#version 450

layout(set = 0, binding = 0) uniform PerFrame {
    mat4 view;
    mat4 projection;
    mat4 lightSpaceMatrix;
    vec4 lightDir;
    vec4 lightColor;
    vec4 ambientColor;
    vec4 viewPos;
    vec4 fogColor;
    vec4 fogParams;
    vec4 shadowParams;
};

layout(set = 1, binding = 0) uniform sampler2D uBaseTexture;
layout(set = 1, binding = 1) uniform sampler2D uLayer1Texture;
layout(set = 1, binding = 2) uniform sampler2D uLayer2Texture;
layout(set = 1, binding = 3) uniform sampler2D uLayer3Texture;
layout(set = 1, binding = 4) uniform sampler2D uLayer1Alpha;
layout(set = 1, binding = 5) uniform sampler2D uLayer2Alpha;
layout(set = 1, binding = 6) uniform sampler2D uLayer3Alpha;

layout(set = 1, binding = 7) uniform TerrainParams {
    int layerCount;
    int hasLayer1;
    int hasLayer2;
    int hasLayer3;
};

layout(set = 0, binding = 1) uniform sampler2DShadow uShadowMap;

layout(location = 0) in vec3 FragPos;
layout(location = 1) in vec3 Normal;
layout(location = 2) in vec2 TexCoord;
layout(location = 3) in vec2 LayerUV;

layout(location = 0) out vec4 outColor;

const float SHADOW_TEXEL = 1.0 / 4096.0;

float sampleShadowPCF(sampler2DShadow smap, vec3 coords) {
    float shadow = 0.0;
    for (int x = -1; x <= 1; ++x) {
        for (int y = -1; y <= 1; ++y) {
            shadow += texture(smap, vec3(coords.xy + vec2(x, y) * SHADOW_TEXEL, coords.z));
        }
    }
    return shadow / 9.0;
}

float sampleAlpha(sampler2D tex, vec2 uv) {
    vec2 edge = min(uv, 1.0 - uv);
    float border = min(edge.x, edge.y);
    float doBlur = step(border, 2.0 / 64.0);
    if (doBlur < 0.5) {
        return texture(tex, uv).r;
    }
    vec2 texel = vec2(1.0 / 64.0);
    float a = 0.0;
    a += texture(tex, uv + vec2(-texel.x, 0.0)).r;
    a += texture(tex, uv + vec2(texel.x, 0.0)).r;
    a += texture(tex, uv + vec2(0.0, -texel.y)).r;
    a += texture(tex, uv + vec2(0.0, texel.y)).r;
    return a * 0.25;
}

void main() {
    vec4 baseColor = texture(uBaseTexture, TexCoord);

    // WoW terrain: layers are blended sequentially, each on top of the previous result.
    // Alpha=1 means the layer fully covers everything below; alpha=0 means invisible.
    vec4 finalColor = baseColor;
    if (hasLayer1 != 0) {
        float a1 = sampleAlpha(uLayer1Alpha, LayerUV);
        finalColor = mix(finalColor, texture(uLayer1Texture, TexCoord), a1);
    }
    if (hasLayer2 != 0) {
        float a2 = sampleAlpha(uLayer2Alpha, LayerUV);
        finalColor = mix(finalColor, texture(uLayer2Texture, TexCoord), a2);
    }
    if (hasLayer3 != 0) {
        float a3 = sampleAlpha(uLayer3Alpha, LayerUV);
        finalColor = mix(finalColor, texture(uLayer3Texture, TexCoord), a3);
    }

    vec3 norm = normalize(Normal);

    // Derivative-based normal mapping: perturb vertex normal using texture detail.
    // Fade out with distance — looks noisy/harsh beyond ~100 units.
    float fragDist = length(viewPos.xyz - FragPos);
    float bumpFade = 1.0 - smoothstep(50.0, 125.0, fragDist);
    if (bumpFade > 0.001) {
        float lum = dot(finalColor.rgb, vec3(0.299, 0.587, 0.114));
        float dLdx = dFdx(lum);
        float dLdy = dFdy(lum);
        vec3 dpdx = dFdx(FragPos);
        vec3 dpdy = dFdy(FragPos);
        float bumpStrength = 9.0 * bumpFade;
        vec3 perturbation = (dLdx * cross(norm, dpdy) + dLdy * cross(dpdx, norm)) * bumpStrength;
        vec3 candidate = norm - perturbation;
        float len2 = dot(candidate, candidate);
        norm = (len2 > 1e-8) ? candidate * inversesqrt(len2) : norm;
    }

    vec3 lightDir2 = normalize(-lightDir.xyz);
    vec3 ambient = ambientColor.rgb * finalColor.rgb;
    float diff = max(abs(dot(norm, lightDir2)), 0.2);
    vec3 diffuse = diff * lightColor.rgb * finalColor.rgb;

    float shadow = 1.0;
    if (shadowParams.x > 0.5) {
        vec3 ldir = normalize(-lightDir.xyz);
        float normalOffset = SHADOW_TEXEL * 2.0 * (1.0 - abs(dot(norm, ldir)));
        vec3 biasedPos = FragPos + norm * normalOffset;
        vec4 lsPos = lightSpaceMatrix * vec4(biasedPos, 1.0);
        vec3 proj = lsPos.xyz / lsPos.w;
        proj.xy = proj.xy * 0.5 + 0.5;
        if (proj.x >= 0.0 && proj.x <= 1.0 && proj.y >= 0.0 && proj.y <= 1.0 && proj.z <= 1.0) {
            float bias = 0.0002;
            shadow = sampleShadowPCF(uShadowMap, vec3(proj.xy, proj.z - bias));
            shadow = mix(1.0, shadow, shadowParams.y);
        }
    }

    vec3 result = ambient + shadow * diffuse;

    float fogFactor = clamp((fogParams.y - fragDist) / (fogParams.y - fogParams.x), 0.0, 1.0);
    result = mix(fogColor.rgb, result, fogFactor);

    outColor = vec4(result, 1.0);
}