#version 430 core
#extension GL_ARB_bindless_texture : require

in vec3 vNormal;
in vec2 vTexCoord;
in vec3 vWorldPos;
in flat uvec2 vTextureHandle;
in flat uint  vTextureLayer;

// uRenderPass values (Phase N.5 Decision 2 — two-pass alpha-test):
//   0 = opaque pass     — discard fragments with alpha < 0.95
//                         (lets the depth write succeed for solid pixels)
//   1 = translucent pass — covers AlphaBlend / Additive / InvAlpha;
//                         discard alpha >= 0.95 (already drawn opaque) and
//                         alpha < 0.05 (skip empty fragments — large
//                         transparent overdraw cost otherwise)
uniform int uRenderPass;

// SceneLighting UBO — IDENTICAL layout to mesh_instanced.frag binding=1.
struct Light {
    vec4 posAndKind;
    vec4 dirAndRange;
    vec4 colorAndIntensity;
    vec4 coneAngleEtc;
};
layout(std140, binding = 1) uniform SceneLighting {
    Light uLights[8];
    vec4  uCellAmbient;
    vec4  uFogParams;
    vec4  uFogColor;
    vec4  uCameraAndTime;
};

vec3 accumulateLights(vec3 N, vec3 worldPos) {
    vec3 lit = uCellAmbient.xyz;
    int activeLights = int(uCellAmbient.w);
    for (int i = 0; i < 8; ++i) {
        if (i >= activeLights) break;
        int kind = int(uLights[i].posAndKind.w);
        vec3 Lcol = uLights[i].colorAndIntensity.xyz * uLights[i].colorAndIntensity.w;
        if (kind == 0) {
            vec3 Ldir = -uLights[i].dirAndRange.xyz;
            float ndl = max(0.0, dot(N, Ldir));
            lit += Lcol * ndl;
        } else {
            vec3 toL = uLights[i].posAndKind.xyz - worldPos;
            float d  = length(toL);
            float range = uLights[i].dirAndRange.w;
            if (d < range && range > 1e-3) {
                vec3 Ldir = toL / max(d, 1e-4);
                float ndl = max(0.0, dot(N, Ldir));
                float atten = 1.0;
                if (kind == 2) {
                    float cos_edge = cos(uLights[i].coneAngleEtc.x * 0.5);
                    float cos_l    = dot(-Ldir, uLights[i].dirAndRange.xyz);
                    atten *= (cos_l > cos_edge) ? 1.0 : 0.0;
                }
                lit += Lcol * ndl * atten;
            }
        }
    }
    return lit;
}

vec3 applyFog(vec3 lit, vec3 worldPos) {
    int mode = int(uFogParams.w);
    if (mode == 0) return lit;
    float d = length(worldPos - uCameraAndTime.xyz);
    float fogStart = uFogParams.x;
    float fogEnd   = uFogParams.y;
    float span = max(1e-3, fogEnd - fogStart);
    float fog = clamp((d - fogStart) / span, 0.0, 1.0);
    return mix(lit, uFogColor.xyz, fog);
}

out vec4 FragColor;

void main() {
    sampler2DArray tex = sampler2DArray(vTextureHandle);
    vec4 color = texture(tex, vec3(vTexCoord, float(vTextureLayer)));

    // Two-pass alpha-test (N.5 Decision 2).
    // A.5 T20: opaque pass writes alpha as-sampled so GL_SAMPLE_ALPHA_TO_COVERAGE
    // derives the MSAA sample mask from it — ClipMap foliage edges become smooth.
    // Discard only fully-transparent (α < 0.05); the GPU handles coverage masking.
    if (uRenderPass == 0) {
        if (color.a < 0.05) discard;        // opaque pass — kill truly empty only (A2C)
    } else {
        // Transparent pass.
        //
        // Phase Post-A.5 (ISSUE #52, 2026-05-10): do NOT discard α≥0.95 here.
        // Native AC transparent-flagged surfaces routinely include
        // effectively-opaque pixels — e.g. the Holtburg lifestone crystal core
        // (surface 0x080011DE) which the spawn manifest classifies as
        // transparent (batch.IsTransparent=True) but whose decoded texture
        // alpha lands ≥0.95 across the visible surface. Those pixels still
        // compose correctly under (SrcAlpha, 1-SrcAlpha) alpha-blending, so
        // discarding them here threw away the whole crystal. The original
        // N.5 §2 rationale (high-α fragments belong in the opaque pass) does
        // not apply when the SURFACE is dat-flagged transparent — those
        // pixels can't reach the opaque pass at all.
        //
        // Keep the α<0.05 short-circuit as a fragment-cost optimization
        // (skip fully-empty pixels — saves blend bandwidth on alpha-keyed
        // sprites with large transparent margins).
        if (color.a < 0.05) discard;
    }

    vec3 N = normalize(vNormal);
    vec3 lit = accumulateLights(N, vWorldPos);

    // Lightning flash — additive scene bump (matches mesh_instanced.frag).
    lit += uFogParams.z * vec3(0.6, 0.6, 0.75);

    // Retail clamp per-channel to 1.0 (r13 §13.1).
    lit = min(lit, vec3(1.0));

    vec3 rgb = color.rgb * lit;
    rgb = applyFog(rgb, vWorldPos);
    FragColor = vec4(rgb, color.a);
}