package cache

import (
	"crypto/sha1"
	"fmt"
	"io/ioutil"
	"os"
	"path/filepath"
	"strings"

	"github.com/djherbis/fscache"
	"github.com/karrick/godirwalk"
	"gopkg.in/djherbis/atime.v1"
	"gopkg.in/djherbis/stream.v1"
)

type spreadFS struct {
	root string
	mode os.FileMode
	init func() error
}

const keyFileExtension = ".key"

// NewSpreadFS returns a FileSystem rooted at directory dir. It
// Dir is created with perms if it doesn't exist.
func NewSpreadFS(dir string, mode os.FileMode) (fscache.FileSystem, error) {
	fs := &spreadFS{root: dir, mode: mode, init: func() error {
		return os.MkdirAll(dir, mode)
	}}
	return fs, fs.init()
}

func (fs *spreadFS) Reload(f func(key string, name string)) error {
	return godirwalk.Walk(fs.root, &godirwalk.Options{
		Callback: func(absoluteFilePath string, de *godirwalk.Dirent) error {
			path, err := filepath.Rel(fs.root, absoluteFilePath)
			if err != nil {
				return nil
			}

			// Skip if name is not in the format XX/XX/XXXXXXXXXXXX.key
			parts := strings.Split(path, string(os.PathSeparator))
			if len(parts) != 3 || len(parts[0]) != 2 || len(parts[1]) != 2 ||
				filepath.Ext(path) != keyFileExtension {
				return nil
			}

			keyFileName := absoluteFilePath
			dataFileName := absoluteFilePath[0 : len(absoluteFilePath)-len(keyFileExtension)]

			// Load the key from the key file. Remove and skip on error
			key, err := ioutil.ReadFile(keyFileName)
			if err != nil {
				_ = fs.Remove(dataFileName)
				return nil
			}

			// If the data file is not readable, remove and skip
			file, err := os.Open(dataFileName)
			defer func() { _ = file.Close() }()
			if err != nil {
				_ = fs.Remove(dataFileName)
				return nil
			}

			f(string(key), dataFileName)
			return nil
		},
		Unsorted: true,
	})
}

func (fs *spreadFS) Create(name string) (stream.File, error) {
	key := fmt.Sprintf("%x", sha1.Sum([]byte(name)))
	path := fmt.Sprintf("%s%c%s", key[0:2], os.PathSeparator, key[2:4])
	err := os.MkdirAll(filepath.Join(fs.root, path), fs.mode)
	if err != nil {
		return nil, err
	}
	absolutePath := filepath.Join(fs.root, path, key)
	err = ioutil.WriteFile(absolutePath+keyFileExtension, []byte(name), 0600)
	if err != nil {
		return nil, err
	}
	return os.OpenFile(absolutePath, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0600)
}

func (fs *spreadFS) Open(name string) (stream.File, error) {
	return os.Open(name)
}

func (fs *spreadFS) Remove(name string) error {
	_ = os.Remove(name + keyFileExtension)
	return os.Remove(name)
}

func (fs *spreadFS) Stat(name string) (fscache.FileInfo, error) {
	stat, err := os.Stat(name)
	if err != nil {
		return fscache.FileInfo{}, err
	}
	return fscache.FileInfo{FileInfo: stat, Atime: atime.Get(stat)}, nil
}

func (fs *spreadFS) RemoveAll() error {
	if err := os.RemoveAll(fs.root); err != nil {
		return err
	}
	return fs.init()
}