// 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 component // import "go.opentelemetry.io/collector/component"

import (
	"context"
	"errors"

	"go.opentelemetry.io/collector/config"
)

var (
	// ErrNilNextConsumer can be returned by receiver, or processor Start factory funcs that create the Component if the
	// expected next Consumer is nil.
	ErrNilNextConsumer = errors.New("nil next Consumer")

	// ErrDataTypeIsNotSupported can be returned by receiver, exporter or processor factory funcs that create the
	// Component if the particular telemetry data type is not supported by the receiver, exporter or processor.
	ErrDataTypeIsNotSupported = errors.New("telemetry type is not supported")
)

// Component is either a receiver, exporter, processor, or an extension.
//
// A component's lifecycle has the following phases:
//
//  1. Creation: The component is created using its respective factory, via a Create* call.
//  2. Start: The component's Start method is called.
//  3. Running: The component is up and running.
//  4. Shutdown: The component's Shutdown method is called and the lifecycle is complete.
//
// Once the lifecycle is complete it may be repeated, in which case a new component
// is created, starts, runs and is shutdown again.
type Component interface {
	// Start tells the component to start. Host parameter can be used for communicating
	// with the host after Start() has already returned. If an error is returned by
	// Start() then the collector startup will be aborted.
	// If this is an exporter component it may prepare for exporting
	// by connecting to the endpoint.
	//
	// If the component needs to perform a long-running starting operation then it is recommended
	// that Start() returns quickly and the long-running operation is performed in background.
	// In that case make sure that the long-running operation does not use the context passed
	// to Start() function since that context will be cancelled soon and can abort the long-running
	// operation. Create a new context from the context.Background() for long-running operations.
	Start(ctx context.Context, host Host) error

	// Shutdown is invoked during service shutdown. After Shutdown() is called, if the component
	// accepted data in any way, it should not accept it anymore.
	//
	// If there are any background operations running by the component they must be aborted before
	// this function returns. Remember that if you started any long-running background operations from
	// the Start() method, those operations must be also cancelled. If there are any buffers in the
	// component, they should be cleared and the data sent immediately to the next component.
	//
	// The component's lifecycle is completed once the Shutdown() method returns. No other
	// methods of the component are called after that. If necessary a new component with
	// the same or different configuration may be created and started (this may happen
	// for example if we want to restart the component).
	Shutdown(ctx context.Context) error
}

// StartFunc specifies the function invoked when the component.Component is being started.
type StartFunc func(context.Context, Host) error

// Start starts the component.
func (f StartFunc) Start(ctx context.Context, host Host) error {
	if f == nil {
		return nil
	}
	return f(ctx, host)
}

// ShutdownFunc specifies the function invoked when the component.Component is being shutdown.
type ShutdownFunc func(context.Context) error

// Shutdown shuts down the component.
func (f ShutdownFunc) Shutdown(ctx context.Context) error {
	if f == nil {
		return nil
	}
	return f(ctx)
}

// Kind represents component kinds.
type Kind int

const (
	_ Kind = iota // skip 0, start types from 1.
	KindReceiver
	KindProcessor
	KindExporter
	KindExtension
)

// StabilityLevel represents the stability level of the component created by the factory.
// The stability level is used to determine if the component should be used in production
// or not. For more details see:
// https://github.com/open-telemetry/opentelemetry-collector#stability-levels
type StabilityLevel int

const (
	StabilityLevelUndefined StabilityLevel = iota // skip 0, start types from 1.
	StabilityLevelUnmaintained
	StabilityLevelDeprecated
	StabilityLevelInDevelopment
	StabilityLevelAlpha
	StabilityLevelBeta
	StabilityLevelStable
)

func (sl StabilityLevel) String() string {
	switch sl {
	case StabilityLevelUnmaintained:
		return "unmaintained"
	case StabilityLevelDeprecated:
		return "deprecated"
	case StabilityLevelInDevelopment:
		return "in development"
	case StabilityLevelAlpha:
		return "alpha"
	case StabilityLevelBeta:
		return "beta"
	case StabilityLevelStable:
		return "stable"
	}
	return "undefined"
}

func (sl StabilityLevel) LogMessage() string {
	switch sl {
	case StabilityLevelUnmaintained:
		return "Unmaintained component. Actively looking for contributors. Component will become deprecated after 6 months of remaining unmaintained."
	case StabilityLevelDeprecated:
		return "Deprecated component. Will be removed in future releases."
	case StabilityLevelInDevelopment:
		return "In development component. May change in the future."
	case StabilityLevelAlpha:
		return "Alpha component. May change in the future."
	case StabilityLevelBeta:
		return "Beta component. May change in the future."
	case StabilityLevelStable:
		return "Stable component."
	}
	return "Stability level of component is undefined"
}

// Factory is implemented by all component factories.
//
// This interface cannot be directly implemented. Implementations must
// use the factory helpers for the appropriate component type.
type Factory interface {
	// Type gets the type of the component created by this factory.
	Type() config.Type

	unexportedFactoryFunc()
}

type baseFactory struct {
	cfgType config.Type
}

func (baseFactory) unexportedFactoryFunc() {}

func (bf baseFactory) Type() config.Type {
	return bf.cfgType
}
