/**
 * CPU-side UV mapping — exact JavaScript mirror of the GLSL in previewMaterial.js.
 * All functions take Three.js Vector3 objects for position/normal and
 * a bounds object { min, max, center, size } (all THREE.Vector3).
 */

export const MODE_PLANAR_XY   = 0;
export const MODE_PLANAR_XZ   = 1;
export const MODE_PLANAR_YZ   = 2;
export const MODE_CYLINDRICAL = 3;
export const MODE_SPHERICAL   = 4;
export const MODE_TRIPLANAR   = 5;
export const MODE_CUBIC       = 6;

const TWO_PI = Math.PI * 2;
const CUBIC_AXIS_EPSILON = 1e-4;

export function getDominantCubicAxis(normal) {
  const ax = Math.abs(normal.x);
  const ay = Math.abs(normal.y);
  const az = Math.abs(normal.z);

  // Treat near-ties as an intentional tie so 45° faces pick one stable axis
  // instead of flipping projection due to tiny normal jitter between triangles.
  if (ax >= ay - CUBIC_AXIS_EPSILON && ax >= az - CUBIC_AXIS_EPSILON) return 'x';
  if (ay >= az - CUBIC_AXIS_EPSILON) return 'y';
  return 'z';
}

export function isAmbiguousCubicNormal(normal) {
  const ax = Math.abs(normal.x);
  const ay = Math.abs(normal.y);
  const az = Math.abs(normal.z);
  const axis = getDominantCubicAxis(normal);
  const primary = axis === 'x' ? ax : axis === 'y' ? ay : az;
  const secondary = axis === 'x' ? Math.max(ay, az) : axis === 'y' ? Math.max(ax, az) : Math.max(ax, ay);
  return primary - secondary <= CUBIC_AXIS_EPSILON;
}

export function getCubicBlendWeights(normal, blend, seamBandWidth = 0.35) {
  const axis = getDominantCubicAxis(normal);
  const ax = Math.abs(normal.x);
  const ay = Math.abs(normal.y);
  const az = Math.abs(normal.z);
  const primary = axis === 'x' ? ax : axis === 'y' ? ay : az;
  const secondary = axis === 'x' ? Math.max(ay, az) : axis === 'y' ? Math.max(ax, az) : Math.max(ax, ay);

  if (blend <= 0.001 || isAmbiguousCubicNormal(normal)) {
    return {
      x: axis === 'x' ? 1 : 0,
      y: axis === 'y' ? 1 : 0,
      z: axis === 'z' ? 1 : 0,
    };
  }

  const oneHot = {
    x: axis === 'x' ? 1 : 0,
    y: axis === 'y' ? 1 : 0,
    z: axis === 'z' ? 1 : 0,
  };

  // Only blend inside a seam band around the cube-face boundary. This keeps
  // strongly dominant faces fully textured even when the slider is barely on.
  const seamWidth = Math.max(seamBandWidth, CUBIC_AXIS_EPSILON * 2);
  const seamMixRaw = 1 - Math.min(1, Math.max(0, (primary - secondary) / seamWidth));
  const seamMix = blend * seamMixRaw * seamMixRaw * (3 - 2 * seamMixRaw);
  if (seamMix <= 0.001) return oneHot;

  // blend=1 should produce a genuinely soft triplanar-style transition.
  // Lower blend values progressively sharpen the weights back toward a single
  // dominant axis without snapping until the slider reaches zero.
  const power = 1 + (1 - seamMix) * 11;
  const sx = Math.pow(ax, power);
  const sy = Math.pow(ay, power);
  const sz = Math.pow(az, power);
  const smoothSum = sx + sy + sz + 1e-6;
  const smooth = {
    x: sx / smoothSum,
    y: sy / smoothSum,
    z: sz / smoothSum,
  };

  const mx = oneHot.x * (1 - seamMix) + smooth.x * seamMix;
  const my = oneHot.y * (1 - seamMix) + smooth.y * seamMix;
  const mz = oneHot.z * (1 - seamMix) + smooth.z * seamMix;
  const sum = mx + my + mz;

  return {
    x: mx / sum,
    y: my / sum,
    z: mz / sum,
  };
}

/**
 * Compute normalised UV coordinates [0, 1) (tiling) for a vertex.
 *
 * @param {{ x:number, y:number, z:number }} pos      vertex position
 * @param {{ x:number, y:number, z:number }} normal   vertex normal (unit)
 * @param {number}  mode    one of the MODE_* constants
 * @param {{ scaleU:number, scaleV:number, offsetU:number, offsetV:number }} settings
 * @param {{ min, max, center, size }} bounds           THREE.Vector3 fields
 * @returns {{ u:number, v:number }}                    tiled UV after scale+offset
 */
export function computeUV(pos, normal, mode, settings, bounds) {
  const { min, size, center } = bounds;
  const { scaleU, scaleV, offsetU, offsetV } = settings;
  const rotRad = (settings.rotation ?? 0) * Math.PI / 180;
  const maxDim = Math.max(size.x, size.y, size.z);
  const md     = Math.max(maxDim, 1e-6);

  let u = 0, v = 0;

  switch (mode) {

    case MODE_PLANAR_XY: {
      u = (pos.x - min.x) / md;
      v = (pos.y - min.y) / md;
      break;
    }

    case MODE_PLANAR_XZ: {
      u = (pos.x - min.x) / md;
      v = (pos.z - min.z) / md;
      break;
    }

    case MODE_PLANAR_YZ: {
      u = (pos.y - min.y) / md;
      v = (pos.z - min.z) / md;
      break;
    }

    case MODE_CYLINDRICAL: {
      // mappingBlend=0 → pure side projection for all faces (original behaviour, no cap seam).
      // mappingBlend>0 → smooth side↔cap blend.
      const r  = Math.max(size.x, size.y) * 0.5;
      const C  = TWO_PI * Math.max(r, 1e-6);
      const rx = pos.x - center.x;
      const ry = pos.y - center.y;
      const blend = settings.mappingBlend ?? 0.0;
      const theta = Math.atan2(ry, rx);
      const uRaw = (theta / TWO_PI) + 0.5;
      const vSide = (pos.z - min.z) / C;

      // Seam smoothing: cross-fade between left-side and right-side texture
      // continuations at the atan2 wrap. Both sides use smoothly varying UVs
      // (shifted by ±1.0 in raw space), preserving full texture detail.
      const seamBand = (settings.seamBandWidth ?? 0.5) * 0.1;
      const seamDist = Math.min(uRaw, 1.0 - uRaw);
      const inSeamZone = seamBand > 0.001 && seamDist < seamBand;

      let sideSamples;
      if (inSeamZone) {
        const d = uRaw < 0.5 ? uRaw : uRaw - 1.0;
        const tRaw = (d + seamBand) / (2.0 * seamBand);
        const t = tRaw * tRaw * (3 - 2 * tRaw); // smoothstep
        const tLeft  = applyTransform(1.0 + d, vSide, scaleU, scaleV, offsetU, offsetV, rotRad);
        const tRight = applyTransform(d,       vSide, scaleU, scaleV, offsetU, offsetV, rotRad);
        sideSamples = [
          { u: tRight.u, v: tRight.v, w: t },
          { u: tLeft.u,  v: tLeft.v,  w: 1 - t },
        ];
      } else {
        const tSide = applyTransform(uRaw, vSide, scaleU, scaleV, offsetU, offsetV, rotRad);
        sideSamples = [{ u: tSide.u, v: tSide.v, w: 1 }];
      }

      if (blend <= 0.001) {
        if (sideSamples.length === 1 && sideSamples[0].w === 1) return sideSamples[0];
        return { triplanar: true, samples: sideSamples };
      }

      const capThreshold = Math.cos((settings.capAngle ?? 20) * Math.PI / 180);
      const blendHalf = (settings.seamBandWidth ?? 0.5) * 0.5;
      const absnz = Math.abs(normal.z);
      const capW = Math.max(0, Math.min(1, (absnz - (capThreshold - blendHalf)) / (2 * blendHalf + 1e-6)));

      if (capW <= 0) {
        if (sideSamples.length === 1 && sideSamples[0].w === 1) return sideSamples[0];
        return { triplanar: true, samples: sideSamples };
      }

      const uCap  = rx / C + 0.5;
      const vCap  = ry / C + 0.5;
      const tCap = applyTransform(uCap, vCap, scaleU, scaleV, offsetU, offsetV, rotRad);

      if (capW >= 1) {
        return tCap;
      }

      // Combine seam-blended side samples with cap sample
      const samples = sideSamples.map(s => ({ u: s.u, v: s.v, w: s.w * (1 - capW) }));
      samples.push({ u: tCap.u, v: tCap.v, w: capW });
      return { triplanar: true, samples };
    }

    case MODE_SPHERICAL: {
      const rx = pos.x - center.x;
      const ry = pos.y - center.y;
      const rz = pos.z - center.z;
      const r  = Math.sqrt(rx*rx + ry*ry + rz*rz);
      const phi   = Math.acos(Math.max(-1, Math.min(1, rz / Math.max(r, 1e-6)))); // [0, PI], Z is up
      const theta = Math.atan2(ry, rx);              // [-PI, PI]
      const uRaw = (theta / TWO_PI) + 0.5;
      const vRaw = phi / Math.PI;

      // Seam smoothing: cross-fade at the atan2 wrap
      const seamBand = (settings.seamBandWidth ?? 0.5) * 0.1;
      const seamDist = Math.min(uRaw, 1.0 - uRaw);
      if (seamBand > 0.001 && seamDist < seamBand) {
        const d = uRaw < 0.5 ? uRaw : uRaw - 1.0;
        const tRaw = (d + seamBand) / (2.0 * seamBand);
        const t = tRaw * tRaw * (3 - 2 * tRaw); // smoothstep
        const tLeft  = applyTransform(1.0 + d, vRaw, scaleU, scaleV, offsetU, offsetV, rotRad);
        const tRight = applyTransform(d,       vRaw, scaleU, scaleV, offsetU, offsetV, rotRad);
        return {
          triplanar: true,
          samples: [
            { u: tRight.u, v: tRight.v, w: t },
            { u: tLeft.u,  v: tLeft.v,  w: 1 - t },
          ],
        };
      }

      u = uRaw;
      v = vRaw;
      break;
    }

    case MODE_CUBIC: {
      const weights = getCubicBlendWeights(normal, settings.mappingBlend ?? 0.0, settings.seamBandWidth ?? 0.35);
      const tYZ = applyTransform((pos.y - min.y) / md, (pos.z - min.z) / md, scaleU, scaleV, offsetU, offsetV, rotRad);
      const tXZ = applyTransform((pos.x - min.x) / md, (pos.z - min.z) / md, scaleU, scaleV, offsetU, offsetV, rotRad);
      const tXY = applyTransform((pos.x - min.x) / md, (pos.y - min.y) / md, scaleU, scaleV, offsetU, offsetV, rotRad);

      if (weights.x > 0.999) return tYZ;
      if (weights.y > 0.999) return tXZ;
      if (weights.z > 0.999) return tXY;

      return {
        triplanar: true,
        samples: [
          { u: tXY.u, v: tXY.v, w: weights.z },
          { u: tXZ.u, v: tXZ.v, w: weights.y },
          { u: tYZ.u, v: tYZ.v, w: weights.x },
        ],
      };
    }

    case MODE_TRIPLANAR:
    default: {
      // World-space normal blending
      const ax = Math.abs(normal.x);
      const ay = Math.abs(normal.y);
      const az = Math.abs(normal.z);
      const pw = 4.0;
      const bx = Math.pow(ax, pw);
      const by = Math.pow(ay, pw);
      const bz = Math.pow(az, pw);
      const sum = bx + by + bz + 1e-6;
      const wx = bx / sum;
      const wy = by / sum;
      const wz = bz / sum;

      const uvXY = {
        u: (pos.x - min.x) / md,
        v: (pos.y - min.y) / md,
        w: wz,
      };
      const uvXZ = {
        u: (pos.x - min.x) / md,
        v: (pos.z - min.z) / md,
        w: wy,
      };
      const uvYZ = {
        u: (pos.y - min.y) / md,
        v: (pos.z - min.z) / md,
        w: wx,
      };

      // Apply scale+offset+rotation and tile each independently
      return {
        triplanar: true,
        samples: [
          { ...applyTransform(uvXY.u, uvXY.v, scaleU, scaleV, offsetU, offsetV, rotRad), w: uvXY.w },
          { ...applyTransform(uvXZ.u, uvXZ.v, scaleU, scaleV, offsetU, offsetV, rotRad), w: uvXZ.w },
          { ...applyTransform(uvYZ.u, uvYZ.v, scaleU, scaleV, offsetU, offsetV, rotRad), w: uvYZ.w },
        ],
      };
    }
  }

  return applyTransform(u, v, scaleU, scaleV, offsetU, offsetV, rotRad);
}

function applyTransform(u, v, scaleU, scaleV, offsetU, offsetV, rotRad) {
  let uu = u / scaleU + offsetU;
  let vv = v / scaleV + offsetV;
  if (rotRad !== 0) {
    const c = Math.cos(rotRad), s = Math.sin(rotRad);
    uu -= 0.5; vv -= 0.5;
    const ru = c * uu - s * vv;
    const rv = s * uu + c * vv;
    uu = ru + 0.5; vv = rv + 0.5;
  }
  return { triplanar: false, u: fract(uu), v: fract(vv) };
}

/** Fractional part, always positive (mirrors GLSL fract) */
function fract(x) { return x - Math.floor(x); }