// Copyright 2016 Google Inc. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//    http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package zoekt

import (
	"bufio"
	"encoding/binary"
	"encoding/json"
	"io"
	"log"
	"sort"
	"time"
)

// FormatVersion is a version number. It is increased every time the
// on-disk index format is changed.
// 5: subrepositories.
// 6: remove size prefix for posting varint list.
// 7: move subrepos into Repository struct.
// 8: move repoMetaData out of indexMetadata
// 9: use bigendian uint64 for trigrams.
// 10: sections for rune offsets.
// 11: file ends in rune offsets.
const IndexFormatVersion = 11

// FeatureVersion is increased if a feature is added that requires reindexing data.
const FeatureVersion = 0

var _ = log.Println

type indexTOC struct {
	fileContents compoundSection
	fileNames    compoundSection
	fileSections compoundSection
	postings     compoundSection
	newlines     compoundSection
	ngramText    simpleSection
	runeOffsets  simpleSection
	fileEndRunes simpleSection

	branchMasks simpleSection
	subRepos    simpleSection

	nameNgramText   simpleSection
	namePostings    compoundSection
	nameRuneOffsets simpleSection
	metaData        simpleSection
	repoMetaData    simpleSection
	nameEndRunes    simpleSection
}

func (t *indexTOC) sections() []section {
	return []section{
		// This must be first, so it can be reliably read across
		// file format versions.
		&t.metaData,
		&t.repoMetaData,
		&t.fileContents,
		&t.fileNames,
		&t.fileSections,
		&t.newlines,
		&t.ngramText,
		&t.postings,
		&t.nameNgramText,
		&t.namePostings,
		&t.branchMasks,
		&t.subRepos,
		&t.runeOffsets,
		&t.nameRuneOffsets,
		&t.fileEndRunes,
		&t.nameEndRunes,
	}
}

func (w *writer) writeTOC(toc *indexTOC) {
	secs := toc.sections()
	w.U32(uint32(len(secs)))
	for _, s := range secs {
		s.write(w)
	}
}

func (s *compoundSection) writeStrings(w *writer, strs []*searchableString) {
	s.start(w)
	for _, f := range strs {
		s.addItem(w, f.data)
	}
	s.end(w)
}

func writePostings(w *writer, s *postingsBuilder, ngramText *simpleSection,
	charOffsets *simpleSection, postings *compoundSection, endRunes *simpleSection) {
	var keys ngramSlice
	for k := range s.postings {
		keys = append(keys, k)
	}
	sort.Sort(keys)

	ngramText.start(w)
	for _, k := range keys {
		var buf [8]byte
		binary.BigEndian.PutUint64(buf[:], uint64(k))
		w.Write(buf[:])
	}
	ngramText.end(w)

	postings.start(w)
	for _, k := range keys {
		postings.addItem(w, s.postings[k])
	}
	postings.end(w)

	charOffsets.start(w)
	w.Write(toSizedDeltas(s.runeOffsets))
	charOffsets.end(w)

	endRunes.start(w)
	w.Write(toSizedDeltas(s.endRunes))
	endRunes.end(w)
}

func (b *IndexBuilder) Write(out io.Writer) error {
	buffered := bufio.NewWriterSize(out, 1<<20)
	defer buffered.Flush()

	w := &writer{w: buffered}
	toc := indexTOC{}

	toc.fileContents.writeStrings(w, b.files)

	toc.newlines.start(w)
	for _, f := range b.files {
		toc.newlines.addItem(w, toSizedDeltas(newLinesIndices(f.data)))
	}
	toc.newlines.end(w)

	toc.branchMasks.start(w)
	for _, m := range b.branchMasks {
		w.U32(m)
	}
	toc.branchMasks.end(w)

	toc.fileSections.start(w)
	for _, s := range b.docSections {
		toc.fileSections.addItem(w, marshalDocSections(s))
	}
	toc.fileSections.end(w)

	writePostings(w, b.contents, &toc.ngramText, &toc.runeOffsets, &toc.postings, &toc.fileEndRunes)

	// names.
	toc.fileNames.writeStrings(w, b.fileNames)

	writePostings(w, b.names, &toc.nameNgramText, &toc.nameRuneOffsets, &toc.namePostings, &toc.nameEndRunes)

	toc.subRepos.start(w)
	w.Write(toSizedDeltas(b.subRepos))
	toc.subRepos.end(w)

	if err := b.writeJSON(&IndexMetadata{
		IndexFormatVersion:  IndexFormatVersion,
		IndexTime:           time.Now(),
		IndexFeatureVersion: FeatureVersion,
	}, &toc.metaData, w); err != nil {
		return err
	}
	if err := b.writeJSON(b.repo, &toc.repoMetaData, w); err != nil {
		return err
	}

	var tocSection simpleSection

	tocSection.start(w)
	w.writeTOC(&toc)
	tocSection.end(w)
	tocSection.write(w)
	return w.err
}

func (b *IndexBuilder) writeJSON(data interface{}, sec *simpleSection, w *writer) error {
	blob, err := json.Marshal(data)
	if err != nil {
		return err
	}
	sec.start(w)
	w.Write(blob)
	sec.end(w)
	return nil
}

func newLinesIndices(in []byte) []uint32 {
	out := make([]uint32, 0, len(in)/30)
	for i, c := range in {
		if c == '\n' {
			out = append(out, uint32(i))
		}
	}
	return out
}