storage/database/database.go

package database

import (
	"encoding/json"
	"log"
	"os"

	"git.phc.dm.unipi.it/phc/storage/store"
)

type Database interface {
	Buckets() ([]string, error)
	CreateBucket(bucket string, options ...any) error

	Bucket(bucket string) (store.Store, error)
}

type bucketInfo struct {
	Name string `json:"name"`
	Path string `json:"path"`
}

type jsonDB struct {
	file string

	BucketsInfo map[string]bucketInfo `json:"buckets"`
}

func NewJSON(file string) Database {
	db := &jsonDB{
		file:        file,
		BucketsInfo: map[string]bucketInfo{},
	}

	err := db.load()
	if err != nil {
		panic(err)
	}

	return db
}

func (db *jsonDB) setup() error {
	if _, err := os.Stat(db.file); !os.IsNotExist(err) {
		return nil
	}

	log.Printf("missing %q, creating empty database file", db.file)

	f, err := os.Create(db.file)
	defer f.Close()
	if err != nil {
		return err
	}

	enc := json.NewEncoder(f)
	enc.SetIndent("", "    ")
	if err := enc.Encode(&db); err != nil {
		return err
	}

	return nil
}

func (db *jsonDB) store() error {
	f, err := os.Create(db.file)
	defer f.Close()
	if err != nil {
		return err
	}

	enc := json.NewEncoder(f)
	enc.SetIndent("", "    ")
	if err := enc.Encode(&db); err != nil {
		return err
	}

	return nil
}

func (db *jsonDB) load() error {
	if err := db.setup(); err != nil {
		return err
	}

	f, err := os.Open(db.file)
	defer f.Close()
	if err != nil {
		return err
	}

	if err := json.NewDecoder(f).Decode(&db); err != nil {
		return err
	}

	return nil
}

func (db *jsonDB) Buckets() ([]string, error) {
	db.load()

	buckets := make([]string, 0, len(db.BucketsInfo))

	for _, b := range db.BucketsInfo {
		buckets = append(buckets, b.Name)
	}

	return buckets, nil
}

func (db *jsonDB) CreateBucket(bucket string, options ...any) error {
	db.load()
	defer db.store()

	bi := bucketInfo{Name: bucket, Path: bucket + "/"}
	if len(options) > 0 {
		bi.Path = options[0].(string)
	}

	db.BucketsInfo[bucket] = bi

	return nil
}

func (db *jsonDB) Bucket(bucket string) (store.Store, error) {
	b := db.BucketsInfo[bucket]

	return &store.DirStore{
		BaseDir: b.Path,
		Prefix:  2,
	}, nil
}