import {lerp} from '../../math.js';

/**
 * Creates chunks of equal length from a linestring
 * @param {number} chunkLength Length of each chunk.
 * @param {Array<number>} flatCoordinates Flat coordinates.
 * @param {number} offset Start offset of the `flatCoordinates`.
 * @param {number} end End offset of the `flatCoordinates`.
 * @param {number} stride Stride.
 * @return {Array<Array<number>>} Chunks of linestrings with stride 2.
 */
export function lineChunk(chunkLength, flatCoordinates, offset, end, stride) {
  const chunks = [];
  let cursor = offset;
  let chunkM = 0;
  let currentChunk = flatCoordinates.slice(offset, 2);
  while (chunkM < chunkLength && cursor + stride < end) {
    const [x1, y1] = currentChunk.slice(-2);
    const x2 = flatCoordinates[cursor + stride];
    const y2 = flatCoordinates[cursor + stride + 1];
    const segmentLength = Math.sqrt(
      (x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1)
    );
    chunkM += segmentLength;
    if (chunkM >= chunkLength) {
      const m = (chunkLength - chunkM + segmentLength) / segmentLength;
      const x = lerp(x1, x2, m);
      const y = lerp(y1, y2, m);
      currentChunk.push(x, y);
      chunks.push(currentChunk);
      currentChunk = [x, y];
      if (chunkM == chunkLength) {
        cursor += stride;
      }
      chunkM = 0;
    } else if (chunkM < chunkLength) {
      currentChunk.push(
        flatCoordinates[cursor + stride],
        flatCoordinates[cursor + stride + 1]
      );
      cursor += stride;
    } else {
      const missing = segmentLength - chunkM;
      const x = lerp(x1, x2, missing / segmentLength);
      const y = lerp(y1, y2, missing / segmentLength);
      currentChunk.push(x, y);
      chunks.push(currentChunk);
      currentChunk = [x, y];
      chunkM = 0;
      cursor += stride;
    }
  }
  if (chunkM > 0) {
    chunks.push(currentChunk);
  }
  return chunks;
}