/*
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 (
	"bufio"
	"fmt"
	"io"
	"strconv"
	"strings"
)

const CRLF = "\r\n"

type Reader struct {
	Path    string
	r       *bufio.Reader
	rsc     io.ReadSeekCloser
	offset  int64
	prevRec *Record
}

func NewReader(warcPath string) (*Reader, error) {
	rsc, err := Open(warcPath)
	if err != nil {
		return nil, err
	}
	return &Reader{
		Path: warcPath,
		rsc:  rsc,
		r:    bufio.NewReader(rsc),
	}, nil
}

func (r *Reader) next() error {
	if r.prevRec == nil {
		return nil
	}
	if _, err := r.r.Discard(int(r.prevRec.Size)); err != nil {
		return err
	}
	r.offset += int64(r.prevRec.HdrLen) + r.prevRec.Size
	for i := 0; i < 2; i++ {
		line, err := r.r.ReadString('\n')
		if err != nil {
			return err
		}
		r.offset += int64(len(line))
		if line != CRLF {
			return fmt.Errorf("non-CRLF: %q", line)
		}
	}
	return nil
}

func (r *Reader) ReadRecord() (*Record, error) {
	r.next()
	line, err := r.r.ReadString('\n')
	if err != nil {
		return nil, err
	}
	if !strings.HasPrefix(line, "WARC/") {
		return nil, fmt.Errorf("non-WARC header: %q", line)
	}
	hdrLen := len(line)
	hdr := NewHeader()
	for {
		line, err := r.r.ReadString('\n')
		if err != nil {
			return nil, err
		}
		hdrLen += len(line)
		if line == CRLF {
			break
		}
		hdr.AddLine(line)
	}
	size, err := strconv.ParseUint(hdr.Get("Content-Length"), 10, 64)
	if err != nil {
		return nil, err
	}
	rec := &Record{
		WARCPath: r.Path,
		Offset:   r.offset,
		Hdr:      hdr,
		HdrLen:   hdrLen,
		Size:     int64(size),
	}
	r.prevRec = rec
	return rec, nil
}

func (r *Reader) Close() error {
	return r.rsc.Close()
}