// Copyright Google Inc. All Rights Reserved.

//

// Licensed under the Apache License, Version 2.0 (the "License");

// you may not use this file except in compliance with the License.

// You may obtain a copy of the License at

//

//     http://www.apache.org/licenses/LICENSE-2.0

//

// Unless required by applicable law or agreed to in writing, software

// distributed under the License is distributed on an "AS-IS" BASIS,

// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

// See the License for the specific language governing permissions and

// limitations under the License.

//

#include "s2/s2shapeutil_edge_wrap.h"

#include "absl/log/absl_check.h"

#include "s2/s2point.h"

#include "s2/s2shape.h"

namespace s2shapeutil {

int NextEdgeWrap(const S2Shape& shape, int edge_id) {

  ABSL_DCHECK_GE(edge_id, 0);

  ABSL_DCHECK_LT(edge_id, shape.num_edges());

  S2Shape::ChainPosition chainpos = shape.chain_position(edge_id);

  S2Shape::Chain chaininfo = shape.chain(chainpos.chain_id);

  // Polygon chains wrap around, point and polylines don't.

  int offset = chainpos.offset;

  switch (shape.dimension()) {

    case 2:

      // Polygon chains always wrap around.

      offset = (offset + 1) % chaininfo.length;

      break;

    case 1:

      // If we're at the end of a polyline, wrap around if it's closed.

      if (offset == chaininfo.length - 1) {

        const S2Shape::Edge& curr = shape.chain_edge(chainpos.chain_id, offset);

        const S2Shape::Edge& next = shape.chain_edge(chainpos.chain_id, 0);

        if (curr.v1 == next.v0) {

          offset = 0;

        } else {

          return -1;

        }

      } else {

        ++offset;

      }

      break;

    default:

      // Points are one per chain.

      return -1;

  }

  return chaininfo.start + offset;

}

int PrevEdgeWrap(const S2Shape& shape, int edge_id) {

  ABSL_DCHECK_GE(edge_id, 0);

  ABSL_DCHECK_LT(edge_id, shape.num_edges());

  S2Shape::ChainPosition chainpos = shape.chain_position(edge_id);

  S2Shape::Chain chaininfo = shape.chain(chainpos.chain_id);

  int offset = chainpos.offset;

  switch (shape.dimension()) {

    case 2:

      // Polygons always wrap around.

      --offset;

      if (offset < 0) {

        offset += chaininfo.length;

      }

      break;

    case 1:

      if (offset == 0) {

        int end = chaininfo.length - 1;

        const S2Shape::Edge& curr = shape.chain_edge(chainpos.chain_id, 0);

        const S2Shape::Edge& prev = shape.chain_edge(chainpos.chain_id, end);

        if (prev.v1 == curr.v0) {

          offset = end;

        } else {

          return -1;

        }

      } else {

        --offset;

      }

      break;

    default:

      // Points are one per chain.

      return -1;

  }

  return chaininfo.start + offset;

}

}  //  namespace s2shapeutil