github.com/dolthub/go-mysql-server@v0.18.0/sql/expression/function/spatial/st_perimeter.go (about)

     1  // Copyright 2020-2022 Dolthub, Inc.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package spatial
    16  
    17  import (
    18  	"fmt"
    19  	"strings"
    20  
    21  	"github.com/dolthub/go-mysql-server/sql"
    22  	"github.com/dolthub/go-mysql-server/sql/expression"
    23  	"github.com/dolthub/go-mysql-server/sql/types"
    24  )
    25  
    26  // Perimeter is a function that returns the Perimeter of a Polygon
    27  // Not in MySQL, basing off: https://postgis.net/docs/ST_Perimeter.html
    28  type Perimeter struct {
    29  	expression.NaryExpression
    30  }
    31  
    32  var _ sql.FunctionExpression = (*Perimeter)(nil)
    33  var _ sql.CollationCoercible = (*Perimeter)(nil)
    34  
    35  // NewSTLength creates a new STX expression.
    36  func NewPerimeter(args ...sql.Expression) (sql.Expression, error) {
    37  	if len(args) != 1 && len(args) != 2 {
    38  		return nil, sql.ErrInvalidArgumentNumber.New("ST_PERIMETER", "1 or 2", len(args))
    39  	}
    40  	return &Perimeter{expression.NaryExpression{ChildExpressions: args}}, nil
    41  }
    42  
    43  // FunctionName implements sql.FunctionExpression
    44  func (p *Perimeter) FunctionName() string {
    45  	return "st_perimeter"
    46  }
    47  
    48  // Description implements sql.FunctionExpression
    49  func (p *Perimeter) Description() string {
    50  	return "returns the perimeter of the given polygon. If given a second argument, will find perimeter projected on spheroid."
    51  }
    52  
    53  // Type implements the sql.Expression interface.
    54  func (p *Perimeter) Type() sql.Type {
    55  	return types.Float64
    56  }
    57  
    58  // CollationCoercibility implements the interface sql.CollationCoercible.
    59  func (*Perimeter) CollationCoercibility(ctx *sql.Context) (collation sql.CollationID, coercibility byte) {
    60  	return sql.Collation_binary, 5
    61  }
    62  
    63  func (p *Perimeter) String() string {
    64  	var args = make([]string, len(p.ChildExpressions))
    65  	for i, arg := range p.ChildExpressions {
    66  		args[i] = arg.String()
    67  	}
    68  	return fmt.Sprintf("%s(%s)", p.FunctionName(), strings.Join(args, ","))
    69  }
    70  
    71  // WithChildren implements the Expression interface.
    72  func (p *Perimeter) WithChildren(children ...sql.Expression) (sql.Expression, error) {
    73  	return NewPerimeter(children...)
    74  }
    75  
    76  // Eval implements the sql.Expression interface.
    77  func (p *Perimeter) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
    78  	// Evaluate argument
    79  	v1, err := p.ChildExpressions[0].Eval(ctx, row)
    80  	if err != nil {
    81  		return nil, err
    82  	}
    83  
    84  	// Return nil if argument is nil
    85  	if v1 == nil {
    86  		return nil, nil
    87  	}
    88  
    89  	// Argument must be a polygon
    90  	poly, ok := v1.(types.Polygon)
    91  	if !ok {
    92  		return nil, sql.ErrInvalidArgument.New(p.FunctionName())
    93  	}
    94  
    95  	// TODO: if SRID is not 0, find geodetic distance
    96  	// If just one argument, return length
    97  	if len(p.ChildExpressions) == 1 {
    98  		var perimeter float64
    99  		for _, l := range poly.Lines {
   100  			perimeter += calculateLength(l)
   101  		}
   102  		return perimeter, nil
   103  	}
   104  
   105  	// TODO: support perimeter along spheroid
   106  	return nil, sql.ErrUnsupportedFeature.New("st_perimeter on spheroid")
   107  }