Daylon Wilkins
132 lines
3.7 KiB
Go
132 lines
3.7 KiB
Go
// Copyright 2023 Dolthub, Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// Copyright 2020 The Cockroach Authors.
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//
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// Use of this software is governed by the Business Source License
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// included in the file licenses/BSL.txt.
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//
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// As of the Change Date specified in that file, in accordance with
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// the Business Source License, use of this software will be governed
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// by the Apache License, Version 2.0, included in the file
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// licenses/APL.txt.
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package geo
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import (
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"github.com/cockroachdb/errors"
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"github.com/twpayne/go-geom"
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)
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// GeomTIterator decomposes geom.T objects into individual components
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// (i.e. either a POINT, LINESTRING or POLYGON) and presents them as an
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// iterator. It automatically decomposes MULTI-* and GEOMETRYCOLLECTION
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// objects. This prevents an allocation compared to decomposing the objects
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// into a geom.T array.
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type GeomTIterator struct {
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g geom.T
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emptyBehavior EmptyBehavior
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// idx is the index into the MULTI-* or GEOMETRYCOLLECTION item.
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idx int
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// subIt is the iterator inside a GeometryCollection.
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// Note GeometryCollections can be nested.
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subIt *GeomTIterator
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}
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// NewGeomTIterator returns a new GeomTIterator.
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func NewGeomTIterator(g geom.T, emptyBehavior EmptyBehavior) GeomTIterator {
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return GeomTIterator{g: g, emptyBehavior: emptyBehavior}
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}
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// Next returns the next geom.T object, a bool as to whether there is an
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// entry and an error if any.
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func (it *GeomTIterator) Next() (geom.T, bool, error) {
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next, hasNext, err := it.next()
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if err != nil || !hasNext {
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return nil, hasNext, err
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}
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for {
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if !next.Empty() {
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return next, hasNext, nil
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}
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switch it.emptyBehavior {
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case EmptyBehaviorOmit:
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next, hasNext, err = it.next()
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if err != nil || !hasNext {
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return nil, hasNext, err
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}
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case EmptyBehaviorError:
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return nil, false, NewEmptyGeometryError()
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default:
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return nil, false, errors.Newf("programmer error: unknown behavior: %T", it.emptyBehavior)
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}
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}
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}
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// next() is the internal method for Next.
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// It handles fetching the next item in the iterator, recursing down structures
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// if necessary. It does not check for emptiness.
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func (it *GeomTIterator) next() (geom.T, bool, error) {
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switch t := it.g.(type) {
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case *geom.Point, *geom.LineString, *geom.Polygon:
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if it.idx == 1 {
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return nil, false, nil
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}
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it.idx++
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return t, true, nil
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case *geom.MultiPoint:
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if it.idx == t.NumPoints() {
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return nil, false, nil
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}
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p := t.Point(it.idx)
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it.idx++
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return p, true, nil
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case *geom.MultiLineString:
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if it.idx == t.NumLineStrings() {
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return nil, false, nil
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}
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p := t.LineString(it.idx)
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it.idx++
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return p, true, nil
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case *geom.MultiPolygon:
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if it.idx == t.NumPolygons() {
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return nil, false, nil
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}
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p := t.Polygon(it.idx)
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it.idx++
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return p, true, nil
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case *geom.GeometryCollection:
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for {
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if it.idx == t.NumGeoms() {
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return nil, false, nil
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}
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if it.subIt == nil {
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it.subIt = &GeomTIterator{g: t.Geom(it.idx), emptyBehavior: it.emptyBehavior}
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}
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ret, next, err := it.subIt.next()
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if err != nil {
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return nil, false, err
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}
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if next {
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return ret, next, nil
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}
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// Reset and move to the next item in the collection.
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it.idx++
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it.subIt = nil
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}
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default:
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return nil, false, errors.Newf("unknown type: %T", t)
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}
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}
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