expr.go

package qb

import (
	"io"
	"strconv"
	"strings"
)

const PlaceHolder = "?"

type builder interface {
	build(b io.StringWriter, arg []interface{}) []interface{} 
}

type expr struct {
	expression string
	arguments  []interface{}
}

func (a *expr) build(b io.StringWriter, arg []interface{}) []interface{} {
	var (
		column = a.expression
		max    = strings.Count(column, PlaceHolder)
	)
	for i, a := range a.arguments {
		if i >= max {
			break
		}
		switch v := a.(type) {
		case builder:
			n := new(strings.Builder)
			arg = append(arg, v.args(n, nil)...)
			column = strings.Replace(column, PlaceHolder, n.String(), 1)
		default:
			arg = append(arg, a)
			column = strings.Replace(column, PlaceHolder, "$"+strconv.Itoa(len(arg)), 1)
		}
	}
	return arg
}

func Expr(expression string, arg ...interface{}) *expr {
	return &expr{
		expression: expression,
		arguments:  arg,
	}
}