golifehk/utils/cache.go

package utils

import (
	"bytes"
	"fmt"
	"io"
	"log"
	"os"
	"path/filepath"
	"time"
)

type CacheStreams struct {
	Local  *bytes.Buffer
	Remote *bytes.Buffer
	Path   string
	Query  func() (io.ReadCloser, error)
}

func (cs *CacheStreams) Commit() error {

	f, err := os.OpenFile(cs.Path, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0644)
	if err != nil {
		return err
	}

	defer f.Close()

	_, err = io.Copy(f, bytes.NewReader(cs.Remote.Bytes()))
	log.Printf("Commit: %s", cs.Path)
	return err
}

func (cs *CacheStreams) Try(Parser func(*bytes.Buffer) error, expires time.Duration, retries int) error {
	var err error
	for i := 0; i < retries; i++ {
		if cs.NotExpired(expires) {
			err = Parser(cs.Local)
			if err == nil {
				log.Printf("Using cache: %s", cs.Path)
				return nil
			}
		}

		err = cs.Reload()
		log.Printf("Reloading (%d): %s", i+1, cs.Path)
		if err != nil {
			log.Printf("Error retrieving data(%s): %s", i+1, err)
		}

		if cs.Remote != nil {
			err = Parser(cs.Remote)
			if err == nil {
				cs.Commit()
				return nil
			}
		}
	}

	return fmt.Errorf("Failed to get data for: %s", cs.Path)
}

func (cs *CacheStreams) Reload() error {

	s, err := cs.Query()
	if err != nil {
		return err
	}

	defer s.Close()

	cs.Remote = bytes.NewBuffer([]byte{})
	_, err = io.Copy(cs.Remote, s)

	return err
}

func (cs *CacheStreams) NotExpired(expires time.Duration) bool {

	cache, err := os.Stat(cs.Path)

	if err == nil {
		expired := cache.ModTime().Add(expires * 1e9)
		return time.Now().Before(expired)
	}

	return false
}

func CacheStreamEx(path string, readStream func() (io.ReadCloser, error)) (*CacheStreams, error) {

	cs := CacheStreams{}
	cs.Path = path
	cs.Query = readStream

	f, err := os.Open(path)
	if err == nil {
		defer f.Close()
		cs.Local = bytes.NewBuffer([]byte{})
		_, err = io.Copy(cs.Local, f)
		if err != nil {
			return nil, err
		}
	}

	return &cs, nil
}

func CacheStream(path string, readStream func() (io.ReadCloser, error), expires time.Duration) (*bytes.Buffer, error) {

	cache, err := os.Stat(path)

	// Check if cache exists and not expired
	if err == nil {
		expired := cache.ModTime().Add(expires * 1e9)
		if time.Now().Before(expired) {
			f, err := os.Open(path)
			if err == nil {
				defer f.Close()
				log.Printf("Using cache: %s", path)
				writeBuff := bytes.NewBuffer([]byte{})
				_, err = io.Copy(writeBuff, f)
				if err == nil {
					return writeBuff, nil
				}
			}
		}
	}

	err = os.MkdirAll(filepath.Dir(path), 0750)
	if err != nil {
		return nil, err
	}

	writeBuff := bytes.NewBuffer([]byte{})

	// Get the reader that return new data
	s, err := readStream()
	if err != nil {
		return nil, err
	}

	defer s.Close()

	_, err = io.Copy(writeBuff, s)
	if err != nil {
		return nil, err
	}

	f, err := os.OpenFile(path, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0644)
	if err != nil {
		return nil, err
	}

	defer f.Close()

	data := writeBuff.Bytes()
	_, err = io.Copy(f, bytes.NewReader(data))
	if err != nil {
		return nil, err
	}

	return writeBuff, nil
}

func ChangedStream(path string, readStream func() (io.Reader, error), dataModTime time.Time) (*bytes.Buffer, error) {

	cache, err := os.Stat(path)

	// Check if cache exists and not expired
	if err == nil {
		if dataModTime.Before(cache.ModTime()) {
			f, err := os.Open(path)
			if err == nil {
				defer f.Close()
				log.Printf("Reading from file: %s", path)
				writeBuff := bytes.NewBuffer([]byte{})
				_, err = io.Copy(writeBuff, f)
				if err == nil {
					return writeBuff, nil
				}
			}
		}
	}

	err = os.MkdirAll(filepath.Dir(path), 0750)
	if err != nil {
		return nil, err
	}

	writeBuff := bytes.NewBuffer([]byte{})

	// Get the reader that return new data
	s, err := readStream()
	if err != nil {
		return nil, err
	}

	_, err = io.Copy(writeBuff, s)
	if err != nil {
		return nil, err
	}

	f, err := os.OpenFile(path, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0644)
	if err != nil {
		return nil, err
	}

	defer f.Close()

	data := writeBuff.Bytes()
	_, err = io.Copy(f, bytes.NewReader(data))
	if err != nil {
		return nil, err
	}

	return writeBuff, nil
}