/*
tofuproxy -- flexible HTTP/WARC proxy with TLS certificates management
Copyright (C) 2021 Sergey Matveev <stargrave@stargrave.org>

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, version 3 of the License.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

package warc

import (
	"encoding/gob"
	"fmt"
	"io"
	"log"
	"os"
	"strconv"
	"sync"
)

const IndexExt = ".idx.gob"

var (
	WARCs  = map[string]map[string]*Record{}
	WARCsM sync.RWMutex

	Incomplete = map[string]*Record{}
)

func Add(warcPath string) error {
	fd, err := os.Open(warcPath + IndexExt)
	if err == nil {
		defer fd.Close()
		var uris map[string]*Record
		if err := gob.NewDecoder(fd).Decode(&uris); err != nil {
			return err
		}
		WARCsM.Lock()
		WARCs[warcPath] = uris
		WARCsM.Unlock()
		return nil
	}
	if err != nil && !os.IsNotExist(err) {
		return err
	}
	r, err := NewReader(warcPath)
	if err != nil {
		return err
	}
	defer r.Close()
	uris := map[string]*Record{}
	for {
		rec, err := r.ReadRecord()
		if err != nil {
			if err == io.EOF {
				break
			}
			return err
		}
		segNum := rec.Hdr.Get("WARC-Segment-Number")
		switch rec.Hdr.Get("WARC-Type") {
		case "response":
			uri := rec.URI()
			if uri == "" {
				continue
			}
			if segNum == "1" {
				Incomplete[rec.Hdr.Get("WARC-Record-ID")] = rec
				continue
			}
			uris[uri] = rec
		case "continuation":
			originID := rec.Hdr.Get("WARC-Segment-Origin-ID")
			incomplete := Incomplete[originID]
			if incomplete == nil {
				return fmt.Errorf("can not find WARC-Segment-Origin-ID: %q", originID)
			}
			segNumExpected := strconv.Itoa(len(incomplete.Continuations) + 1 + 1)
			if segNum != segNumExpected {
				return fmt.Errorf(
					"unexpected WARC-Segment-Number %s != %s",
					segNum, segNumExpected,
				)
			}
			incomplete.Continuations = append(incomplete.Continuations, rec)
			if rec.Hdr.Get("WARC-Segment-Total-Length") != "" {
				WARCsM.Lock()
				WARCs[incomplete.WARCPath][incomplete.URI()] = incomplete
				WARCsM.Unlock()
				delete(Incomplete, originID)
			}
		}
	}
	WARCsM.Lock()
	WARCs[warcPath] = uris
	WARCsM.Unlock()
	return nil
}

func SaveIndexes() error {
	WARCsM.RLock()
	defer WARCsM.RUnlock()
	for warcPath, uris := range WARCs {
		p := warcPath + IndexExt
		if _, err := os.Stat(p); err == nil {
			continue
		}
		fd, err := os.OpenFile(
			p+".tmp",
			os.O_CREATE|os.O_WRONLY|os.O_EXCL,
			os.FileMode(0666),
		)
		if err != nil {
			return err
		}
		if err = gob.NewEncoder(fd).Encode(&uris); err != nil {
			fd.Close()
			return err
		}
		fd.Close()
		if err = os.Rename(p+".tmp", p); err != nil {
			return err
		}
		log.Println("saved:", p)
	}
	return nil
}