package store

// persistent key-value store
// multiple key-value store can be managed by a single db connection
// each store has a name, before usage the name of the store must be
// ensured to exist
//
// TODO: this is a toy implementation

import (
	"io/ioutil"
	"os"
	"path/filepath"
)

type Conn struct {
	path string
}

type NotFoundError struct {
	Path string
}

type AlreadyExistsError struct {
	Path string
}

func (e NotFoundError) Error() string {
	return "not found: " + e.Path
}

func (e AlreadyExistsError) Error() string {
	return "already exists: " + e.Path
}

// Open db connection
func Open(root string) (c *Conn, err error) {
	c = new(Conn)
	c.path, err = filepath.Abs(root)
	if err != nil {
		return
	}
	err = os.MkdirAll(c.path, 0755)
	if err != nil {
		return
	}
	return
}

// Get the value of k
func (c *Conn) Get(name, k string) (v []byte, err error) {
	v, err = ioutil.ReadFile(filepath.Join(c.path, name, k))
	if err != nil {
		if p, ok := err.(*os.PathError); ok && p.Err == os.ENOENT {
			err = NotFoundError{name + "/" + k}
		}
	}
	return
}

// Ensure k-v store with the given name exists
func (c *Conn) Ensure(name string) (err error) {
	return os.MkdirAll(filepath.Join(c.path, name), 0755)
}

// Set k to v
func (c *Conn) Set(name, k string, v []byte) (err error) {
	fn := filepath.Join(c.path, name, k)
	f, err := os.OpenFile(fn+".tmp", os.O_CREATE|os.O_TRUNC|os.O_WRONLY|os.O_SYNC, 0666)
	if err != nil {
		return
	}
	defer f.Close()
	_, err = f.Write(v)
	if err != nil {
		return
	}
	err = os.Rename(fn+".tmp", fn)
	return
}

// Set k to v, but fail if k already exists
func (c *Conn) Insert(name, k string, v []byte) (err error) {
	fn := filepath.Join(c.path, name, k)
	f, err := os.OpenFile(fn, os.O_CREATE|os.O_EXCL|os.O_WRONLY|os.O_SYNC, 0666)
	if err != nil {
		if p, ok := err.(*os.PathError); ok && p.Err == os.EEXIST {
			err = AlreadyExistsError{name + "/" + k}
		}
		return
	}
	defer f.Close()
	_, err = f.Write(v)
	return
}

// Append v to value of k
func (c *Conn) Append(name, k string, v []byte) (err error) {
	fn := filepath.Join(c.path, name, k)
	f, err := os.OpenFile(fn, os.O_CREATE|os.O_APPEND|os.O_WRONLY|os.O_SYNC, 0666)
	if err != nil {
		return
	}
	defer f.Close()
	_, err = f.Write(v)
	return
}

// Close db connection
func (c *Conn) Close() (err error) {
	return
}