charm.go

// Copyright 2011, 2012, 2013 Canonical Ltd.
// Licensed under the LGPLv3, see LICENCE file for details.

package charm

import (
	"fmt"
	"os"
	"strings"

	"github.com/juju/collections/set"
	"github.com/juju/errors"
	"github.com/juju/loggo"
)

var logger = loggo.GetLogger("juju.charm")

// CharmMeta describes methods that inform charm operation.
type CharmMeta interface {
	Meta() *Meta
	Manifest() *Manifest
}

// The Charm interface is implemented by any type that
// may be handled as a charm.
type Charm interface {
	CharmMeta
	Config() *Config
	Metrics() *Metrics
	Actions() *Actions
	Revision() int
}

// ReadCharm reads a Charm from path, which can point to either a charm archive or a
// charm directory.
func ReadCharm(path string) (charm Charm, err error) {
	info, err := os.Stat(path)
	if err != nil {
		return nil, errors.Trace(err)
	}
	if info.IsDir() {
		charm, err = ReadCharmDir(path)
	} else {
		charm, err = ReadCharmArchive(path)
	}
	if err != nil {
		return nil, errors.Trace(err)
	}

	return charm, errors.Trace(CheckMeta(charm))
}

// FormatSelectionReason represents the reason for a format version selection.
type FormatSelectionReason = string

const (
	// SelectionManifest states that it found a manifest.
	SelectionManifest FormatSelectionReason = "manifest"
	// SelectionBases states that there was at least 1 base.
	SelectionBases FormatSelectionReason = "bases"
	// SelectionSeries states that there was at least 1 series.
	SelectionSeries FormatSelectionReason = "series"
	// SelectionContainers states that there was at least 1 container.
	SelectionContainers FormatSelectionReason = "containers"
)

var (
	// formatV2Set defines what in reality is a v2 metadata.
	formatV2Set = set.NewStrings(SelectionBases, SelectionContainers)
)

// MetaFormatReasons returns the format and why the selection was done. We can
// then inspect the reasons to understand the reasoning.
func MetaFormatReasons(ch CharmMeta) (Format, []FormatSelectionReason) {
	manifest := ch.Manifest()

	// To better inform users of why a metadata selection was preferred over
	// another, we deduce why a format is selected over another.
	reasons := set.NewStrings()
	if manifest != nil {
		reasons.Add(SelectionManifest)
		if len(manifest.Bases) > 0 {
			reasons.Add(SelectionBases)
		}
	}
	if len(ch.Meta().Series) > 0 {
		reasons.Add(SelectionSeries)
	}

	// To be a format v1 you can have no series with no bases or containers, or
	// just have a series slice.
	format := FormatV1
	if !reasons.Contains(SelectionSeries) && reasons.Intersection(formatV2Set).Size() > 0 {
		format = FormatV2
	}

	return format, reasons.SortedValues()
}

// MetaFormat returns the underlying format from checking the charm for the
// right values.
func MetaFormat(ch CharmMeta) Format {
	format, _ := MetaFormatReasons(ch)
	return format
}

// CheckMeta determines the version of the metadata used by this charm,
// then checks that it is valid as appropriate.
func CheckMeta(ch CharmMeta) error {
	format, reasons := MetaFormatReasons(ch)
	return ch.Meta().Check(format, reasons...)
}

// SeriesForCharm takes a requested series and a list of series supported by a
// charm and returns the series which is relevant.
// If the requested series is empty, then the first supported series is used,
// otherwise the requested series is validated against the supported series.
func SeriesForCharm(requestedSeries string, supportedSeries []string) (string, error) {
	// Old charm with no supported series.
	if len(supportedSeries) == 0 {
		if requestedSeries == "" {
			return "", errMissingSeries
		}
		return requestedSeries, nil
	}
	// Use the charm default.
	if requestedSeries == "" {
		return supportedSeries[0], nil
	}
	for _, s := range supportedSeries {
		if s == requestedSeries {
			return requestedSeries, nil
		}
	}
	return "", &unsupportedSeriesError{requestedSeries, supportedSeries}
}

// errMissingSeries is used to denote that SeriesForCharm could not determine
// a series because a legacy charm did not declare any.
var errMissingSeries = fmt.Errorf("series not specified and charm does not define any")

// IsMissingSeriesError returns true if err is an errMissingSeries.
func IsMissingSeriesError(err error) bool {
	return err == errMissingSeries
}

// UnsupportedSeriesError represents an error indicating that the requested series
// is not supported by the charm.
type unsupportedSeriesError struct {
	requestedSeries string
	supportedSeries []string
}

func (e *unsupportedSeriesError) Error() string {
	return fmt.Sprintf(
		"series %q not supported by charm, supported series are: %s",
		e.requestedSeries, strings.Join(e.supportedSeries, ","),
	)
}

// NewUnsupportedSeriesError returns an error indicating that the requested series
// is not supported by a charm.
func NewUnsupportedSeriesError(requestedSeries string, supportedSeries []string) error {
	return &unsupportedSeriesError{requestedSeries, supportedSeries}
}

// IsUnsupportedSeriesError returns true if err is an UnsupportedSeriesError.
func IsUnsupportedSeriesError(err error) bool {
	_, ok := err.(*unsupportedSeriesError)
	return ok
}