featurebase/sql3/planner/inbuiltfunctionsstring.go

package planner

import (
	"github.com/molecula/featurebase/v3/sql3"
	"github.com/molecula/featurebase/v3/sql3/parser"
)

func (p *ExecutionPlanner) analyseFunctionReverse(call *parser.Call, scope parser.Statement) (parser.Expr, error) {
	//one argument
	if len(call.Args) != 1 {
		return nil, sql3.NewErrCallParameterCountMismatch(call.Rparen.Line, call.Rparen.Column, call.Name.Name, 1, len(call.Args))
	}

	if !typeIsString(call.Args[0].DataType()) {
		return nil, sql3.NewErrStringExpressionExpected(call.Args[0].Pos().Line, call.Args[0].Pos().Column)
	}

	call.ResultDataType = parser.NewDataTypeString()

	return call, nil
}

// reverses the string
func (n *callPlanExpression) EvaluateReverse(currentRow []interface{}) (interface{}, error) {
	argOneEval, err := n.args[0].Evaluate(currentRow)
	if err != nil {
		return nil, err
	}

	stringArgOne, ok := argOneEval.(string)
	if !ok {
		return nil, sql3.NewErrInternalf("unexpected type converion %T", argOneEval)
	}

	// reverse the string
	runes := []rune(stringArgOne)
	for i, j := 0, len(runes)-1; i < j; i, j = i+1, j-1 {
		runes[i], runes[j] = runes[j], runes[i]
	}
	return string(runes), nil
}