/*
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 (
	"compress/gzip"
	"fmt"
	"io"
	"os"
	"path"

	"github.com/klauspost/compress/zstd"
)

type Compressed struct {
	r      io.ReadCloser
	fd     *os.File
	offset int64
}

func (c *Compressed) Read(p []byte) (int, error) {
	n, err := c.r.Read(p)
	c.offset += int64(n)
	return n, err
}

func (c *Compressed) Close() error {
	c.r.Close()
	return c.fd.Close()
}

func (c *Compressed) Seek(offset int64, whence int) (int64, error) {
	if whence != io.SeekStart {
		panic("can only seek from the start")
	}
	if _, err := io.CopyN(io.Discard, c, offset-c.offset); err != nil {
		return 0, err
	}
	c.offset = offset
	return c.offset, nil
}

func Open(warcPath string) (io.ReadSeekCloser, error) {
	ext := path.Ext(warcPath)
	switch ext {
	case ".warc":
		return os.Open(warcPath)
	case ".gz":
		fd, err := os.Open(warcPath)
		if err != nil {
			return nil, err
		}
		gzr, err := gzip.NewReader(fd)
		if err != nil {
			return nil, err
		}
		gzr.Multistream(true)
		return &Compressed{r: gzr, fd: fd}, nil
	case ".zst":
		fd, err := os.Open(warcPath)
		if err != nil {
			return nil, err
		}
		zstdr, err := zstd.NewReader(fd)
		if err != nil {
			return nil, err
		}
		return &Compressed{r: zstdr.IOReadCloser(), fd: fd}, nil
	}
	return nil, fmt.Errorf("unknown extensions: %s", ext)
}