/*
Copyright 2021 The Kubernetes 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 volume

import (
	"fmt"
	"io"
	"os"
	"runtime"

	"k8s.io/apimachinery/pkg/api/resource"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
)

var _ MetricsProvider = &metricsBlock{}

// metricsBlock represents a MetricsProvider that detects the size of the
// BlockMode Volume.
type metricsBlock struct {
	// the device node where the volume is attached to.
	device string
}

// NewMetricsStatfs creates a new metricsBlock with the device node of the
// Volume.
func NewMetricsBlock(device string) MetricsProvider {
	return &metricsBlock{device}
}

// See MetricsProvider.GetMetrics
// GetMetrics detects the size of the BlockMode volume for the device node
// where the Volume is attached.
//
// Note that only the capacity of the device can be detected with standard
// tools. Storage systems may have more information that they can provide by
// going through specialized APIs.
func (mb *metricsBlock) GetMetrics() (*Metrics, error) {
	// TODO: Windows does not yet support VolumeMode=Block
	if runtime.GOOS == "windows" {
		return nil, NewNotImplementedError("Windows does not support Block volumes")
	}

	metrics := &Metrics{Time: metav1.Now()}
	if mb.device == "" {
		return metrics, NewNoPathDefinedError()
	}

	err := mb.getBlockInfo(metrics)
	if err != nil {
		return metrics, err
	}

	return metrics, nil
}

// getBlockInfo fetches metrics.Capacity by opening the device and seeking to
// the end.
func (mb *metricsBlock) getBlockInfo(metrics *Metrics) error {
	dev, err := os.Open(mb.device)
	if err != nil {
		return fmt.Errorf("unable to open device %q: %w", mb.device, err)
	}
	defer dev.Close()

	end, err := dev.Seek(0, io.SeekEnd)
	if err != nil {
		return fmt.Errorf("failed to detect size of %q: %w", mb.device, err)
	}

	metrics.Capacity = resource.NewQuantity(end, resource.BinarySI)

	return nil
}
