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rpad_lpad.go
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rpad_lpad.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"
"reflect"
"strings"
"gopkg.in/src-d/go-errors.v1"
"github.com/dolthub/go-mysql-server/sql"
"github.com/dolthub/go-mysql-server/sql/types"
)
var ErrDivisionByZero = errors.NewKind("division by zero")
type padType rune
const (
lPadType padType = 'l'
rPadType padType = 'r'
)
func NewLeftPad(e ...sql.Expression) (sql.Expression, error) {
return NewPad(lPadType, e...)
}
func NewRightPad(e ...sql.Expression) (sql.Expression, error) {
return NewPad(rPadType, e...)
}
// NewPad creates a new Pad expression.
func NewPad(pType padType, args ...sql.Expression) (sql.Expression, error) {
argLen := len(args)
if argLen != 3 {
return nil, sql.ErrInvalidArgumentNumber.New(string(pType)+"pad", "3", argLen)
}
return &Pad{args[0], args[1], args[2], pType}, nil
}
// Pad is a function that pads a string with another string.
type Pad struct {
str sql.Expression
length sql.Expression
padStr sql.Expression
padType padType
}
var _ sql.FunctionExpression = (*Pad)(nil)
var _ sql.CollationCoercible = (*Pad)(nil)
// FunctionName implements sql.FunctionExpression
func (p *Pad) FunctionName() string {
if p.padType == lPadType {
return "lpad"
} else if p.padType == rPadType {
return "rpad"
} else {
panic("unknown name for pad type")
}
}
// Description implements sql.FunctionExpression
func (p *Pad) Description() string {
if p.padType == lPadType {
return "returns the string str, left-padded with the string padstr to a length of len characters."
} else if p.padType == rPadType {
return "returns the string str, right-padded with the string padstr to a length of len characters."
} else {
panic("unknown description for pad type")
}
}
// Children implements the Expression interface.
func (p *Pad) Children() []sql.Expression {
return []sql.Expression{p.str, p.length, p.padStr}
}
// Resolved implements the Expression interface.
func (p *Pad) Resolved() bool {
return p.str.Resolved() && p.length.Resolved() && (p.padStr.Resolved())
}
// IsNullable implements the Expression interface.
func (p *Pad) IsNullable() bool {
return p.str.IsNullable() || p.length.IsNullable() || p.padStr.IsNullable()
}
// Type implements the Expression interface.
func (p *Pad) Type() sql.Type { return types.LongText }
// CollationCoercibility implements the interface sql.CollationCoercible.
func (p *Pad) CollationCoercibility(ctx *sql.Context) (collation sql.CollationID, coercibility byte) {
leftCollation, leftCoercibility := sql.GetCoercibility(ctx, p.str)
rightCollation, rightCoercibility := sql.GetCoercibility(ctx, p.padStr)
return sql.ResolveCoercibility(leftCollation, leftCoercibility, rightCollation, rightCoercibility)
}
func (p *Pad) String() string {
if p.padType == lPadType {
return fmt.Sprintf("lpad(%s, %s, %s)", p.str, p.length, p.padStr)
}
return fmt.Sprintf("rpad(%s, %s, %s)", p.str, p.length, p.padStr)
}
// WithChildren implements the Expression interface.
func (p *Pad) WithChildren(children ...sql.Expression) (sql.Expression, error) {
return NewPad(p.padType, children...)
}
// Eval implements the Expression interface.
func (p *Pad) Eval(
ctx *sql.Context,
row sql.Row,
) (interface{}, error) {
str, err := p.str.Eval(ctx, row)
if err != nil {
return nil, err
}
if str == nil {
return nil, nil
}
str, _, err = types.LongText.Convert(str)
if err != nil {
return nil, sql.ErrInvalidType.New(reflect.TypeOf(str))
}
length, err := p.length.Eval(ctx, row)
if err != nil {
return nil, err
}
if length == nil {
return nil, nil
}
length, _, err = types.Int64.Convert(length)
if err != nil {
return nil, err
}
padStr, err := p.padStr.Eval(ctx, row)
if err != nil {
return nil, err
}
if padStr == nil {
return nil, nil
}
padStr, _, err = types.LongText.Convert(padStr)
if err != nil {
return nil, err
}
return padString(str.(string), length.(int64), padStr.(string), p.padType)
}
func padString(str string, length int64, padStr string, padType padType) (string, error) {
if length <= 0 {
return "", nil
}
if int64(len(str)) >= length {
return str[:length], nil
}
if len(padStr) == 0 {
return "", nil
}
padLen := int(length - int64(len(str)))
quo, rem, err := divmod(int64(padLen), int64(len(padStr)))
if err != nil {
return "", err
}
if padType == lPadType {
result := strings.Repeat(padStr, int(quo)) + padStr[:rem] + str
return result[:length], nil
}
result := str + strings.Repeat(padStr, int(quo)) + padStr[:rem]
return result[(int64(len(result)) - length):], nil
}
func divmod(a, b int64) (quotient, remainder int64, err error) {
if b == 0 {
return 0, 0, ErrDivisionByZero.New()
}
quotient = a / b
remainder = a % b
return
}