// Copyright 2009 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 io provides basic interfaces to I/O primitives.
// Its primary job is to wrap existing implementations of such primitives,
// such as those in package os, into shared public interfaces that
// abstract the functionality, plus some other related primitives.
//
// Because these interfaces and primitives wrap lower-level operations with
// various implementations, unless otherwise informed clients should not
// assume they are safe for parallel execution.
package io

import "errors"

// Seek whence values.
const (
	SeekStart   = 0 // seek relative to the origin of the file
	SeekCurrent = 1 // seek relative to the current offset
	SeekEnd     = 2 // seek relative to the end
)

// ErrShortWrite means that a write accepted fewer bytes than requested
// but failed to return an explicit error.
var ErrShortWrite = errors.New("short write")

// ErrShortBuffer means that a read required a longer buffer than was provided.
var ErrShortBuffer = errors.New("short buffer")

// EOF is the error returned by Read when no more input is available.
// Functions should return EOF only to signal a graceful end of input.
// If the EOF occurs unexpectedly in a structured data stream,
// the appropriate error is either ErrUnexpectedEOF or some other error
// giving more detail.
var EOF = errors.New("EOF")

// ErrUnexpectedEOF means that EOF was encountered in the
// middle of reading a fixed-size block or data structure.
var ErrUnexpectedEOF = errors.New("unexpected EOF")

// ErrNoProgress is returned by some clients of an io.Reader when
// many calls to Read have failed to return any data or error,
// usually the sign of a broken io.Reader implementation.
var ErrNoProgress = errors.New("multiple Read calls return no data or error")

// Reader is the interface that wraps the basic Read method.
//
// Read reads up to len(p) bytes into p. It returns the number of bytes
// read (0 <= n <= len(p)) and any error encountered. Even if Read
// returns n < len(p), it may use all of p as scratch space during the call.
// If some data is available but not len(p) bytes, Read conventionally
// returns what is available instead of waiting for more.
//
// When Read encounters an error or end-of-file condition after
// successfully reading n > 0 bytes, it returns the number of
// bytes read. It may return the (non-nil) error from the same call
// or return the error (and n == 0) from a subsequent call.
// An instance of this general case is that a Reader returning
// a non-zero number of bytes at the end of the input stream may
// return either err == EOF or err == nil. The next Read should
// return 0, EOF.
//
// Callers should always process the n > 0 bytes returned before
// considering the error err. Doing so correctly handles I/O errors
// that happen after reading some bytes and also both of the
// allowed EOF behaviors.
//
// Implementations of Read are discouraged from returning a
// zero byte count with a nil error, except when len(p) == 0.
// Callers should treat a return of 0 and nil as indicating that
// nothing happened; in particular it does not indicate EOF.
//
// Implementations must not retain p.
type Reader interface {
	Read(p []byte) (n int, err error)
}

// Writer is the interface that wraps the basic Write method.
//
// Write writes len(p) bytes from p to the underlying data stream.
// It returns the number of bytes written from p (0 <= n <= len(p))
// and any error encountered that caused the write to stop early.
// Write must return a non-nil error if it returns n < len(p).
// Write must not modify the slice data, even temporarily.
//
// Implementations must not retain p.
type Writer interface {
	Write(p []byte) (n int, err error)
}

// Closer is the interface that wraps the basic Close method.
//
// The behavior of Close after the first call is undefined.
// Specific implementations may document their own behavior.
type Closer interface {
	Close() error
}

// Seeker is the interface that wraps the basic Seek method.
//
// Seek sets the offset for the next Read or Write to offset,
// interpreted according to whence:
// SeekStart means relative to the start of the file,
// SeekCurrent means relative to the current offset, and
// SeekEnd means relative to the end.
// Seek returns the new offset relative to the start of the
// file and an error, if any.
//
// Seeking to an offset before the start of the file is an error.
// Seeking to any positive offset is legal, but the behavior of subsequent
// I/O operations on the underlying object is implementation-dependent.
type Seeker interface {
	Seek(offset int64, whence int) (int64, error)
}

// ReadWriter is the interface that groups the basic Read and Write methods.
type ReadWriter interface {
	Reader
	Writer
}

// ReadCloser is the interface that groups the basic Read and Close methods.
type ReadCloser interface {
	Reader
	Closer
}

// WriteCloser is the interface that groups the basic Write and Close methods.
type WriteCloser interface {
	Writer
	Closer
}

// ReadWriteCloser is the interface that groups the basic Read, Write and Close methods.
type ReadWriteCloser interface {
	Reader
	Writer
	Closer
}

// ReadSeeker is the interface that groups the basic Read and Seek methods.
type ReadSeeker interface {
	Reader
	Seeker
}

// WriteSeeker is the interface that groups the basic Write and Seek methods.
type WriteSeeker interface {
	Writer
	Seeker
}

// ReadWriteSeeker is the interface that groups the basic Read, Write and Seek methods.
type ReadWriteSeeker interface {
	Reader
	Writer
	Seeker
}

// ReaderFrom is the interface that wraps the ReadFrom method.
//
// ReadFrom reads data from r until EOF or error.
// The return value n is the number of bytes read.
// Any error except io.EOF encountered during the read is also returned.
//
// The Copy function uses ReaderFrom if available.
type ReaderFrom interface {
	ReadFrom(r Reader) (n int64, err error)
}

// WriterTo is the interface that wraps the WriteTo method.
//
// WriteTo writes data to w until there's no more data to write or
// when an error occurs. The return value n is the number of bytes
// written. Any error encountered during the write is also returned.
//
// The Copy function uses WriterTo if available.
type WriterTo interface {
	WriteTo(w Writer) (n int64, err error)
}

// ReaderAt is the interface that wraps the basic ReadAt method.
//
// ReadAt reads len(p) bytes into p starting at offset off in the
// underlying input source. It returns the number of bytes
// read (0 <= n <= len(p)) and any error encountered.
//
// When ReadAt returns n < len(p), it returns a non-nil error
// explaining why more bytes were not returned. In this respect,
// ReadAt is stricter than Read.
//
// Even if ReadAt returns n < len(p), it may use all of p as scratch
// space during the call. If some data is available but not len(p) bytes,
// ReadAt blocks until either all the data is available or an error occurs.
// In this respect ReadAt is different from Read.
//
// If the n = len(p) bytes returned by ReadAt are at the end of the
// input source, ReadAt may return either err == EOF or err == nil.
//
// If ReadAt is reading from an input source with a seek offset,
// ReadAt should not affect nor be affected by the underlying
// seek offset.
//
// Clients of ReadAt can execute parallel ReadAt calls on the
// same input source.
//
// Implementations must not retain p.
type ReaderAt interface {
	ReadAt(p []byte, off int64) (n int, err error)
}

// WriterAt is the interface that wraps the basic WriteAt method.
//
// WriteAt writes len(p) bytes from p to the underlying data stream
// at offset off. It returns the number of bytes written from p (0 <= n <= len(p))
// and any error encountered that caused the write to stop early.
// WriteAt must return a non-nil error if it returns n < len(p).
//
// If WriteAt is writing to a destination with a seek offset,
// WriteAt should not affect nor be affected by the underlying
// seek offset.
//
// Clients of WriteAt can execute parallel WriteAt calls on the same
// destination if the ranges do not overlap.
//
// Implementations must not retain p.
type WriterAt interface {
	WriteAt(p []byte, off int64) (n int, err error)
}

// ByteReader is the interface that wraps the ReadByte method.
//
// ReadByte reads and returns the next byte from the input or
// any error encountered. If ReadByte returns an error, no input
// byte was consumed, and the returned byte value is undefined.
type ByteReader interface {
	ReadByte() (byte, error)
}

// ByteScanner is the interface that adds the UnreadByte method to the
// basic ReadByte method.
//
// UnreadByte causes the next call to ReadByte to return the same byte
// as the previous call to ReadByte.
// It may be an error to call UnreadByte twice without an intervening
// call to ReadByte.
type ByteScanner interface {
	ByteReader
	UnreadByte() error
}

// ByteWriter is the interface that wraps the WriteByte method.
type ByteWriter interface {
	WriteByte(c byte) error
}

// RuneReader is the interface that wraps the ReadRune method.
//
// ReadRune reads a single UTF-8 encoded Unicode character
// and returns the rune and its size in bytes. If no character is
// available, err will be set.
type RuneReader interface {
	ReadRune() (r rune, size int, err error)
}

// RuneScanner is the interface that adds the UnreadRune method to the
// basic ReadRune method.
//
// UnreadRune causes the next call to ReadRune to return the same rune
// as the previous call to ReadRune.
// It may be an error to call UnreadRune twice without an intervening
// call to ReadRune.
type RuneScanner interface {
	RuneReader
	UnreadRune() error
}

// WriteString writes the contents of the string s to w, which accepts a slice of bytes.
// If w implements a "WriteString(string) (int, error)" method, it is invoked directly.
// Otherwise, w.Write is called exactly once.
func WriteString(w Writer, s string) (n int, err error) {
	return 0, nil
}

// ReadAtLeast reads from r into buf until it has read at least min bytes.
// It returns the number of bytes copied and an error if fewer bytes were read.
// The error is EOF only if no bytes were read.
// If an EOF happens after reading fewer than min bytes,
// ReadAtLeast returns ErrUnexpectedEOF.
// If min is greater than the length of buf, ReadAtLeast returns ErrShortBuffer.
// On return, n >= min if and only if err == nil.
func ReadAtLeast(r Reader, buf []byte, min int) (n int, err error) {
	return 0, nil
}

// ReadFull reads exactly len(buf) bytes from r into buf.
// It returns the number of bytes copied and an error if fewer bytes were read.
// The error is EOF only if no bytes were read.
// If an EOF happens after reading some but not all the bytes,
// ReadFull returns ErrUnexpectedEOF.
// On return, n == len(buf) if and only if err == nil.
func ReadFull(r Reader, buf []byte) (n int, err error) {
	return 0, nil
}

// CopyN copies n bytes (or until an error) from src to dst.
// It returns the number of bytes copied and the earliest
// error encountered while copying.
// On return, written == n if and only if err == nil.
//
// If dst implements the ReaderFrom interface,
// the copy is implemented using it.
func CopyN(dst Writer, src Reader, n int64) (written int64, err error) {
	return 0, nil
}

// Copy copies from src to dst until either EOF is reached
// on src or an error occurs. It returns the number of bytes
// copied and the first error encountered while copying, if any.
//
// A successful Copy returns err == nil, not err == EOF.
// Because Copy is defined to read from src until EOF, it does
// not treat an EOF from Read as an error to be reported.
//
// If src implements the WriterTo interface,
// the copy is implemented by calling src.WriteTo(dst).
// Otherwise, if dst implements the ReaderFrom interface,
// the copy is implemented by calling dst.ReadFrom(src).
func Copy(dst Writer, src Reader) (written int64, err error) {
	return 0, nil
}

// CopyBuffer is identical to Copy except that it stages through the
// provided buffer (if one is required) rather than allocating a
// temporary one. If buf is nil, one is allocated; otherwise if it has
// zero length, CopyBuffer panics.
func CopyBuffer(dst Writer, src Reader, buf []byte) (written int64, err error) {
	return 0, nil
}

// LimitReader returns a Reader that reads from r
// but stops with EOF after n bytes.
// The underlying implementation is a *LimitedReader.
func LimitReader(r Reader, n int64) Reader { return nil }

// A LimitedReader reads from R but limits the amount of
// data returned to just N bytes. Each call to Read
// updates N to reflect the new amount remaining.
// Read returns EOF when N <= 0 or when the underlying R returns EOF.
type LimitedReader struct {
	R Reader // underlying reader
	N int64  // max bytes remaining
}

func (l *LimitedReader) Read(p []byte) (n int, err error) {
	return 0, nil
}

// NewSectionReader returns a SectionReader that reads from r
// starting at offset off and stops with EOF after n bytes.
func NewSectionReader(r ReaderAt, off int64, n int64) *SectionReader {
	return nil
}

// SectionReader implements Read, Seek, and ReadAt on a section
// of an underlying ReaderAt.
type SectionReader struct {
	unexported struct{}
}

func (s *SectionReader) Read(p []byte) (n int, err error) {
	return 0, nil
}

func (s *SectionReader) Seek(offset int64, whence int) (int64, error) {
	return 0, nil
}

func (s *SectionReader) ReadAt(p []byte, off int64) (n int, err error) {
	return 0, nil
}

// Size returns the size of the section in bytes.
func (s *SectionReader) Size() int64 { return 0 }

// TeeReader returns a Reader that writes to w what it reads from r.
// All reads from r performed through it are matched with
// corresponding writes to w. There is no internal buffering -
// the write must complete before the read completes.
// Any error encountered while writing is reported as a read error.
func TeeReader(r Reader, w Writer) Reader {
	return nil
}

// MultiReader returns a Reader that's the logical concatenation of
// the provided input readers. They're read sequentially. Once all
// inputs have returned EOF, Read will return EOF.  If any of the readers
// return a non-nil, non-EOF error, Read will return that error.
func MultiReader(readers ...Reader) Reader {
	return nil
}

// MultiWriter creates a writer that duplicates its writes to all the
// provided writers, similar to the Unix tee(1) command.
func MultiWriter(writers ...Writer) Writer {
	return nil
}

// ErrClosedPipe is the error used for read or write operations on a closed pipe.
var ErrClosedPipe = errors.New("io: read/write on closed pipe")

// A PipeReader is the read half of a pipe.
type PipeReader struct {
	unexported struct{}
}

// Read implements the standard Read interface:
// it reads data from the pipe, blocking until a writer
// arrives or the write end is closed.
// If the write end is closed with an error, that error is
// returned as err; otherwise err is EOF.
func (r *PipeReader) Read(data []byte) (n int, err error) {
	return 0, nil
}

// Close closes the reader; subsequent writes to the
// write half of the pipe will return the error ErrClosedPipe.
func (r *PipeReader) Close() error {
	return nil
}

// CloseWithError closes the reader; subsequent writes
// to the write half of the pipe will return the error err.
func (r *PipeReader) CloseWithError(err error) error {
	return nil
}

// A PipeWriter is the write half of a pipe.
type PipeWriter struct {
	unexported struct{}
}

// Write implements the standard Write interface:
// it writes data to the pipe, blocking until one or more readers
// have consumed all the data or the read end is closed.
// If the read end is closed with an error, that err is
// returned as err; otherwise err is ErrClosedPipe.
func (w *PipeWriter) Write(data []byte) (n int, err error) {
	return 0, nil
}

// Close closes the writer; subsequent reads from the
// read half of the pipe will return no bytes and EOF.
func (w *PipeWriter) Close() error {
	return nil
}

// CloseWithError closes the writer; subsequent reads from the
// read half of the pipe will return no bytes and the error err,
// or EOF if err is nil.
//
// CloseWithError always returns nil.
func (w *PipeWriter) CloseWithError(err error) error {
	return nil
}

// Pipe creates a synchronous in-memory pipe.
// It can be used to connect code expecting an io.Reader
// with code expecting an io.Writer.
//
// Reads and Writes on the pipe are matched one to one
// except when multiple Reads are needed to consume a single Write.
// That is, each Write to the PipeWriter blocks until it has satisfied
// one or more Reads from the PipeReader that fully consume
// the written data.
// The data is copied directly from the Write to the corresponding
// Read (or Reads); there is no internal buffering.
//
// It is safe to call Read and Write in parallel with each other or with Close.
// Parallel calls to Read and parallel calls to Write are also safe:
// the individual calls will be gated sequentially.
func Pipe() (*PipeReader, *PipeWriter) {
	return nil, nil
}