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

import (
	"errors"
	"io"
)

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

type Options struct {

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

type ContentFunc func(io.Writer) (int64, error)

// 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")
	ErrContentAbort   = errors.New("content pipe aborted")
)

func DefaultPool(allocSize int) Pool {
	return newPool(allocSize)
}

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

func (f ContentFunc) WriteTo(w io.Writer) (int64, error) {
	return f(w)
}

// similar to bufio.Reader, but with pooled buffering internally
func BufferedReader(in io.Reader, o Options) Reader {
	if in == nil {
		return Reader{}
	}

	if o.Pool == nil {
		o.Pool = DefaultPool(1 << 12)
	}

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

// similar to a pipe, but with dynamic and pooled buffering internally
// the individual Write calls are blocked until the reading end requests more data
// WriterTo instances need to be safe to call in goroutines other than they were created in
// if it returns with nil error, it will be interpreted as EOF on the reader side
// unfinished calls to the passed in io.Writer will return with ErrContentAbort when the buffer
// needs to be consumed
func BufferedContent(c io.WriterTo, o Options) Reader {
	if c == nil {
		return Reader{}
	}

	if o.Pool == nil {
		o.Pool = DefaultPool(1 << 12)
	}

	return Reader{reader: &reader{options: o, in: mkcontent(c)}}
}

// - 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) {
	if r.reader == nil {
		return 0, io.EOF
	}

	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) {
	if r.reader == nil {
		return nil, false, io.EOF
	}

	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) {
	if r.reader == nil {
		return nil, 0, io.EOF
	}

	return r.reader.readUTF8(max)
}

// not a copy
// error only when nothing buffered
func (r Reader) Peek(max int) ([]byte, error) {
	if r.reader == nil {
		return nil, io.EOF
	}

	return r.reader.peek(max)
}

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

	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) {
	if r.reader == nil {
		return 0, nil
	}

	return r.reader.writeTo(w)
}