zntg/ui/copyresources.go

package ui

import (
	"io"
	"os"

	"opslag.de/schobers/zntg"
)

var _ PhysicalResources = &CopyResources{}

// CopyResources copies the resource to a temporary directory when fetched. Optionally the resource is fetched as well before opening.
type CopyResources struct {
	Source Resources

	copy *zntg.Dir

	mustCopyBeforeOpen bool
}

func newCopyResources(prefix string, source Resources, mustCopyBeforeOpen bool) (*CopyResources, error) {
	copy, err := zntg.NewTempDir(prefix)
	if nil != err {
		return nil, err
	}
	return &CopyResources{source, copy, mustCopyBeforeOpen}, nil
}

// NewCopyResources creates a proxy that copies resources first to disk. Copy on OpenResource only happens when mustCopyBeforeOpen is set to true.
func NewCopyResources(prefix string, source Resources, mustCopyBeforeOpen bool) (*CopyResources, error) {
	return newCopyResources(prefix, source, false)
}

// FetchResource copies the file from the source to disk and returns the path to it.
func (r *CopyResources) FetchResource(name string) (string, error) {
	path := r.copy.FilePath(name)
	if !zntg.FileExists(path) {
		src, err := r.Source.OpenResource(name)
		if err != nil {
			return "", err
		}
		defer src.Close()

		err = r.copy.Write(name, src)
		if nil != err {
			return "", err
		}
	}
	return path, nil
}

// OpenResource opens the (optionally copied) resource.
func (r *CopyResources) OpenResource(name string) (io.ReadCloser, error) {
	if r.mustCopyBeforeOpen {
		path, err := r.FetchResource(name)
		if err != nil {
			return nil, err
		}
		return os.Open(path)
	}
	return r.Source.OpenResource(name)
}

// Destroy destroy the copy of the resources.
func (r *CopyResources) Destroy() error {
	return r.copy.Destroy()
}