#version 450

const int MAX_LIGHTS = 4;

struct Light {
    vec4 direction;
    vec4 color;
};

layout(location = 0) in vec2 fragUV;
layout(location = 1) in vec3 fragNormal;
layout(location = 2) in vec3 fragWorldPos;
layout(location = 3) in vec4 fragLightPos;

layout(location = 0) out vec4 outColor;

layout(set = 0, binding = 0) uniform UniformBufferObject {
    mat4 view;
    mat4 proj;
    mat4 lightSpace;
    vec4 ambientColor;
    Light lights[MAX_LIGHTS];
} ubo;

layout(set = 1, binding = 0) uniform sampler2D texSampler;

// 阴影深度图：手动对比（非 comparison sampler，逻辑清晰且免 format feature 依赖）
layout(set = 2, binding = 0) uniform sampler2D shadowMap;

// 主光（lights[0]）阴影因子：出光视锥外/未被遮挡 = 1.0
float ShadowFactor(vec3 N, vec3 L)
{
    vec3 proj = fragLightPos.xyz / fragLightPos.w;
    proj = proj * 0.5 + 0.5;   // NDC [-1,1] -> UV [0,1]

    if (proj.x < 0.0 || proj.x > 1.0 ||
        proj.y < 0.0 || proj.y > 1.0 ||
        proj.z > 1.0) {
        return 1.0;   // 光视锥外：不施加阴影（边界由 border color 兜底）
    }

    // 斜率缩放偏差，缓解 shadow acne
    float bias = max(0.004 * (1.0 - dot(N, L)), 0.0008);
    float closest = texture(shadowMap, proj.xy).r;

    return (proj.z - bias > closest) ? 0.25 : 1.0;
}

void main() {
    vec3 albedo = texture(texSampler, fragUV).rgb;
    vec3 N = normalize(fragNormal);

    vec3 result = ubo.ambientColor.rgb * albedo;

    for (int i = 0; i < MAX_LIGHTS; ++i) {
        vec3 L = normalize(-ubo.lights[i].direction.xyz);
        float diff = max(dot(N, L), 0.0);
        float shadow = (i == 0) ? ShadowFactor(N, L) : 1.0;
        result += ubo.lights[i].color.rgb * ubo.lights[i].color.a * diff * albedo * shadow;
    }

    outColor = vec4(result, 1.0);
}