dictyBase/modware-order

package arangodb

import (
    "errors"

    "github.com/dictyBase/modware-order/internal/model"
)

// PairWiseIterator is the container for iterator.
type PairWiseIterator struct {
    slice []*model.OrderDoc
    // keeps track of the first index
    firstIdx int
    // keeps track of the next index in the pair
    secondIdx int
    // last index of the slice
    lastIdx int
    // toogle the state for fetching the first pair
    firstPair bool
}

// NewPairWiseIterator is the constructor, returns error in case of empty or
// slice with single element.
func NewPairWiseIterator(mrd []*model.OrderDoc) (*PairWiseIterator, error) {
    if len(mrd) <= 1 {
        return &PairWiseIterator{}, errors.New("not enough element to fetch pairs")
    }

    return &PairWiseIterator{
        slice:     mrd,
        firstIdx:  0,
        secondIdx: 1,
        lastIdx:   len(mrd) - 1,
        firstPair: true,
    }, nil
}

// NextPair moves the iteration to the next pair. If NextPair() returns true
// the pair could be retrieved by Pair() method. If it is called for the first
// time it points to the first pair.
func (p *PairWiseIterator) NextPair() bool {
    if p.firstPair {
        p.firstPair = false

        return true
    }
    if p.secondIdx == p.lastIdx {
        return false
    }
    p.firstIdx++
    p.secondIdx++

    return true
}

// Pair retrieves the pair of elements from the slice.
func (p *PairWiseIterator) Pair() (*model.OrderDoc, *model.OrderDoc) {
    return p.slice[p.firstIdx], p.slice[p.secondIdx]
}