/**
 * @module ol/geom/flat/closest
 */
import {lerp, squaredDistance as squaredDx} from '../../math.js';

/**
 * Returns the point on the 2D line segment flatCoordinates[offset1] to
 * flatCoordinates[offset2] that is closest to the point (x, y).  Extra
 * dimensions are linearly interpolated.
 * @param {Array<number>} flatCoordinates Flat coordinates.
 * @param {number} offset1 Offset 1.
 * @param {number} offset2 Offset 2.
 * @param {number} stride Stride.
 * @param {number} x X.
 * @param {number} y Y.
 * @param {Array<number>} closestPoint Closest point.
 */
function assignClosest(
  flatCoordinates,
  offset1,
  offset2,
  stride,
  x,
  y,
  closestPoint
) {
  const x1 = flatCoordinates[offset1];
  const y1 = flatCoordinates[offset1 + 1];
  const dx = flatCoordinates[offset2] - x1;
  const dy = flatCoordinates[offset2 + 1] - y1;
  let offset;
  if (dx === 0 && dy === 0) {
    offset = offset1;
  } else {
    const t = ((x - x1) * dx + (y - y1) * dy) / (dx * dx + dy * dy);
    if (t > 1) {
      offset = offset2;
    } else if (t > 0) {
      for (let i = 0; i < stride; ++i) {
        closestPoint[i] = lerp(
          flatCoordinates[offset1 + i],
          flatCoordinates[offset2 + i],
          t
        );
      }
      closestPoint.length = stride;
      return;
    } else {
      offset = offset1;
    }
  }
  for (let i = 0; i < stride; ++i) {
    closestPoint[i] = flatCoordinates[offset + i];
  }
  closestPoint.length = stride;
}

/**
 * Return the squared of the largest distance between any pair of consecutive
 * coordinates.
 * @param {Array<number>} flatCoordinates Flat coordinates.
 * @param {number} offset Offset.
 * @param {number} end End.
 * @param {number} stride Stride.
 * @param {number} max Max squared delta.
 * @return {number} Max squared delta.
 */
export function maxSquaredDelta(flatCoordinates, offset, end, stride, max) {
  let x1 = flatCoordinates[offset];
  let y1 = flatCoordinates[offset + 1];
  for (offset += stride; offset < end; offset += stride) {
    const x2 = flatCoordinates[offset];
    const y2 = flatCoordinates[offset + 1];
    const squaredDelta = squaredDx(x1, y1, x2, y2);
    if (squaredDelta > max) {
      max = squaredDelta;
    }
    x1 = x2;
    y1 = y2;
  }
  return max;
}

/**
 * @param {Array<number>} flatCoordinates Flat coordinates.
 * @param {number} offset Offset.
 * @param {Array<number>} ends Ends.
 * @param {number} stride Stride.
 * @param {number} max Max squared delta.
 * @return {number} Max squared delta.
 */
export function arrayMaxSquaredDelta(
  flatCoordinates,
  offset,
  ends,
  stride,
  max
) {
  for (let i = 0, ii = ends.length; i < ii; ++i) {
    const end = ends[i];
    max = maxSquaredDelta(flatCoordinates, offset, end, stride, max);
    offset = end;
  }
  return max;
}

/**
 * @param {Array<number>} flatCoordinates Flat coordinates.
 * @param {number} offset Offset.
 * @param {Array<Array<number>>} endss Endss.
 * @param {number} stride Stride.
 * @param {number} max Max squared delta.
 * @return {number} Max squared delta.
 */
export function multiArrayMaxSquaredDelta(
  flatCoordinates,
  offset,
  endss,
  stride,
  max
) {
  for (let i = 0, ii = endss.length; i < ii; ++i) {
    const ends = endss[i];
    max = arrayMaxSquaredDelta(flatCoordinates, offset, ends, stride, max);
    offset = ends[ends.length - 1];
  }
  return max;
}

/**
 * @param {Array<number>} flatCoordinates Flat coordinates.
 * @param {number} offset Offset.
 * @param {number} end End.
 * @param {number} stride Stride.
 * @param {number} maxDelta Max delta.
 * @param {boolean} isRing Is ring.
 * @param {number} x X.
 * @param {number} y Y.
 * @param {Array<number>} closestPoint Closest point.
 * @param {number} minSquaredDistance Minimum squared distance.
 * @param {Array<number>} [tmpPoint] Temporary point object.
 * @return {number} Minimum squared distance.
 */
export function assignClosestPoint(
  flatCoordinates,
  offset,
  end,
  stride,
  maxDelta,
  isRing,
  x,
  y,
  closestPoint,
  minSquaredDistance,
  tmpPoint
) {
  if (offset == end) {
    return minSquaredDistance;
  }
  let i, squaredDistance;
  if (maxDelta === 0) {
    // All points are identical, so just test the first point.
    squaredDistance = squaredDx(
      x,
      y,
      flatCoordinates[offset],
      flatCoordinates[offset + 1]
    );
    if (squaredDistance < minSquaredDistance) {
      for (i = 0; i < stride; ++i) {
        closestPoint[i] = flatCoordinates[offset + i];
      }
      closestPoint.length = stride;
      return squaredDistance;
    }
    return minSquaredDistance;
  }
  tmpPoint = tmpPoint ? tmpPoint : [NaN, NaN];
  let index = offset + stride;
  while (index < end) {
    assignClosest(
      flatCoordinates,
      index - stride,
      index,
      stride,
      x,
      y,
      tmpPoint
    );
    squaredDistance = squaredDx(x, y, tmpPoint[0], tmpPoint[1]);
    if (squaredDistance < minSquaredDistance) {
      minSquaredDistance = squaredDistance;
      for (i = 0; i < stride; ++i) {
        closestPoint[i] = tmpPoint[i];
      }
      closestPoint.length = stride;
      index += stride;
    } else {
      // Skip ahead multiple points, because we know that all the skipped
      // points cannot be any closer than the closest point we have found so
      // far.  We know this because we know how close the current point is, how
      // close the closest point we have found so far is, and the maximum
      // distance between consecutive points.  For example, if we're currently
      // at distance 10, the best we've found so far is 3, and that the maximum
      // distance between consecutive points is 2, then we'll need to skip at
      // least (10 - 3) / 2 == 3 (rounded down) points to have any chance of
      // finding a closer point.  We use Math.max(..., 1) to ensure that we
      // always advance at least one point, to avoid an infinite loop.
      index +=
        stride *
        Math.max(
          ((Math.sqrt(squaredDistance) - Math.sqrt(minSquaredDistance)) /
            maxDelta) |
            0,
          1
        );
    }
  }
  if (isRing) {
    // Check the closing segment.
    assignClosest(
      flatCoordinates,
      end - stride,
      offset,
      stride,
      x,
      y,
      tmpPoint
    );
    squaredDistance = squaredDx(x, y, tmpPoint[0], tmpPoint[1]);
    if (squaredDistance < minSquaredDistance) {
      minSquaredDistance = squaredDistance;
      for (i = 0; i < stride; ++i) {
        closestPoint[i] = tmpPoint[i];
      }
      closestPoint.length = stride;
    }
  }
  return minSquaredDistance;
}

/**
 * @param {Array<number>} flatCoordinates Flat coordinates.
 * @param {number} offset Offset.
 * @param {Array<number>} ends Ends.
 * @param {number} stride Stride.
 * @param {number} maxDelta Max delta.
 * @param {boolean} isRing Is ring.
 * @param {number} x X.
 * @param {number} y Y.
 * @param {Array<number>} closestPoint Closest point.
 * @param {number} minSquaredDistance Minimum squared distance.
 * @param {Array<number>} [tmpPoint] Temporary point object.
 * @return {number} Minimum squared distance.
 */
export function assignClosestArrayPoint(
  flatCoordinates,
  offset,
  ends,
  stride,
  maxDelta,
  isRing,
  x,
  y,
  closestPoint,
  minSquaredDistance,
  tmpPoint
) {
  tmpPoint = tmpPoint ? tmpPoint : [NaN, NaN];
  for (let i = 0, ii = ends.length; i < ii; ++i) {
    const end = ends[i];
    minSquaredDistance = assignClosestPoint(
      flatCoordinates,
      offset,
      end,
      stride,
      maxDelta,
      isRing,
      x,
      y,
      closestPoint,
      minSquaredDistance,
      tmpPoint
    );
    offset = end;
  }
  return minSquaredDistance;
}

/**
 * @param {Array<number>} flatCoordinates Flat coordinates.
 * @param {number} offset Offset.
 * @param {Array<Array<number>>} endss Endss.
 * @param {number} stride Stride.
 * @param {number} maxDelta Max delta.
 * @param {boolean} isRing Is ring.
 * @param {number} x X.
 * @param {number} y Y.
 * @param {Array<number>} closestPoint Closest point.
 * @param {number} minSquaredDistance Minimum squared distance.
 * @param {Array<number>} [tmpPoint] Temporary point object.
 * @return {number} Minimum squared distance.
 */
export function assignClosestMultiArrayPoint(
  flatCoordinates,
  offset,
  endss,
  stride,
  maxDelta,
  isRing,
  x,
  y,
  closestPoint,
  minSquaredDistance,
  tmpPoint
) {
  tmpPoint = tmpPoint ? tmpPoint : [NaN, NaN];
  for (let i = 0, ii = endss.length; i < ii; ++i) {
    const ends = endss[i];
    minSquaredDistance = assignClosestArrayPoint(
      flatCoordinates,
      offset,
      ends,
      stride,
      maxDelta,
      isRing,
      x,
      y,
      closestPoint,
      minSquaredDistance,
      tmpPoint
    );
    offset = ends[ends.length - 1];
  }
  return minSquaredDistance;
}