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locate.go
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locate.go
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// Copyright 2020-2021 Dolthub, Inc.
//
// 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.
package function
import (
"fmt"
"strings"
"github.com/gabereiser/go-mysql-server/sql"
"github.com/gabereiser/go-mysql-server/sql/expression"
"github.com/gabereiser/go-mysql-server/sql/types"
)
// Locate returns the position of the first occurrence of a substring in a string.
// If the substring is not found within the original string, this function returns 0.
// This function performs a case-insensitive search.
type Locate struct {
expression.NaryExpression
}
var _ sql.FunctionExpression = (*Locate)(nil)
// NewLocate returns a new Locate function.
func NewLocate(exprs ...sql.Expression) (sql.Expression, error) {
if len(exprs) < 2 || len(exprs) > 3 {
return nil, sql.ErrInvalidArgumentNumber.New("LOCATE", "2 or 3", len(exprs))
}
return &Locate{expression.NaryExpression{ChildExpressions: exprs}}, nil
}
// FunctionName implements sql.FunctionExpression
func (l *Locate) FunctionName() string {
return "locate"
}
// Description implements sql.FunctionExpression
func (l *Locate) Description() string {
return "returns the position of the first occurrence of a substring in a string."
}
// WithChildren implements the Expression interface.
func (l *Locate) WithChildren(children ...sql.Expression) (sql.Expression, error) {
if len(children) < 2 || len(children) > 3 {
return nil, sql.ErrInvalidChildrenNumber.New(l, len(children), 2)
}
return &Locate{expression.NaryExpression{ChildExpressions: children}}, nil
}
// Type implements the sql.Expression interface.
func (l *Locate) Type() sql.Type { return types.Int32 }
func (l *Locate) String() string {
switch len(l.ChildExpressions) {
case 2:
return fmt.Sprintf("%s(%s,%s)", l.FunctionName(), l.ChildExpressions[0], l.ChildExpressions[1])
case 3:
return fmt.Sprintf("%s(%s,%s,%s)", l.FunctionName(), l.ChildExpressions[0], l.ChildExpressions[1], l.ChildExpressions[2])
}
return ""
}
func (l *Locate) DebugString() string {
switch len(l.ChildExpressions) {
case 2:
return fmt.Sprintf("%s(%s,%s)", l.FunctionName(), sql.DebugString(l.ChildExpressions[0]), sql.DebugString(l.ChildExpressions[1]))
case 3:
return fmt.Sprintf("%s(%s,%s,%s)", l.FunctionName(), sql.DebugString(l.ChildExpressions[0]), sql.DebugString(l.ChildExpressions[1]), sql.DebugString(l.ChildExpressions[2]))
}
return ""
}
// Eval implements the sql.Expression interface.
func (l *Locate) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
if len(l.ChildExpressions) < 2 || len(l.ChildExpressions) > 3 {
return nil, nil
}
substrVal, err := l.ChildExpressions[0].Eval(ctx, row)
if err != nil {
return nil, err
}
if substrVal == nil {
return nil, nil
}
substr, ok := substrVal.(string)
if !ok {
return nil, sql.ErrInvalidArgumentDetails.New("locate", "substring must be a string")
}
strVal, err := l.ChildExpressions[1].Eval(ctx, row)
if err != nil {
return nil, err
}
if strVal == nil {
return nil, nil
}
str, ok := strVal.(string)
if !ok {
return nil, sql.ErrInvalidArgumentDetails.New("locate", "string must be a string")
}
position := 1
if len(l.ChildExpressions) == 3 {
posVal, err := l.ChildExpressions[2].Eval(ctx, row)
if err != nil {
return nil, err
}
if posVal != nil {
posInt, err := types.Int32.Convert(posVal)
if err != nil {
return nil, sql.ErrInvalidArgumentDetails.New("locate", "start must be an integer")
}
position = int(posInt.(int32))
}
}
// Edge cases that cannot be handled by strings.Index.
switch {
// Position 0 doesn't exist.
case position == 0 || (len(str) > 0 && position > len(str)):
return int32(0), nil
// Locate("", "") returns 1 if start is 1.
case len(substr) == 0 && len(str) == 0:
if position == 1 {
return int32(1), nil
}
return int32(0), nil
}
res := strings.Index(strings.ToLower(str[position-1:]), strings.ToLower(substr))
if res == -1 {
return int32(0), nil
}
return int32(res + position), nil
}