// Copyright The OpenTelemetry Authors
//
// 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
//
//     http://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.

package otlpmetricgrpc // import "go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc"

import (
	"context"
	"errors"
	"sync"
	"time"

	"google.golang.org/genproto/googleapis/rpc/errdetails"
	"google.golang.org/grpc"
	"google.golang.org/grpc/codes"
	"google.golang.org/grpc/metadata"
	"google.golang.org/grpc/status"

	"go.opentelemetry.io/otel/exporters/otlp/internal/retry"
	"go.opentelemetry.io/otel/exporters/otlp/otlpmetric"
	"go.opentelemetry.io/otel/exporters/otlp/otlpmetric/internal/otlpconfig"
	colmetricpb "go.opentelemetry.io/proto/otlp/collector/metrics/v1"
	metricpb "go.opentelemetry.io/proto/otlp/metrics/v1"
)

type client struct {
	endpoint      string
	dialOpts      []grpc.DialOption
	metadata      metadata.MD
	exportTimeout time.Duration
	requestFunc   retry.RequestFunc

	// stopCtx is used as a parent context for all exports. Therefore, when it
	// is canceled with the stopFunc all exports are canceled.
	stopCtx context.Context
	// stopFunc cancels stopCtx, stopping any active exports.
	stopFunc context.CancelFunc

	// ourConn keeps track of where conn was created: true if created here on
	// Start, or false if passed with an option. This is important on Shutdown
	// as the conn should only be closed if created here on start. Otherwise,
	// it is up to the processes that passed the conn to close it.
	ourConn bool
	conn    *grpc.ClientConn
	mscMu   sync.RWMutex
	msc     colmetricpb.MetricsServiceClient
}

// Compile time check *client implements otlpmetric.Client.
var _ otlpmetric.Client = (*client)(nil)

// NewClient creates a new gRPC metric client.
func NewClient(opts ...Option) otlpmetric.Client {
	return newClient(opts...)
}

func newClient(opts ...Option) *client {
	cfg := otlpconfig.NewGRPCConfig(asGRPCOptions(opts)...)

	ctx, cancel := context.WithCancel(context.Background())

	c := &client{
		endpoint:      cfg.Metrics.Endpoint,
		exportTimeout: cfg.Metrics.Timeout,
		requestFunc:   cfg.RetryConfig.RequestFunc(retryable),
		dialOpts:      cfg.DialOptions,
		stopCtx:       ctx,
		stopFunc:      cancel,
		conn:          cfg.GRPCConn,
	}

	if len(cfg.Metrics.Headers) > 0 {
		c.metadata = metadata.New(cfg.Metrics.Headers)
	}

	return c
}

// Start establishes a gRPC connection to the collector.
func (c *client) Start(ctx context.Context) error {
	if c.conn == nil {
		// If the caller did not provide a ClientConn when the client was
		// created, create one using the configuration they did provide.
		conn, err := grpc.DialContext(ctx, c.endpoint, c.dialOpts...)
		if err != nil {
			return err
		}
		// Keep track that we own the lifecycle of this conn and need to close
		// it on Shutdown.
		c.ourConn = true
		c.conn = conn
	}

	// The otlpmetric.Client interface states this method is called just once,
	// so no need to check if already started.
	c.mscMu.Lock()
	c.msc = colmetricpb.NewMetricsServiceClient(c.conn)
	c.mscMu.Unlock()

	return nil
}

var errAlreadyStopped = errors.New("the client is already stopped")

// Stop shuts down the client.
//
// Any active connections to a remote endpoint are closed if they were created
// by the client. Any gRPC connection passed during creation using
// WithGRPCConn will not be closed. It is the caller's responsibility to
// handle cleanup of that resource.
//
// This method synchronizes with the UploadMetrics method of the client. It
// will wait for any active calls to that method to complete unimpeded, or it
// will cancel any active calls if ctx expires. If ctx expires, the context
// error will be forwarded as the returned error. All client held resources
// will still be released in this situation.
//
// If the client has already stopped, an error will be returned describing
// this.
func (c *client) Stop(ctx context.Context) error {
	// Acquire the c.mscMu lock within the ctx lifetime.
	acquired := make(chan struct{})
	go func() {
		c.mscMu.Lock()
		close(acquired)
	}()
	var err error
	select {
	case <-ctx.Done():
		// The Stop timeout is reached. Kill any remaining exports to force
		// the clear of the lock and save the timeout error to return and
		// signal the shutdown timed out before cleanly stopping.
		c.stopFunc()
		err = ctx.Err()

		// To ensure the client is not left in a dirty state c.msc needs to be
		// set to nil. To avoid the race condition when doing this, ensure
		// that all the exports are killed (initiated by c.stopFunc).
		<-acquired
	case <-acquired:
	}
	// Hold the mscMu lock for the rest of the function to ensure no new
	// exports are started.
	defer c.mscMu.Unlock()

	// The otlpmetric.Client interface states this method is called only
	// once, but there is no guarantee it is called after Start. Ensure the
	// client is started before doing anything and let the called know if they
	// made a mistake.
	if c.msc == nil {
		return errAlreadyStopped
	}

	// Clear c.msc to signal the client is stopped.
	c.msc = nil

	if c.ourConn {
		closeErr := c.conn.Close()
		// A context timeout error takes precedence over this error.
		if err == nil && closeErr != nil {
			err = closeErr
		}
	}
	return err
}

var errShutdown = errors.New("the client is shutdown")

// UploadMetrics sends a batch of spans.
//
// Retryable errors from the server will be handled according to any
// RetryConfig the client was created with.
func (c *client) UploadMetrics(ctx context.Context, protoMetrics *metricpb.ResourceMetrics) error {
	// Hold a read lock to ensure a shut down initiated after this starts does
	// not abandon the export. This read lock acquire has less priority than a
	// write lock acquire (i.e. Stop), meaning if the client is shutting down
	// this will come after the shut down.
	c.mscMu.RLock()
	defer c.mscMu.RUnlock()

	if c.msc == nil {
		return errShutdown
	}

	ctx, cancel := c.exportContext(ctx)
	defer cancel()

	return c.requestFunc(ctx, func(iCtx context.Context) error {
		_, err := c.msc.Export(iCtx, &colmetricpb.ExportMetricsServiceRequest{
			ResourceMetrics: []*metricpb.ResourceMetrics{protoMetrics},
		})
		// nil is converted to OK.
		if status.Code(err) == codes.OK {
			// Success.
			return nil
		}
		return err
	})
}

// exportContext returns a copy of parent with an appropriate deadline and
// cancellation function.
//
// It is the callers responsibility to cancel the returned context once its
// use is complete, via the parent or directly with the returned CancelFunc, to
// ensure all resources are correctly released.
func (c *client) exportContext(parent context.Context) (context.Context, context.CancelFunc) {
	var (
		ctx    context.Context
		cancel context.CancelFunc
	)

	if c.exportTimeout > 0 {
		ctx, cancel = context.WithTimeout(parent, c.exportTimeout)
	} else {
		ctx, cancel = context.WithCancel(parent)
	}

	if c.metadata.Len() > 0 {
		ctx = metadata.NewOutgoingContext(ctx, c.metadata)
	}

	// Unify the client stopCtx with the parent.
	go func() {
		select {
		case <-ctx.Done():
		case <-c.stopCtx.Done():
			// Cancel the export as the shutdown has timed out.
			cancel()
		}
	}()

	return ctx, cancel
}

// retryable returns if err identifies a request that can be retried and a
// duration to wait for if an explicit throttle time is included in err.
func retryable(err error) (bool, time.Duration) {
	//func retryable(err error) (bool, time.Duration) {
	s := status.Convert(err)
	switch s.Code() {
	case codes.Canceled,
		codes.DeadlineExceeded,
		codes.ResourceExhausted,
		codes.Aborted,
		codes.OutOfRange,
		codes.Unavailable,
		codes.DataLoss:
		return true, throttleDelay(s)
	}

	// Not a retry-able error.
	return false, 0
}

// throttleDelay returns a duration to wait for if an explicit throttle time
// is included in the response status.
func throttleDelay(status *status.Status) time.Duration {
	for _, detail := range status.Details() {
		if t, ok := detail.(*errdetails.RetryInfo); ok {
			return t.RetryDelay.AsDuration()
		}
	}
	return 0
}