// Copyright 2019 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// Code generated by gapic-generator. DO NOT EDIT.

package cloudtasks

import (
	"context"
	"fmt"
	"math"
	"time"

	"github.com/golang/protobuf/proto"
	gax "github.com/googleapis/gax-go/v2"
	"google.golang.org/api/iterator"
	"google.golang.org/api/option"
	"google.golang.org/api/transport"
	taskspb "google.golang.org/genproto/googleapis/cloud/tasks/v2beta3"
	iampb "google.golang.org/genproto/googleapis/iam/v1"
	"google.golang.org/grpc"
	"google.golang.org/grpc/codes"
	"google.golang.org/grpc/metadata"
)

// CallOptions contains the retry settings for each method of Client.
type CallOptions struct {
	ListQueues         []gax.CallOption
	GetQueue           []gax.CallOption
	CreateQueue        []gax.CallOption
	UpdateQueue        []gax.CallOption
	DeleteQueue        []gax.CallOption
	PurgeQueue         []gax.CallOption
	PauseQueue         []gax.CallOption
	ResumeQueue        []gax.CallOption
	GetIamPolicy       []gax.CallOption
	SetIamPolicy       []gax.CallOption
	TestIamPermissions []gax.CallOption
	ListTasks          []gax.CallOption
	GetTask            []gax.CallOption
	CreateTask         []gax.CallOption
	DeleteTask         []gax.CallOption
	RunTask            []gax.CallOption
}

func defaultClientOptions() []option.ClientOption {
	return []option.ClientOption{
		option.WithEndpoint("cloudtasks.googleapis.com:443"),
		option.WithScopes(DefaultAuthScopes()...),
	}
}

func defaultCallOptions() *CallOptions {
	retry := map[[2]string][]gax.CallOption{
		{"default", "idempotent"}: {
			gax.WithRetry(func() gax.Retryer {
				return gax.OnCodes([]codes.Code{
					codes.DeadlineExceeded,
					codes.Unavailable,
				}, gax.Backoff{
					Initial:    100 * time.Millisecond,
					Max:        60000 * time.Millisecond,
					Multiplier: 1.3,
				})
			}),
		},
	}
	return &CallOptions{
		ListQueues:         retry[[2]string{"default", "idempotent"}],
		GetQueue:           retry[[2]string{"default", "idempotent"}],
		CreateQueue:        retry[[2]string{"default", "non_idempotent"}],
		UpdateQueue:        retry[[2]string{"default", "non_idempotent"}],
		DeleteQueue:        retry[[2]string{"default", "idempotent"}],
		PurgeQueue:         retry[[2]string{"default", "non_idempotent"}],
		PauseQueue:         retry[[2]string{"default", "non_idempotent"}],
		ResumeQueue:        retry[[2]string{"default", "non_idempotent"}],
		GetIamPolicy:       retry[[2]string{"default", "idempotent"}],
		SetIamPolicy:       retry[[2]string{"default", "non_idempotent"}],
		TestIamPermissions: retry[[2]string{"default", "idempotent"}],
		ListTasks:          retry[[2]string{"default", "idempotent"}],
		GetTask:            retry[[2]string{"default", "idempotent"}],
		CreateTask:         retry[[2]string{"default", "non_idempotent"}],
		DeleteTask:         retry[[2]string{"default", "idempotent"}],
		RunTask:            retry[[2]string{"default", "non_idempotent"}],
	}
}

// Client is a client for interacting with Cloud Tasks API.
//
// Methods, except Close, may be called concurrently. However, fields must not be modified concurrently with method calls.
type Client struct {
	// The connection to the service.
	conn *grpc.ClientConn

	// The gRPC API client.
	client taskspb.CloudTasksClient

	// The call options for this service.
	CallOptions *CallOptions

	// The x-goog-* metadata to be sent with each request.
	xGoogMetadata metadata.MD
}

// NewClient creates a new cloud tasks client.
//
// Cloud Tasks allows developers to manage the execution of background
// work in their applications.
func NewClient(ctx context.Context, opts ...option.ClientOption) (*Client, error) {
	conn, err := transport.DialGRPC(ctx, append(defaultClientOptions(), opts...)...)
	if err != nil {
		return nil, err
	}
	c := &Client{
		conn:        conn,
		CallOptions: defaultCallOptions(),

		client: taskspb.NewCloudTasksClient(conn),
	}
	c.setGoogleClientInfo()
	return c, nil
}

// Connection returns the client's connection to the API service.
func (c *Client) Connection() *grpc.ClientConn {
	return c.conn
}

// Close closes the connection to the API service. The user should invoke this when
// the client is no longer required.
func (c *Client) Close() error {
	return c.conn.Close()
}

// setGoogleClientInfo sets the name and version of the application in
// the `x-goog-api-client` header passed on each request. Intended for
// use by Google-written clients.
func (c *Client) setGoogleClientInfo(keyval ...string) {
	kv := append([]string{"gl-go", versionGo()}, keyval...)
	kv = append(kv, "gapic", versionClient, "gax", gax.Version, "grpc", grpc.Version)
	c.xGoogMetadata = metadata.Pairs("x-goog-api-client", gax.XGoogHeader(kv...))
}

// ListQueues lists queues.
//
// Queues are returned in lexicographical order.
func (c *Client) ListQueues(ctx context.Context, req *taskspb.ListQueuesRequest, opts ...gax.CallOption) *QueueIterator {
	md := metadata.Pairs("x-goog-request-params", fmt.Sprintf("%s=%v", "parent", req.GetParent()))
	ctx = insertMetadata(ctx, c.xGoogMetadata, md)
	opts = append(c.CallOptions.ListQueues[0:len(c.CallOptions.ListQueues):len(c.CallOptions.ListQueues)], opts...)
	it := &QueueIterator{}
	req = proto.Clone(req).(*taskspb.ListQueuesRequest)
	it.InternalFetch = func(pageSize int, pageToken string) ([]*taskspb.Queue, string, error) {
		var resp *taskspb.ListQueuesResponse
		req.PageToken = pageToken
		if pageSize > math.MaxInt32 {
			req.PageSize = math.MaxInt32
		} else {
			req.PageSize = int32(pageSize)
		}
		err := gax.Invoke(ctx, func(ctx context.Context, settings gax.CallSettings) error {
			var err error
			resp, err = c.client.ListQueues(ctx, req, settings.GRPC...)
			return err
		}, opts...)
		if err != nil {
			return nil, "", err
		}
		return resp.Queues, 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)
	it.pageInfo.MaxSize = int(req.PageSize)
	return it
}

// GetQueue gets a queue.
func (c *Client) GetQueue(ctx context.Context, req *taskspb.GetQueueRequest, opts ...gax.CallOption) (*taskspb.Queue, error) {
	md := metadata.Pairs("x-goog-request-params", fmt.Sprintf("%s=%v", "name", req.GetName()))
	ctx = insertMetadata(ctx, c.xGoogMetadata, md)
	opts = append(c.CallOptions.GetQueue[0:len(c.CallOptions.GetQueue):len(c.CallOptions.GetQueue)], opts...)
	var resp *taskspb.Queue
	err := gax.Invoke(ctx, func(ctx context.Context, settings gax.CallSettings) error {
		var err error
		resp, err = c.client.GetQueue(ctx, req, settings.GRPC...)
		return err
	}, opts...)
	if err != nil {
		return nil, err
	}
	return resp, nil
}

// CreateQueue creates a queue.
//
// Queues created with this method allow tasks to live for a maximum of 31
// days. After a task is 31 days old, the task will be deleted regardless of
// whether it was dispatched or not.
//
// WARNING: Using this method may have unintended side effects if you are
// using an App Engine queue.yaml or queue.xml file to manage your queues.
// Read
// Overview of Queue Management and
// queue.yaml (at https://cloud.google.com/tasks/docs/queue-yaml) before using
// this method.
func (c *Client) CreateQueue(ctx context.Context, req *taskspb.CreateQueueRequest, opts ...gax.CallOption) (*taskspb.Queue, error) {
	md := metadata.Pairs("x-goog-request-params", fmt.Sprintf("%s=%v", "parent", req.GetParent()))
	ctx = insertMetadata(ctx, c.xGoogMetadata, md)
	opts = append(c.CallOptions.CreateQueue[0:len(c.CallOptions.CreateQueue):len(c.CallOptions.CreateQueue)], opts...)
	var resp *taskspb.Queue
	err := gax.Invoke(ctx, func(ctx context.Context, settings gax.CallSettings) error {
		var err error
		resp, err = c.client.CreateQueue(ctx, req, settings.GRPC...)
		return err
	}, opts...)
	if err != nil {
		return nil, err
	}
	return resp, nil
}

// UpdateQueue updates a queue.
//
// This method creates the queue if it does not exist and updates
// the queue if it does exist.
//
// Queues created with this method allow tasks to live for a maximum of 31
// days. After a task is 31 days old, the task will be deleted regardless of
// whether it was dispatched or not.
//
// WARNING: Using this method may have unintended side effects if you are
// using an App Engine queue.yaml or queue.xml file to manage your queues.
// Read
// Overview of Queue Management and
// queue.yaml (at https://cloud.google.com/tasks/docs/queue-yaml) before using
// this method.
func (c *Client) UpdateQueue(ctx context.Context, req *taskspb.UpdateQueueRequest, opts ...gax.CallOption) (*taskspb.Queue, error) {
	md := metadata.Pairs("x-goog-request-params", fmt.Sprintf("%s=%v", "queue.name", req.GetQueue().GetName()))
	ctx = insertMetadata(ctx, c.xGoogMetadata, md)
	opts = append(c.CallOptions.UpdateQueue[0:len(c.CallOptions.UpdateQueue):len(c.CallOptions.UpdateQueue)], opts...)
	var resp *taskspb.Queue
	err := gax.Invoke(ctx, func(ctx context.Context, settings gax.CallSettings) error {
		var err error
		resp, err = c.client.UpdateQueue(ctx, req, settings.GRPC...)
		return err
	}, opts...)
	if err != nil {
		return nil, err
	}
	return resp, nil
}

// DeleteQueue deletes a queue.
//
// This command will delete the queue even if it has tasks in it.
//
// Note: If you delete a queue, a queue with the same name can't be created
// for 7 days.
//
// WARNING: Using this method may have unintended side effects if you are
// using an App Engine queue.yaml or queue.xml file to manage your queues.
// Read
// Overview of Queue Management and
// queue.yaml (at https://cloud.google.com/tasks/docs/queue-yaml) before using
// this method.
func (c *Client) DeleteQueue(ctx context.Context, req *taskspb.DeleteQueueRequest, opts ...gax.CallOption) error {
	md := metadata.Pairs("x-goog-request-params", fmt.Sprintf("%s=%v", "name", req.GetName()))
	ctx = insertMetadata(ctx, c.xGoogMetadata, md)
	opts = append(c.CallOptions.DeleteQueue[0:len(c.CallOptions.DeleteQueue):len(c.CallOptions.DeleteQueue)], opts...)
	err := gax.Invoke(ctx, func(ctx context.Context, settings gax.CallSettings) error {
		var err error
		_, err = c.client.DeleteQueue(ctx, req, settings.GRPC...)
		return err
	}, opts...)
	return err
}

// PurgeQueue purges a queue by deleting all of its tasks.
//
// All tasks created before this method is called are permanently deleted.
//
// Purge operations can take up to one minute to take effect. Tasks
// might be dispatched before the purge takes effect. A purge is irreversible.
func (c *Client) PurgeQueue(ctx context.Context, req *taskspb.PurgeQueueRequest, opts ...gax.CallOption) (*taskspb.Queue, error) {
	md := metadata.Pairs("x-goog-request-params", fmt.Sprintf("%s=%v", "name", req.GetName()))
	ctx = insertMetadata(ctx, c.xGoogMetadata, md)
	opts = append(c.CallOptions.PurgeQueue[0:len(c.CallOptions.PurgeQueue):len(c.CallOptions.PurgeQueue)], opts...)
	var resp *taskspb.Queue
	err := gax.Invoke(ctx, func(ctx context.Context, settings gax.CallSettings) error {
		var err error
		resp, err = c.client.PurgeQueue(ctx, req, settings.GRPC...)
		return err
	}, opts...)
	if err != nil {
		return nil, err
	}
	return resp, nil
}

// PauseQueue pauses the queue.
//
// If a queue is paused then the system will stop dispatching tasks
// until the queue is resumed via
// [ResumeQueue][google.cloud.tasks.v2beta3.CloudTasks.ResumeQueue]. Tasks can
// still be added when the queue is paused. A queue is paused if its
// [state][google.cloud.tasks.v2beta3.Queue.state] is
// [PAUSED][google.cloud.tasks.v2beta3.Queue.State.PAUSED].
func (c *Client) PauseQueue(ctx context.Context, req *taskspb.PauseQueueRequest, opts ...gax.CallOption) (*taskspb.Queue, error) {
	md := metadata.Pairs("x-goog-request-params", fmt.Sprintf("%s=%v", "name", req.GetName()))
	ctx = insertMetadata(ctx, c.xGoogMetadata, md)
	opts = append(c.CallOptions.PauseQueue[0:len(c.CallOptions.PauseQueue):len(c.CallOptions.PauseQueue)], opts...)
	var resp *taskspb.Queue
	err := gax.Invoke(ctx, func(ctx context.Context, settings gax.CallSettings) error {
		var err error
		resp, err = c.client.PauseQueue(ctx, req, settings.GRPC...)
		return err
	}, opts...)
	if err != nil {
		return nil, err
	}
	return resp, nil
}

// ResumeQueue resume a queue.
//
// This method resumes a queue after it has been
// [PAUSED][google.cloud.tasks.v2beta3.Queue.State.PAUSED] or
// [DISABLED][google.cloud.tasks.v2beta3.Queue.State.DISABLED]. The state of a
// queue is stored in the queue's
// [state][google.cloud.tasks.v2beta3.Queue.state]; after calling this method
// it will be set to
// [RUNNING][google.cloud.tasks.v2beta3.Queue.State.RUNNING].
//
// WARNING: Resuming many high-QPS queues at the same time can
// lead to target overloading. If you are resuming high-QPS
// queues, follow the 500/50/5 pattern described in
// Managing Cloud Tasks Scaling
// Risks (at https://cloud.google.com/tasks/docs/manage-cloud-task-scaling).
func (c *Client) ResumeQueue(ctx context.Context, req *taskspb.ResumeQueueRequest, opts ...gax.CallOption) (*taskspb.Queue, error) {
	md := metadata.Pairs("x-goog-request-params", fmt.Sprintf("%s=%v", "name", req.GetName()))
	ctx = insertMetadata(ctx, c.xGoogMetadata, md)
	opts = append(c.CallOptions.ResumeQueue[0:len(c.CallOptions.ResumeQueue):len(c.CallOptions.ResumeQueue)], opts...)
	var resp *taskspb.Queue
	err := gax.Invoke(ctx, func(ctx context.Context, settings gax.CallSettings) error {
		var err error
		resp, err = c.client.ResumeQueue(ctx, req, settings.GRPC...)
		return err
	}, opts...)
	if err != nil {
		return nil, err
	}
	return resp, nil
}

// GetIamPolicy gets the access control policy for a
// [Queue][google.cloud.tasks.v2beta3.Queue]. Returns an empty policy if the
// resource exists and does not have a policy set.
//
// Authorization requires the following
// Google IAM (at https://cloud.google.com/iam) permission on the specified
// resource parent:
//
//   cloudtasks.queues.getIamPolicy
func (c *Client) GetIamPolicy(ctx context.Context, req *iampb.GetIamPolicyRequest, opts ...gax.CallOption) (*iampb.Policy, error) {
	md := metadata.Pairs("x-goog-request-params", fmt.Sprintf("%s=%v", "resource", req.GetResource()))
	ctx = insertMetadata(ctx, c.xGoogMetadata, md)
	opts = append(c.CallOptions.GetIamPolicy[0:len(c.CallOptions.GetIamPolicy):len(c.CallOptions.GetIamPolicy)], opts...)
	var resp *iampb.Policy
	err := gax.Invoke(ctx, func(ctx context.Context, settings gax.CallSettings) error {
		var err error
		resp, err = c.client.GetIamPolicy(ctx, req, settings.GRPC...)
		return err
	}, opts...)
	if err != nil {
		return nil, err
	}
	return resp, nil
}

// SetIamPolicy sets the access control policy for a
// [Queue][google.cloud.tasks.v2beta3.Queue]. Replaces any existing policy.
//
// Note: The Cloud Console does not check queue-level IAM permissions yet.
// Project-level permissions are required to use the Cloud Console.
//
// Authorization requires the following
// Google IAM (at https://cloud.google.com/iam) permission on the specified
// resource parent:
//
//   cloudtasks.queues.setIamPolicy
func (c *Client) SetIamPolicy(ctx context.Context, req *iampb.SetIamPolicyRequest, opts ...gax.CallOption) (*iampb.Policy, error) {
	md := metadata.Pairs("x-goog-request-params", fmt.Sprintf("%s=%v", "resource", req.GetResource()))
	ctx = insertMetadata(ctx, c.xGoogMetadata, md)
	opts = append(c.CallOptions.SetIamPolicy[0:len(c.CallOptions.SetIamPolicy):len(c.CallOptions.SetIamPolicy)], opts...)
	var resp *iampb.Policy
	err := gax.Invoke(ctx, func(ctx context.Context, settings gax.CallSettings) error {
		var err error
		resp, err = c.client.SetIamPolicy(ctx, req, settings.GRPC...)
		return err
	}, opts...)
	if err != nil {
		return nil, err
	}
	return resp, nil
}

// TestIamPermissions returns permissions that a caller has on a
// [Queue][google.cloud.tasks.v2beta3.Queue]. If the resource does not exist,
// this will return an empty set of permissions, not a
// [NOT_FOUND][google.rpc.Code.NOT_FOUND] error.
//
// Note: This operation is designed to be used for building permission-aware
// UIs and command-line tools, not for authorization checking. This operation
// may "fail open" without warning.
func (c *Client) TestIamPermissions(ctx context.Context, req *iampb.TestIamPermissionsRequest, opts ...gax.CallOption) (*iampb.TestIamPermissionsResponse, error) {
	md := metadata.Pairs("x-goog-request-params", fmt.Sprintf("%s=%v", "resource", req.GetResource()))
	ctx = insertMetadata(ctx, c.xGoogMetadata, md)
	opts = append(c.CallOptions.TestIamPermissions[0:len(c.CallOptions.TestIamPermissions):len(c.CallOptions.TestIamPermissions)], opts...)
	var resp *iampb.TestIamPermissionsResponse
	err := gax.Invoke(ctx, func(ctx context.Context, settings gax.CallSettings) error {
		var err error
		resp, err = c.client.TestIamPermissions(ctx, req, settings.GRPC...)
		return err
	}, opts...)
	if err != nil {
		return nil, err
	}
	return resp, nil
}

// ListTasks lists the tasks in a queue.
//
// By default, only the [BASIC][google.cloud.tasks.v2beta3.Task.View.BASIC]
// view is retrieved due to performance considerations;
// [response_view][google.cloud.tasks.v2beta3.ListTasksRequest.response_view]
// controls the subset of information which is returned.
//
// The tasks may be returned in any order. The ordering may change at any
// time.
func (c *Client) ListTasks(ctx context.Context, req *taskspb.ListTasksRequest, opts ...gax.CallOption) *TaskIterator {
	md := metadata.Pairs("x-goog-request-params", fmt.Sprintf("%s=%v", "parent", req.GetParent()))
	ctx = insertMetadata(ctx, c.xGoogMetadata, md)
	opts = append(c.CallOptions.ListTasks[0:len(c.CallOptions.ListTasks):len(c.CallOptions.ListTasks)], opts...)
	it := &TaskIterator{}
	req = proto.Clone(req).(*taskspb.ListTasksRequest)
	it.InternalFetch = func(pageSize int, pageToken string) ([]*taskspb.Task, string, error) {
		var resp *taskspb.ListTasksResponse
		req.PageToken = pageToken
		if pageSize > math.MaxInt32 {
			req.PageSize = math.MaxInt32
		} else {
			req.PageSize = int32(pageSize)
		}
		err := gax.Invoke(ctx, func(ctx context.Context, settings gax.CallSettings) error {
			var err error
			resp, err = c.client.ListTasks(ctx, req, settings.GRPC...)
			return err
		}, opts...)
		if err != nil {
			return nil, "", err
		}
		return resp.Tasks, 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)
	it.pageInfo.MaxSize = int(req.PageSize)
	return it
}

// GetTask gets a task.
func (c *Client) GetTask(ctx context.Context, req *taskspb.GetTaskRequest, opts ...gax.CallOption) (*taskspb.Task, error) {
	md := metadata.Pairs("x-goog-request-params", fmt.Sprintf("%s=%v", "name", req.GetName()))
	ctx = insertMetadata(ctx, c.xGoogMetadata, md)
	opts = append(c.CallOptions.GetTask[0:len(c.CallOptions.GetTask):len(c.CallOptions.GetTask)], opts...)
	var resp *taskspb.Task
	err := gax.Invoke(ctx, func(ctx context.Context, settings gax.CallSettings) error {
		var err error
		resp, err = c.client.GetTask(ctx, req, settings.GRPC...)
		return err
	}, opts...)
	if err != nil {
		return nil, err
	}
	return resp, nil
}

// CreateTask creates a task and adds it to a queue.
//
// Tasks cannot be updated after creation; there is no UpdateTask command.
//
//   For [App Engine queues][google.cloud.tasks.v2beta3.AppEngineHttpQueue],
//   the maximum task size is
//   100KB.
func (c *Client) CreateTask(ctx context.Context, req *taskspb.CreateTaskRequest, opts ...gax.CallOption) (*taskspb.Task, error) {
	md := metadata.Pairs("x-goog-request-params", fmt.Sprintf("%s=%v", "parent", req.GetParent()))
	ctx = insertMetadata(ctx, c.xGoogMetadata, md)
	opts = append(c.CallOptions.CreateTask[0:len(c.CallOptions.CreateTask):len(c.CallOptions.CreateTask)], opts...)
	var resp *taskspb.Task
	err := gax.Invoke(ctx, func(ctx context.Context, settings gax.CallSettings) error {
		var err error
		resp, err = c.client.CreateTask(ctx, req, settings.GRPC...)
		return err
	}, opts...)
	if err != nil {
		return nil, err
	}
	return resp, nil
}

// DeleteTask deletes a task.
//
// A task can be deleted if it is scheduled or dispatched. A task
// cannot be deleted if it has executed successfully or permanently
// failed.
func (c *Client) DeleteTask(ctx context.Context, req *taskspb.DeleteTaskRequest, opts ...gax.CallOption) error {
	md := metadata.Pairs("x-goog-request-params", fmt.Sprintf("%s=%v", "name", req.GetName()))
	ctx = insertMetadata(ctx, c.xGoogMetadata, md)
	opts = append(c.CallOptions.DeleteTask[0:len(c.CallOptions.DeleteTask):len(c.CallOptions.DeleteTask)], opts...)
	err := gax.Invoke(ctx, func(ctx context.Context, settings gax.CallSettings) error {
		var err error
		_, err = c.client.DeleteTask(ctx, req, settings.GRPC...)
		return err
	}, opts...)
	return err
}

// RunTask forces a task to run now.
//
// When this method is called, Cloud Tasks will dispatch the task, even if
// the task is already running, the queue has reached its
// [RateLimits][google.cloud.tasks.v2beta3.RateLimits] or is
// [PAUSED][google.cloud.tasks.v2beta3.Queue.State.PAUSED].
//
// This command is meant to be used for manual debugging. For
// example, [RunTask][google.cloud.tasks.v2beta3.CloudTasks.RunTask] can be
// used to retry a failed task after a fix has been made or to manually force
// a task to be dispatched now.
//
// The dispatched task is returned. That is, the task that is returned
// contains the [status][Task.status] after the task is dispatched but
// before the task is received by its target.
//
// If Cloud Tasks receives a successful response from the task's
// target, then the task will be deleted; otherwise the task's
// [schedule_time][google.cloud.tasks.v2beta3.Task.schedule_time] will be
// reset to the time that
// [RunTask][google.cloud.tasks.v2beta3.CloudTasks.RunTask] was called plus
// the retry delay specified in the queue's
// [RetryConfig][google.cloud.tasks.v2beta3.RetryConfig].
//
// [RunTask][google.cloud.tasks.v2beta3.CloudTasks.RunTask] returns
// [NOT_FOUND][google.rpc.Code.NOT_FOUND] when it is called on a
// task that has already succeeded or permanently failed.
func (c *Client) RunTask(ctx context.Context, req *taskspb.RunTaskRequest, opts ...gax.CallOption) (*taskspb.Task, error) {
	md := metadata.Pairs("x-goog-request-params", fmt.Sprintf("%s=%v", "name", req.GetName()))
	ctx = insertMetadata(ctx, c.xGoogMetadata, md)
	opts = append(c.CallOptions.RunTask[0:len(c.CallOptions.RunTask):len(c.CallOptions.RunTask)], opts...)
	var resp *taskspb.Task
	err := gax.Invoke(ctx, func(ctx context.Context, settings gax.CallSettings) error {
		var err error
		resp, err = c.client.RunTask(ctx, req, settings.GRPC...)
		return err
	}, opts...)
	if err != nil {
		return nil, err
	}
	return resp, nil
}

// QueueIterator manages a stream of *taskspb.Queue.
type QueueIterator struct {
	items    []*taskspb.Queue
	pageInfo *iterator.PageInfo
	nextFunc func() error

	// InternalFetch is for use by the Google Cloud Libraries only.
	// It is not part of the stable interface of this package.
	//
	// InternalFetch returns results from a single call to the underlying RPC.
	// The number of results is no greater than pageSize.
	// If there are no more results, nextPageToken is empty and err is nil.
	InternalFetch func(pageSize int, pageToken string) (results []*taskspb.Queue, nextPageToken string, err error)
}

// PageInfo supports pagination. See the google.golang.org/api/iterator package for details.
func (it *QueueIterator) PageInfo() *iterator.PageInfo {
	return it.pageInfo
}

// Next returns the next result. Its second return value is iterator.Done if there are no more
// results. Once Next returns Done, all subsequent calls will return Done.
func (it *QueueIterator) Next() (*taskspb.Queue, error) {
	var item *taskspb.Queue
	if err := it.nextFunc(); err != nil {
		return item, err
	}
	item = it.items[0]
	it.items = it.items[1:]
	return item, nil
}

func (it *QueueIterator) bufLen() int {
	return len(it.items)
}

func (it *QueueIterator) takeBuf() interface{} {
	b := it.items
	it.items = nil
	return b
}

// TaskIterator manages a stream of *taskspb.Task.
type TaskIterator struct {
	items    []*taskspb.Task
	pageInfo *iterator.PageInfo
	nextFunc func() error

	// InternalFetch is for use by the Google Cloud Libraries only.
	// It is not part of the stable interface of this package.
	//
	// InternalFetch returns results from a single call to the underlying RPC.
	// The number of results is no greater than pageSize.
	// If there are no more results, nextPageToken is empty and err is nil.
	InternalFetch func(pageSize int, pageToken string) (results []*taskspb.Task, nextPageToken string, err error)
}

// PageInfo supports pagination. See the google.golang.org/api/iterator package for details.
func (it *TaskIterator) PageInfo() *iterator.PageInfo {
	return it.pageInfo
}

// Next returns the next result. Its second return value is iterator.Done if there are no more
// results. Once Next returns Done, all subsequent calls will return Done.
func (it *TaskIterator) Next() (*taskspb.Task, error) {
	var item *taskspb.Task
	if err := it.nextFunc(); err != nil {
		return item, err
	}
	item = it.items[0]
	it.items = it.items[1:]
	return item, nil
}

func (it *TaskIterator) bufLen() int {
	return len(it.items)
}

func (it *TaskIterator) takeBuf() interface{} {
	b := it.items
	it.items = nil
	return b
}
