database.go

package liber

import (
	"bytes"
	cryptorand "crypto/rand"
	"encoding/binary"
	"encoding/json"
	"errors"
	"math/rand"
	"os"
	"path/filepath"
	"strconv"
	"time"

	"github.com/blevesearch/bleve"
	"github.com/jmhodges/levigo"
)

var (
	BookBucket = []byte("ebook")
	FileBucket = []byte("file")

	keySeparator = byte('/')
)

type BookId uint64

func (id BookId) String() string {
	return strconv.FormatUint(uint64(id), 10)
}

func (id BookId) Key() []byte {
	var buf bytes.Buffer
	binary.Write(&buf, binary.LittleEndian, id)
	return buf.Bytes()
}

func init() {
	// Seed the RNG to a random value.
	var seed int64
	binary.Read(cryptorand.Reader, binary.LittleEndian, &seed)
	rand.Seed(seed)
}

func NewID() BookId {
	return BookId(rand.Int63())
}

func ParseID(s string) BookId {
	id, _ := strconv.ParseUint(s, 10, 64)
	return BookId(id)
}

func metadataDocumentMapping() *bleve.DocumentMapping {
	md := bleve.NewDocumentMapping()

	titleFieldMapping := bleve.NewTextFieldMapping()
	titleFieldMapping.Analyzer = "en"
	titleFieldMapping.Store = false
	md.AddFieldMappingsAt("Title", titleFieldMapping)

	authorFieldMapping := bleve.NewTextFieldMapping()
	authorFieldMapping.Store = false
	md.AddFieldMappingsAt("Creator", authorFieldMapping)

	nostoreFieldMapping := bleve.NewTextFieldMapping()
	nostoreFieldMapping.Store = false
	nostoreFieldMapping.IncludeInAll = false
	md.AddFieldMappingsAt("Description", nostoreFieldMapping)
	md.AddFieldMappingsAt("ISBN", nostoreFieldMapping)

	for _, ignore := range []string{"Sources", "Date", "Publisher", "Format", "Keywords", "Language"} {
		md.AddSubDocumentMapping(ignore, bleve.NewDocumentDisabledMapping())
	}

	return md
}

func defaultIndexMapping() *bleve.IndexMapping {
	i := bleve.NewIndexMapping()
	i.AddDocumentMapping("ebook", metadataDocumentMapping())
	i.DefaultAnalyzer = "en"
	return i
}

type Book struct {
	Id        BookId
	Path      string
	CoverPath string
	FileType  string
	Metadata  *Metadata
}

func (b *Book) Type() string {
	return "ebook"
}

type File struct {
	Path  string
	Mtime time.Time
	Size  int64
	Error bool
	Id    BookId
}

func (f *File) HasChanged(info os.FileInfo) bool {
	return !info.ModTime().Equal(f.Mtime) || info.Size() != f.Size
}

type Database struct {
	leveldb       *levigo.DB
	leveldbCache  *levigo.Cache
	leveldbFilter *levigo.FilterPolicy

	index bleve.Index
}

func NewDb(path string) (*Database, error) {
	// Make sure that path exists.
	if _, err := os.Stat(path); err != nil {
		if err := os.Mkdir(path, 0700); err != nil {
			return nil, err
		}
	}

	// Initialize our database and the index.
	d := &Database{}
	if err := d.setupLevelDb(filepath.Join(path, "db")); err != nil {
		return nil, err
	}
	if err := d.setupIndex(filepath.Join(path, "index")); err != nil {
		return nil, err
	}
	return d, nil
}

func (db *Database) setupLevelDb(path string) error {
	opts := levigo.NewOptions()
	db.leveldbCache = levigo.NewLRUCache(2 << 28)
	opts.SetCache(db.leveldbCache)
	db.leveldbFilter = levigo.NewBloomFilter(10)
	opts.SetFilterPolicy(db.leveldbFilter)
	opts.SetCreateIfMissing(true)
	leveldb, err := levigo.Open(path, opts)
	if err != nil {
		return err
	}
	db.leveldb = leveldb
	return nil
}

func (db *Database) setupIndex(path string) error {
	var err error
	if _, serr := os.Stat(path); serr == nil {
		db.index, err = bleve.Open(path)
	} else {
		db.index, err = bleve.New(path, defaultIndexMapping())
	}
	if err != nil {
		return err
	}
	return nil
}

func (db *Database) Close() {
	db.index.Close()
	db.leveldb.Close()
	db.leveldbCache.Close()
	db.leveldbFilter.Close()
}

func (db *Database) GetBook(bookid BookId) (*Book, error) {
	var b Book
	if err := db.Get(BookBucket, bookid.Key(), &b); err != nil {
		return nil, err
	}
	return &b, nil
}

func (db *Database) GetFile(path string) (*File, error) {
	var f File
	if err := db.Get(FileBucket, []byte(path), &f); err != nil {
		return nil, err
	}
	return &f, nil
}

func (db *Database) Get(bucket, key []byte, obj interface{}) error {
	ro := levigo.NewReadOptions()
	defer ro.Close()
	data, err := db.leveldb.Get(ro, bktToKey(bucket, key))
	if err != nil {
		return err
	}
	return json.Unmarshal(data, obj)
}

func (db *Database) PutBook(b *Book) error {
	if err := db.Put(BookBucket, b.Id.Key(), b); err != nil {
		return err
	}
	return db.index.Index(b.Id.String(), b.Metadata)
}

func (db *Database) PutFile(f *File) error {
	return db.Put(FileBucket, []byte(f.Path), f)
}

func (db *Database) Put(bucket, key []byte, obj interface{}) error {
	data, err := json.Marshal(obj)
	if err != nil {
		return err
	}

	wo := levigo.NewWriteOptions()
	defer wo.Close()

	return db.leveldb.Put(wo, bktToKey(bucket, key), data)
}

func (db *Database) DeleteBook(bookid BookId) error {
	db.Delete(BookBucket, bookid.Key())
	return db.index.Delete(bookid.String())
}

func (db *Database) Delete(bucket, key []byte) error {
	wo := levigo.NewWriteOptions()
	defer wo.Close()
	return db.leveldb.Delete(wo, bktToKey(bucket, key))
}

type DatabaseIterator struct {
	db   *levigo.DB
	snap *levigo.Snapshot
	iter *levigo.Iterator
	ro   *levigo.ReadOptions
	end  []byte
}

func (i *DatabaseIterator) Close() {
	i.iter.Close()
	i.ro.Close()
	i.db.ReleaseSnapshot(i.snap)
}

func (i *DatabaseIterator) Next() {
	i.iter.Next()
}

func (i *DatabaseIterator) Valid() bool {
	return i.iter.Valid() && (bytes.Compare(i.iter.Key(), i.end) < 0)
}

func (i *DatabaseIterator) Id() BookId {
	return keyToId(i.iter.Key())
}

func (i *DatabaseIterator) Value(obj interface{}) error {
	return json.Unmarshal(i.iter.Value(), obj)
}

// Scan an entire bucket.
func (db *Database) Scan(bucket []byte) *DatabaseIterator {
	snap := db.leveldb.NewSnapshot()
	ro := levigo.NewReadOptions()
	ro.SetFillCache(false)
	ro.SetSnapshot(snap)
	it := db.leveldb.NewIterator(ro)
	start, end := keyRange(bucket)
	it.Seek(start)
	return &DatabaseIterator{
		db:   db.leveldb,
		snap: snap,
		ro:   ro,
		iter: it,
		end:  end,
	}
}

type SearchResult struct {
	Results    []*Book
	NumResults int
}

func (db *Database) doSearch(query bleve.Query, offset, limit int) (*SearchResult, error) {
	req := bleve.NewSearchRequestOptions(query, limit, offset, false)
	result, err := db.index.Search(req)
	if err != nil {
		return nil, err
	}

	sr := SearchResult{NumResults: int(result.Total)}
	for _, r := range result.Hits {
		if book, err := db.GetBook(ParseID(r.ID)); err == nil {
			sr.Results = append(sr.Results, book)
		}
	}
	return &sr, nil
}

// Search the database with a query string.
func (db *Database) Search(queryStr string, offset, limit int) (*SearchResult, error) {
	return db.doSearch(bleve.NewQueryStringQuery(queryStr), offset, limit)
}

// Autocomplete runs a fuzzy search for a term.
func (db *Database) Autocomplete(term string) (*SearchResult, error) {
	return db.doSearch(bleve.NewFuzzyQuery(term), 0, 20)
}

// Find a book matching the given metadata, if possible.
func (db *Database) Find(m *Metadata) (*Book, error) {
	var query bleve.Query

	if len(m.ISBN) > 0 {
		var queries []bleve.Query
		for _, isbn := range m.ISBN {
			q := bleve.NewTermQuery(isbn)
			q.SetField("ISBN")
			queries = append(queries, q)
		}
		query = bleve.NewDisjunctionQuery(queries)
	} else {
		var queries []bleve.Query
		if m.Title != "" {
			q := bleve.NewMatchQuery(m.Title)
			q.SetField("Title")
			queries = append(queries, q)
		}
		if len(m.Creator) > 0 {
			for _, a := range m.Creator {
				q := bleve.NewMatchQuery(a)
				q.SetField("Creator")
				queries = append(queries, q)
			}
		}
		if len(queries) == 0 {
			return nil, errors.New("insufficient metadata for query")
		}
		query = bleve.NewConjunctionQuery(queries)
	}

	search := bleve.NewSearchRequest(query)
	result, err := db.index.Search(search)
	if err != nil {
		return nil, err
	}
	for _, r := range result.Hits {
		book, err := db.GetBook(ParseID(r.ID))
		if err != nil {
			continue
		}
		if book.Metadata.Equals(m) {
			return book, nil
		}
	}
	return nil, errors.New("no matches found")
}

func bktToKey(bucket, key []byte) []byte {
	return bytes.Join([][]byte{bucket, key}, []byte{keySeparator})
}

// Input is a full key (including bucket).
func keyToId(key []byte) BookId {
	n := bytes.Index(key, []byte{keySeparator})
	if n < 0 {
		return 0
	}

	var id uint64
	binary.Read(bytes.NewReader(key[n+1:]), binary.LittleEndian, &id)
	return BookId(id)
}

func keyRange(prefix []byte) ([]byte, []byte) {
	start := make([]byte, len(prefix)+1)
	end := make([]byte, len(prefix)+1)
	copy(start, prefix)
	copy(end, prefix)
	start[len(prefix)] = keySeparator
	end[len(prefix)] = keySeparator + 1
	return start, end
}