import {lerp} from '@math.gl/core';

const DEFAULT_INDICES = new Uint32Array([0, 2, 1, 0, 3, 2]);
const DEFAULT_TEX_COORDS = new Float32Array([0, 1, 0, 0, 1, 0, 1, 1]);

/*
  1 ---- 2
  |      |
  |      |
  0 ---- 3
*/
/* eslint-disable max-statements */
export default function createMesh(bounds, resolution) {
  if (!resolution) {
    return createQuad(bounds);
  }
  const maxXSpan = Math.max(
    Math.abs(bounds[0][0] - bounds[3][0]),
    Math.abs(bounds[1][0] - bounds[2][0])
  );
  const maxYSpan = Math.max(
    Math.abs(bounds[1][1] - bounds[0][1]),
    Math.abs(bounds[2][1] - bounds[3][1])
  );
  const uCount = Math.ceil(maxXSpan / resolution) + 1;
  const vCount = Math.ceil(maxYSpan / resolution) + 1;

  const vertexCount = (uCount - 1) * (vCount - 1) * 6;
  const indices = new Uint32Array(vertexCount);
  const texCoords = new Float32Array(uCount * vCount * 2);
  const positions = new Float64Array(uCount * vCount * 3);

  // Tesselate
  let vertex = 0;
  let index = 0;
  for (let u = 0; u < uCount; u++) {
    const ut = u / (uCount - 1);
    for (let v = 0; v < vCount; v++) {
      const vt = v / (vCount - 1);
      const p = interpolateQuad(bounds, ut, vt);

      positions[vertex * 3 + 0] = p[0];
      positions[vertex * 3 + 1] = p[1];
      positions[vertex * 3 + 2] = p[2] || 0;

      texCoords[vertex * 2 + 0] = ut;
      texCoords[vertex * 2 + 1] = 1 - vt;

      if (u > 0 && v > 0) {
        indices[index++] = vertex - vCount;
        indices[index++] = vertex - vCount - 1;
        indices[index++] = vertex - 1;
        indices[index++] = vertex - vCount;
        indices[index++] = vertex - 1;
        indices[index++] = vertex;
      }

      vertex++;
    }
  }
  return {
    vertexCount,
    positions,
    indices,
    texCoords
  };
}

function createQuad(bounds) {
  const positions = new Float64Array(12);
  // [[minX, minY], [minX, maxY], [maxX, maxY], [maxX, minY]]
  for (let i = 0; i < bounds.length; i++) {
    positions[i * 3 + 0] = bounds[i][0];
    positions[i * 3 + 1] = bounds[i][1];
    positions[i * 3 + 2] = bounds[i][2] || 0;
  }

  return {
    vertexCount: 6,
    positions,
    indices: DEFAULT_INDICES,
    texCoords: DEFAULT_TEX_COORDS
  };
}

function interpolateQuad(quad, ut, vt) {
  return lerp(lerp(quad[0], quad[1], vt), lerp(quad[3], quad[2], vt), ut);
}