// Copyright 2017, the Blazer authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package b2

import (
	"bytes"
	"crypto/sha1"
	"errors"
	"fmt"
	"hash"
	"io"
	"io/ioutil"
	"os"
	"strings"
	"sync"
)

type readResetter interface {
	Read([]byte) (int, error)
	Reset() error
}

type resetter struct {
	rs io.ReadSeeker
}

func (r resetter) Read(p []byte) (int, error) { return r.rs.Read(p) }
func (r resetter) Reset() error               { _, err := r.rs.Seek(0, 0); return err }

func newResetter(p []byte) readResetter { return resetter{rs: bytes.NewReader(p)} }

type writeBuffer interface {
	io.Writer
	Len() int
	Reader() (readResetter, error)
	Hash() string // sha1 or whatever it is
	Close() error
}

// nonBuffer doesn't buffer anything, but passes values directly from the
// source readseeker.  Many nonBuffers can point at different parts of the same
// underlying source, and be accessed by multiple goroutines simultaneously.
func newNonBuffer(rs io.ReaderAt, offset, size int64) writeBuffer {
	return &nonBuffer{
		r:    io.NewSectionReader(rs, offset, size),
		size: int(size),
		hsh:  sha1.New(),
	}
}

type nonBuffer struct {
	r    *io.SectionReader
	size int
	hsh  hash.Hash

	isEOF bool
	buf   *strings.Reader
}

func (nb *nonBuffer) Len() int                      { return nb.size + 40 }
func (nb *nonBuffer) Hash() string                  { return "hex_digits_at_end" }
func (nb *nonBuffer) Close() error                  { return nil }
func (nb *nonBuffer) Reader() (readResetter, error) { return nb, nil }
func (nb *nonBuffer) Write([]byte) (int, error)     { return 0, errors.New("writes not supported") }

func (nb *nonBuffer) Read(p []byte) (int, error) {
	if nb.isEOF {
		return nb.buf.Read(p)
	}
	n, err := io.TeeReader(nb.r, nb.hsh).Read(p)
	if err == io.EOF {
		err = nil
		nb.isEOF = true
		nb.buf = strings.NewReader(fmt.Sprintf("%x", nb.hsh.Sum(nil)))
	}
	return n, err
}

func (nb *nonBuffer) Reset() error {
	nb.hsh.Reset()
	nb.isEOF = false
	_, err := nb.r.Seek(0, 0)
	return err
}

type memoryBuffer struct {
	buf *bytes.Buffer
	hsh hash.Hash
	w   io.Writer
	mux sync.Mutex
}

var bufpool *sync.Pool

func init() {
	bufpool = &sync.Pool{}
	bufpool.New = func() interface{} { return &bytes.Buffer{} }
}

func newMemoryBuffer() *memoryBuffer {
	mb := &memoryBuffer{
		hsh: sha1.New(),
	}
	mb.buf = bufpool.Get().(*bytes.Buffer)
	mb.w = io.MultiWriter(mb.hsh, mb.buf)
	return mb
}

func (mb *memoryBuffer) Write(p []byte) (int, error)   { return mb.w.Write(p) }
func (mb *memoryBuffer) Len() int                      { return mb.buf.Len() }
func (mb *memoryBuffer) Reader() (readResetter, error) { return newResetter(mb.buf.Bytes()), nil }
func (mb *memoryBuffer) Hash() string                  { return fmt.Sprintf("%x", mb.hsh.Sum(nil)) }

func (mb *memoryBuffer) Close() error {
	mb.mux.Lock()
	defer mb.mux.Unlock()
	if mb.buf == nil {
		return nil
	}
	mb.buf.Truncate(0)
	bufpool.Put(mb.buf)
	mb.buf = nil
	return nil
}

type fileBuffer struct {
	f   *os.File
	hsh hash.Hash
	w   io.Writer
	s   int
}

func newFileBuffer(loc string) (*fileBuffer, error) {
	f, err := ioutil.TempFile(loc, "blazer")
	if err != nil {
		return nil, err
	}
	fb := &fileBuffer{
		f:   f,
		hsh: sha1.New(),
	}
	fb.w = io.MultiWriter(fb.f, fb.hsh)
	return fb, nil
}

func (fb *fileBuffer) Write(p []byte) (int, error) {
	n, err := fb.w.Write(p)
	fb.s += n
	return n, err
}

func (fb *fileBuffer) Len() int     { return fb.s }
func (fb *fileBuffer) Hash() string { return fmt.Sprintf("%x", fb.hsh.Sum(nil)) }

func (fb *fileBuffer) Reader() (readResetter, error) {
	if _, err := fb.f.Seek(0, 0); err != nil {
		return nil, err
	}
	return &fr{f: fb.f}, nil
}

func (fb *fileBuffer) Close() error {
	fb.f.Close()
	return os.Remove(fb.f.Name())
}

// wraps *os.File so that the http package doesn't see it as an io.Closer
type fr struct {
	f *os.File
}

func (r *fr) Read(p []byte) (int, error) { return r.f.Read(p) }
func (r *fr) Reset() error               { _, err := r.f.Seek(0, 0); return err }
