// Package fs is a simple Datastore implementation that stores keys
// as directories and files, mirroring the key. That is, the key
// "/foo/bar" is stored as file "PATH/foo/bar/.dsobject".
//
// This means key some segments will not work. For example, the
// following keys will result in unwanted behavior:
//
//     - "/foo/./bar"
//     - "/foo/../bar"
//     - "/foo\x00bar"
//
// Keys that only differ in case may be confused with each other on
// case insensitive file systems, for example in OS X.
//
// This package is intended for exploratory use, where the user would
// examine the file system manually, and should only be used with
// human-friendly, trusted keys. You have been warned.
package fs

import (
	"fmt"
	"io/ioutil"
	"log"
	"os"
	"path/filepath"
	"strings"

	ds "github.com/ipfs/go-datastore"
	query "github.com/ipfs/go-datastore/query"
)

var ObjectKeySuffix = ".dsobject"

// Datastore uses a uses a file per key to store values.
type Datastore struct {
	path string
}

// NewDatastore returns a new fs Datastore at given `path`
func NewDatastore(path string) (ds.Datastore, error) {
	if !isDir(path) {
		return nil, fmt.Errorf("Failed to find directory at: %v (file? perms?)", path)
	}

	return &Datastore{path: path}, nil
}

// KeyFilename returns the filename associated with `key`
func (d *Datastore) KeyFilename(key ds.Key) string {
	return filepath.Join(d.path, key.String(), ObjectKeySuffix)
}

// Put stores the given value.
func (d *Datastore) Put(key ds.Key, value interface{}) (err error) {

	// TODO: maybe use io.Readers/Writers?
	// r, err := dsio.CastAsReader(value)
	// if err != nil {
	// 	return err
	// }

	val, ok := value.([]byte)
	if !ok {
		return ds.ErrInvalidType
	}

	fn := d.KeyFilename(key)

	// mkdirall above.
	err = os.MkdirAll(filepath.Dir(fn), 0755)
	if err != nil {
		return err
	}

	return ioutil.WriteFile(fn, val, 0666)
}

// Get returns the value for given key
func (d *Datastore) Get(key ds.Key) (value interface{}, err error) {
	fn := d.KeyFilename(key)
	if !isFile(fn) {
		return nil, ds.ErrNotFound
	}

	return ioutil.ReadFile(fn)
}

// Has returns whether the datastore has a value for a given key
func (d *Datastore) Has(key ds.Key) (exists bool, err error) {
	return ds.GetBackedHas(d, key)
}

// Delete removes the value for given key
func (d *Datastore) Delete(key ds.Key) (err error) {
	fn := d.KeyFilename(key)
	if !isFile(fn) {
		return ds.ErrNotFound
	}

	return os.Remove(fn)
}

// Query implements Datastore.Query
func (d *Datastore) Query(q query.Query) (query.Results, error) {

	results := make(chan query.Result)

	walkFn := func(path string, info os.FileInfo, err error) error {
		// remove ds path prefix
		if strings.HasPrefix(path, d.path) {
			path = path[len(d.path):]
		}

		if !info.IsDir() {
			if strings.HasSuffix(path, ObjectKeySuffix) {
				path = path[:len(path)-len(ObjectKeySuffix)]
			}
			key := ds.NewKey(path)
			entry := query.Entry{Key: key.String(), Value: query.NotFetched}
			results <- query.Result{Entry: entry}
		}
		return nil
	}

	go func() {
		filepath.Walk(d.path, walkFn)
		close(results)
	}()
	r := query.ResultsWithChan(q, results)
	r = query.NaiveQueryApply(q, r)
	return r, nil
}

// isDir returns whether given path is a directory
func isDir(path string) bool {
	finfo, err := os.Stat(path)
	if err != nil {
		return false
	}

	return finfo.IsDir()
}

// isFile returns whether given path is a file
func isFile(path string) bool {
	finfo, err := os.Stat(path)
	if err != nil {
		return false
	}

	return !finfo.IsDir()
}

func (d *Datastore) Close() error {
	return nil
}

func (d *Datastore) Batch() (ds.Batch, error) {
	return ds.NewBasicBatch(d), nil
}

// DiskUsage returns the disk size used by the datastore in bytes.
func (d *Datastore) DiskUsage() (uint64, error) {
	var du uint64
	err := filepath.Walk(d.path, func(p string, f os.FileInfo, err error) error {
		if err != nil {
			log.Println(err)
			return err
		}
		if f != nil {
			du += uint64(f.Size())
		}
		return nil
	})
	return du, err
}