// alternative to bufio
// meant to be used with buffer from pool
package buffer

import (
	"io"
	"errors"
)

type Pool interface {
	Get() ([]byte, error)
	Put([]byte)
}

type ContentWriter interface {
	WriteTo(io.WriteCloser) (int, error)
}

type Options struct {

	// defaults to new instance created by DefaultPool()
	Pool Pool

	// may differ, default 512
	ReadSize int
}

// initialize with NewReader or ReaderFrom
// uninitialized reader panics
// reads from the underlying reader until the first error, but only returns an error when the buffer is empty
// once the underlying reader returned an error, it doesn't attempt to read from it anymore
// the pool yes, the reader does not support concurrent access
type Reader struct {
	reader *reader
}

var ErrZeroAllocation = errors.New("zero allocation")

func DefaultPool() Pool {
	return newPool()
}

func NoPool(allocSize int) Pool {
	return noPool{allocSize: allocSize}
}

func ReaderFrom(in io.Reader, o Options) Reader {
	if o.Pool == nil {
		o.Pool = DefaultPool()
	}

	if o.ReadSize <= 0 {
		o.ReadSize = 1 << 9
	}

	return Reader{reader: &reader{options: o, in: in}}
}

func ReaderFromContent(w ContentWriter, o Options) Reader {
	return Reader{}
}

// - it returns an error only when the underlying reader returned an error and the internal buffer is empty
// - if the underlying reader returns zero read length and nil error, and the buffer is empty, it returns zero
// read length and nil error. It's up the calling code to decide how to proceed in such cases
func (r Reader) Read(p []byte) (int, error) {
	return r.reader.read(p)
}

// copy
// data and err when no delimiter found
// - when found the delimiter within max, consumes until and including the delimiter, and returns the consumed
// bytes, true, and nil error. If the underlying reader returned meanwhile a non-nil error, including EOF, it
// will be returned on subsequent reads after the internal buffer was consumed
// - when not found the delimiter within max, and the underlying reader didn't return an error, it returns zero
// length bytes, false and nil error
// - when not found the delimiter within max, and the underlying reader returned an error, it returns the
// buffered bytes, false and a nil error
// - when the buffer is empty, and the underlying reader previously returned an error, it returns zero length
// bytes, false, and the error
func (r Reader) ReadBytes(delimiter []byte, max int) ([]byte, bool, error) {
	return r.reader.readBytes(delimiter, max)
}

// only returns an error when the underlying reader returned an error, or the used pool returned an error
func (r Reader) ReadUTF8(max int) ([]rune, int, error) {
	return r.reader.readUTF8(max)
}

// not a copy
func (r Reader) Peek(max int) ([]byte, error) {
	return r.reader.peek(max)
}

// not a copy
// can be wrong after error
func (r Reader) Buffered() []byte {
	return r.reader.buffered()
}

// important that the writer must not modify the slice data, as defined in the io.Writer interface
func (r Reader) WriteTo(w io.Writer) (int64, error) {
	return r.reader.writeTo(w)
}