iter.go

package stripe

import (
	"net/url"
	"reflect"
)

// Query is the function used to get a page listing.
type Query func(url.Values) ([]interface{}, ListMeta, error)

// Iter represents an interator used for list pagination.
// Iterators are not thread-safe, so they should not be consumed
// across multiple goroutines.
type Iter struct {
	stop   bool
	query  Query
	qs     url.Values
	values []interface{}
	meta   ListMeta
	params ListParams
	cur    int
	err    error
}

// GetIter returns a new iterator for a given query and its options.
func GetIter(params *ListParams, qs *url.Values, query Query) *Iter {
	iter := &Iter{}
	iter.query = query

	p := params
	if p == nil {
		p = &ListParams{}
	}
	iter.params = *p

	q := qs
	if q == nil {
		q = &url.Values{}
	}
	iter.qs = *q

	return iter
}

// Next returns the next entry in the page.
// By default, this loads a new page each time it's done with the current one.
func (i *Iter) Next() (interface{}, error) {
	// if the previous invocation resulted in us being complete,
	// no point in doing any work
	if i.stop {
		return nil, i.err
	}

	// initial run when we have no page loaded
	if len(i.values) == 0 {
		i.values, i.meta, i.err = i.query(i.qs)
	}

	// either there was a failure or no results were returned
	if i.err != nil || i.cur == len(i.values) {
		i.stop = true
		return nil, i.err
	}

	ret := i.values[i.cur]
	i.cur += 1

	// we haven't reached the end of the page
	if i.cur != len(i.values) {
		return ret, i.err
	}

	// otherwise we may need to fetch the next page
	// if there are no more results or we're supposed to stop after a
	// single page just bail
	if i.params.Single || !i.meta.More {
		i.stop = true
	} else {
		// determine if we're moving forward or backwards in paging
		if len(i.params.End) != 0 {
			i.params.End = reflect.ValueOf(i.values[0]).Elem().FieldByName("Id").String()
			i.qs.Set(endbefore, i.params.End)
		} else {
			i.params.Start = reflect.ValueOf(i.values[i.cur-1]).Elem().FieldByName("Id").String()
			i.qs.Set(startafter, i.params.Start)
		}

		// now actually load the next page
		i.values, i.meta, i.err = i.query(i.qs)

		if i.err != nil {
			i.stop = true
			return nil, i.err
		}

		i.cur = 0
	}

	return ret, i.err
}

// Stop returns true if there are no more iterations to be performed.
func (i *Iter) Stop() bool {
	return i.stop
}

// Meta returns the list metadata.
func (i *Iter) Meta() *ListMeta {
	return &i.meta
}