package kvm

import (
	"encoding/xml"
	"fmt"
)

const bytesPerGiB = 1 << 30

func overlayVolumeName(name string) string { return name + ".qcow2" }

func seedVolumeName(name string) string { return name + "-seed.iso" }

// volumeSpec describes a storage volume to create. A non-empty BackingPath
// makes it a copy-on-write overlay of that file.
type volumeSpec struct {
	Name          string
	SizeBytes     int64
	Format        string
	BackingPath   string
	BackingFormat string
}

func overlayVolume(name string, sizeGB int64, basePath, baseFormat string) volumeSpec {
	return volumeSpec{
		Name:          overlayVolumeName(name),
		SizeBytes:     sizeGB * bytesPerGiB,
		Format:        formatQcow2,
		BackingPath:   basePath,
		BackingFormat: baseFormat,
	}
}

func rawVolume(name string, sizeBytes int64) volumeSpec {
	return volumeSpec{Name: name, SizeBytes: sizeBytes, Format: formatRaw}
}

// buildVolumeXML renders the volume for StorageVolCreateXML. Capacity is
// always given in bytes so no libvirt unit-suffix ambiguity (G vs GiB) can
// creep in.
func buildVolumeXML(v volumeSpec) (string, error) {
	x := volumeXML{
		Type:     "file",
		Name:     v.Name,
		Capacity: sizeXML{Unit: "bytes", Value: v.SizeBytes},
		Target:   volumeTargetXML{Format: formatXML{Type: v.Format}},
	}
	if v.BackingPath != "" {
		x.BackingStore = &backingStoreXML{Path: v.BackingPath, Format: formatXML{Type: v.BackingFormat}}
	}
	out, err := xml.Marshal(x)
	if err != nil {
		return "", fmt.Errorf("marshalling volume xml: %w", err)
	}
	return string(out), nil
}

type volumeXML struct {
	XMLName      xml.Name         `xml:"volume"`
	Type         string           `xml:"type,attr"`
	Name         string           `xml:"name"`
	Capacity     sizeXML          `xml:"capacity"`
	Target       volumeTargetXML  `xml:"target"`
	BackingStore *backingStoreXML `xml:"backingStore"`
}

type volumeTargetXML struct {
	Format formatXML `xml:"format"`
}

type formatXML struct {
	Type string `xml:"type,attr"`
}

type backingStoreXML struct {
	Path   string    `xml:"path"`
	Format formatXML `xml:"format"`
}