package pgx

import (
	"fmt"
)

// DataRowReader is used by SelectFunc to process incoming rows.
type DataRowReader struct {
	mr                *MessageReader
	FieldDescriptions []FieldDescription
	currentFieldIdx   int
}

// ReadValue returns the next value from the current row.
func (r *DataRowReader) ReadValue() interface{} {
	fieldDescription := r.FieldDescriptions[r.currentFieldIdx]
	r.currentFieldIdx++

	size := r.mr.ReadInt32()
	if size > -1 {
		if vt, present := ValueTranscoders[fieldDescription.DataType]; present {
			switch fieldDescription.FormatCode {
			case 0:
				return vt.DecodeText(r.mr, size)
			case 1:
				return vt.DecodeBinary(r.mr, size)
			default:
				return ProtocolError(fmt.Sprintf("Unknown field description format code: %v", fieldDescription.FormatCode))
			}
		} else {
			return r.mr.ReadString(size)
		}
	} else {
		return nil
	}
}