// Copyright 2019, 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 healthcheckextension

import (
	"errors"
	"sync/atomic"

	"go.uber.org/zap"

	"github.com/open-telemetry/opentelemetry-collector/component"
	"github.com/open-telemetry/opentelemetry-collector/config/configmodels"
)

const (
	// The value of extension "type" in configuration.
	typeStr = "health_check"
)

// ExtensionFactory is the factory for the extension.
type Factory struct {
}

// Type gets the type of the config created by this factory.
func (f *Factory) Type() string {
	return typeStr
}

// CreateDefaultConfig creates the default configuration for the extension.
func (f *Factory) CreateDefaultConfig() configmodels.Extension {
	return &Config{
		ExtensionSettings: configmodels.ExtensionSettings{
			TypeVal: typeStr,
			NameVal: typeStr,
		},
		Port: 13133,
	}
}

// CreateExtension creates the extension based on this config.
func (f *Factory) CreateExtension(
	logger *zap.Logger,
	cfg configmodels.Extension,
) (component.ServiceExtension, error) {
	config := cfg.(*Config)

	// The runtime settings are global to the application, so while in principle it
	// is possible to have more than one instance, running multiple does not bring
	// any value to the service.
	// In order to avoid this issue we will allow the creation of a single
	// instance once per process while keeping the private function that allow
	// the creation of multiple instances for unit tests. Summary: only a single
	// instance can be created via the factory.
	if !atomic.CompareAndSwapInt32(&instanceState, instanceNotCreated, instanceCreated) {
		return nil, errors.New("only a single instance can be created per process")
	}

	return newServer(*config, logger)
}

// See comment in CreateExtension how these are used.
var instanceState int32

const (
	instanceNotCreated int32 = 0
	instanceCreated    int32 = 1
)
