#version 430 core
layout(location = 0) in vec3  aPos;
layout(location = 1) in vec3  aNormal;
layout(location = 2) in uvec4 aPacked0;  // bytes: baseTex, baseAlpha(255), ovl0Tex, ovl0Alpha
layout(location = 3) in uvec4 aPacked1;  // bytes: ovl1Tex, ovl1Alpha, ovl2Tex, ovl2Alpha
layout(location = 4) in uvec4 aPacked2;  // bytes: road0Tex, road0Alpha, road1Tex, road1Alpha
layout(location = 5) in uvec4 aPacked3;  // bits: rot fields + splitDir (see below)

uniform mat4 uView;
uniform mat4 uProjection;

// Phase G.1+G.2: sky/scene UBO. Terrain reads uLights[0] for the sun
// (slot 0 is reserved) plus uCellAmbient for outdoor ambient; the fog
// fields are consumed by the fragment stage.
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;
};

out vec2  vBaseUV;
out vec3  vWorldNormal;
out vec3  vWorldPos;
out vec3  vLightingRGB;  // pre-computed sun+ambient contribution for retail-style AdjustPlanes bake
// Per-layer "UV.xy in cell-local 0..1 space, tex index .z, alpha index .w".
// Negative .z means "layer not present, skip it in the fragment shader."
out vec4  vOverlay0;
out vec4  vOverlay1;
out vec4  vOverlay2;
out vec4  vRoad0;
out vec4  vRoad1;
flat out float vBaseTexIdx;

// Retail's "ambient floor" constant from the decompiled AdjustPlanes
// path (r13 §7, DAT_00796344). Even a back-lit vertex sees at least
// this fraction of the sun color — NOT additive with ambient.
const float MIN_FACTOR = 0.08;

// Port of WorldBuilder's Landscape.vert unpackOverlayLayer: sentinel-check
// 255 → -1 (shader skips), then rotate the cell-local UV by the overlay's
// 90° rotation count.
vec4 unpackOverlayLayer(uint texIdxU, uint alphaIdxU, uint rotIdx, vec2 baseUV) {
    float texIdx   = float(texIdxU);
    float alphaIdx = float(alphaIdxU);
    if (texIdx   >= 254.0) texIdx   = -1.0;
    if (alphaIdx >= 254.0) alphaIdx = -1.0;

    vec2 rotatedUV = baseUV;
    if      (rotIdx == 1u) rotatedUV = vec2(1.0 - baseUV.y,       baseUV.x);
    else if (rotIdx == 2u) rotatedUV = vec2(1.0 - baseUV.x, 1.0 - baseUV.y);
    else if (rotIdx == 3u) rotatedUV = vec2(      baseUV.y, 1.0 - baseUV.x);

    return vec4(rotatedUV.x, rotatedUV.y, texIdx, alphaIdx);
}

void main() {
    // Unpack rotation fields from aPacked3. Bit layout (data3):
    //   .x  (byte 0): bits 0-1 rotBase (unused), 2-3 rotOvl0, 4-5 rotOvl1, 6-7 rotOvl2
    //   .y  (byte 1): bits 0-1 rotRd0 (= data3 bit 8-9),
    //                 bits 2-3 rotRd1 (= data3 bit 10-11),
    //                 bit  4   splitDir (= data3 bit 12)
    uint rotOvl0 = (aPacked3.x >> 2u) & 3u;
    uint rotOvl1 = (aPacked3.x >> 4u) & 3u;
    uint rotOvl2 = (aPacked3.x >> 6u) & 3u;
    uint rotRd0  =  aPacked3.y        & 3u;
    uint rotRd1  = (aPacked3.y >> 2u) & 3u;
    uint splitDir= (aPacked3.y >> 4u) & 1u;

    // Derive which of the 4 cell corners this vertex represents from
    // gl_VertexID % 6. The CPU-side LandblockMesh emits vertices in a
    // specific order for each split direction; the tables below must stay
    // in lockstep with LandblockMesh.Build's SWtoNE/SEtoNW branches.
    // 2026-04-21 fix: geometry re-derived to match ACE's ConstructPolygons
    // convention. SWtoNE (cut BL→TR, y=x diagonal) now maps to the {BL,BR,TR}
    // + {BL,TR,TL} triangle pair; SEtoNW (cut BR→TL, x+y=1 diagonal) maps to
    // {BL,BR,TL} + {BR,TR,TL}.
    int vIdx = gl_VertexID % 6;
    int corner = 0;
    if (splitDir == 0u) {
        // SWtoNE order: BL, BR, TR, BL, TR, TL  → corners 0, 1, 2, 0, 2, 3
        if      (vIdx == 0) corner = 0;
        else if (vIdx == 1) corner = 1;
        else if (vIdx == 2) corner = 2;
        else if (vIdx == 3) corner = 0;
        else if (vIdx == 4) corner = 2;
        else                corner = 3;
    } else {
        // SEtoNW order: BL, BR, TL, BR, TR, TL  → corners 0, 1, 3, 1, 2, 3
        if      (vIdx == 0) corner = 0;
        else if (vIdx == 1) corner = 1;
        else if (vIdx == 2) corner = 3;
        else if (vIdx == 3) corner = 1;
        else if (vIdx == 4) corner = 2;
        else                corner = 3;
    }

    vec2 baseUV;
    if      (corner == 0) baseUV = vec2(0.0, 1.0);
    else if (corner == 1) baseUV = vec2(1.0, 1.0);
    else if (corner == 2) baseUV = vec2(1.0, 0.0);
    else                  baseUV = vec2(0.0, 0.0);

    vBaseUV = baseUV;
    vWorldPos = aPos;
    vWorldNormal = normalize(aNormal);

    // Retail AdjustPlanes bake (r13 §7):
    //   L = max(N · -sunDir, MIN_FACTOR)
    //   vertex.color = sun_color * L + ambient_color
    //
    // Slot 0 of the UBO is the sun (directional). We read its forward
    // vector and pre-multiplied color, apply the ambient floor, layer
    // in the scene ambient separately.
    vec3 sunDir  = uLights[0].dirAndRange.xyz;
    vec3 sunCol  = uLights[0].colorAndIntensity.xyz * uLights[0].colorAndIntensity.w;
    float L = max(dot(vWorldNormal, -sunDir), MIN_FACTOR);
    vLightingRGB = sunCol * L + uCellAmbient.xyz;

    float baseTex = float(aPacked0.x);
    if (baseTex >= 254.0) baseTex = -1.0;
    vBaseTexIdx = baseTex;

    vOverlay0 = unpackOverlayLayer(aPacked0.z, aPacked0.w, rotOvl0, baseUV);
    vOverlay1 = unpackOverlayLayer(aPacked1.x, aPacked1.y, rotOvl1, baseUV);
    vOverlay2 = unpackOverlayLayer(aPacked1.z, aPacked1.w, rotOvl2, baseUV);
    vRoad0    = unpackOverlayLayer(aPacked2.x, aPacked2.y, rotRd0,  baseUV);
    vRoad1    = unpackOverlayLayer(aPacked2.z, aPacked2.w, rotRd1,  baseUV);

    gl_Position = uProjection * uView * vec4(aPos, 1.0);
}