scratch/scribble.go
2015-11-21 22:36:00 +05:00

251 lines
5.8 KiB
Go

// scribble is a tiny JSON database
package scribble
import (
"encoding/json"
"fmt"
"github.com/jcelliott/lumber"
"io/ioutil"
"os"
"path/filepath"
"sync"
)
const Version = "1.0.3"
type (
//
Logger interface {
Fatal(string, ...interface{})
Error(string, ...interface{})
Warn(string, ...interface{})
Info(string, ...interface{})
Debug(string, ...interface{})
Trace(string, ...interface{})
}
// a Driver is what is used to interact with the scribble database. It runs
// transactions, and provides log output
Driver struct {
mutex sync.Mutex
mutexes map[string]sync.Mutex
dir string // the directory where scribble will create the database
log Logger // the logger scribble will log to
}
)
type Options struct {
Logger
}
// New creates a new scribble database at the desired directory location, and
// returns a *Driver to then use for interacting with the database
func New(dir string, opt *Options) (driver *Driver, err error) {
var options Options
if opt == nil {
options = Options{}
} else {
options = *opt
}
//
dir = filepath.Clean(dir)
// ensure the database location doesn't already exist (we don't want to overwrite
// any existing files/database)
if _, err := os.Stat(dir); err == nil {
fmt.Printf("Unable to create database, '%s' already exists. Please specify a different location.\n", dir)
os.Exit(1)
}
//
if options.Logger == nil {
options.Logger = lumber.NewConsoleLogger(lumber.INFO)
}
//
driver = &Driver{
dir: dir,
mutexes: make(map[string]sync.Mutex),
log: options.Logger,
}
options.Logger.Info("Creating scribble database at '%v'...\n", dir)
// create database
return driver, os.MkdirAll(dir, 0755)
}
// Write locks the database and attempts to write the record to the database under
// the [collection] specified with the [resource] name given
func (d *Driver) Write(collection, resource string, v interface{}) error {
// ensure there is a place to save record
if collection == "" {
return fmt.Errorf("Missing collection - no place to save record!")
}
// ensure there is a resource (name) to save record as
if resource == "" {
return fmt.Errorf("Missing resource - unable to save record (no name)!")
}
mutex := d.getOrCreateMutex(collection)
mutex.Lock()
defer mutex.Unlock()
//
dir := filepath.Join(d.dir, collection)
fnlPath := filepath.Join(dir, resource+".json")
tmpPath := fnlPath + ".tmp"
// create collection directory
if err := os.MkdirAll(dir, 0755); err != nil {
return err
}
//
b, err := json.MarshalIndent(v, "", "\t")
if err != nil {
return err
}
// write marshaled data to the temp file
if err := ioutil.WriteFile(tmpPath, b, 0644); err != nil {
return err
}
// move final file into place
return os.Rename(tmpPath, fnlPath)
}
// Read a record from the database
func (d *Driver) Read(collection, resource string, v interface{}) error {
// ensure there is a place to save record
if collection == "" {
return fmt.Errorf("Missing collection - no place to save record!")
}
// ensure there is a resource (name) to save record as
if resource == "" {
return fmt.Errorf("Missing resource - unable to save record (no name)!")
}
//
record := filepath.Join(d.dir, collection, resource)
// check to see if file exists
if _, err := stat(record); err != nil {
return err
}
// read record from database
b, err := ioutil.ReadFile(record + ".json")
if err != nil {
return err
}
// unmarshal data
return json.Unmarshal(b, &v)
}
// ReadAll records from a collection; this is returned as a slice of strings because
// there is no way of knowing what type the record is.
func (d *Driver) ReadAll(collection string) ([]string, error) {
// ensure there is a collection to read
if collection == "" {
return nil, fmt.Errorf("Missing collection - unable to record location!")
}
//
dir := filepath.Join(d.dir, collection)
// check to see if collection (directory) exists
if _, err := stat(dir); err != nil {
return nil, err
}
// read all the files in the transaction.Collection; an error here just means
// the collection is either empty or doesn't exist
files, _ := ioutil.ReadDir(dir)
// the files read from the database
var records []string
// iterate over each of the files, attempting to read the file. If successful
// append the files to the collection of read files
for _, file := range files {
b, err := ioutil.ReadFile(filepath.Join(dir, file.Name()))
if err != nil {
return nil, err
}
// append read file
records = append(records, string(b))
}
// unmarhsal the read files as a comma delimeted byte array
return records, nil
}
// Delete locks that database and then attempts to remove the collection/resource
// specified by [path]
func (d *Driver) Delete(collection, resource string) error {
path := filepath.Join(collection, resource)
//
mutex := d.getOrCreateMutex(path)
mutex.Lock()
defer mutex.Unlock()
//
dir := filepath.Join(d.dir, path)
switch fi, err := stat(dir); {
// if fi is nil or error is not nil return
case fi == nil, err != nil:
return fmt.Errorf("Unable to find file or directory named %v\n", path)
// remove directory and all contents
case fi.Mode().IsDir():
return os.RemoveAll(dir)
// remove file
case fi.Mode().IsRegular():
return os.RemoveAll(dir + ".json")
}
return nil
}
//
func stat(path string) (fi os.FileInfo, err error) {
// check for dir, if path isn't a directory check to see if it's a file
if fi, err = os.Stat(path); os.IsNotExist(err) {
fi, err = os.Stat(path + ".json")
}
return
}
// getOrCreateMutex creates a new collection specific mutex any time a collection
// is being modfied to avoid unsafe operations
func (d *Driver) getOrCreateMutex(collection string) sync.Mutex {
d.mutex.Lock()
defer d.mutex.Unlock()
m, ok := d.mutexes[collection]
// if the mutex doesn't exist make it
if !ok {
m = sync.Mutex{}
d.mutexes[collection] = m
}
return m
}