// PROCITY Lane B — wind.js  (round 17, v3.2 — "wind sway ships or dies")
// Weather-driven vertex-shader sway for street foliage. Parked since R7 with the note "touches shared
// materials"; the R16 standard is measurement-over-brief, and the measurement here is: the gum-tree
// material is B-owned street geometry (furniture.js), so this is ENTIRELY Lane B — no C/E material seam.
//
// ONE shared uniform set, referenced by the tree material via applyWind(). Amplitude stays 0 until the
// weather system drives it (updateWind, called from weather.update). With weather OFF — ?weather=0, or
// ?classic=1 where weather is never constructed — updateWind never runs, uWindAmp stays 0, the injected
// displacement is exactly `... * 0.0 == 0.0`, and trees render byte-identical to no-sway (verified). So
// the classic covenant and ?weather=0 both hold by construction.
//
// SCOPE (measured, per R16 discipline): gum-tree BILLBOARDS only. Awnings are rigid posted-verandah box
// slabs (buildings.js) — a structural verandah roof does not flutter, so swaying it would read wrong; it
// is intentionally excluded (not a cross-lane blocker — a physical one). Fabric-canopy flutter, if ever
// wanted, is a separate v3.3 item (the striped canopies share the rigid awning InstancedMesh today).
//
// Cost: ~0 draws — a handful of ALU ops added to the tree InstancedMesh's existing vertex program.

export const windUniforms = {
  uWindTime: { value: 0 },
  uWindAmp: { value: 0 },   // 0 = dead calm ⇒ zero displacement ⇒ byte-identical (weather off / classic)
};

// Patch a material's vertex program: sway top vertices horizontally (top-weighted, base planted). A
// per-instance phase from world position desyncs neighbouring trees. Guarded for instanced use so the
// same material would still compile if ever drawn non-instanced.
export function applyWind(material, { topY = 4.4 } = {}) {
  material.onBeforeCompile = (shader) => {
    shader.uniforms.uWindTime = windUniforms.uWindTime;
    shader.uniforms.uWindAmp = windUniforms.uWindAmp;
    shader.vertexShader = 'uniform float uWindTime;\nuniform float uWindAmp;\n' + shader.vertexShader;
    shader.vertexShader = shader.vertexShader.replace(
      '#include <begin_vertex>',
      [
        '#include <begin_vertex>',
        'float wPhase = position.x * 0.1 + position.z * 0.1;',
        '#ifdef USE_INSTANCING',
        '  wPhase = instanceMatrix[3].x * 0.15 + instanceMatrix[3].z * 0.15;',
        '#endif',
        `float wH = clamp(position.y / ${topY.toFixed(1)}, 0.0, 1.0); wH *= wH;`,   // top-weighted, base planted
        'float wS = sin(uWindTime + wPhase) + 0.4 * sin(uWindTime * 2.3 + wPhase * 1.7);',
        'transformed.x += wS * uWindAmp * wH;',
        'transformed.z += cos(uWindTime * 0.8 + wPhase) * uWindAmp * wH * 0.5;',
      ].join('\n')
    );
  };
  material.needsUpdate = true;
}

// Drive from weather.update(dt): base breeze on any weather-on boot (clear included), gusts scaling with
// rain intensity. NEVER called when weather is absent ⇒ uWindAmp stays 0 (byte-identical, see header).
export function updateWind(dt, intensity = 0) {
  windUniforms.uWindTime.value += dt * 1.6;
  windUniforms.uWindAmp.value = 0.05 + Math.max(0, intensity) * 0.30;   // calm ~0.05 m top sway → gusty ~0.35 m
}