package s3manager

import (

	"io"

	"sync"

)

// ReadSeekerWriteTo defines an interface implementing io.WriteTo and io.ReadSeeker

type ReadSeekerWriteTo interface {

	io.ReadSeeker

	io.WriterTo

}

// BufferedReadSeekerWriteTo wraps a BufferedReadSeeker with an io.WriteAt

// implementation.

type BufferedReadSeekerWriteTo struct {

	*BufferedReadSeeker

}

// WriteTo writes to the given io.Writer from BufferedReadSeeker until there's no more data to write or

// an error occurs. Returns the number of bytes written and any error encountered during the write.

func (b *BufferedReadSeekerWriteTo) WriteTo(writer io.Writer) (int64, error) {

	return io.Copy(writer, b.BufferedReadSeeker)

}

// ReadSeekerWriteToProvider provides an implementation of io.WriteTo for an io.ReadSeeker

type ReadSeekerWriteToProvider interface {

	GetWriteTo(seeker io.ReadSeeker) (r ReadSeekerWriteTo, cleanup func())

}

// BufferedReadSeekerWriteToPool uses a sync.Pool to create and reuse

// []byte slices for buffering parts in memory

type BufferedReadSeekerWriteToPool struct {

	pool sync.Pool

}

// NewBufferedReadSeekerWriteToPool will return a new BufferedReadSeekerWriteToPool that will create

// a pool of reusable buffers . If size is less then < 64 KiB then the buffer

// will default to 64 KiB. Reason: io.Copy from writers or readers that don't support io.WriteTo or io.ReadFrom

// respectively will default to copying 32 KiB.

func NewBufferedReadSeekerWriteToPool(size int) *BufferedReadSeekerWriteToPool {

	if size < 65536 {

		size = 65536

	}

	return &BufferedReadSeekerWriteToPool{

		pool: sync.Pool{New: func() interface{} {

			return make([]byte, size)

		}},

	}

}

// GetWriteTo will wrap the provided io.ReadSeeker with a BufferedReadSeekerWriteTo.

// The provided cleanup must be called after operations have been completed on the

// returned io.ReadSeekerWriteTo in order to signal the return of resources to the pool.

func (p *BufferedReadSeekerWriteToPool) GetWriteTo(seeker io.ReadSeeker) (r ReadSeekerWriteTo, cleanup func()) {

	buffer := p.pool.Get().([]byte)

	r = &BufferedReadSeekerWriteTo{BufferedReadSeeker: NewBufferedReadSeeker(seeker, buffer)}

	cleanup = func() {

		p.pool.Put(buffer)

	}

	return r, cleanup

}