// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
// All rights reserved.

// iterator.go
package expr

import (
	"errors"
	"fmt"
)

// Operator names

const (
	initName    = "init"
	cleanName   = "clean"
	resetName   = "reset"
	nextName    = "next"
	currentName = "current"
	indexName   = "index"
	countName   = "count"
)

type Iterator interface {
	Next() (item any, err error) // must return io.EOF after the last item
	Current() (item any, err error)
	Index() int
}

type ExtIterator interface {
	Iterator
	HasOperation(name string) bool
	CallOperation(name string, args []any) (value any, err error)
}

func errNoOperation(name string) error {
	return fmt.Errorf("no %s() function defined in the data-source", name)
}

func errInvalidDataSource() error {
	return errors.New("invalid data-source")
}