package fs

import (
	"errors"
	"fmt"
	"github.com/dotcloud/docker/future"
	"io"
	"io/ioutil"
	"os"
	"path"
	"path/filepath"
)

type LayerStore struct {
	Root string
}

func NewLayerStore(root string) (*LayerStore, error) {
	abspath, err := filepath.Abs(root)
	if err != nil {
		return nil, err
	}
	// Create the root directory if it doesn't exists
	if err := os.Mkdir(root, 0700); err != nil && !os.IsExist(err) {
		return nil, err
	}
	return &LayerStore{
		Root: abspath,
	}, nil
}

func (store *LayerStore) List() []string {
	files, err := ioutil.ReadDir(store.Root)
	if err != nil {
		return []string{}
	}
	var layers []string
	for _, st := range files {
		if st.IsDir() {
			layers = append(layers, path.Join(store.Root, st.Name()))
		}
	}
	return layers
}

func (store *LayerStore) Get(id string) string {
	if !store.Exists(id) {
		return ""
	}
	return store.layerPath(id)
}

func (store *LayerStore) rootExists() (bool, error) {
	if stat, err := os.Stat(store.Root); err != nil {
		if os.IsNotExist(err) {
			return false, nil
		}
		return false, err
	} else if !stat.IsDir() {
		return false, errors.New("Not a directory: " + store.Root)
	}
	return true, nil
}

func (store *LayerStore) Init() error {
	if exists, err := store.rootExists(); err != nil {
		return err
	} else if exists {
		return nil
	}
	return os.Mkdir(store.Root, 0700)
}

func (store *LayerStore) Mktemp() (string, error) {
	tmpName := future.RandomId()
	tmpPath := path.Join(store.Root, "tmp-"+tmpName)
	if err := os.Mkdir(tmpPath, 0700); err != nil {
		return "", err
	}
	return tmpPath, nil
}

func (store *LayerStore) layerPath(id string) string {
	return path.Join(store.Root, id)
}

func (store *LayerStore) AddLayer(id string, archive Archive) (string, error) {
	if _, err := os.Stat(store.layerPath(id)); err == nil {
		return "", fmt.Errorf("Layer already exists: %v", id)
	}
	errors := make(chan error)
	// Untar
	tmp, err := store.Mktemp()
	defer os.RemoveAll(tmp)
	if err != nil {
		return "", fmt.Errorf("Mktemp failed: %s", err)
	}

	untarR, untarW := io.Pipe()
	go func() {
		errors <- Untar(untarR, tmp)
	}()
	_, err = io.Copy(untarW, archive)
	untarW.Close()
	if err != nil {
		return "", err
	}
	// Wait for goroutines
	for i := 0; i < 1; i += 1 {
		select {
		case err := <-errors:
			{
				if err != nil {
					return "", err
				}
			}
		}
	}
	layer := store.layerPath(id)
	if !store.Exists(id) {
		if err := os.Rename(tmp, layer); err != nil {
			return "", fmt.Errorf("Could not rename temp dir to layer %s: %s", layer, err)
		}
	}
	return layer, nil
}

func (store *LayerStore) Exists(id string) bool {
	st, err := os.Stat(store.layerPath(id))
	if err != nil {
		return false
	}
	return st.IsDir()
}