// ReadCharmURL reads a charm identity file from the supplied path.
func ReadCharmURL(path string) (*charm.URL, error) {
	surl := ""
	if err := utils.ReadYaml(path, &surl); err != nil {
		return nil, err
	}
	return charm.ParseURL(surl)
}

func readUnsafe(opsfile string) (*operation.State, error) {
	var st operation.State
	if err := utils.ReadYaml(opsfile, &st); err != nil {
		if os.IsNotExist(err) {
			return nil, operation.ErrNoStateFile
		}
	}
	return &st, nil
}

// Read reads the current meter status information from disk.
func (f *StateFile) Read() (string, string, error) {
	var st state
	if err := utils.ReadYaml(f.path, &st); err != nil {
		if os.IsNotExist(err) {
			return "", "", nil
		}
		return "", "", errors.Trace(err)
	}
	return st.Code, st.Info, nil
}

// Read reads a State from the file. If the file does not exist it returns
// ErrNoStateFile.
func (f *StateFile) Read() (*State, error) {
	var st State
	if err := utils.ReadYaml(f.path, &st); err != nil {
		if os.IsNotExist(err) {
			return nil, ErrNoStateFile
		}
	}
	if err := st.validate(); err != nil {
		return nil, errors.Errorf("cannot read %q: %v", f.path, err)
	}
	return &st, nil
}

func (s *tmpfsFilesystemSource) readFilesystemInfo(tag names.FilesystemTag) (storage.FilesystemInfo, error) {
	var info filesystemInfo
	if err := utils.ReadYaml(s.filesystemInfoFile(tag), &info); err != nil {
		return storage.FilesystemInfo{}, errors.Annotate(err, "reading filesystem info from disk")
	}
	if info.Size == nil {
		return storage.FilesystemInfo{}, errors.New("invalid filesystem info: missing size")
	}
	return storage.FilesystemInfo{
		FilesystemId: tag.String(),
		Size:         *info.Size,
	}, nil
}

// loadManifest loads, from dataPath, the manifest for the charm identified by the
// identity file at the supplied path within the charm directory.
func (d *manifestDeployer) loadManifest(urlFilePath string) (*charm.URL, set.Strings, error) {
	url, err := ReadCharmURL(d.CharmPath(urlFilePath))
	if err != nil {
		return nil, nil, err
	}
	name := charm.Quote(url.String())
	path := filepath.Join(d.DataPath(manifestsDataPath), name)
	manifest := []string{}
	err = utils.ReadYaml(path, &manifest)
	if os.IsNotExist(err) {
		logger.Warningf("manifest not found at %q: files from charm %q may be left unremoved", path, url)
		err = nil
	}
	return url, set.NewStrings(manifest...), err
}

// ReadStateDir loads a StateDir from the subdirectory of dirPath named
// for the supplied RelationId. If the directory does not exist, no error
// is returned,
func ReadStateDir(dirPath string, relationId int) (d *StateDir, err error) {
	d = &StateDir{
		filepath.Join(dirPath, strconv.Itoa(relationId)),
		State{relationId, map[string]int64{}, ""},
	}
	defer errors.Maskf(&err, "cannot load relation state from %q", d.path)
	if _, err := os.Stat(d.path); os.IsNotExist(err) {
		return d, nil
	} else if err != nil {
		return nil, err
	}
	fis, err := ioutil.ReadDir(d.path)
	if err != nil {
		return nil, err
	}
	for _, fi := range fis {
		// Entries with names ending in "-" followed by an integer must be
		// files containing valid unit data; all other names are ignored.
		name := fi.Name()
		i := strings.LastIndex(name, "-")
		if i == -1 {
			continue
		}
		svcName := name[:i]
		unitId := name[i+1:]
		if _, err := strconv.Atoi(unitId); err != nil {
			continue
		}
		unitName := svcName + "/" + unitId
		var info diskInfo
		if err = utils.ReadYaml(filepath.Join(d.path, name), &info); err != nil {
			return nil, fmt.Errorf("invalid unit file %q: %v", name, err)
		}
		if info.ChangeVersion == nil {
			return nil, fmt.Errorf(`invalid unit file %q: "changed-version" not set`, name)
		}
		d.state.Members[unitName] = *info.ChangeVersion
		if info.ChangedPending {
			if d.state.ChangedPending != "" {
				return nil, fmt.Errorf("%q and %q both have pending changed hooks", d.state.ChangedPending, unitName)
			}
			d.state.ChangedPending = unitName
		}
	}
	return d, nil
}

// readStateFile loads a stateFile from the subdirectory of dirPath named
// for the supplied storage tag. If the directory does not exist, no error
// is returned.
func readStateFile(dirPath string, tag names.StorageTag) (d *stateFile, err error) {
	filename := strings.Replace(tag.Id(), "/", "-", -1)
	d = &stateFile{
		filepath.Join(dirPath, filename),
		state{storage: tag},
	}
	defer errors.DeferredAnnotatef(&err, "cannot load storage %q state from %q", tag.Id(), d.path)
	if _, err := os.Stat(d.path); os.IsNotExist(err) {
		return d, nil
	} else if err != nil {
		return nil, err
	}
	var info diskInfo
	if err := utils.ReadYaml(d.path, &info); err != nil {
		return nil, errors.Errorf("invalid storage state file %q: %v", d.path, err)
	}
	if info.Attached == nil {
		return nil, errors.Errorf("invalid storage state file %q: missing 'attached'", d.path)
	}
	d.state.attached = *info.Attached
	return d, nil
}

// load loads the "machine info" file and parse the content into the info
// object.
func (info *machineInfo) load() error {
	return utils.ReadYaml(_MAASInstanceFilename, info)
}