// Copyright 2015 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package bio implements seekable buffered I/O.
package bio

import (
	"bufio"
	"log"
	"os"
)

// Reader implements a seekable buffered io.Reader.
type Reader struct {
	f *os.File
	*bufio.Reader
}

// Writer implements a seekable buffered io.Writer.
type Writer struct {
	f *os.File
	*bufio.Writer
}

// Create creates the file named name and returns a Writer
// for that file.
func Create(name string) (*Writer, error) {
	f, err := os.Create(name)
	if err != nil {
		return nil, err
	}
	return &Writer{f: f, Writer: bufio.NewWriter(f)}, nil
}

// Open returns a Reader for the file named name.
func Open(name string) (*Reader, error) {
	f, err := os.Open(name)
	if err != nil {
		return nil, err
	}
	return &Reader{f: f, Reader: bufio.NewReader(f)}, nil
}

func (r *Reader) Seek(offset int64, whence int) int64 {
	if whence == 1 {
		offset -= int64(r.Buffered())
	}
	off, err := r.f.Seek(offset, whence)
	if err != nil {
		log.Fatalf("seeking in output: %v", err)
	}
	r.Reset(r.f)
	return off
}

func (w *Writer) Seek(offset int64, whence int) int64 {
	if err := w.Flush(); err != nil {
		log.Fatalf("writing output: %v", err)
	}
	off, err := w.f.Seek(offset, whence)
	if err != nil {
		log.Fatalf("seeking in output: %v", err)
	}
	return off
}

func (r *Reader) Offset() int64 {
	off, err := r.f.Seek(0, 1)
	if err != nil {
		log.Fatalf("seeking in output [0, 1]: %v", err)
	}
	off -= int64(r.Buffered())
	return off
}

func (w *Writer) Offset() int64 {
	if err := w.Flush(); err != nil {
		log.Fatalf("writing output: %v", err)
	}
	off, err := w.f.Seek(0, 1)
	if err != nil {
		log.Fatalf("seeking in output [0, 1]: %v", err)
	}
	return off
}

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

func (w *Writer) Close() error {
	err := w.Flush()
	err1 := w.f.Close()
	if err == nil {
		err = err1
	}
	return err
}