// tofuproxy -- flexible HTTP/HTTPS proxy, TLS terminator, X.509 TOFU
//              manager, WARC/geminispace browser
// Copyright (C) 2021-2024 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"
	"errors"
	"fmt"
	"io"
	"io/fs"
	"log"
	"os"
	"strconv"
	"sync"
	"time"
)

const IndexExt = ".idx.gob"

var (
	WARCs        = map[string]map[string]*Record{}
	WARCsOffsets = map[string][]Offset{}
	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
		var offsets []Offset
		dec := gob.NewDecoder(fd)
		if err := dec.Decode(&uris); err != nil {
			return err
		}
		if err := dec.Decode(&offsets); err != nil {
			return err
		}
		WARCsM.Lock()
		WARCs[warcPath] = uris
		WARCsOffsets[warcPath] = offsets
		WARCsM.Unlock()
		log.Println("loaded marshalled index:", warcPath+IndexExt)
		return nil
	}
	if err != nil && !errors.Is(err, fs.ErrNotExist) {
		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
		}
		rec.HdrLines = nil
		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") != "" {
				if incomplete.WARCPath == warcPath {
					uris[incomplete.URI()] = incomplete
				} else {
					WARCsM.Lock()
					WARCs[incomplete.WARCPath][incomplete.URI()] = incomplete
					WARCsM.Unlock()
				}
				delete(Incomplete, originID)
			}
		}
	}
	r.Close()
	WARCsM.Lock()
	WARCs[warcPath] = uris
	WARCsOffsets[warcPath] = r.offsets
	WARCsM.Unlock()
	return nil
}

func SaveIndices() error {
	WARCsM.RLock()
	defer WARCsM.RUnlock()
	for warcPath, uris := range WARCs {
		p := warcPath + IndexExt
		if _, err := os.Stat(p); err == nil {
			continue
		}
		tmpSuffix := strconv.FormatInt(time.Now().UnixNano()+int64(os.Getpid()), 16)
		fd, err := os.OpenFile(
			p+tmpSuffix,
			os.O_WRONLY|os.O_CREATE|os.O_EXCL,
			os.FileMode(0666),
		)
		if err != nil {
			return err
		}
		enc := gob.NewEncoder(fd)
		if err = enc.Encode(&uris); err != nil {
			fd.Close()
			return err
		}
		offsets := WARCsOffsets[warcPath]
		if err = enc.Encode(&offsets); err != nil {
			fd.Close()
			return err
		}
		if err = fd.Close(); err != nil {
			return err
		}
		if err = os.Rename(p+tmpSuffix, p); err != nil {
			return err
		}
		log.Println("saved:", p)
	}
	return nil
}