4(0.8, 0.8, 0.8, 1.0);
    if (useTexture != 0) {
        albedoSample = texture(tex, texCoord);
        if (albedoSample.a < 0.1)
            discard;
        albedoSample.rgb = pow(albedoSample.rgb, vec3(2.2));
    }

    albedoSample.rgb = mix(albedoSample.rgb, colorOverride.rgb, colorOverride.w);

    vec3 albedo = albedoSample.rgb;
    float metal = clamp(metallic, 0.0, 1.0);
    float rough = clamp(roughness, 0.04, 1.0);

    vec3 N = normalize(normal);
    vec3 V = normalize(viewPos - FragPos);
    vec3 L = normalize(-dirLight.direction);
    vec3 H = normalize(V + L);
    float NdotV = max(dot(N, V), 1e-4);
    float NdotL = max(dot(N, L), 0.0);

    vec3 F0 = mix(vec3(0.04), albedo, metal);
    vec3 F = FresnelSchlick(max(dot(H, V), 0.0), F0);
    float NDF = DistributionGGX(N, H, rough);
    float G = GeometrySmith(N, V, L, rough);
    vec3 specular = (NDF * G * F) / max(4.0 * NdotV * NdotL, 1e-4);
    vec3 kD = (vec3(1.0) - F) * (1.0 - metal);
    vec3 radiance = dirLight.color * dirLight.intensity;

    float shadow = ShadowCalculation(fragposlightspace, N, L);
    vec3 direct = (kD * albedo / PI + specular) * radiance * NdotL * shadow;

    vec3 ambientF = FresnelSchlickRoughness(NdotV, F0, rough);
    vec3 ambientKD = (vec3(1.0) - ambientF) * (1.0 - metal);
    vec3 irradiance = pow(textureLod(environmentMap, N, 7.0).rgb, vec3(2.2)) * envIntensity;
    vec3 R = reflect(-V, N);
    vec3 prefiltered = pow(textureLod(environmentMap, R, rough * 7.0).rgb, vec3(2.2)) * envIntensity;
    vec3 specularIBL = prefiltered * EnvironmentBRDF(F0, rough, NdotV);
    vec3 ambient = (ambientKD * irradiance * albedo + specularIBL) * ao;

    FragColor = vec4(direct + ambient, albedoSample.a);
}