// ListMonitoredResourceDescriptors lists the monitored resource descriptors used by Stackdriver Logging.
func (c *Client) ListMonitoredResourceDescriptors(ctx context.Context, req *loggingpb.ListMonitoredResourceDescriptorsRequest) *MonitoredResourceDescriptorIterator {
	md, _ := metadata.FromContext(ctx)
	ctx = metadata.NewContext(ctx, metadata.Join(md, c.metadata))
	it := &MonitoredResourceDescriptorIterator{}

	fetch := func(pageSize int, pageToken string) (string, error) {
		var resp *loggingpb.ListMonitoredResourceDescriptorsResponse
		req.PageToken = pageToken
		if pageSize > math.MaxInt32 {
			req.PageSize = math.MaxInt32
		} else {
			req.PageSize = int32(pageSize)
		}
		err := gax.Invoke(ctx, func(ctx context.Context) error {
			var err error
			resp, err = c.client.ListMonitoredResourceDescriptors(ctx, req)
			return err
		}, c.CallOptions.ListMonitoredResourceDescriptors...)
		if err != nil {
			return "", err
		}
		it.items = append(it.items, resp.ResourceDescriptors...)
		return resp.NextPageToken, nil
	}
	bufLen := func() int { return len(it.items) }
	takeBuf := func() interface{} {
		b := it.items
		it.items = nil
		return b
	}

	it.pageInfo, it.nextFunc = iterator.NewPageInfo(fetch, bufLen, takeBuf)
	return it
}

// ListSubscriptions lists matching subscriptions.
func (c *SubscriberClient) ListSubscriptions(ctx context.Context, req *pubsubpb.ListSubscriptionsRequest) *SubscriptionIterator {
	md, _ := metadata.FromContext(ctx)
	ctx = metadata.NewContext(ctx, metadata.Join(md, c.metadata))
	it := &SubscriptionIterator{}
	it.InternalFetch = func(pageSize int, pageToken string) ([]*pubsubpb.Subscription, string, error) {
		var resp *pubsubpb.ListSubscriptionsResponse
		req.PageToken = pageToken
		if pageSize > math.MaxInt32 {
			req.PageSize = math.MaxInt32
		} else {
			req.PageSize = int32(pageSize)
		}
		err := gax.Invoke(ctx, func(ctx context.Context) error {
			var err error
			resp, err = c.subscriberClient.ListSubscriptions(ctx, req)
			return err
		}, c.CallOptions.ListSubscriptions...)
		if err != nil {
			return nil, "", err
		}
		return resp.Subscriptions, resp.NextPageToken, nil
	}
	fetch := func(pageSize int, pageToken string) (string, error) {
		items, nextPageToken, err := it.InternalFetch(pageSize, pageToken)
		if err != nil {
			return "", err
		}
		it.items = append(it.items, items...)
		return nextPageToken, nil
	}
	it.pageInfo, it.nextFunc = iterator.NewPageInfo(fetch, it.bufLen, it.takeBuf)
	return it
}

// Primes returns a iterator which returns a sequence of prime numbers.
// If non-zero, max specifies the maximum number which could possibly be
// returned.
func Primes(max int) *SieveIterator {
	it := &SieveIterator{pos: 2, max: max}
	it.pageInfo, it.nextFunc = iterator.NewPageInfo(
		it.fetch,
		func() int { return len(it.items) },
		func() interface{} { b := it.items; it.items = nil; return b })
	return it
}

// Items is a sample implementation of an iterator-creating method.
func (c *Client) Items(ctx context.Context) *ItemIterator {
	it := &ItemIterator{s: c.s}
	it.pageInfo, it.nextFunc = iterator.NewPageInfo(
		it.fetch,
		func() int { return len(it.items) },
		func() interface{} { b := it.items; it.items = nil; return b })
	return it
}

// Entries returns an EntryIterator for iterating over log entries. By default,
// the log entries will be restricted to those from the project passed to
// NewClient. This may be overridden by passing a ProjectIDs option. Requires ReadScope or AdminScope.
func (c *Client) Entries(ctx context.Context, opts ...EntriesOption) *EntryIterator {
	it := &EntryIterator{
		it: c.lClient.ListLogEntries(ctx, listLogEntriesRequest(c.projectID, opts)),
	}
	it.pageInfo, it.nextFunc = iterator.NewPageInfo(
		it.fetch,
		func() int { return len(it.items) },
		func() interface{} { b := it.items; it.items = nil; return b })
	return it
}

// Metrics returns a MetricIterator for iterating over all Metrics in the Client's project.
// Requires ReadScope or AdminScope.
func (c *Client) Metrics(ctx context.Context) *MetricIterator {
	it := &MetricIterator{
		it: c.mClient.ListLogMetrics(ctx, &logpb.ListLogMetricsRequest{Parent: c.parent()}),
	}
	it.pageInfo, it.nextFunc = iterator.NewPageInfo(
		it.fetch,
		func() int { return len(it.items) },
		func() interface{} { b := it.items; it.items = nil; return b })
	return it
}

// Tables returns an iterator over the tables in the Dataset.
func (d *Dataset) Tables(ctx context.Context) *TableIterator {
	it := &TableIterator{
		ctx:     ctx,
		dataset: d,
	}
	it.pageInfo, it.nextFunc = iterator.NewPageInfo(
		it.fetch,
		func() int { return len(it.tables) },
		func() interface{} { b := it.tables; it.tables = nil; return b })
	return it
}

// ResourceDescriptors returns a ResourceDescriptorIterator
// for iterating over MonitoredResourceDescriptors. Requires ReadScope or AdminScope.
// See https://cloud.google.com/logging/docs/api/v2/#monitored-resources for an explanation of
// monitored resources.
// See https://cloud.google.com/logging/docs/api/v2/resource-list for a list of monitored resources.
func (c *Client) ResourceDescriptors(ctx context.Context) *ResourceDescriptorIterator {
	it := &ResourceDescriptorIterator{
		it: c.lClient.ListMonitoredResourceDescriptors(ctx,
			&logpb.ListMonitoredResourceDescriptorsRequest{}),
	}
	it.pageInfo, it.nextFunc = iterator.NewPageInfo(
		it.fetch,
		func() int { return len(it.items) },
		func() interface{} { b := it.items; it.items = nil; return b })
	return it
}

// DatasetsInProject returns an iterator over the datasets in the provided project.
func (c *Client) DatasetsInProject(ctx context.Context, projectID string) *DatasetIterator {
	it := &DatasetIterator{
		ctx:       ctx,
		service:   c.service,
		projectID: projectID,
	}
	it.pageInfo, it.nextFunc = iterator.NewPageInfo(
		it.fetch,
		func() int { return len(it.items) },
		func() interface{} { b := it.items; it.items = nil; return b })
	return it
}

// Buckets returns an iterator over the buckets in the project. You may
// optionally set the iterator's Prefix field to restrict the list to buckets
// whose names begin with the prefix. By default, all buckets in the project
// are returned.
func (c *Client) Buckets(ctx context.Context, projectID string) *BucketIterator {
	it := &BucketIterator{
		ctx:       ctx,
		client:    c,
		projectID: projectID,
	}
	it.pageInfo, it.nextFunc = iterator.NewPageInfo(
		it.fetch,
		func() int { return len(it.buckets) },
		func() interface{} { b := it.buckets; it.buckets = nil; return b })
	return it
}

func newRowIterator(ctx context.Context, s service, pf pageFetcher) *RowIterator {
	it := &RowIterator{
		ctx:     ctx,
		service: s,
		pf:      pf,
	}
	it.pageInfo, it.nextFunc = iterator.NewPageInfo(
		it.fetch,
		func() int { return len(it.rows) },
		func() interface{} { r := it.rows; it.rows = nil; return r })
	return it
}

// Objects returns an iterator over the objects in the bucket that match the Query q.
// If q is nil, no filtering is done.
func (b *BucketHandle) Objects(ctx context.Context, q *Query) *ObjectIterator {
	it := &ObjectIterator{
		ctx:    ctx,
		bucket: b,
	}
	it.pageInfo, it.nextFunc = iterator.NewPageInfo(
		it.fetch,
		func() int { return len(it.items) },
		func() interface{} { b := it.items; it.items = nil; return b })
	if q != nil {
		it.query = *q
	}
	return it
}