// 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 builder // import "go.opentelemetry.io/collector/service/internal/builder"

import (
	"context"
	"errors"
	"fmt"

	"go.uber.org/multierr"
	"go.uber.org/zap"

	"go.opentelemetry.io/collector/component"
	"go.opentelemetry.io/collector/config"
	"go.opentelemetry.io/collector/consumer"
	"go.opentelemetry.io/collector/service/internal/components"
	"go.opentelemetry.io/collector/service/internal/fanoutconsumer"
)

var errUnusedReceiver = errors.New("receiver defined but not used by any pipeline")

// builtReceiver is a receiver that is built based on a config. It can have
// a trace and/or a metrics component.
type builtReceiver struct {
	logger   *zap.Logger
	receiver component.Receiver
}

// Start starts the receiver.
func (rcv *builtReceiver) Start(ctx context.Context, host component.Host) error {
	return rcv.receiver.Start(ctx, components.NewHostWrapper(host, rcv.logger))
}

// Shutdown stops the receiver.
func (rcv *builtReceiver) Shutdown(ctx context.Context) error {
	return rcv.receiver.Shutdown(ctx)
}

// Receivers is a map of receivers created from receiver configs.
type Receivers map[config.ComponentID]*builtReceiver

// ShutdownAll stops all receivers.
func (rcvs Receivers) ShutdownAll(ctx context.Context) error {
	var err error
	for _, rcv := range rcvs {
		err = multierr.Append(err, rcv.Shutdown(ctx))
	}

	return err
}

// StartAll starts all receivers.
func (rcvs Receivers) StartAll(ctx context.Context, host component.Host) error {
	for _, rcv := range rcvs {
		rcv.logger.Info("Receiver is starting...")

		if err := rcv.Start(ctx, host); err != nil {
			return err
		}
		rcv.logger.Info("Receiver started.")
	}
	return nil
}

// receiversBuilder builds receivers from config.
type receiversBuilder struct {
	config         *config.Config
	builtPipelines BuiltPipelines
	factories      map[config.Type]component.ReceiverFactory
}

// BuildReceivers builds Receivers from config.
func BuildReceivers(
	settings component.TelemetrySettings,
	buildInfo component.BuildInfo,
	cfg *config.Config,
	builtPipelines BuiltPipelines,
	factories map[config.Type]component.ReceiverFactory,
) (Receivers, error) {
	rb := &receiversBuilder{cfg, builtPipelines, factories}

	receivers := make(Receivers)
	for recvID, recvCfg := range cfg.Receivers {
		set := component.ReceiverCreateSettings{
			TelemetrySettings: component.TelemetrySettings{
				Logger: settings.Logger.With(
					zap.String(components.ZapKindKey, components.ZapKindReceiver),
					zap.String(components.ZapNameKey, recvID.String())),
				TracerProvider: settings.TracerProvider,
				MeterProvider:  settings.MeterProvider,
				MetricsLevel:   cfg.Telemetry.Metrics.Level,
			},
			BuildInfo: buildInfo,
		}

		rcv, err := rb.buildReceiver(context.Background(), set, recvID, recvCfg)
		if err != nil {
			if errors.Is(err, errUnusedReceiver) {
				set.Logger.Info("Ignoring receiver as it is not used by any pipeline")
				continue
			}
			return nil, err
		}
		receivers[recvID] = rcv
	}

	return receivers, nil
}

// hasReceiver returns true if the pipeline is attached to specified receiver.
func hasReceiver(pipeline *config.Pipeline, receiverID config.ComponentID) bool {
	for _, id := range pipeline.Receivers {
		if id == receiverID {
			return true
		}
	}
	return false
}

type attachedPipelines map[config.DataType][]*builtPipeline

func (rb *receiversBuilder) findPipelinesToAttach(receiverID config.ComponentID) (attachedPipelines, error) {
	// A receiver may be attached to multiple pipelines. Pipelines may consume different
	// data types. We need to compile the list of pipelines of each type that must be
	// attached to this receiver according to configuration.

	pipelinesToAttach := make(attachedPipelines)

	// Iterate over all pipelines.
	for pipelineID, pipelineCfg := range rb.config.Service.Pipelines {
		// Get the first processor of the pipeline.
		pipelineProcessor := rb.builtPipelines[pipelineID]
		if pipelineProcessor == nil {
			return nil, fmt.Errorf("cannot find pipeline %q", pipelineID)
		}

		// Is this receiver attached to the pipeline?
		if hasReceiver(pipelineCfg, receiverID) {
			if _, exists := pipelinesToAttach[pipelineID.Type()]; !exists {
				pipelinesToAttach[pipelineID.Type()] = make([]*builtPipeline, 0)
			}

			// Yes, add it to the list of pipelines of corresponding data type.
			pipelinesToAttach[pipelineID.Type()] = append(pipelinesToAttach[pipelineID.Type()], pipelineProcessor)
		}
	}

	return pipelinesToAttach, nil
}

func attachReceiverToPipelines(
	ctx context.Context,
	set component.ReceiverCreateSettings,
	factory component.ReceiverFactory,
	dataType config.DataType,
	id config.ComponentID,
	cfg config.Receiver,
	rcv *builtReceiver,
	builtPipelines []*builtPipeline,
) error {
	// There are pipelines of the specified data type that must be attached to
	// the receiver. Create the receiver of corresponding data type and make
	// sure its output is fanned out to all attached pipelines.
	var err error
	var createdReceiver component.Receiver

	switch dataType {
	case config.TracesDataType:
		junction := buildFanoutTraceConsumer(builtPipelines)
		createdReceiver, err = factory.CreateTracesReceiver(ctx, set, cfg, junction)

	case config.MetricsDataType:
		junction := buildFanoutMetricConsumer(builtPipelines)
		createdReceiver, err = factory.CreateMetricsReceiver(ctx, set, cfg, junction)

	case config.LogsDataType:
		junction := buildFanoutLogConsumer(builtPipelines)
		createdReceiver, err = factory.CreateLogsReceiver(ctx, set, cfg, junction)

	default:
		err = component.ErrDataTypeIsNotSupported
	}

	if err != nil {
		if errors.Is(err, component.ErrDataTypeIsNotSupported) {
			return fmt.Errorf(
				"receiver %v does not support %s but it was used in a %s pipeline",
				id, dataType, dataType)
		}
		return fmt.Errorf("cannot create receiver %v: %w", id, err)
	}

	// Check if the factory really created the receiver.
	if createdReceiver == nil {
		return fmt.Errorf("factory for %v produced a nil receiver", id)
	}

	if rcv.receiver != nil {
		// The receiver was previously created for this config. This can happen if the
		// same receiver type supports more than one data type. In that case we expect
		// that CreateTracesReceiver and CreateMetricsReceiver return the same value.
		if rcv.receiver != createdReceiver {
			return fmt.Errorf(
				"factory for %q is implemented incorrectly: "+
					"CreateTracesReceiver, CreateMetricsReceiver and CreateLogsReceiver must return "+
					"the same receiver pointer when creating receivers of different data types",
				id,
			)
		}
	}
	rcv.receiver = createdReceiver

	set.Logger.Info("Receiver was built.", zap.String("datatype", string(dataType)))

	return nil
}

func (rb *receiversBuilder) buildReceiver(ctx context.Context, set component.ReceiverCreateSettings, id config.ComponentID, cfg config.Receiver) (*builtReceiver, error) {

	// First find pipelines that must be attached to this receiver.
	pipelinesToAttach, err := rb.findPipelinesToAttach(id)
	if err != nil {
		return nil, err
	}

	// Prepare to build the receiver.
	factory := rb.factories[id.Type()]
	if factory == nil {
		return nil, fmt.Errorf("receiver factory not found for: %v", cfg.ID())
	}
	rcv := &builtReceiver{
		logger: set.Logger,
	}

	// Now we have list of pipelines broken down by data type. Iterate for each data type.
	for dataType, pipelines := range pipelinesToAttach {
		if len(pipelines) == 0 {
			// No pipelines of this data type are attached to this receiver.
			continue
		}

		// Attach the corresponding part of the receiver to all pipelines that require
		// this data type.
		if err = attachReceiverToPipelines(ctx, set, factory, dataType, id, cfg, rcv, pipelines); err != nil {
			return nil, err
		}
	}

	if rcv.receiver == nil {
		return nil, errUnusedReceiver
	}

	return rcv, nil
}

func buildFanoutTraceConsumer(pipelines []*builtPipeline) consumer.Traces {
	var pipelineConsumers []consumer.Traces
	for _, pipeline := range pipelines {
		pipelineConsumers = append(pipelineConsumers, pipeline.firstTC)
	}
	// Create a junction point that fans out to all pipelines.
	return fanoutconsumer.NewTraces(pipelineConsumers)
}

func buildFanoutMetricConsumer(pipelines []*builtPipeline) consumer.Metrics {
	var pipelineConsumers []consumer.Metrics
	for _, pipeline := range pipelines {
		pipelineConsumers = append(pipelineConsumers, pipeline.firstMC)
	}
	// Create a junction point that fans out to all pipelines.
	return fanoutconsumer.NewMetrics(pipelineConsumers)
}

func buildFanoutLogConsumer(pipelines []*builtPipeline) consumer.Logs {
	var pipelineConsumers []consumer.Logs
	for _, pipeline := range pipelines {
		pipelineConsumers = append(pipelineConsumers, pipeline.firstLC)
	}
	// Create a junction point that fans out to all pipelines.
	return fanoutconsumer.NewLogs(pipelineConsumers)
}
