yr/pkg/cache/cache.go

package cache

import (
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"strings"
	"time"
)

type Cache[T any] struct {
	Path string
}

// New Cache where default path is os.TempDir()
func New[T any](path string) *Cache[T] {
	if path == "" {
		path = os.TempDir()
	}
	return &Cache[T]{path}
}

var (
	ErrorUnableToMarshalJSON        = errors.New("unable to marshal as JSON")
	ErrorUnableToEnsureCacheDir     = errors.New("unable to ensure cache-dir is present")
	ErrorUnableToWriteCache         = errors.New("unable to write data to cache file")
	ErrorUnableToOpenCacheFile      = errors.New("unable to open cache")
	ErrorUnableToReadCacheFile      = errors.New("unable to read cache")
	ErrorUnableToUnmarshalCacheFile = errors.New("unable to unmarshal JSON from cache-file")
	ErrorUnableToReadCachePath      = errors.New("unable to read from cache path")
)

// Add data as JSON-file into cache-dir, returns nil if success
func (c *Cache[T]) Add(name string, data any) error {
	j, err := json.MarshalIndent(data, "", " ")
	if err != nil {
		return ErrorUnableToMarshalJSON
	}
	err = os.MkdirAll(c.Path, 0646)
	if err != nil {
		return ErrorUnableToEnsureCacheDir
	}

	filePath := filepath.Join(c.Path, filename(name))
	d := []byte(j)
	err = os.WriteFile(filePath, d, 0646)
	if err != nil {
		return ErrorUnableToWriteCache
	}

	return nil
}

// Get data from JSON-file from cache-dir, returns nil if no result
func (c *Cache[T]) Get(name string) (*T, error) {
	filePath := filepath.Join(c.Path, filename(name))
	if _, err := os.Stat(filePath); errors.Is(err, os.ErrNotExist) {
		return nil, nil
	}

	rawFile, err := os.Open(filePath)
	if err != nil {
		return nil, ErrorUnableToOpenCacheFile
	}

	var result T

	bytes, err := io.ReadAll(rawFile)
	if err != nil {
		return nil, ErrorUnableToReadCacheFile
	}

	err = json.Unmarshal(bytes, &result)
	if err != nil {
		return nil, ErrorUnableToUnmarshalCacheFile
	}

	return &result, nil
}

type Saved[T any] struct {
	Filename string
	Item     T
}

func (c *Cache[T]) List() ([]Saved[T], error) {
	var result []Saved[T]
	filenames, err := list(c.Path)
	if err != nil {
		return nil, ErrorUnableToReadCachePath
	}

	if len(filenames) == 0 {
		return result, nil
	}

	for _, f := range filenames {
		cached, err := c.Get(f)
		if err != nil {
			return nil, err
		}
		result = append(result, Saved[T]{Filename: f, Item: *(cached)})

	}

	return result, nil
}

func list(path string) ([]string, error) {
	dir, err := os.ReadDir(path)
	if err != nil {
		return nil, ErrorUnableToReadCachePath
	}
	var filenames []string

	for _, item := range dir {
		if !item.IsDir() && strings.Contains(item.Name(), prefix) {
			tmp := strings.ReplaceAll(strings.ReplaceAll(item.Name(), ".json", ""), prefix, "")
			filenames = append(filenames, tmp)
		}
	}
	return filenames, nil

}

func (c *Cache[T]) Clear() error {
	files, err := list(c.Path)
	if err != nil {
		return err
	}
	for _, f := range files {
		filePath := filepath.Join(c.Path, filename(f))

		err = os.Remove(filePath)
		if err != nil {
			return err
		}
	}
	return nil
}

var prefix = "yr-"

func filename(name string) string {
	return fmt.Sprintf("%s%s.json", prefix, name)
}

// Returns if t is expired
func IsExpired(expire time.Time, now *time.Time) bool {
	if now == nil {
		tmp := time.Now()
		now = &tmp
	}

	return now.After(expire)
}