/**
 * @module ol/geom/flat/interpolate
 */
import {binarySearch} from '../../array.js';
import {lerp} from '../../math.js';


/**
 * @param {Array.<number>} flatCoordinates Flat coordinates.
 * @param {number} offset Offset.
 * @param {number} end End.
 * @param {number} stride Stride.
 * @param {number} fraction Fraction.
 * @param {Array.<number>=} opt_dest Destination.
 * @return {Array.<number>} Destination.
 */
export function interpolatePoint(flatCoordinates, offset, end, stride, fraction, opt_dest) {
  let pointX = NaN;
  let pointY = NaN;
  const n = (end - offset) / stride;
  if (n === 1) {
    pointX = flatCoordinates[offset];
    pointY = flatCoordinates[offset + 1];
  } else if (n == 2) {
    pointX = (1 - fraction) * flatCoordinates[offset] +
        fraction * flatCoordinates[offset + stride];
    pointY = (1 - fraction) * flatCoordinates[offset + 1] +
        fraction * flatCoordinates[offset + stride + 1];
  } else if (n !== 0) {
    let x1 = flatCoordinates[offset];
    let y1 = flatCoordinates[offset + 1];
    let length = 0;
    const cumulativeLengths = [0];
    for (let i = offset + stride; i < end; i += stride) {
      const x2 = flatCoordinates[i];
      const y2 = flatCoordinates[i + 1];
      length += Math.sqrt((x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1));
      cumulativeLengths.push(length);
      x1 = x2;
      y1 = y2;
    }
    const target = fraction * length;
    const index = binarySearch(cumulativeLengths, target);
    if (index < 0) {
      const t = (target - cumulativeLengths[-index - 2]) /
          (cumulativeLengths[-index - 1] - cumulativeLengths[-index - 2]);
      const o = offset + (-index - 2) * stride;
      pointX = lerp(
        flatCoordinates[o], flatCoordinates[o + stride], t);
      pointY = lerp(
        flatCoordinates[o + 1], flatCoordinates[o + stride + 1], t);
    } else {
      pointX = flatCoordinates[offset + index * stride];
      pointY = flatCoordinates[offset + index * stride + 1];
    }
  }
  if (opt_dest) {
    opt_dest[0] = pointX;
    opt_dest[1] = pointY;
    return opt_dest;
  } else {
    return [pointX, pointY];
  }
}


/**
 * @param {Array.<number>} flatCoordinates Flat coordinates.
 * @param {number} offset Offset.
 * @param {number} end End.
 * @param {number} stride Stride.
 * @param {number} m M.
 * @param {boolean} extrapolate Extrapolate.
 * @return {ol.Coordinate} Coordinate.
 */
export function lineStringCoordinateAtM(flatCoordinates, offset, end, stride, m, extrapolate) {
  if (end == offset) {
    return null;
  }
  let coordinate;
  if (m < flatCoordinates[offset + stride - 1]) {
    if (extrapolate) {
      coordinate = flatCoordinates.slice(offset, offset + stride);
      coordinate[stride - 1] = m;
      return coordinate;
    } else {
      return null;
    }
  } else if (flatCoordinates[end - 1] < m) {
    if (extrapolate) {
      coordinate = flatCoordinates.slice(end - stride, end);
      coordinate[stride - 1] = m;
      return coordinate;
    } else {
      return null;
    }
  }
  // FIXME use O(1) search
  if (m == flatCoordinates[offset + stride - 1]) {
    return flatCoordinates.slice(offset, offset + stride);
  }
  let lo = offset / stride;
  let hi = end / stride;
  while (lo < hi) {
    const mid = (lo + hi) >> 1;
    if (m < flatCoordinates[(mid + 1) * stride - 1]) {
      hi = mid;
    } else {
      lo = mid + 1;
    }
  }
  const m0 = flatCoordinates[lo * stride - 1];
  if (m == m0) {
    return flatCoordinates.slice((lo - 1) * stride, (lo - 1) * stride + stride);
  }
  const m1 = flatCoordinates[(lo + 1) * stride - 1];
  const t = (m - m0) / (m1 - m0);
  coordinate = [];
  for (let i = 0; i < stride - 1; ++i) {
    coordinate.push(lerp(flatCoordinates[(lo - 1) * stride + i],
      flatCoordinates[lo * stride + i], t));
  }
  coordinate.push(m);
  return coordinate;
}


/**
 * @param {Array.<number>} flatCoordinates Flat coordinates.
 * @param {number} offset Offset.
 * @param {Array.<number>} ends Ends.
 * @param {number} stride Stride.
 * @param {number} m M.
 * @param {boolean} extrapolate Extrapolate.
 * @param {boolean} interpolate Interpolate.
 * @return {ol.Coordinate} Coordinate.
 */
export function lineStringsCoordinateAtM(
  flatCoordinates, offset, ends, stride, m, extrapolate, interpolate) {
  if (interpolate) {
    return lineStringCoordinateAtM(
      flatCoordinates, offset, ends[ends.length - 1], stride, m, extrapolate);
  }
  let coordinate;
  if (m < flatCoordinates[stride - 1]) {
    if (extrapolate) {
      coordinate = flatCoordinates.slice(0, stride);
      coordinate[stride - 1] = m;
      return coordinate;
    } else {
      return null;
    }
  }
  if (flatCoordinates[flatCoordinates.length - 1] < m) {
    if (extrapolate) {
      coordinate = flatCoordinates.slice(flatCoordinates.length - stride);
      coordinate[stride - 1] = m;
      return coordinate;
    } else {
      return null;
    }
  }
  for (let i = 0, ii = ends.length; i < ii; ++i) {
    const end = ends[i];
    if (offset == end) {
      continue;
    }
    if (m < flatCoordinates[offset + stride - 1]) {
      return null;
    } else if (m <= flatCoordinates[end - 1]) {
      return lineStringCoordinateAtM(
        flatCoordinates, offset, end, stride, m, false);
    }
    offset = end;
  }
  return null;
}